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Harrison Ford

Harrison Ford (born July 13, 1942) is an American actor. Regarded as a cinematic cultural icon, he has been a leading man in films of several genres and starred in many major box-office successes, particularly in the 1980s and 1990s. His films have grossed more than $5.4billion in North America and more than $9.3billion worldwide. Ford is the recipient of various accolades, including the AFI Life Achievement Award, the Cecil B. DeMille Award, an Honorary César, and an Honorary Palme d'Or, in addition to an Academy Award nomination.

Ford made his film debut in an uncredited appearance in Dead Heat on a Merry-Go-Round (1966) and went on to play supporting roles in such films as Journey to Shiloh (1968), Getting Straight (1970), American Graffiti (1973), and The Conversation (1974). He gained worldwide fame for his starring role as Han Solo in the epic space opera film Star Wars (1977), a role he reprised in four sequels over the next four decades. The multimedia franchise became a global cultural phenomenon. Ford is also known for his portrayal of the titular character in the popular media franchise Indiana Jones, beginning with the action-adventure film Raiders of the Lost Ark (1981). He played the character in four additional sequels over the next four decades and also starred as Rick Deckard in the cult science fiction film Blade Runner (1982) and its sequel Blade Runner 2049 (2017), and portrayed Jack Ryan in the spy thriller films Patriot Games (1992) and Clear and Present Danger (1994).

Ford's on-screen career spans six decades in both film and television. He received a nomination for the Academy Award for Best Actor for his role as a detective who envelopes himself in the Amish community in the crime thriller Witness (1985). Ford has also starred in films such as The Mosquito Coast (1986), Working Girl (1988), Presumed Innocent (1990), Regarding Henry (1991), The Fugitive (1993), Sabrina (1995), The Devil's Own (1997), Air Force One (1997), Six Days, Seven Nights (1998), Random Hearts (1999), What Lies Beneath (2000), K-19: The Widowmaker (2002), Firewall (2006), Morning Glory (2010), Cowboys & Aliens (2011) 42 (2013), The Age of Adaline (2015), and The Call of the Wild (2020). Ford has since starred in the Paramount+ western series 1923 (2022–present) and the Apple TV+ comedy series Shrinking (2023–present).

Outside of acting, Ford is a licensed pilot; he has often assisted the emergency services in rescue missions near his home in Wyoming, and he chaired an aviation education program for youth from 2004 to 2009. Ford is also an environmental activist, having served as the inaugural vice chair of Conservation International since 1991.

Early life and education
Harrison Ford was born at the Swedish Covenant Hospital in Chicago, Illinois, on July 13, 1942, to former radio actress Dorothy (née Nidelman) and advertising executive and former actor John William "Christopher" Ford. His younger brother, Terence, was born in 1945. Their father was a Catholic of Irish descent, while their mother was an Ashkenazi Jew whose parents were emigrants from Minsk, Belarus, then in the Russian Empire. When asked in which religion he and his brother were raised, Ford jokingly responded "Democrat" and more seriously stated that they were raised to be "liberals of every stripe". When asked about what influence his Jewish and Irish Catholic ancestry may have had on him, he quipped, "As a man I've always felt Irish, as an actor I've always felt Jewish."

Ford was a Boy Scout, achieving the second-highest rank of Life Scout. He worked at Napowan Adventure Base Scout Camp as a counselor for the Reptile Study merit badge. Because of this, he and director Steven Spielberg later decided to depict the young Indiana Jones as a Life Scout in Indiana Jones and the Last Crusade (1989). Ford graduated in 1960 from Maine East High School in Park Ridge, Illinois. His voice was the first student voice broadcast on his high school's new radio station, WMTH, and he was its first sportscaster during his senior year. He attended Ripon College in Ripon, Wisconsin, where he was a philosophy major and a member of the Sigma Nu fraternity. A self-described "late bloomer", Ford took a drama class in the final quarter of his senior year to get over his shyness and became fascinated with acting. Ford was expelled from college four days before graduation.

1964–1976
In 1964, after a season of summer stock with the Belfry Players in Wisconsin, Ford traveled to Los Angeles and eventually signed a contract with Columbia Pictures' new talent program. His first known role was an uncredited one as a bellhop in Dead Heat on a Merry-Go-Round (1966). There is little record of his non-speaking (or "extra") roles in film. Ford was at the bottom of the hiring list, having offended producer Jerry Tokofsky after he played a bellboy in the feature. According to one anecdote, Tokofsky told Ford that when actor Tony Curtis delivered a bag of groceries, he could tell that Curtis was a movie star whereas Ford wasn't; Ford immediately retorted that if Curtis was truly a talented actor, he would've delivered them like a bellhop. Ford was apparently fired soon after.

His speaking roles continued next with Luv (1967), though he was still uncredited. He was finally credited as "Harrison J. Ford" in the 1967 Western film A Time for Killing, starring Glenn Ford, George Hamilton and Inger Stevens, but the "J" did not stand for anything since he has no middle name. It was added to avoid confusion with a silent film actor named Harrison Ford, who appeared in more than 80 films between 1915 and 1932 and died in 1957. Ford later said that he was unaware of the existence of the earlier actor until he came upon a star with his own name on the Hollywood Walk of Fame. Ford soon dropped the "J" and worked for Universal Studios, playing minor roles in many television series throughout the late 1960s and early 1970s, including Gunsmoke, Ironside, The Virginian, The F.B.I., Love, American Style and Kung Fu. He appeared in the western Journey to Shiloh (1968) and had an uncredited, non-speaking role in Michelangelo Antonioni's 1970 film Zabriskie Point as an arrested student protester. In 1968, he also worked as a camera operator for one of the Doors' tours. French filmmaker Jacques Demy chose Ford for the lead role of his first American film, Model Shop (1969), but the head of Columbia Pictures thought Ford had "no future" in the film business and told Demy to hire a more experienced actor. The part eventually went to Gary Lockwood. Ford later commented that the experience had been nevertheless a positive one because Demy was the first to show such faith in him.

Not happy with the roles offered to him, Ford became a self-taught professional carpenter to support his then-wife and two young sons. Clients at this time included the writers Joan Didion and John Gregory Dunne, who lived on the beach at Malibu. Ford appears in the documentary Joan Didion: The Center Will Not Hold. He and his wife became friends of the writers. Casting director and fledgling producer Fred Roos championed the young Ford and secured him an audition with George Lucas for the role of Bob Falfa, which Ford went on to play in American Graffiti (1973). Ford's relationship with Lucas profoundly affected his career later. After director Francis Ford Coppola's film The Godfather was a success, he hired Ford to expand his office and gave him small roles in his next two films, The Conversation (1974) and Apocalypse Now (1979); in the latter film, Ford played an army colonel named "G. Lucas".

1977–1997
Ford's work in American Graffiti eventually landed him his first starring film role, when Lucas hired him to read lines for actors auditioning for roles in Lucas's upcoming epic space-opera film Star Wars (1977). Lucas was eventually won over by Ford's performance during these line reads and cast him as Han Solo. Star Wars became one of the most successful and groundbreaking films of all time, and brought Ford, and his co-stars Mark Hamill and Carrie Fisher, widespread recognition. Ford began to be cast in bigger roles in films throughout the late 1970s, including Heroes (1977), Force 10 from Navarone (1978) and Hanover Street (1979). He also co-starred alongside Gene Wilder in the buddy-comedy western The Frisco Kid (1979), playing a bank robber with a heart of gold. Ford returned to star in the successful Star Wars sequels The Empire Strikes Back (1980) and Return of the Jedi (1983), as well as the Star Wars Holiday Special (1978). Ford wanted Lucas to kill off Han Solo at the end of Return of the Jedi, saying, "That would have given the whole film a bottom," but Lucas refused.

Ford's status as a leading actor was solidified with Raiders of the Lost Ark (1981), an action-adventure collaboration between Lucas and Steven Spielberg that gave Ford his second franchise role as the heroic, globe-trotting archaeologist Indiana Jones. Like Star Wars, the film was massively successful; it became the highest-grossing film of the year. Spielberg was interested in casting Ford from the beginning, but Lucas was not, having already worked with him in American Graffiti and Star Wars. Lucas relented after Tom Selleck was unable to accept. Ford went on to reprise the role throughout the rest of the decade in the prequel Indiana Jones and the Temple of Doom (1984), and the sequel Indiana Jones and the Last Crusade (1989). During the June 1983 filming of Temple of Doom in London, Ford herniated a disc in his back. The 40-year-old actor was forced to fly back to Los Angeles for surgery and returned six weeks later.

Following his leading-man success as Indiana Jones, Ford played Rick Deckard in Ridley Scott's dystopian science-fiction film Blade Runner (1982). Compared to his experiences on the Star Wars and Indiana Jones films, Ford had a difficult time with the production. He recalled to Vanity Fair, "It was a long slog. I didn't really find it that physically difficult—I thought it was mentally difficult." Ford and Scott also had differing views on the nature of his character, Deckard, that persist decades later. While not initially a success, Blade Runner became a cult classic and one of Ford's most highly regarded films. Ford proved his versatility throughout the 1980s with dramatic parts in films such as Witness (1985), The Mosquito Coast (1986), and Frantic (1988), as well as the romantic male lead opposite Melanie Griffith and Sigourney Weaver in the comedy-drama Working Girl (1988). Witness and The Mosquito Coast allowed Ford to explore his potential as a dramatic actor, and both performances were widely acclaimed. Ford later recalled that working with director Peter Weir on Witness and The Mosquito Coast were two of the best experiences of his career.

In late 1991, Ford was slated to portray company lawyer A. Philip Randolph in an action-historical film entitled Night Ride Down, which would have been set around a labor union strike in the 1930s. Paramount Pictures shelved the project, after Ford quit the film over script changes he disagreed with. In the years that followed, Ford became the second actor to portray Jack Ryan in two films of the film series based on the literary character created by Tom Clancy: Patriot Games (1992) and Clear and Present Danger (1994), both co-starring Anne Archer and James Earl Jones. Ford took over the role from Alec Baldwin, who had played Ryan in The Hunt for Red October (1990). This led to long-lasting resentment from Baldwin, who said that he had wanted to reprise the role but Ford had negotiated with Paramount behind his back. Ford played leading roles in other action-based thrillers throughout the decade, such as The Fugitive (1993), The Devil's Own (1997), and Air Force One (1997). For his performance in The Fugitive, which co-starred Tommy Lee Jones, Ford received some of the best reviews of his career, including from Roger Ebert, who concluded that, "Ford is once again the great modern movie everyman. As an actor, nothing he does seems merely for show, and in the face of this melodramatic material he deliberately plays down, lays low, gets on with business instead of trying to exploit the drama in meaningless acting flourishes."

Ford played more straight dramatic roles in Presumed Innocent (1990) and Regarding Henry (1991), and another romantic lead role in Sabrina (1995), a remake of the classic 1954 film of the same name. Ford established working relationships with many well-regarded directors during this time, including Weir, Alan J. Pakula, Mike Nichols, Phillip Noyce, and Sydney Pollack, collaborating twice with each of them. This was the most lucrative period of Ford's career. From 1977 to 1997, he appeared in 14 films that reached the top 15 in the yearly domestic box-office rankings, 12 of which reached the top ten. Six of the films he appeared in during this time were nominated for the Academy Award for Best Picture, among other awards: Star Wars, Apocalypse Now, Raiders of the Lost Ark, Witness, Working Girl, and The Fugitive.

1998–2014
In the late 1990s, Ford started appearing in several critically derided and/or commercially disappointing films that failed to match his earlier successes, including Six Days, Seven Nights (1998), Random Hearts (1999), K-19: The Widowmaker (2002), Hollywood Homicide (2003), Firewall (2006) and Extraordinary Measures (2010). One exception was What Lies Beneath (2000), which grossed over $155million in the United States and $291million worldwide. Ford served as an executive producer on K-19: The Widowmaker and Extraordinary Measures, both of which were based on true events.

In 2004, Ford declined a chance to star in the thriller Syriana, later commenting that "I didn't feel strongly enough about the truth of the material and I think I made a mistake." The role went to George Clooney, who won an Oscar and a Golden Globe for his work. Before that, Ford had passed on a role in another Stephen Gaghan-written film, that of Robert Wakefield in Traffic, which went to Michael Douglas.

In 2008, Ford enjoyed success with the release of Indiana Jones and the Kingdom of the Crystal Skull, the first Indiana Jones film in 19 years and another collaboration with Lucas and Spielberg. The film received generally positive reviews and was the second-highest-grossing film worldwide in 2008. Ford later said he would like to star in another sequel "if it didn't take another 20 years to digest."

Other 2008 work included Crossing Over, directed by Wayne Kramer. In the film, Ford plays an ICE/Homeland Security Investigations Special Agent, working alongside Ashley Judd and Ray Liotta. He also narrated a feature documentary film about the Dalai Lama, Dalai Lama Renaissance. Ford filmed the medical drama Extraordinary Measures in 2009 in Portland, Oregon. Released on January 22, 2010, the film also starred Brendan Fraser and Alan Ruck. Also in 2010, he co-starred in the film Morning Glory, along with Rachel McAdams, Diane Keaton and Patrick Wilson. Although the film was a disappointment at the box office, Ford's performance was well received by critics, some of whom thought it was his best role in years. In July 2011, Ford starred alongside Daniel Craig and Olivia Wilde in the science-fiction/western hybrid film Cowboys & Aliens. To promote the film, he appeared at the San Diego Comic-Con International and, apparently surprised by the warm welcome, told the audience, "I just wanted to make a living as an actor. I didn't know about this." Also in 2011, Ford starred in Japanese commercials advertising the video game Uncharted 3: Drake's Deception for the PlayStation 3.

2013 began a trend that saw Ford accepting more diverse supporting roles. That year, he co-starred in the corporate espionage thriller Paranoia with Liam Hemsworth and Gary Oldman, whom he had previously worked with in Air Force One, and also appeared in Ender's Game, 42 and Anchorman 2: The Legend Continues. His performance as Branch Rickey in the film 42 was praised by many critics and garnered Ford a nomination as best supporting actor for the Satellite Awards. In 2014, he appeared in The Expendables 3, and the following year, co-starred with Blake Lively in the romantic drama The Age of Adaline to positive reviews.

2015–present
Ford reprised the role of Han Solo in the long-awaited Star Wars sequel Star Wars: The Force Awakens (2015), which was highly successful, like its predecessors. During filming on June 11, 2014, Ford suffered what was said to be a fractured ankle when a hydraulic door fell on him. He was airlifted to John Radcliffe Hospital in Oxford, England, for treatment. Ford's son Ben released details on his father's injury, saying that his ankle would likely need a plate and screws, and that filming could be altered slightly, with the crew needing to shoot Ford from the waist up for a short time until he recovered. Ford made his return to filming in mid-August, after a two-month layoff as he recovered from his injury. Ford's character was killed off in The Force Awakens, but it was subsequently announced, via a casting call, that Ford would return in some capacity as Solo in Episode VIII. In February 2016, when the cast for Episode VIII was confirmed, it was indicated that Ford would not reprise his role in the film after all. When Ford was asked whether Solo could come back in "some form", he replied, "Anything is possible in space." He eventually made an uncredited appearance as a vision in Star Wars: The Rise of Skywalker (2019).

On February 26, 2015, Alcon Entertainment announced Ford would reprise his role as Rick Deckard in Denis Villeneuve's science fiction sequel film Blade Runner 2049. The film, and Ford's performance, was very well received by critics upon its release in October 2017. Scott Collura of IGN called it a "deep, rich, smart film that's visually awesome and full of great sci-fi concepts" and Ford's role "a quiet, sort of gut-wrenching interpretation to Deckard and what he must've gone through in the past three decades." The film grossed $259.3million worldwide, short of the estimated $400million that it needed to break even. In 2019, Ford had his first voice role in an animated film, as a dog named Rooster in The Secret Life of Pets 2. With filming of a fifth Indiana Jones film delayed by a year, Ford headlined a big-budget adaptation of Jack London's The Call of the Wild, playing prospector John Thornton. The film was released in February 2020 to a mixed critical reception and its theatrical release was shortened due to the impact of the COVID-19 pandemic on the film industry.

In 2022, Ford was cast to star alongside Helen Mirren in the Paramount+ western drama series 1923. The two had previously starred together 36 years earlier in The Mosquito Coast. The series premiered in December 2022 to positive reviews, and it is set to run for a total of two seasons. That same year, it was announced that Ford would star in the Apple TV+ comedy drama series Shrinking. The series premiered in January 2023 to positive reviews, with Ford receiving praise for his performance. In a 2023 interview with The Hollywood Reporter, it was revealed that he accepted the roles in both 1923 and Shrinking despite there not being a script at the time.

Ford reprised the role of Indiana Jones in Indiana Jones and the Dial of Destiny (2023), which he stated was his last appearance as the character. The film received generally positive reviews, with many critics highlighting Ford's performance. In October 2022, Ford was cast as Thaddeus "Thunderbolt" Ross in the 2025 superhero films Captain America: Brave New World and Thunderbolts*, set in the Marvel Cinematic Universe, replacing William Hurt, who played the character in previous MCU films.

Personal life
Ford has been married three times and has four biological children and one adopted child. He was first married to Mary Marquardt from 1964 until their divorce in 1979. They had two sons, born in 1966 and 1969. The older son co-owns Ford's Filling Station, a gastropub located at Terminal 5 in Los Angeles International Airport. The younger son is owner of the Ludwig Clothing company and previously owned Strong Sports Gym and the Kim Sing Theater.

Ford's second marriage was to screenwriter Melissa Mathison from March 1983 until their separation in 2000; they divorced in 2004. They had a son, born in 1987, and a daughter, born in 1990. Mathison died in 2015. Ford began dating actress Calista Flockhart after they met at the 2002 Golden Globe Awards. He proposed to Flockhart over Valentine's Day weekend in 2009. They married on June 15, 2010, in Santa Fe, New Mexico, where Ford was filming Cowboys & Aliens. They are the parents of a son, born in 2001, whom Flockhart had adopted before meeting Ford. Ford commented on his parenting choices in 2023: "I can tell you this: If I’d been less successful, I’d probably be a better parent."

Ford and Flockhart live on an 800 acre ranch in Jackson, Wyoming, where he has lived since the 1980s and approximately half of which he has donated as a nature reserve. They retain a base in the Brentwood neighborhood of Los Angeles. Ford is one of Hollywood's most private actors, guarding much of his personal life. In her 2016 autobiography The Princess Diarist, his co-star Carrie Fisher claimed that she and Ford had a three-month affair in 1976 during the filming of Star Wars.

Aviation
Ford is a licensed pilot of both fixed-wing aircraft and helicopters. On several occasions, he has personally provided emergency helicopter services at the request of local authorities in Wyoming, in one instance rescuing a hiker overcome by dehydration.

Ford began flight training in the 1960s at Wild Rose Idlewild Airport in Wild Rose, Wisconsin, flying in a Piper PA-22 Tri-Pacer, but at $15 an hour, he could not afford to continue the training. In the mid-1990s, he bought a used Gulfstream II and asked one of his pilots, Terry Bender, to give him flying lessons. They started flying a Cessna 182 out of Jackson, Wyoming, later switching to Teterboro Airport in Teterboro, New Jersey, flying a Cessna 206, the aircraft in which he made his first solo flight.

Ford's aircraft are kept at Santa Monica Airport. The Bell 407 helicopter is often kept and flown in Jackson and has been used by Ford in two mountain rescues during his assigned duty time with Teton County Search and Rescue. During one of the rescues, Ford recovered a hiker who had become lost and disoriented. She boarded his helicopter and promptly vomited into one of the rescuers' caps, unaware of who the pilot was until much later; "I can't believe I barfed in Harrison Ford's helicopter!" she said later.

Ford flies his de Havilland Canada DHC-2 Beaver (N28S) more than any of his other aircraft, and has repeatedly said that he likes this aircraft and the sound of its Pratt & Whitney R-985 radial engine. According to Ford, it had been flown in the CIA's Air America operations and was riddled with bullet holes that had to be patched up.

In March 2004, Ford officially became chairman of the Experimental Aircraft Association (EAA)'s Young Eagles program, founded by then-EAA president Tom Poberezny and fellow actor-pilot Cliff Robertson. Ford was asked to take the position by Greg Anderson, Senior Vice President of the EAA at the time, to replace General Chuck Yeager, who was vacating the post that he had held for many years. Ford at first was hesitant, but later accepted the offer and has made appearances with the Young Eagles at the EAA AirVenture Oshkosh gathering at Oshkosh, Wisconsin, for two years. In July 2005, at the gathering in Oshkosh, Ford agreed to accept the position for another two years. He has flown over 280 children as part of the Young Eagles program, usually in his DHC-2 Beaver, which can seat the actor and five children. Ford stepped down as program chairman in 2009 and was replaced by Captain Chesley Sullenberger and First Officer Jeff Skiles. He is involved with the EAA chapter in Driggs, Idaho, just over the Teton Range from Jackson, Wyoming. On July 28, 2016, Ford flew the two millionth Young Eagle at the EAA AirVenture convention, making it the most successful aviation-youth introduction program in history.

As of 2009, Ford appears in Internet advertisements for General Aviation Serves America, a campaign by the advocacy group Aircraft Owners and Pilots Association (AOPA). He has also appeared in several independent aviation documentaries, including Wings Over the Rockies (2009), Flying the Feathered Edge: The Bob Hoover Project (2014), and Living in the Age of Airplanes (2015).

Ford is an honorary board member of the humanitarian aviation organization Wings of Hope, and is known for having made several trips to Washington, D.C., to fight for pilots' rights. He has also donated substantial funds to aerobatic champion Sean Tucker's charitable program, The Bob Hoover Academy (named after legendary aviator Bob Hoover), which educates at-risk teens in central California and teaches them how to fly.

Incidents
On August 22, 1987, Ford was traveling as a passenger with Clint Eastwood and Sondra Locke aboard a Gulfstream III when the jet experienced engine troubles during a Paris-to-L.A. flight and was forced to land in Bangor, Maine. After repairs were made, the trio resumed their flight the following day.

On October 23, 1999, Ford was involved in the crash of a Bell 206L4 LongRanger helicopter. The NTSB accident report states that Ford was piloting the aircraft over the Lake Piru riverbed near Santa Clarita, California, on a routine training flight. While making his second attempt at an autorotation with powered recovery, the aircraft was unable to recover power after the sudden drop in altitude. It landed hard and began skidding forward in the loose gravel before flipping onto its side. Neither Ford nor the instructor pilot suffered any injuries, though the helicopter was seriously damaged.

On March 5, 2015, Ford's plane, believed to be a Ryan PT-22 Recruit, made an emergency landing on the Penmar Golf Course in Venice, California after it lost engine power. He was taken to Ronald Reagan UCLA Medical Center, where he was reported to be in fair to moderate condition. Ford suffered a broken pelvis and broken ankle during the accident, as well as other injuries.

On February 13, 2017, Ford landed an Aviat Husky at John Wayne Airport in Orange County, California, on the taxiway left of runway 20L. A Boeing 737 was holding short of the runway on the taxiway when Ford overflew them.

On April 24, 2020, at the Los Angeles Hawthorne Airport while piloting his Husky, Ford crossed a runway where another aircraft was landing. According to the FAA, the two planes were about 3,600 feet from each other and there was no danger of a crash. A representative of Ford later said that he "misheard" an instruction given to him by air traffic control.

Environmental work
Ford is vice-chair of Conservation International, an American nonprofit environmental organization headquartered in Arlington, Virginia. The organization's intent is to protect nature. Since 1992, Ford has lent his voice to a series of public service messages promoting environmental involvement for EarthShare, an American federation of environmental and conservation charities. He has acted as a spokesperson for Restore Hetch Hetchy, a non-profit organization dedicated to restoring Yosemite National Park's Hetch Hetchy Valley to its original condition. Ford also appears in the documentary series Years of Living Dangerously, which reports on people affected by and seeking solutions to climate change.

In 1993, the arachnologist Norman Platnick named a new species of spider Calponia harrisonfordi, and in 2002 the entomologist Edward O. Wilson named a new ant species Pheidole harrisonfordi (in recognition of Harrison's work as Vice Chairman of Conservation International). The Peruvian snake species Tachymenoides harrisonfordi was named for Ford in 2023.

In September 2013, Ford, while filming an environmental documentary in Indonesia, interviewed the Indonesian Forestry Minister, Zulkifli Hasan. After the interview, Ford and his crew were accused of "harassing state institutions" and publicly threatened with deportation. Questions within the interview concerned the Tesso Nilo National Park, Sumatra. It was alleged the Minister of Forestry was given no prior warning of questions nor the chance to explain the challenges of catching illegal loggers. Ford was provided an audience with the Indonesian President, Susilo Bambang Yudhoyono, during which he expressed concerns regarding Indonesia's environmental degradation and the government efforts to address climate change. In response, the President explained Indonesia's commitment to preserving its oceans and forests.

In 2019, on behalf of Conservation International, Ford gave an impassioned speech during the United Nations' Climate Action Summit in New York on the destruction of the Amazon rainforest and its effect on climate change for the rest of the world. Ford urged his audience to listen to 'angry young people' trying to make a difference in the situation, emphasizing, "The most important thing we can do for them is to get the hell out of their way."

Political views
Like his parents, Ford is a lifelong Democrat. On September 7, 1995, Ford testified before the U.S. Senate Foreign Relations Committee in support of the Dalai Lama and an independent Tibet. In 2007, he narrated the documentary Dalai Lama Renaissance. In 2000, Ford donated a thousand dollars to the presidential campaigns of Bill Bradley, Al Gore, and John McCain. In 2003, he publicly condemned the Iraq War and called for "regime change" in the United States. He also criticized Hollywood for making movies which were "more akin to video games than stories about human life and relationships", and he called for more gun control in the United States. In 2009, Ford signed a petition calling for the release of film director Roman Polanski, who had been arrested in Switzerland in relation to his 1977 charge for drugging and raping a 13-year-old girl.

After Republican presidential candidate Donald Trump said his favorite role of Ford's was Air Force One because he "stood up for America", Ford responded that it was just a film and made critical statements against Trump's presidential bid. For his first time ever endorsing a political candidate for office, Ford endorsed Joe Biden's 2020 presidential campaign against Trump. He said that he wanted to "encourage people to support candidates that will support the environment" and felt that under Trump, the U.S. had "lost some of our credibility in the world". Along with Mark Hamill, Ford worked with the anti-Trump Republican group The Lincoln Project to produce and narrate a 2020 election ad attacking Trump's disparaging of Anthony Fauci.

Archaeology
Following on his success portraying the archaeologist Indiana Jones, Ford also plays a part in supporting the work of professional archaeologists. He serves as a General Trustee on the Governing Board of the Archaeological Institute of America (AIA), North America's oldest and largest organization devoted to the world of archaeology. Ford assists them in their mission of increasing public awareness of archaeology and preventing looting and the illegal antiquities trade.

Filmography
Selected credits:

 * American Graffiti (1973)
 * The Conversation (1974)
 * Star Wars (1977)
 * Apocalypse Now (1979)
 * The Empire Strikes Back (1980)
 * Raiders of the Lost Ark (1981)
 * Blade Runner (1982)
 * Return of the Jedi (1983)
 * Indiana Jones and the Temple of Doom (1984)
 * Witness (1985)
 * The Mosquito Coast (1986)
 * Working Girl (1988)
 * Indiana Jones and the Last Crusade (1989)
 * Presumed Innocent (1990)
 * Regarding Henry (1991)
 * Patriot Games (1992)
 * The Fugitive (1993)
 * Clear and Present Danger (1994)
 * Sabrina (1995)
 * The Devil's Own (1997)
 * Air Force One (1997)
 * Six Days, Seven Nights (1998)
 * What Lies Beneath (2000)
 * K-19: The Widowmaker (2002)
 * Firewall (2006)
 * Indiana Jones and the Kingdom of the Crystal Skull (2008)
 * Extraordinary Measures (2010)
 * Morning Glory (2010)
 * Cowboys & Aliens (2011)
 * 42 (2013)
 * The Age of Adaline (2015)
 * Star Wars: The Force Awakens (2015)
 * Blade Runner 2049 (2017)
 * The Call of the Wild (2020)
 * Indiana Jones and the Dial of Destiny (2023)
 * Captain America: Brave New World (2025)
 * Thunderbolts* (2025)

Awards and nominations
Throughout his career, Ford has received significant recognition for his work in the entertainment industry. In 1986, he was nominated for Best Actor at the 58th Academy Awards for his performance in Witness, a role for which he also received BAFTA and Golden Globe nominations in the same category. Three additional Golden Globe nominations went to Ford in 1987, 1994 and 1996 for his performances in The Mosquito Coast, The Fugitive and Sabrina. In 2000, he was the recipient of the AFI Life Achievement Award from the American Film Institute for his body of work, presented to him by two of his closest collaborators and fellow industry giants, George Lucas and Steven Spielberg. In 2002, he was given the Cecil B. DeMille Award, another career achievement honor, from the Hollywood Foreign Press Association at the 59th Golden Globe Awards ceremony. On May 30, 2003, Ford received a star on the Hollywood Walk of Fame.

In 2006, he received the Jules Verne Award, given to an actor who has "encouraged the spirit of adventure and imagination" throughout their career. He was presented with the first-ever Hero Award at the 2007 Scream Awards for his many iconic roles, including Indiana Jones and Han Solo (both of which earned him a collective three Saturn Awards for Best Actor in 1982, 2024 and 2016, respectively), and in 2008 he received the Spike TV's Guy's Choice Award for "Brass Balls". In 2015, Ford received the Albert R. Broccoli Britannia Award for Worldwide Contribution to Entertainment from BAFTA Los Angeles. In 2018, Ford was honored by the SAG-AFTRA Foundation with the Artists Inspiration Award for both his acting and philanthropic work alongside fellow honoree Lady Gaga. SAG-AFTRA Foundation Board President JoBeth Williams in the press release said, "Harrison Ford is an acting legend in every known galaxy, but what many do not know are the decades of philanthropic service and leadership he has given to Conservation International to help protect our planet."

Other prestigious film honors for Ford include an Honorary Cesar, an Honorary Palme d'Or from the Cannes Film Festival, the Career Achievement Award from the Hollywood Film Awards, the Kirk Douglas Award for Excellence in Film from the Santa Barbara International Film Festival, the Box Office Star of the Century Award from the National Association of Theatre Owners and the Lifetime Achievement Award from both the Locarno Film Festival and the Zurich Film Festival.

Ford has also been honored multiple times for his involvement in general aviation, receiving the Living Legends of Aviation Award and the Experimental Aircraft Association's Freedom of Flight Award in 2009, the Wright Brothers Memorial Trophy in 2010, and the Al Ueltschi Humanitarian Award in 2013. Flying magazine ranked him number 48 on their 2013 list of the 51 Heroes of Aviation. In 2024, it was announced that Ford would be a recipient of the Disney Legend Award for his outstanding contributions to The Walt Disney Company.

title: Harrison Ford


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Barents Sea

The Barents Sea (, also ; Barentshavet, ; Баренцево море) is a marginal sea of the Arctic Ocean, located off the northern coasts of Norway and Russia and divided between Norwegian and Russian territorial waters. It was known earlier among Russians as the Northern Sea, Pomorsky Sea or Murman Sea ("Norse Sea"); the current name of the sea is after the historical Dutch navigator Willem Barentsz.

The Barents Sea is a rather shallow shelf sea with an average depth of 230 m, and it is an important site for both fishing and hydrocarbon exploration. It is bordered by the Kola Peninsula to the south, the shelf edge towards the Norwegian Sea to the west, the archipelagos of Svalbard to the northwest, Franz Josef Land to the northeast and Novaya Zemlya to the east. The islands of Novaya Zemlya, an extension of the northern end of the Ural Mountains, separate the Barents Sea from the Kara Sea.

Although part of the Arctic Ocean, the Barents Sea has been characterised as "turning into the Atlantic" or in the process of being "Atlantified" because of its status as "the Arctic warming hot spot." Hydrologic changes due to global warming have led to a reduction in sea ice and in the stratification of the water column, which could produce major changes in weather in Eurasia. One prediction is that, as the Barents Sea's permanent ice-free area grows, evaporation will increase, leading to increased winter snowfalls in much of continental Europe.

Geography
The southern half of the Barents Sea, including the ports of Murmansk (Russia) and Vardø (Norway) remain ice-free year-round due to the warm North Atlantic drift. In September, the entire Barents Sea is more or less completely ice-free. In 1944, Finland's territory also reached the Barents Sea. The Liinakhamari harbour in the Pechengsky District was Finland's only ice-free winter harbour until it was ceded to the Soviet Union.

There are three main types of water masses in the Barents Sea: Warm, salty Atlantic water (temperature >3 °C, salinity >35) from the North Atlantic drift; cold Arctic water (temperature <0 °C, salinity <35) from the north; and warm, but not very salty, coastal water (temperature >3 °C, salinity <34.7). Between the Atlantic and Polar waters, a front called the Polar Front is formed. In the western parts of the sea (close to Bear Island), this front is determined by the bottom topography and is therefore relatively sharp and stable from year to year, while in the east (towards Novaya Zemlya), it can be quite diffuse and its position can vary markedly between years.

The lands of Novaya Zemlya attained most of their early Holocene coastal deglaciation approximately 10,000 years before the present.

Extent
The International Hydrographic Organization defines the limits of the "Barentsz Sea" [sic] as follows:

 * On the west: The northeastern limit of the Norwegian Sea [A line joining the southernmost point of West Spitzbergen [sic] to North Cape of Bear Island, through this island to Cape Bull and thence on to North Cape in Norway (25°45'E)].

 * On the northwest: The eastern shore of West Spitzbergen [sic], Hinlopen Strait up to 80° latitude north; south and east coasts of North-East Land [the island of Nordaustlandet ] to Cape Leigh Smith (80.08333°N, 28°W).

 * On the north: Cape Leigh Smith across the Islands Bolshoy Ostrov (Great Island) [ Storøya ], Gilles [ Kvitøya ] and Victoria; Cape Mary Harmsworth (southwestern extremity of Alexandra Land) along the northern coasts of Franz-Josef Land as far as Cape Kohlsaat (81.23333°N, 65.16667°W).

 * On the east: Cape Kohlsaat to Cape Zhelaniya (Desire); west and southwest coast of Novaya Zemlya to Cape Kussov Noss and thence to western entrance Cape, Dolgaya Bay (70.25°N, 58.41667°W) on Vaigach Island. Through Vaigach Island to Cape Greben; thence to Cape Belyi Noss on the mainland.

 * On the south: The northern limit of the White Sea [A line joining Svyatoi Nos (Murmansk Coast, 39°47'E) and Cape Kanin].

Other islands in the Barents Sea include Chaichy and Timanets.

Geology
The Barents Sea was originally formed from two major continental collisions: the Caledonian orogeny, in which the Baltica and Laurentia collided to form Laurasia, and a subsequent collision between Laurasia and Western Siberia. Most of its geological history is dominated by extensional tectonics, caused by the collapse of the Caledonian and Uralian orogenic belts and the break-up of Pangaea. These events created the major rift basins that dominate the Barents Shelf, along with various platforms and structural highs. The later geological history of the Barents Sea is dominated by Late Cenozoic uplift, particularly that caused by Quaternary glaciation, which has resulted in erosion and deposition of significant sediment.

Ecology
Due to the North Atlantic drift, the Barents Sea has a high biological production compared to other oceans of similar latitude. The spring bloom of phytoplankton can start quite early near the ice edge because the fresh water from the melting ice makes up a stable water layer on top of the seawater. The phytoplankton bloom feeds zooplankton such as Calanus finmarchicus, Calanus glacialis, Calanus hyperboreus, Oithona spp., and krill. The zooplankton feeders include young cod, capelin, polar cod, whales, and little auk. The capelin is a key food for top predators such as the north-east Arctic cod, harp seals, and seabirds such as the common guillemot and Brunnich's guillemot. The fisheries of the Barents Sea, in particular the cod fisheries, are of great importance for both Norway and Russia.

SIZEX-89 was an international winter experiment in 1989 for which the main objectives were to perform sensor signature studies of different ice types to develop SAR algorithms for ice variables, such as ice types, ice concentrations and ice kinematics. Although previous research suggested that predation by whales may be the cause of depleting fish stocks, more recent research suggests that marine mammal consumption has only a trivial influence on fisheries. A model assessing the effects of fisheries and climate was far more accurate at describing trends in fish abundance. There is a genetically distinct polar bear population associated with the Barents Sea.

Pollution
The Barents Sea is "among the most polluted places on Earth" due to accumulated marine garbage, decades of Soviet nuclear tests, radioactive waste dumping and industrial pollution. The elevated pollution has caused elevated rates of disease among locals. With rising military buildup and increased use of shipping lanes heading east through the Arctic, there are concerns that a further increase in pollution is likely, not least from the increased risk of future oil spills from ships not properly equipped for the environment.

Name
The Barents Sea was formerly known to Russians as Murmanskoye More, or the "Sea of Murmans" (i.e., their term for Norwegians). It appears with this name in sixteenth-century maps, including Gerard Mercator's Map of the Arctic published in his 1595 atlas. Its eastern corner, in the region of the Pechora River's estuary, has been known as Pechorskoye Morye, that is, Pechora Sea. It was also known as Pomorsky Morye, after the first inhabitants of its shores, the Pomors.

This sea was given its present name by Europeans in honour of Willem Barentsz, a Dutch navigator and explorer. Barentsz was the leader of early expeditions to the far north, at the end of the sixteenth century.

The Barents Sea has been called by sailors "The Devil's Dance Floor" due to its unpredictability and difficulty level.

Ocean rowers call it "Devil's Jaw". In 2017, after the first recorded complete man-powered crossing of the Barents Sea from Tromsø to Longyearbyen in a rowboat by the Polar Row expedition, captain Fiann Paul was asked by Norwegian TV2 how a rower would name the Barents Sea. Fiann responded that he would name it "Devil's Jaw", adding that the winds you constantly battle are like breath from the devil's nostrils while he holds you in his jaws.

Modern era
Seabed mapping was completed in 1933; the first full map was produced by Russian marine geologist Maria Klenova.

The Barents Sea was the site of a notable World War II engagement which later became known as the Battle of the Barents Sea. Under the command of Oskar Kummetz, German warships sank minelayer HMS Bramble and destroyer HMS Achates (H12) but lost destroyer GERMAN DESTROYER Z16 Friedrich Eckoldt. Also, the German cruiser GERMAN CRUISER Admiral Hipper was severely damaged by British gunfire. The Germans later retreated and the British convoy arrived safely at Murmansk shortly afterwards.

During the Cold War, the Soviet Red Banner Northern Fleet used the southern reaches of the sea as a ballistic missile submarine bastion, a strategy that Russia continued. Nuclear contamination from dumped Russian naval reactors is an environmental concern in the Barents Sea.

Political status
For decades there was a boundary dispute between Norway and Russia regarding the position of the boundary between their respective claims to the Barents Sea. The Norwegians favoured a median line, based on the Geneva Convention of 1958, whereas the Russians favoured a meridian- based sector line, based on a Soviet decision of 1926. A neutral "grey" zone between the competing claims had an area of 175000 km2, which is approximately 12% of the total area of the Barents Sea. The two countries started negotiations on the location of the boundary in 1974 and agreed to a moratorium on hydrocarbon exploration in 1976.

Twenty years after the fall of the Soviet Union, in 2010 Norway and Russia signed an agreement that placed the boundary equidistant from their competing claims. This was ratified and went into force on 7 July 2011, opening the grey zone for hydrocarbon exploration.

Oil and gas
Encouraged by the success of oil exploration and production in the North Sea in the 1960s, Norway began hydrocarbon exploration in the Barents Sea in 1969. They acquired seismic reflection surveys through the following years, which were analysed to understand the location of the main sedimentary basins. NorskHydro drilled the first well in 1980, which was a dry hole, and the first discoveries were made the following year: the Alke and Askeladden gas fields. Several more discoveries were made on the Norwegian side of the Barents Sea throughout the 1980s, including the important Snøhvit field.

However, interest in the area began to wane due to a succession of dry holes, wells containing only gas (which was cheap at the time), and the prohibitive costs of developing wells in such a remote area. Interest in the area was reignited in the late 2000s after the Snovhit field was finally brought into production and two new large discoveries were made.

The Russians began exploration in their territory around the same time, encouraged by their success in the Timan-Pechora Basin. They drilled their first wells in the early 1980s, and some very large gas fields were discovered throughout this decade. The Shtokman field was discovered in 1988 and is classed as a giant gas field: currently the 5th-largest gas field in the world. Similar practical difficulties Barents Sea resulted in a decline in Russian exploration, aggravated by the nation's political instability of the 1990s.

Fishing
The Barents Sea contains the world's largest remaining cod population, as well as important stocks of haddock and capelin. Fishing is managed jointly by Russia and Norway in the form of the Joint Norwegian–Russian Fisheries Commission, established in 1976, in an attempt to keep track of how many fish are leaving the ecosystem due to fishing. The Joint Norwegian-Russian Fisheries Commission sets Total Allowable Catches (TACs) for multiple species throughout their migratory tracks. Through the Commission, Norway and Russia also exchange fishing quotas and catch statistics to ensure the TACs are not being violated.

However there are problems with reporting under this system, and researchers believe that they do not have accurate data for the effects of fishing on the Barents Sea ecosystem. Cod is one of the major catches. A large portion of catches are not reported when the fishing boats land, to account for profits that are being lost to high taxes and fees. Since many fishermen do not strictly follow the TACs and rules set forth by the Commission, the amount of fish being extracted annually from the Barents Sea is underestimated.

Barents Sea biodiversity and marine bioprospecting
The Barents Sea, where temperate waters from the Gulf Stream and cold waters from the Arctic meet, is home to an enormous diversity of organisms, which are well-adapted to the extreme conditions of their marine habitats. This makes these arctic species very attractive for marine bioprospecting. Marine bioprospecting may be defined as the search for bioactive molecules and compounds from marine sources that have new, unique properties and the potential for commercial applications. Amongst others, applications include medicines, food and feed, textiles, cosmetics and the process industry.

The Norwegian government strategically supports the development of marine bioprospecting as it has the potential to contribute to new and sustainable wealth creation. Tromsø and the northern areas of Norway play a central role in this strategy. They have excellent access to unique Arctic marine organisms, existing marine industries, and R&D competence and infrastructure in this region. Since 2007, science and industry have cooperated closely on bioprospecting and the development and commercialization of new products.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Barents Sea


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Convulsion

A convulsion is a medical condition where the body muscles contract and relax rapidly and repeatedly, resulting in uncontrolled shaking. Because epileptic seizures typically include convulsions, the term convulsion is often used as a synonym for seizure. However, not all epileptic seizures result in convulsions, and not all convulsions are caused by epileptic seizures. Non-epileptic convulsions have no relation with epilepsy, and are caused by non-epileptic seizures.

Convulsions can be caused by epilepsy, infections (including a severe form of listeriosis which is caused by eating food contaminated by Listeria Monocytogenes), brain trauma, or other medical conditions. They can also occur from an electric shock or improperly enriched air for scuba diving.

The word fit is sometimes used to mean a convulsion or epileptic seizure.

Signs and symptoms
A person having a convulsion may experience several different symptoms, such as a brief blackout, confusion, drooling, loss of bowel or bladder control, sudden shaking of the entire body, uncontrollable muscle spasms, or temporary cessation of breathing. Symptoms usually last from a few seconds to several minutes, although they can last longer.

Convulsions in children are not necessarily benign, and may lead to brain damage if prolonged. In these patients, the frequency of occurrence should not downplay their significance, as a worsening seizure state may reflect the damage caused by successive attacks. Symptoms may include:

 * Lack of awareness
 * Loss of consciousness
 * Eyes rolling back
 * Changes to breathing
 * Stiffening of the arms, legs, or whole body
 * Jerky movements of the arms, legs, body, or head
 * Lack of control over movements
 * Inability to respond

Causes
Most convulsions are the result of abnormal electrical activity in the brain. Often, a specific cause is not clear. Numerous conditions can cause a convulsion.

Convulsions can be caused by specific chemicals in the blood, as well as infections like meningitis or encephalitis. Other possibilities include celiac disease, head trauma, stroke, or lack of oxygen to the brain. Sometimes the convulsion can be caused by genetic defects or brain tumors. Convulsions can also occur when the blood sugar is too low or there is a deficiency of vitamin B6 (pyridoxine). The pathophysiology of convulsion remains ambiguous.

Convulsions may also be caused by epileptic seizures, febrile seizures, non-epileptic seizures, or paroxysmal kinesigenic dyskinesia. In rare cases, it may be triggered by reactions to certain medications, such as antidepressants, stimulants, and antihistamines.

Epileptic seizures
Epilepsy is a neuronal disorder with multifactorial manifestations. It is a noncontagious illness and is usually associated with sudden attacks of seizures, which are an immediate and initial anomaly in the electrical activity of the brain that disrupts part or all of the body. Various areas of the brain can be disturbed by epileptic events. Epileptic seizures can have contrary clinical features. Epileptic seizures can have long-lasting effects on cerebral blood flow.

Various kinds of epileptic seizures affect 60 million people worldwide.

Generalized seizures
The most common type of seizure is called a generalized seizure, also known as a generalized convulsion. This is characterized by a loss of consciousness which may lead to the person collapsing. The body stiffens for about a minute and then jerks uncontrollably for the next minute. During this, the patient may fall and injure themselves or bite their tongue, their eyes roll back, and lose control of their bladder. A familial history of seizures puts a person at a greater risk of developing them. Generalized seizures have been broadly classified into two categories: motor and non-motor.

A generalized tonic-clonic seizure (GTCS), also known as a grand mal seizure, is a whole-body seizure that has a tonic phase followed by clonic muscle retrenchments. GTCSs can happen in people of all ages. GTCSs are very hazardous, and they increase the risk of injuries and sudden unexpected death in epilepsy (SUDEP). SUDEP is a sudden, unexpected, nontraumatic death in patients with epilepsy. Strong convulsions that are related to GTCSs can also cause falls and severe injuries.

Not all generalized seizures produce convulsions. For example, in an absence seizure, also known as a petit mal seizure, the brain experiences electrical disturbances but the body remains motionless and unresponsive.

Febrile convulsion
A common cause of convulsions in children is febrile seizures, a type of seizure associated with a high body temperature. This high temperature is a usual immune response to infection, and in febrile convulsions, the reason for the fever is extra-cranial (such as a body-wide viral infection). In Nigeria, malaria—which can cause sudden, high fevers—is a significant cause of convulsions among children under 5 years of age.

Febrile seizures fall into two categories: simple and complex. A simple febrile seizure is generalized, occurs singularly, and lasts less than 15 minutes. A complex febrile seizure can be focused in an area of the body, occur more than once, and lasts for more than 15 minutes. Febrile seizures affect 2–4% of children in the United States and Western Europe, it is the most common childhood seizure. The exact reason for febrile convulsion is unidentified, though it might be the outcome of the interchange between environmental and genetic factors.

Psychogenic non-epileptic seizures
Psychogenic non-epileptic seizures (PNES) are described as neurobehavioral conditions or "psychogenic illnesses" which occur not due to the electrical disturbances in a person's brain but due to mental and emotional stress. PNES are an important differential diagnosis and a common occurrence in epilepsy centers. According to the 5th Edison of Diagnostic and Statistical Manual of Mental Disorders (DSM 5), PNES is classified as a "conversion disorder" or Functional Neurologic Symptom Disorder characterized by alterations in behavior, motor activity, consciousness, and sensation. A few neuroimaging (functional and structural) studies suggest that PNES may replicate sensorimotor alterations, emotional regulation, cognitive control, and integration of neural circuits.

Paroxysmal kinesigenic dyskinesia
There is a linkage between infantile convulsion and paroxysmal dyskinesia. Paroxysmal kinesigenic dyskinesia (PKD) is characterized by sudden involuntary movement caused by sudden stress or excitement. The relationship between convulsion and PKD is mainly due to the common mechanism of pathophysiology.

title: Convulsion


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X-ray astronomy

X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray astronomy uses a type of space telescope that can see x-ray radiation which standard optical telescopes, such as the Mauna Kea Observatories, cannot.

X-ray emission is expected from astronomical objects that contain extremely hot gases at temperatures from about a million kelvin (K) to hundreds of millions of kelvin (MK). Moreover, the maintenance of the E-layer of ionized gas high in the Earth's thermosphere also suggested a strong extraterrestrial source of X-rays. Although theory predicted that the Sun and the stars would be prominent X-ray sources, there was no way to verify this because Earth's atmosphere blocks most extraterrestrial X-rays. It was not until ways of sending instrument packages to high altitudes were developed that these X-ray sources could be studied.

The existence of solar X-rays was confirmed early in the mid-twentieth century by V-2s converted to sounding rockets, and the detection of extra-terrestrial X-rays has been the primary or secondary mission of multiple satellites since 1958. The first cosmic (beyond the Solar System) X-ray source was discovered by a sounding rocket in 1962. Called Scorpius X-1 (Sco X-1) (the first X-ray source found in the constellation Scorpius), the X-ray emission of Scorpius X-1 is 10,000 times greater than its visual emission, whereas that of the Sun is about a million times less. In addition, the energy output in X-rays is 100,000 times greater than the total emission of the Sun in all wavelengths.

Many thousands of X-ray sources have since been discovered. In addition, the intergalactic space in galaxy clusters is filled with a hot, but very dilute gas at a temperature between 100 and 1000 megakelvins (MK). The total amount of hot gas is five to ten times the total mass in the visible galaxies.

History of X-ray astronomy
In 1927, E.O. Hulburt of the US Naval Research Laboratory and associates Gregory Breit and Merle A. Tuve of the Carnegie Institution of Washington explored the possibility of equipping Robert H. Goddard's rockets to explore the upper atmosphere. "Two years later, he proposed an experimental program in which a rocket might be instrumented to explore the upper atmosphere, including detection of ultraviolet radiation and X-rays at high altitudes".

In the late 1930s, the presence of a very hot, tenuous gas surrounding the Sun was inferred indirectly from optical coronal lines of highly ionized species. The Sun has been known to be surrounded by a hot tenuous corona. In the mid-1940s radio observations revealed a radio corona around the Sun.

The beginning of the search for X-ray sources from above the Earth's atmosphere was on August 5, 1948 12:07 GMT. A US Army (formerly German) V-2 rocket as part of Project Hermes was launched from White Sands Proving Grounds. The first solar X-rays were recorded by T. Burnight.

Through the 1960s, 70s, 80s, and 90s, the sensitivity of detectors increased greatly during the 60 years of X-ray astronomy. In addition, the ability to focus X-rays has developed enormously—allowing the production of high-quality images of many fascinating celestial objects.

Sounding rocket flights
The first sounding rocket flights for X-ray research were accomplished at the White Sands Missile Range in New Mexico with a V-2 rocket on January 28, 1949. A detector was placed in the nose cone section and the rocket was launched in a suborbital flight to an altitude just above the atmosphere. X-rays from the Sun were detected by the U.S. Naval Research Laboratory Blossom experiment on board.

An Aerobee 150 rocket launched on June 19, 1962 (UTC) detected the first X-rays emitted from a source outside our solar system (Scorpius X-1). It is now known that such X-ray sources as Sco X-1 are compact stars, such as neutron stars or black holes. Material falling into a black hole may emit X-rays, but the black hole itself does not. The energy source for the X-ray emission is gravity. Infalling gas and dust is heated by the strong gravitational fields of these and other celestial objects. Based on discoveries in this new field of X-ray astronomy, starting with Scorpius X-1, Riccardo Giacconi received the Nobel Prize in Physics in 2002.

The largest drawback to rocket flights is their very short duration (just a few minutes above the atmosphere before the rocket falls back to Earth) and their limited field of view. A rocket launched from the United States will not be able to see sources in the southern sky; a rocket launched from Australia will not be able to see sources in the northern sky.

X-ray Quantum Calorimeter (XQC) project
In astronomy, the interstellar medium (or ISM) is the gas and cosmic dust that pervade interstellar space: the matter that exists between the star systems within a galaxy. It fills interstellar space and blends smoothly into the surrounding intergalactic medium. The interstellar medium consists of an extremely dilute (by terrestrial standards) mixture of ions, atoms, molecules, larger dust grains, cosmic rays, and (galactic) magnetic fields. The energy that occupies the same volume, in the form of electromagnetic radiation, is the interstellar radiation field.

Of interest is the hot ionized medium (HIM) consisting of a coronal cloud ejection from star surfaces at 106-107 K which emits X-rays. The ISM is turbulent and full of structure on all spatial scales. Stars are born deep inside large complexes of molecular clouds, typically a few parsecs in size. During their lives and deaths, stars interact physically with the ISM. Stellar winds from young clusters of stars (often with giant or supergiant HII regions surrounding them) and shock waves created by supernovae inject enormous amounts of energy into their surroundings, which leads to hypersonic turbulence. The resultant structures are stellar wind bubbles and superbubbles of hot gas. The Sun is currently traveling through the Local Interstellar Cloud, a denser region in the low-density Local Bubble.

To measure the spectrum of the diffuse X-ray emission from the interstellar medium over the energy range 0.07 to 1 keV, NASA launched a Black Brant 9 from White Sands Missile Range, New Mexico on May 1, 2008. The Principal Investigator for the mission is Dr. Dan McCammon of the University of Wisconsin–Madison.

Balloons
Balloon flights can carry instruments to altitudes of up to 40 km above sea level, where they are above as much as 99.997% of the Earth's atmosphere. Unlike a rocket where data are collected during a brief few minutes, balloons are able to stay aloft for much longer. However, even at such altitudes, much of the X-ray spectrum is still absorbed. X-rays with energies less than 35 keV (5,600 aJ) cannot reach balloons. On July 21, 1964, the Crab Nebula supernova remnant was discovered to be a hard X-ray (15–60 keV) source by a scintillation counter flown on a balloon launched from Palestine, Texas, United States. This was likely the first balloon-based detection of X-rays from a discrete cosmic X-ray source.

High-energy focusing telescope
The high-energy focusing telescope (HEFT) is a balloon-borne experiment to image astrophysical sources in the hard X-ray (20–100 keV) band. Its maiden flight took place in May 2005 from Fort Sumner, New Mexico, USA. The angular resolution of HEFT is c. 1.5'. Rather than using a grazing-angle X-ray telescope, HEFT makes use of a novel tungsten-silicon multilayer coatings to extend the reflectivity of nested grazing-incidence mirrors beyond 10 keV. HEFT has an energy resolution of 1.0 keV full width at half maximum at 60 keV. HEFT was launched for a 25-hour balloon flight in May 2005. The instrument performed within specification and observed Tau X-1, the Crab Nebula.

High-resolution gamma-ray and hard X-ray spectrometer (HIREGS)
A balloon-borne experiment called the High-resolution gamma-ray and hard X-ray spectrometer (HIREGS) observed X-ray and gamma-rays emissions from the Sun and other astronomical objects. It was launched from McMurdo Station, Antarctica in December 1991 and 1992. Steady winds carried the balloon on a circumpolar flight lasting about two weeks each time.

Rockoons
The rockoon, a blend of rocket and balloon, was a solid fuel rocket that, rather than being immediately lit while on the ground, was first carried into the upper atmosphere by a gas-filled balloon. Then, once separated from the balloon at its maximum height, the rocket was automatically ignited. This achieved a higher altitude, since the rocket did not have to move through the lower thicker air layers that would have required much more chemical fuel.

The original concept of "rockoons" was developed by Cmdr. Lee Lewis, Cmdr. G. Halvorson, S. F. Singer, and James A. Van Allen during the Aerobee rocket firing cruise of the USS Norton Sound (AVM-1) on March 1, 1949.

From July 17 to July 27, 1956, the Naval Research Laboratory (NRL) shipboard launched eight Deacon rockoons for solar ultraviolet and X-ray observations at ~30° N ~121.6° W, southwest of San Clemente Island, apogee: 120 km.

X-ray telescopes and mirrors

Satellites are needed because X-rays are absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray telescopes (XRTs) have varying directionality or imaging ability based on glancing angle reflection rather than refraction or large deviation reflection. This limits them to much narrower fields of view than visible or UV telescopes. The mirrors can be made of ceramic or metal foil.

The first X-ray telescope in astronomy was used to observe the Sun. The first X-ray picture (taken with a grazing incidence telescope) of the Sun was taken in 1963, by a rocket-borne telescope. On April 19, 1960, the very first X-ray image of the sun was taken using a pinhole camera on an Aerobee-Hi rocket.

The utilization of X-ray mirrors for extrasolar X-ray astronomy simultaneously requires:
 * the ability to determine the location at the arrival of an X-ray photon in two dimensions and
 * a reasonable detection efficiency.

X-ray astronomy detectors
X-ray astronomy detectors have been designed and configured primarily for energy and occasionally for wavelength detection using a variety of techniques usually limited to the technology of the time.

X-ray detectors collect individual X-rays (photons of X-ray electromagnetic radiation) and count the number of photons collected (intensity), the energy (0.12 to 120 keV) of the photons collected, wavelength (c. 0.008–8 nm), or how fast the photons are detected (counts per hour), to tell us about the object that is emitting them.

Astrophysical sources of X-rays
Several types of astrophysical objects emit, fluoresce, or reflect X-rays, from galaxy clusters, through black holes in active galactic nuclei (AGN) to galactic objects such as supernova remnants, stars, and binary stars containing a white dwarf (cataclysmic variable stars and super soft X-ray sources), neutron star or black hole (X-ray binaries). Some Solar System bodies emit X-rays, the most notable being the Moon, although most of the X-ray brightness of the Moon arises from reflected solar X-rays. A combination of many unresolved X-ray sources is thought to produce the observed X-ray background. The X-ray continuum can arise from bremsstrahlung, black-body radiation, synchrotron radiation, or what is called inverse Compton scattering of lower-energy photons by relativistic electrons, knock-on collisions of fast protons with atomic electrons, and atomic recombination, with or without additional electron transitions.

An intermediate-mass X-ray binary (IMXB) is a binary star system where one of the components is a neutron star or a black hole. The other component is an intermediate mass star.

Hercules X-1 is composed of a neutron star accreting matter from a normal star (HZ Herculis) probably due to Roche lobe overflow. X-1 is the prototype for the massive X-ray binaries although it falls on the borderline,, between high- and low-mass X-ray binaries.

In July 2020, astronomers reported the observation of a "hard tidal disruption event candidate" associated with ASASSN-20hx, located near the nucleus of galaxy NGC 6297, and noted that the observation represented one of the "very few tidal disruption events with hard powerlaw X-ray spectra".

Celestial X-ray sources
The celestial sphere has been divided into 88 constellations. The International Astronomical Union (IAU) constellations are areas of the sky. Each of these contains remarkable X-ray sources. Some of them have been identified from astrophysical modeling to be galaxies or black holes at the centers of galaxies. Some are pulsars. As with sources already successfully modeled by X-ray astrophysics, striving to understand the generation of X-rays by the apparent source helps to understand the Sun, the universe as a whole, and how these affect us on Earth. Constellations are an astronomical device for handling observation and precision independent of current physical theory or interpretation. Astronomy has been around for a long time. Physical theory changes with time. With respect to celestial X-ray sources, X-ray astrophysics tends to focus on the physical reason for X-ray brightness, whereas X-ray astronomy tends to focus on their classification, order of discovery, variability, resolvability, and their relationship with nearby sources in other constellations.

Within the constellations Orion and Eridanus and stretching across them is a soft X-ray "hot spot" known as the Orion-Eridanus Superbubble, the Eridanus Soft X-ray Enhancement, or simply the Eridanus Bubble, a 25° area of interlocking arcs of Hα emitting filaments. Soft X-rays are emitted by hot gas (T ~ 2–3 MK) in the interior of the superbubble. This bright object forms the background for the "shadow" of a filament of gas and dust. The filament is shown by the overlaid contours, which represent 100 micrometre emission from dust at a temperature of about 30 K as measured by IRAS. Here the filament absorbs soft X-rays between 100 and 300 eV, indicating that the hot gas is located behind the filament. This filament may be part of a shell of neutral gas that surrounds the hot bubble. Its interior is energized by ultraviolet (UV) light and stellar winds from hot stars in the Orion OB1 association. These stars energize a superbubble about 1200 lys across which is observed in the visual (Hα) and X-ray portions of the spectrum.

Explorational X-ray astronomy
Usually observational astronomy is considered to occur on Earth's surface (or beneath it in neutrino astronomy). The idea of limiting observation to Earth includes orbiting the Earth. As soon as the observer leaves the cozy confines of Earth, the observer becomes a deep space explorer. Except for Explorer 1 and Explorer 3 and the earlier satellites in the series, usually if a probe is going to be a deep space explorer it leaves the Earth or an orbit around the Earth.

For a satellite or space probe to qualify as a deep space X-ray astronomer/explorer or "astronobot"/explorer, all it needs to carry aboard is an XRT or X-ray detector and leave Earth's orbit.

Ulysses was launched October 6, 1990, and reached Jupiter for its "gravitational slingshot" in February 1992. It passed the south solar pole in June 1994 and crossed the ecliptic equator in February 1995. The solar X-ray and cosmic gamma-ray burst experiment (GRB) had 3 main objectives: study and monitor solar flares, detect and localize cosmic gamma-ray bursts, and in-situ detection of Jovian aurorae. Ulysses was the first satellite carrying a gamma burst detector which went outside the orbit of Mars. The hard X-ray detectors operated in the range 15–150 keV. The detectors consisted of 23-mm thick × 51-mm diameter CsI(Tl) crystals mounted via plastic light tubes to photomultipliers. The hard detector changed its operating mode depending on (1) measured count rate, (2) ground command, or (3) change in spacecraft telemetry mode. The trigger level was generally set for 8-sigma above background and the sensitivity is 10−6 erg/cm2 (1 nJ/m2). When a burst trigger is recorded, the instrument switches to record high resolution data, recording it to a 32-kbit memory for a slow telemetry read out. Burst data consist of either 16 s of 8-ms resolution count rates or 64 s of 32-ms count rates from the sum of the 2 detectors. There were also 16 channel energy spectra from the sum of the 2 detectors (taken either in 1, 2, 4, 16, or 32 second integrations). During 'wait' mode, the data were taken either in 0.25 or 0.5 s integrations and 4 energy channels (with shortest integration time being 8 s). Again, the outputs of the 2 detectors were summed.

The Ulysses soft X-ray detectors consisted of 2.5-mm thick × 0.5 cm2 area Si surface barrier detectors. A 100 mg/cm2 beryllium foil front window rejected the low energy X-rays and defined a conical FOV of 75° (half-angle). These detectors were passively cooled and operate in the temperature range −35 to −55 °C. This detector had 6 energy channels, covering the range 5–20 keV.

Theoretical X-ray astronomy
Theoretical X-ray astronomy is a branch of theoretical astronomy that deals with the theoretical astrophysics and theoretical astrochemistry of X-ray generation, emission, and detection as applied to astronomical objects.

Like theoretical astrophysics, theoretical X-ray astronomy uses a wide variety of tools which include analytical models to approximate the behavior of a possible X-ray source and computational numerical simulations to approximate the observational data. Once potential observational consequences are available they can be compared with experimental observations. Observers can look for data that refutes a model or helps in choosing between several alternate or conflicting models.

Theorists also try to generate or modify models to take into account new data. In the case of an inconsistency, the general tendency is to try to make minimal modifications to the model to fit the data. In some cases, a large amount of inconsistent data over time may lead to total abandonment of a model.

Most of the topics in astrophysics, astrochemistry, astrometry, and other fields that are branches of astronomy studied by theoreticians involve X-rays and X-ray sources. Many of the beginnings for a theory can be found in an Earth-based laboratory where an X-ray source is built and studied.

Dynamos
Dynamo theory describes the process through which a rotating, convecting, and electrically conducting fluid acts to maintain a magnetic field. This theory is used to explain the presence of anomalously long-lived magnetic fields in astrophysical bodies. If some of the stellar magnetic fields are really induced by dynamos, then field strength might be associated with rotation rate.

Astronomical models
From the observed X-ray spectrum, combined with spectral emission results for other wavelength ranges, an astronomical model addressing the likely source of X-ray emission can be constructed. For example, with Scorpius X-1 the X-ray spectrum steeply drops off as X-ray energy increases up to 20 keV, which is likely for a thermal-plasma mechanism. In addition, there is no radio emission, and the visible continuum is roughly what would be expected from a hot plasma fitting the observed X-ray flux. The plasma could be a coronal cloud of a central object or a transient plasma, where the energy source is unknown, but could be related to the idea of a close binary.

In the Crab Nebula X-ray spectrum there are three features that differ greatly from Scorpius X-1: its spectrum is much harder, its source diameter is in light-years (ly)s, not astronomical units (AU), and its radio and optical synchrotron emission are strong. Its overall X-ray luminosity rivals the optical emission and could be that of a nonthermal plasma. However, the Crab Nebula appears as an X-ray source that is a central freely expanding ball of dilute plasma, where the energy content is 100 times the total energy content of the large visible and radio portion, obtained from the unknown source.

The "Dividing Line" as giant stars evolve to become red giants also coincides with the Wind and Coronal Dividing Lines. To explain the drop in X-ray emission across these dividing lines, a number of models have been proposed:
 * 1) low transition region densities, leading to low emission in coronae,
 * 2) high-density wind extinction of coronal emission,
 * 3) only cool coronal loops become stable,
 * 4) changes in a magnetic field structure to that an open topology, leading to a decrease of magnetically confined plasma, or
 * 5) changes in the magnetic dynamo character, leading to the disappearance of stellar fields leaving only small-scale, turbulence-generated fields among red giants.

Analytical X-ray astronomy
High-mass X-ray binaries (HMXBs) are composed of OB supergiant companion stars and compact objects, usually neutron stars (NS) or black holes (BH). Supergiant X-ray binaries (SGXBs) are HMXBs in which the compact objects orbit massive companions with orbital periods of a few days (3–15 d), and in circular (or slightly eccentric) orbits. SGXBs show typical the hard X-ray spectra of accreting pulsars and most show strong absorption as obscured HMXBs. X-ray luminosity (Lx) increases up to 1036 erg·s−1 (1029 watts).

The mechanism triggering the different temporal behavior observed between the classical SGXBs and the recently discovered supergiant fast X-ray transients (SFXT)s is still debated.

Stellar X-ray astronomy
The first detection of stellar x-rays occurred on April 5, 1974, with the detection of X-rays from Capella. A rocket flight on that date briefly calibrated its attitude control system when a star sensor pointed the payload axis at Capella (α Aur). During this period, X-rays in the range 0.2–1.6 keV were detected by an X-ray reflector system co-aligned with the star sensor. The X-ray luminosity of Lx = 1031 erg·s−1 (1024 W) is four orders of magnitude above the Sun's X-ray luminosity.

Stellar coronae
Coronal stars, or stars within a coronal cloud, are ubiquitous among the stars in the cool half of the Hertzsprung-Russell diagram. Experiments with instruments aboard Skylab and Copernicus have been used to search for soft X-ray emission in the energy range ~0.14–0.284 keV from stellar coronae. The experiments aboard ANS succeeded in finding X-ray signals from Capella and Sirius (α CMa). X-ray emission from an enhanced solar-like corona was proposed for the first time. The high temperature of Capella's corona as obtained from the first coronal X-ray spectrum of Capella using HEAO 1 required magnetic confinement unless it was a free-flowing coronal wind.

In 1977 Proxima Centauri is discovered to be emitting high-energy radiation in the XUV. In 1978, α Cen was identified as a low-activity coronal source. With the operation of the Einstein observatory, X-ray emission was recognized as a characteristic feature common to a wide range of stars covering essentially the whole Hertzsprung-Russell diagram. The Einstein initial survey led to significant insights:
 * X-ray sources abound among all types of stars, across the Hertzsprung-Russell diagram and across most stages of evolution,
 * the X-ray luminosities and their distribution along the main sequence were not in agreement with the long-favored acoustic heating theories, but were now interpreted as the effect of magnetic coronal heating, and
 * stars that are otherwise similar reveal large differences in their X-ray output if their rotation period is different.

To fit the medium-resolution spectrum of UX Arietis, subsolar abundances were required.

Stellar X-ray astronomy is contributing toward a deeper understanding of
 * magnetic fields in magnetohydrodynamic dynamos,
 * the release of energy in tenuous astrophysical plasmas through various plasma-physical processes, and
 * the interactions of high-energy radiation with the stellar environment.

Current wisdom has it that the massive coronal main sequence stars are late-A or early F stars, a conjecture that is supported both by observation and by theory.

Young, low-mass stars
Newly formed stars are known as pre-main-sequence stars during the stage of stellar evolution before they reach the main-sequence. Stars in this stage (ages <10 million years) produce X-rays in their stellar coronae. However, their X-ray emission is 103 to 105 times stronger than for main-sequence stars of similar masses.

X-ray emission for pre–main-sequence stars was discovered by the Einstein Observatory. This X-ray emission is primarily produced by magnetic reconnection flares in the stellar coronae, with many small flares contributing to the "quiescent" X-ray emission from these stars. Pre–main sequence stars have large convection zones, which in turn drive strong dynamos, producing strong surface magnetic fields. This leads to the high X-ray emission from these stars, which lie in the saturated X-ray regime, unlike main-sequence stars that show rotational modulation of X-ray emission. Other sources of X-ray emission include accretion hotspots and collimated outflows.

X-ray emission as an indicator of stellar youth is important for studies of star-forming regions. Most star-forming regions in the Milky Way Galaxy are projected on Galactic-Plane fields with numerous unrelated field stars. It is often impossible to distinguish members of a young stellar cluster from field-star contaminants using optical and infrared images alone. X-ray emission can easily penetrate moderate absorption from molecular clouds, and can be used to identify candidate cluster members.

Unstable winds
Given the lack of a significant outer convection zone, theory predicts the absence of a magnetic dynamo in earlier A stars. In early stars of spectral type O and B, shocks developing in unstable winds are the likely source of X-rays.

Coolest M dwarfs
Beyond spectral type M5, the classical αω dynamo can no longer operate as the internal structure of dwarf stars changes significantly: they become fully convective. As a distributed (or α2) dynamo may become relevant, both the magnetic flux on the surface and the topology of the magnetic fields in the corona should systematically change across this transition, perhaps resulting in some discontinuities in the X-ray characteristics around spectral class dM5. However, observations do not seem to support this picture: long-time lowest-mass X-ray detection, VB 8 (M7e V), has shown steady emission at levels of X-ray luminosity (LX) ≈ 1026 erg·s−1 (1019 W) and flares up to an order of magnitude higher. Comparison with other late M dwarfs shows a rather continuous trend.

Strong X-ray emission from Herbig Ae/Be stars
Herbig Ae/Be stars are pre-main sequence stars. As to their X-ray emission properties, some are
 * reminiscent of hot stars,
 * others point to coronal activity as in cool stars, in particular the presence of flares and very high temperatures.

The nature of these strong emissions has remained controversial with models including
 * unstable stellar winds,
 * colliding winds,
 * magnetic coronae,
 * disk coronae,
 * wind-fed magnetospheres,
 * accretion shocks,
 * the operation of a shear dynamo,
 * the presence of unknown late-type companions.

K giants
The FK Com stars are giants of spectral type K with an unusually rapid rotation and signs of extreme activity. Their X-ray coronae are among the most luminous (LX ≥ 1032 erg·s−1 or 1025 W) and the hottest known with dominant temperatures up to 40 MK. However, the current popular hypothesis involves a merger of a close binary system in which the orbital angular momentum of the companion is transferred to the primary.

Pollux is the brightest star in the constellation Gemini, despite its Beta designation, and the 17th brightest in the sky. Pollux is a giant orange K star that makes an interesting color contrast with its white "twin", Castor. Evidence has been found for a hot, outer, magnetically supported corona around Pollux, and the star is known to be an X-ray emitter.

Eta Carinae
New X-ray observations by the Chandra X-ray Observatory show three distinct structures: an outer, horseshoe-shaped ring about 2 light years in diameter, a hot inner core about 3 light-months in diameter, and a hot central source less than 1 light-month in diameter which may contain the superstar that drives the whole show. The outer ring provides evidence of another large explosion that occurred over 1,000 years ago. These three structures around Eta Carinae are thought to represent shock waves produced by matter rushing away from the superstar at supersonic speeds. The temperature of the shock-heated gas ranges from 60 MK in the central regions to 3 MK on the horseshoe-shaped outer structure. "The Chandra image contains some puzzles for existing ideas of how a star can produce such hot and intense X-rays," says Prof. Kris Davidson of the University of Minnesota. Davidson is principal investigator for the Eta Carina observations by the Hubble Space Telescope. "In the most popular theory, X-rays are made by colliding gas streams from two stars so close together that they'd look like a point source to us. But what happens to gas streams that escape to farther distances? The extended hot stuff in the middle of the new image gives demanding new conditions for any theory to meet."

Amateur X-ray astronomy
Collectively, amateur astronomers observe a variety of celestial objects and phenomena sometimes with equipment that they build themselves. The United States Air Force Academy (USAFA) is the home of the US's only undergraduate satellite program, and has and continues to develop the FalconLaunch sounding rockets. In addition to any direct amateur efforts to put X-ray astronomy payloads into space, there are opportunities that allow student-developed experimental payloads to be put on board commercial sounding rockets as a free-of-charge ride.

There are major limitations to amateurs observing and reporting experiments in X-ray astronomy: the cost of building an amateur rocket or balloon to place a detector high enough and the cost of appropriate parts to build a suitable X-ray detector.

Major questions in X-ray astronomy
As X-ray astronomy uses a major spectral probe to peer into the source, it is a valuable tool in efforts to understand many puzzles.

Stellar magnetic fields
Magnetic fields are ubiquitous among stars, yet we do not understand precisely why, nor have we fully understood the bewildering variety of plasma physical mechanisms that act in stellar environments. Some stars, for example, seem to have magnetic fields, fossil stellar magnetic fields left over from their period of formation, while others seem to generate the field anew frequently.

Extrasolar X-ray source astrometry
With the initial detection of an extrasolar X-ray source, the first question usually asked is "What is the source?" An extensive search is often made in other wavelengths such as visible or radio for possible coincident objects. Many of the verified X-ray locations still do not have readily discernible sources. X-ray astrometry becomes a serious concern that results in ever greater demands for finer angular resolution and spectral radiance.

There are inherent difficulties in making X-ray/optical, X-ray/radio, and X-ray/X-ray identifications based solely on positional coincidents, especially with handicaps in making identifications, such as the large uncertainties in positional determinants made from balloons and rockets, poor source separation in the crowded region toward the galactic center, source variability, and the multiplicity of source nomenclature.

X‐ray source counterparts to stars can be identified by calculating the angular separation between source centroids and the position of the star. The maximum allowable separation is a compromise between a larger value to identify as many real matches as possible and a smaller value to minimize the probability of spurious matches. "An adopted matching criterion of 40" finds nearly all possible X‐ray source matches while keeping the probability of any spurious matches in the sample to 3%."

Solar X-ray astronomy
All of the detected X-ray sources at, around, or near the Sun appear to be associated with processes in the corona, which is its outer atmosphere.

Coronal heating problem
In the area of solar X-ray astronomy, there is the coronal heating problem. The photosphere of the Sun has an effective temperature of 5,570 K yet its corona has an average temperature of 1–2 × 106 K. However, the hottest regions are 8–20 × 106 K. The high temperature of the corona shows that it is heated by something other than direct heat conduction from the photosphere.

It is thought that the energy necessary to heat the corona is provided by turbulent motion in the convection zone below the photosphere, and two main mechanisms have been proposed to explain coronal heating. The first is wave heating, in which sound, gravitational or magnetohydrodynamic waves are produced by turbulence in the convection zone. These waves travel upward and dissipate in the corona, depositing their energy in the ambient gas in the form of heat. The other is magnetic heating, in which magnetic energy is continuously built up by photospheric motion and released through magnetic reconnection in the form of large solar flares and myriad similar but smaller events—nanoflares.

Currently, it is unclear whether waves are an efficient heating mechanism. All waves except Alfvén waves have been found to dissipate or refract before reaching the corona. In addition, Alfvén waves do not easily dissipate in the corona. Current research focus has therefore shifted towards flare heating mechanisms.

Coronal mass ejection
A coronal mass ejection (CME) is an ejected plasma consisting primarily of electrons and protons (in addition to small quantities of heavier elements such as helium, oxygen, and iron), plus the entraining coronal closed magnetic field regions. Evolution of these closed magnetic structures in response to various photospheric motions over different time scales (convection, differential rotation, meridional circulation) somehow leads to the CME. Small-scale energetic signatures such as plasma heating (observed as compact soft X-ray brightening) may be indicative of impending CMEs.

The soft X-ray sigmoid (an S-shaped intensity of soft X-rays) is an observational manifestation of the connection between coronal structure and CME production. "Relating the sigmoids at X-ray (and other) wavelengths to magnetic structures and current systems in the solar atmosphere is the key to understanding their relationship to CMEs."

The first detection of a Coronal mass ejection (CME) as such was made on December 1, 1971, by R. Tousey of the US Naval Research Laboratory using OSO 7. Earlier observations of coronal transients or even phenomena observed visually during solar eclipses are now understood as essentially the same thing.

The largest geomagnetic perturbation, resulting presumably from a "prehistoric" CME, coincided with the first-observed solar flare, in 1859. The flare was observed visually by Richard Christopher Carrington and the geomagnetic storm was observed with the recording magnetograph at Kew Gardens. The same instrument recorded a crotchet, an instantaneous perturbation of the Earth's ionosphere by ionizing soft X-rays. This could not easily be understood at the time because it predated the discovery of X-rays (by Roentgen) and the recognition of the ionosphere (by Kennelly and Heaviside).

Exotic X-ray sources
A microquasar is a smaller cousin of a quasar that is a radio emitting X-ray binary, with an often resolvable pair of radio jets. LSI+61°303 is a periodic, radio-emitting binary system that is also the gamma-ray source, CG135+01. Observations are revealing a growing number of recurrent X-ray transients, characterized by short outbursts with very fast rise times (tens of minutes) and typical durations of a few hours that are associated with OB supergiants and hence define a new class of massive X-ray binaries: Supergiant Fast X-ray Transients (SFXTs). Observations made by Chandra indicate the presence of loops and rings in the hot X-ray emitting gas that surrounds Messier 87. A magnetar is a type of neutron star with an extremely powerful magnetic field, the decay of which powers the emission of copious amounts of high-energy electromagnetic radiation, particularly X-rays and gamma rays.

X-ray dark stars

During the solar cycle, as shown in the sequence of images at right, at times the Sun is almost X-ray dark, almost an X-ray variable. Betelgeuse, on the other hand, appears to be always X-ray dark. Hardly any X-rays are emitted by red giants. There is a rather abrupt onset of X-ray emission around spectral type A7-F0, with a large range of luminosities developing across spectral class F. Altair is spectral type A7V and Vega is A0V. Altair's total X-ray luminosity is at least an order of magnitude larger than the X-ray luminosity for Vega. The outer convection zone of early F stars is expected to be very shallow and absent in A-type dwarfs, yet the acoustic flux from the interior reaches a maximum for late A and early F stars provoking investigations of magnetic activity in A-type stars along three principal lines. Chemically peculiar stars of spectral type Bp or Ap are appreciable magnetic radio sources, most Bp/Ap stars remain undetected, and of those reported early on as producing X-rays only few of them can be identified as probably single stars. X-ray observations offer the possibility to detect (X-ray dark) planets as they eclipse part of the corona of their parent star while in transit. "Such methods are particularly promising for low-mass stars as a Jupiter-like planet could eclipse a rather significant coronal area."

X-ray dark planets and comets
X-ray observations offer the possibility to detect (X-ray dark) planets as they eclipse part of the corona of their parent star while in transit. "Such methods are particularly promising for low-mass stars as a Jupiter-like planet could eclipse a rather significant coronal area."

As X-ray detectors have become more sensitive, they have observed that some planets and other normally X-ray non-luminescent celestial objects under certain conditions emit, fluoresce, or reflect X-rays.

Comet Lulin

NASA's Swift Gamma-Ray Burst Mission satellite was monitoring Comet Lulin as it closed to 63 Gm of Earth. For the first time, astronomers can see simultaneous UV and X-ray images of a comet. "The solar wind—a fast-moving stream of particles from the sun—interacts with the comet's broader cloud of atoms. This causes the solar wind to light up with X-rays, and that's what Swift's XRT sees", said Stefan Immler, of the Goddard Space Flight Center. This interaction, called charge exchange, results in X-rays from most comets when they pass within about three times Earth's distance from the Sun. Because Lulin is so active, its atomic cloud is especially dense. As a result, the X-ray-emitting region extends far sunward of the comet.

title: X-ray astronomy


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Extragalactic astronomy

Extragalactic astronomy is the branch of astronomy concerned with objects outside the Milky Way galaxy. In other words, it is the study of all astronomical objects which are not covered by galactic astronomy.

The closest objects in extragalactic astronomy include the galaxies of the Local Group, which are close enough to allow very detailed analyses of their contents (e.g. supernova remnants, stellar associations). As instrumentation has improved, distant objects can now be examined in more detail and so extragalactic astronomy includes objects at nearly the edge of the observable universe. Research into distant galaxies (outside of our local group) is valuable for studying aspects of the universe such as galaxy evolution and Active Galactic Nuclei (AGN) which give insight into physical phenomena (e.g. super massive black hole accretion and the presence of dark matter ). It is through extragalactic astronomy that astronomers and physicists are able to study the effects of General Relativity such as gravitational lensing and gravitational waves, that are otherwise impossible (or nearly impossible) to study on a galactic scale.

A key interest in Extragalactic Astronomy is the study of how galaxies behave and interact through the universe. Astronomer's methodologies depend — from theoretical to observation based methods.

Galaxies form in various ways. In most Cosmological N-body simulations, the earliest galaxies in the cosmos formed in the first hundreds of millions of years.

These primordial galaxies formed as the enormous reservoirs of gas and dust in the early universe collapsed in on themselves, giving birth to the first stars, now known as Population III Stars. These stars were of enormous masses in the range of 300 to perhaps 3 million solar masses. Due to their large mass, these stars had extremely short lifespans.

Famous examples

 * Hubble Deep Field
 * LIGO's detection of gravitational waves
 * Chandra Deep Field South

Topics

 * Active Galactic Nuclei (AGN), Quasars
 * Dark Matter
 * Galaxy clusters, Superclusters
 * Intergalactic stars
 * Intergalactic dust
 * the observable universe
 * Radio galaxies
 * Supernovae
 * Extragalactic planet

title: Extragalactic astronomy