What is the Chandra X-ray Observatory?

The Chandra X-ray Observatory is a United States satellite and one of NASA's "Great Observatories" designed to create high-resolution images of celestial X-ray sources. It has been in operation since 1999 and was named to honor Subrahmanyan Chandrasekhar, a pioneer in stellar evolution. Launched on July 23, 1999, the Chandra X-ray Observatory studies black holes, supernova remnants, starburst galaxies, and exotic objects at the farthest reaches of the universe. It focuses X-rays using four pairs of nested iridium mirrors and can create a high-resolution spectrum to measure the temperatures, densities, and composition of glowing plasma clouds in space. The Chandra X-ray Observatory Center, located at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, manages Chandra.

Why does the Chandra X-ray Observatory study X-rays from space?

The Chandra X-ray Observatory studies X-rays from space because Earth's atmosphere absorbs them, necessitating high-altitude telescopes to detect them. X-ray astronomy helps scientists study objects in space, as many astronomical sources emit X-rays. As a "high-energy" facility, Chandra's primary focus is black holes, supernova remnants, starburst galaxies, and exotic objects at the farthest reaches of the universe. The study of X-rays from these sources provides valuable insights into the nature and quantity of black holes, the evolution of stars and galaxies, and the composition of supernova remnants.

When was the Chandra X-ray Observatory launched and by whom?

The Chandra X-ray Observatory is a United States satellite designed to produce high-resolution images of celestial X-ray sources. It is one of NASA's "Great Observatories" satellites and has been in operation since 1999. The space shuttle Columbia deployed Chandra on July 23, 1999, after which a solid-rocket stage propelled it into a highly elliptical orbit.

How does the Chandra X-ray Observatory detect and observe X-rays?

The Chandra X-ray Observatory captures high-resolution images of celestial X-ray sources. Launched in 1999, Chandra focuses X-rays using four pairs of nested iridium mirrors. A transmission grating can be inserted to create a high-resolution spectrum to study source characteristics and measure temperatures, densities, and the composition of glowing plasma clouds in space. Chandra's primary focus includes black holes, supernova remnants, starburst galaxies, and exotic objects at the farthest reaches of the universe. It found evidence that giant black holes were much more active in the past. It also confirmed a supermassive black hole at the Milky Way's centre and found direct proof of dark matter in merging galaxy clusters.

What important discoveries has the Chandra X-ray Observatory made?

The Chandra X-ray Observatory , launched in 1999, is a U.S. satellite designed for high-resolution images of celestial X-ray sources. It focuses on black holes, starburst galaxies, supernova remnants, and exotic objects at the farthest reaches of the universe. Chandra found that starburst galaxies have a higher number of intermediate-size black holes that merge at the center. It also found evidence that giant black holes were more active in the past. Chandra confirmed a supermassive black hole at the Milky Way Galaxy's center and direct proof of dark matter in merging galaxy clusters. Additionally, Chandra observed a possible extrasolar planet in another galaxy.

How has the Chandra X-ray Observatory helped scientists learn about black holes, supernovas, or other extreme objects in space?

The Chandra X-ray Observatory, launched in 1999, is a U.S. satellite designed to capture high-resolution images of celestial X-ray sources. As a "high-energy" facility, Chandra primarily focuses on black holes , supernova remnants , starburst galaxies, and other exotic objects at the farthest reaches of the universe. Chandra's findings include the confirmation of a supermassive black hole at the center of the Milky Way Galaxy and the discovery of a higher number of intermediate-size black holes in starburst galaxies. Additionally, Chandra provided direct evidence of dark matter through observations of merging galaxy clusters. Because Earth’s atmosphere absorbs most X-rays, astronomical observations in the X-ray region must be made from orbiting satellites.

Chandra X-ray Observatory

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Images

Cassiopeia A supernova remnant, in a false-colour composite image synthesized from observations gathered in different spectral regions by three space-based observatories. Red areas, representing infrared data from the Spitzer Space Telescope, highlight warm dust in the remnant's outer shell. Yellow areas, representing visible-light data collected by the Hubble Space Telescope, show delicate filamentary structures made of warmer gases. Green and blue areas are X-ray data from the Chandra X-ray Observatory and reveal hot gas that was created when ejected material from the supernova collided at very high velocity with the surrounding gas and dust.

Crab Nebula as seen by the Chandra X-ray Observatory.

At a Glance

Chandra X-ray Observatory summary

Chandra X-ray Observatory

United States satellite

Also known as: Advanced X-Ray Astrophysics Facility

Written by

David M. Harland

Fact-checked by

Britannica Editors

Last updated

Nov. 12, 2026 •History

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NASA’s Chandra Finds Source of Star’s Mysterious Outbursts • Nov. 9, 2026, 1:55 PM ET (NASA Science (.gov))

Top Questions

What is the Chandra X-ray Observatory?
The Chandra X-ray Observatory is a United States satellite and one of NASA's "Great Observatories" designed to create high-resolution images of celestial X-ray sources. It has been in operation since 1999 and was named to honor Subrahmanyan Chandrasekhar, a pioneer in stellar evolution.

Launched on July 23, 1999, the Chandra X-ray Observatory studies black holes, supernova remnants, starburst galaxies, and exotic objects at the farthest reaches of the universe. It focuses X-rays using four pairs of nested iridium mirrors and can create a high-resolution spectrum to measure the temperatures, densities, and composition of glowing plasma clouds in space. The Chandra X-ray Observatory Center, located at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, manages Chandra.
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1. Chandra X-ray Observatory
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Why does the Chandra X-ray Observatory study X-rays from space?
The Chandra X-ray Observatory studies X-rays from space because Earth's atmosphere absorbs them, necessitating high-altitude telescopes to detect them. X-ray astronomy helps scientists study objects in space, as many astronomical sources emit X-rays. As a "high-energy" facility, Chandra's primary focus is black holes, supernova remnants, starburst galaxies, and exotic objects at the farthest reaches of the universe. The study of X-rays from these sources provides valuable insights into the nature and quantity of black holes, the evolution of stars and galaxies, and the composition of supernova remnants.
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When was the Chandra X-ray Observatory launched and by whom?
The Chandra X-ray Observatory is a United States satellite designed to produce high-resolution images of celestial X-ray sources. It is one of NASA's "Great Observatories" satellites and has been in operation since 1999. The space shuttle Columbia deployed Chandra on July 23, 1999, after which a solid-rocket stage propelled it into a highly elliptical orbit.
1 Britannica Source
1. Chandra X-ray Observatory
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does the Chandra X-ray Observatory detect and observe X-rays?
The Chandra X-ray Observatory captures high-resolution images of celestial X-ray sources. Launched in 1999, Chandra focuses X-rays using four pairs of nested iridium mirrors. A transmission grating can be inserted to create a high-resolution spectrum to study source characteristics and measure temperatures, densities, and the composition of glowing plasma clouds in space.

Chandra's primary focus includes black holes, supernova remnants, starburst galaxies, and exotic objects at the farthest reaches of the universe. It found evidence that giant black holes were much more active in the past. It also confirmed a supermassive black hole at the Milky Way's centre and found direct proof of dark matter in merging galaxy clusters.
1 Britannica Source
1. Chandra X-ray Observatory
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What important discoveries has the Chandra X-ray Observatory made?
The Chandra X-ray Observatory, launched in 1999, is a U.S. satellite designed for high-resolution images of celestial X-ray sources. It focuses on black holes, starburst galaxies, supernova remnants, and exotic objects at the farthest reaches of the universe.

Chandra found that starburst galaxies have a higher number of intermediate-size black holes that merge at the center. It also found evidence that giant black holes were more active in the past. Chandra confirmed a supermassive black hole at the Milky Way Galaxy's center and direct proof of dark matter in merging galaxy clusters. Additionally, Chandra observed a possible extrasolar planet in another galaxy.
1 Britannica Source
1. Chandra X-ray Observatory
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How has the Chandra X-ray Observatory helped scientists learn about black holes, supernovas, or other extreme objects in space?
The Chandra X-ray Observatory, launched in 1999, is a U.S. satellite designed to capture high-resolution images of celestial X-ray sources. As a "high-energy" facility, Chandra primarily focuses on black holes, supernova remnants, starburst galaxies, and other exotic objects at the farthest reaches of the universe.

Chandra's findings include the confirmation of a supermassive black hole at the center of the Milky Way Galaxy and the discovery of a higher number of intermediate-size black holes in starburst galaxies. Additionally, Chandra provided direct evidence of dark matter through observations of merging galaxy clusters. Because Earth’s atmosphere absorbs most X-rays, astronomical observations in the X-ray region must be made from orbiting satellites.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Chandra X-ray Observatory, U.S. satellite, one of the National Aeronautics and Space Administration (NASA) fleet of “Great Observatories” satellites, which is designed to make high-resolution images of celestial X-ray sources. In operation since 1999, it is named in honour of Subrahmanyan Chandrasekhar, a pioneer of the field of stellar evolution.

Chandra was preceded by two X-ray satellites, the U.S. Einstein Observatory (1978–81) and the multinational Röntgensatellit (1990–99), which produced surveys across the entire sky of sources emitting at X-ray wavelengths. Chandra (originally known as the Advanced X-Ray Astrophysics Facility) was designed to study individual sources in detail. Following deployment by the space shuttle Columbia on July 23, 1999, a solid-rocket stage boosted the observatory into a highly elliptical orbit with an apogee, or farthest position from Earth, of 140,000 km (87,000 miles) and a perigee, or closest position to Earth, of 10,000 km (6,200 miles) in order to remain above the worst interference by Earth’s radiation and to provide long periods of uninterrupted study of almost any part of the sky.

In effect, Chandra is to X-ray astronomy what the Hubble Space Telescope is to optical astronomy. It focuses X-rays by using four pairs of nested iridium mirrors, with an aperture of 1.2 metres (4 feet) and a focal length of 10 metres (33 feet), and is capable of unprecedented spatial resolution. A transmission grating can be inserted into the optical path before the camera to create a high-resolution spectrum in the energy range of 0.07–10 keV (kiloelectron volts, or thousand electron volts) to investigate the characteristics of sources in this range and measure the temperatures, densities, and composition of the glowing plasma clouds that pervade space.

View of the Andromeda Galaxy (Messier 31, M31).

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As a “high-energy” facility, Chandra has as its primary focus black holes, supernova remnants, starburst galaxies, and the panoply of exotic objects at the farthest reaches of the universe. Much of a starburst galaxy’s luminosity is produced outside of the core region, and Chandra found that these galaxies have a proportionally higher number of intermediate-size black holes that sink to the centre, where they merge with each other. In following up on the Hubble Space Telescope’s “deep field” study of the earliest period of galaxy formation, Chandra found evidence that giant black holes were much more active in the past than now, so that after an initial period of extreme activity they appear to grow quiescent. (Supermassive black holes in the cores of galaxies are believed to have been responsible for the quasar phase of a galaxy’s life.) By detecting emissions from infalling material, Chandra confirmed that there is a quiescent supermassive black hole at the centre of the Milky Way Galaxy. In addition, Chandra found direct proof of the existence of dark matter in the merging of two galaxy clusters in which the hot gas (which is ordinary visible matter) was slowed by the drag effect of one cluster passing through the other, whereas the mass was not, which showed that most of the mass is dark matter. Observations of four other galaxy clusters showed that dark energy, the dominant component of the universe, has not changed greatly over time, suggesting that the universe’s expansion might continue indefinitely. Chandra also observed the first possible extrasolar planet in another galaxy when it saw an eclipse of an X-ray binary in M51 (about 28 million light-years away) that was likely caused by a planet about the size of Saturn.

Chandra was later complemented in December 1999 by Europe’s X-ray Multi-Mirror Mission (XMM-Newton, named for Sir Isaac Newton), which carries a cluster of coaligned X-ray telescopes, and from July 2005 to June 2015 by the joint U.S.-Japanese Suzaku satellite, which carried five X-ray telescopes. These later facilities have larger mirrors and are sensitive to higher energies, but, because there is an inherent trade-off in mirror design, their larger light-collecting area has been secured at the expense of higher-resolution imaging.

Chandra is managed by the Chandra X-ray Observatory Center, which is located at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

David M. Harland

Chandra X-ray Observatory

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