Editing Chandra X-ray Observatory

{{Short description|NASA space telescope launched in 1999}}
{{Use American English|date=June 2024}}
{{Use mdy dates|date=June 2024}}
{{Infobox spaceflight
| name               = Chandra X-ray Observatory
| names_list         = Advanced X-ray Astrophysics Facility (AXAF)
| image              = Chandra artist illustration.jpg
| image_caption      = Illustration of Chandra
| image_size         = 275px
| mission_type       = X-ray astronomy
| operator           = [[NASA]]{{\}}[[Smithsonian Astrophysical Observatory|SAO]]{{\}}CXC
| COSPAR_ID          = 1999-040B
| SATCAT             = 25867
| website            = https://chandra.harvard.edu/
| mission_duration   = Planned: 5 years <br> Elapsed: {{time interval|23 July 1999|sep=,}}
| manufacturer       = [[TRW Inc.]]
| launch_mass        = {{convert|12930|lb|kg|-1|order=flip|abbr=on}}<ref name="chandra-quick-facts">{{cite web |url=https://www.nasa.gov/centers/marshall/news/background/facts/cxoquick.html |title=Chandra X-ray Observatory Quick Facts |publisher=Marshall Space Flight Center |access-date=September 16, 2017 |archive-date=February 12, 2022 |archive-url=https://web.archive.org/web/20220212002150/https://www.nasa.gov/centers/marshall/news/background/facts/cxoquick.html }}</ref>
| dry_mass           = {{convert|10560|lb|kg|-1|order=flip|abbr=on}}<ref name="chandra-quick-facts" />
| payload_mass       = 
| dimensions         = Deployed: {{convert|13.8|xx|19.5|m|ft|1|abbr=on}}<ref name="chandraspecs">{{cite web |url=http://chandra.harvard.edu/about/specs.html |title=Chandra Specifications |publisher=NASA/Harvard |access-date=September 3, 2015}}</ref> <br /> Stowed: {{convert|38.7|xx|14.0|ft|m|1|order=flip|abbr=on}}<ref name="chandra-quick-facts" />
| power              = 2,350 W<ref name="chandraspecs" />
| launch_date        = {{start-date|July 23, 1999, 04:30:59.984}}&nbsp;UTC<ref name="spacefacts">{{cite web |url=http://www.spacefacts.de/mission/english/sts-93.htm |title=International Flight No. 210: STS-93 |work=Spacefacts.de |access-date=April 29, 2018}}</ref>
| launch_rocket      = {{OV|Columbia}} ([[STS-93]])
| launch_site        = [[Kennedy Space Center|Kennedy]], [[Kennedy Space Center Launch Complex 39B|LC-39B]]
| entered_service    = 
| disposal_type      = <!--deorbited, decommissioned, placed in a graveyard orbit, etc-->
| deactivated        = <!--when craft was decommissioned-->
| last_contact       = <!--when last signal received if not decommissioned-->
| decay_date         = <!--when craft re-entered the atmosphere, not needed if it landed-->
<!--{{end-date||timezone=yes}}&nbsp;UTC-->| orbit_reference    = [[Geocentric orbit|Geocentric]]
| orbit_regime       = [[Highly elliptical orbit|Highly elliptical]]
| orbit_semimajor    = {{convert|80795.9|km|mi|abbr=on}}
| orbit_eccentricity = 0.743972
| orbit_periapsis    = {{convert|14307.9|km|mi|abbr=on}}
| orbit_apoapsis     = {{convert|134527.6|km|mi|abbr=on}}
| orbit_inclination  = 76.7156°
| orbit_period       = 3809.3 min
| orbit_RAAN         = 305.3107°
| orbit_arg_periapsis = 267.2574°
| orbit_mean_anomaly = 0.3010°
| orbit_mean_motion  = 0.3780 rev/day
| orbit_epoch        = September 4, 2015, 04:37:54&nbsp;UTC<ref name="heavens-above">{{cite web |url=http://www.heavens-above.com/orbit.aspx?satid=25867 |title=Chandra X-Ray Observatory - Orbit |work=Heavens Above |date=September 3, 2015 |access-date=September 3, 2015}}</ref>
| orbit_rev_number   = 1358
| apsis              = gee
| telescope_type     = [[Wolter telescope|Wolter type 1]]<ref name="cxc-overview">{{cite web |url=http://cxc.harvard.edu/cdo/about_chandra/overview_cxo.html |title=The Chandra X-ray Observatory: Overview |publisher=Chandra X-ray Center |access-date=September 3, 2015}}</ref>
| telescope_diameter = {{convert|3.9|ft|m|order=flip|abbr=on}}<ref name="chandraspecs" />
| telescope_focal_length = {{convert|32.8|ft|m|order=flip|abbr=on}}<ref name="chandraspecs" />
| telescope_area     = {{convert|0.04|m2|abbr=on}}<ref name="chandraspecs" />
| telescope_wavelength = [[X-ray]]: 0.12–12&nbsp;[[nanometre|nm]] (0.1–10&nbsp;[[kiloelectronvolt|keV]])<ref name="Ridpath2012">{{cite book |url=https://books.google.com/books?id=O31j9UJ3U4oC&pg=PA82 |title=The Dictionary of Astronomy |publisher=Oxford University Press |first=Ian |last=Ridpath |edition=2nd |page=82 |date=2012 |isbn=978-0-19-960905-5}}</ref>
| telescope_resolution = 0.5 arcsec<ref name="chandraspecs" />
| instruments_list   = {{Infobox spaceflight/Instruments
   | acronym1 = ACIS | name1 = [[Advanced CCD Imaging Spectrometer]]
   | acronym2 = HRC  | name2 = High Resolution Camera
   | acronym3 = HETG | name3 = High Energy Transmission Grating
   | acronym4 = LETG | name4 = Low Energy Transmission Grating
 }}
| programme             = '''[[Great Observatories program|NASA Great Observatories]]'''
| previous_mission      = [[Compton Gamma Ray Observatory|Compton]]
| next_mission          = [[Spitzer Space Telescope|Spitzer]]
| programme2            = '''[[Large Strategic Science Missions]]'''<br><small>''Astrophysics Division''</small>
| previous_mission2     = [[Compton Gamma Ray Observatory|Compton]]
| next_mission2         = [[James Webb Space Telescope|JWST]]
}}

The '''Chandra X-ray Observatory''' ('''CXO'''), previously known as the '''Advanced X-ray Astrophysics Facility''' ('''AXAF'''), is a [[Flagship program|Flagship-class]] [[space telescope]] launched aboard the {{OV|102}} during [[STS-93]] by [[NASA]] on July 23, 1999. Chandra is sensitive to [[X-ray astronomy|X-ray sources]] 100 times fainter than any previous [[X-ray telescope]], enabled by the high [[angular resolution]] of its mirrors. Since the [[Earth's atmosphere]] absorbs the vast majority of [[X-ray]]s, they are not detectable from Earth-based [[telescope]]s; therefore space-based telescopes are required to make these observations. Chandra is an Earth [[satellite]] in a 64-hour orbit, and its mission is ongoing {{as of|2025|lc=y}}. Chandra is one of the [[Great Observatories program|Great Observatories]], along with the [[Hubble Space Telescope]], [[Compton Gamma Ray Observatory]] (1991–2000), and the [[Spitzer Space Telescope]] (2003–2020). The telescope is named after the Nobel Prize-winning Indian-American astrophysicist [[Subrahmanyan Chandrasekhar]].<ref name="cowinners1998" /> Its mission is similar to that of [[ESA]]'s [[XMM-Newton]] spacecraft, also launched in 1999 but the two telescopes have different design foci, as Chandra has a much higher angular resolution and XMM-Newton higher spectroscopy throughput.

In response to a decrease in NASA funding in 2024 by the [[United States Congress|US Congress]], Chandra is threatened with an early cancellation despite having more than a decade of operation left. The cancellation has been referred to as a potential "extinction-level" event for [[X-ray astronomy]] in the US.{{Citation needed|date=April 2025}} A group of astronomers have put together a public outreach project to try to get enough American citizens to persuade the US Congress to provide enough funding to avoid early termination of the observatory.<ref>{{cite web |title=Act Now |url=https://www.savechandra.org/act |website=Save the Chandra X-ray Observatory |access-date=May 25, 2024 }}</ref>

==History==
In 1976, the Chandra X-ray Observatory (called AXAF at the time) was proposed to NASA by [[Riccardo Giacconi]] and Harvey Tananbaum. Preliminary work began the following year at [[Marshall Space Flight Center]] (MSFC) and the [[Smithsonian Astrophysical Observatory]] (SAO), where the telescope is now operated for NASA<ref>{{cite web |title=Chandra X-ray Center |url=https://cxc.cfa.harvard.edu/ |website=CXC.CFA.Harvard.edu |access-date=February 21, 2022 }}</ref> at the Chandra X-ray Center in the [[Harvard-Smithsonian Center for Astrophysics|Center for Astrophysics {{!}} Harvard & Smithsonian]]. In the meantime, in 1978, NASA launched the first imaging X-ray telescope, [[Einstein Observatory|Einstein]] (HEAO-2), into orbit. Work continued on the AXAF project throughout the 1980s and 1990s. In 1992, to reduce costs, the spacecraft was redesigned. Four of the twelve planned mirrors were eliminated, as were two of the six scientific instruments. AXAF's planned orbit was changed to an elliptical one, reaching one third of the way to the Moon's at its farthest point. This eliminated the possibility of improvement or repair by the [[Space Shuttle program|Space Shuttle]] but put the observatory above the Earth's [[Van Allen radiation belt|radiation belts]] for most of its orbit. AXAF was assembled and tested by [[TRW Inc.|TRW]] (now [[Northrop Grumman]] Aerospace Systems) in [[Redondo Beach, California|Redondo Beach]], [[California]].

[[File:STS-93 launch.jpg|thumb|left|[[Space Shuttle Columbia|Space Shuttle ''Columbia'']], [[STS-93]] launches in 1999]]

AXAF was renamed Chandra as part of a contest held by NASA in 1998, which drew more than 6,000 submissions worldwide.<ref name="harvard20131031">{{cite web |url=http://chandra.harvard.edu/chronicle/0413/name/ |title=Tyrel Johnson & Jatila van der Veen - Winners of the Chandra-Naming Contest - Where Are They Now? |publisher=Center for Astrophysics {{!}} Harvard & Smithsonian |first=Wallace |last=Tucker |date=October 31, 2013 |access-date=January 12, 2014 }}</ref> The contest winners, Jatila van der Veen and Tyrel Johnson (then a high school teacher and high school student, respectively), suggested the name in honor of Nobel Prize–winning [[Indian-American]] [[astrophysicist]] [[Subrahmanyan Chandrasekhar]]. He is known for his work in determining the [[Chandrasekhar limit|maximum mass]] of [[white dwarf]] stars, leading to greater understanding of high energy astronomical phenomena such as [[neutron star]]s and [[black hole]]s.<ref name="cowinners1998">{{cite web |url=http://chandra.harvard.edu/contest/co_winners.html |title=And the Co-Winners Are... |publisher=Center for Astrophysics {{!}} Harvard & Smithsonian |date=1998 |archive-date=January 12, 2014 |archive-url=https://web.archive.org/web/20140112205117/http://chandra.harvard.edu/contest/co_winners.html }}</ref> Fittingly, the name Chandra means "moon" in [[Sanskrit]].<ref>{{cite web |url=https://www.behindthename.com/name/chandra |title=Meaning, origin and history of the name Chandra |website=Behind the Name |access-date=June 19, 2024 }}</ref>

Originally scheduled to be launched in December 1998,<ref name="harvard20131031" /> the spacecraft was delayed several months, eventually being launched on July 23, 1999, at 04:31&nbsp;UTC by {{OV|Columbia}} during [[STS-93]]. Chandra was deployed by [[Catherine Coleman|Cady Coleman]]<ref>{{cite web |publisher=NASA |title=Image: July 23, 1999, Chandra X-ray Observatory Awaits Deployment |url=https://chandra.harvard.edu/press/bios/coleman_bio.html |website=Phys.org |access-date=February 21, 2022 }}</ref> from ''Columbia'' at 11:47&nbsp;UTC. The Inertial Upper Stage's first stage motor ignited at 12:48&nbsp;UTC, and after burning for 125 seconds and separating, the second stage ignited at 12:51&nbsp;UTC and burned for 117 seconds.<ref>{{cite web |url=http://www1.msfc.nasa.gov:80/NEWSROOM/news/status/chandrastatus/chandrastatus27.html |title=Chandra X-ray Observatory Status Report: July 23, 1999 6:00 p.m. EDT |series=Marshall Space Flight Center Status Reports |publisher=NASA |first=Dave |last=Drachlis |date=July 23, 1999 |archive-url=https://web.archive.org/web/20000226004401/http://www1.msfc.nasa.gov/NEWSROOM/news/status/chandrastatus/chandrastatus27.html |archive-date=February 26, 2000 }}</ref> At {{convert|22753|kg|lb}},<ref name="chandra-quick-facts" /> it was the heaviest payload ever launched by the shuttle, a consequence of the two-stage [[Inertial Upper Stage]] booster rocket system needed to transport the spacecraft to its high orbit.

Chandra has been returning data since the month after it launched. It is operated by the SAO at the Chandra X-ray Center in [[Cambridge, Massachusetts]], with assistance from [[MIT]] and [[Northrop Grumman]] Space Technology. The ACIS CCDs suffered particle damage during early radiation belt passages. To prevent further damage, the instrument is now removed from the telescope's focal plane during passages.

Although Chandra was initially given an expected lifetime of 5 years, on September 4, 2001, NASA extended its lifetime to 10 years "based on the observatory's outstanding results."<ref>{{cite web |url=http://chandra.harvard.edu/chronicle/0301/extended_mission.html |title=Chandra's Mission Extended to 2009 |publisher=Center for Astrophysics {{!}} Harvard & Smithsonian |date=September 28, 2001}}</ref> Physically Chandra could last much longer. A 2004 study performed at the Chandra X-ray Center indicated that the observatory could last at least 15 years.<ref>{{cite journal |title=The Development and Scientific Impact of the Chandra X-Ray Observatory |journal=International Journal of Modern Physics D |first=Daniel A. |last=Schwartz |volume=13 |issue=7 |pages=1239–1248 |date=August 2004 |doi=10.1142/S0218271804005377 |arxiv=astro-ph/0402275 |bibcode=2004IJMPD..13.1239S|s2cid=858689 }}</ref> It is active as of 2024 and has an upcoming schedule of observations published by the Chandra X-ray Center.<ref>{{cite web |title=CXO Long-term Schedule |url=https://cxc.harvard.edu/target_lists/longsched.html |website=CXC.Harvard.edu |access-date=February 21, 2022 }}</ref>

In July 2008, the [[International X-ray Observatory]], a joint project between [[ESA]], [[NASA]] and [[JAXA]], was proposed as the next major X-ray observatory but was later canceled.<ref>{{cite web |url=http://constellation.gsfc.nasa.gov/ |title=International X-ray Observatory |publisher=NASA |archive-url=https://web.archive.org/web/20080303062108/http://constellation.gsfc.nasa.gov/ |archive-date=March 3, 2008 }}</ref> ESA later resurrected a downsized version of the project as the [[Advanced Telescope for High Energy Astrophysics]] (ATHENA), with a proposed launch in 2028.<ref name="space20131101">{{cite news |url=http://www.space.com/23440-athena-xray-space-telescope-2028.html |title=X-ray Space Telescope of the Future Could Launch in 2028 |work=Space.com |first=Elizabeth |last=Howell |date=November 1, 2013 |access-date=January 1, 2014 }}</ref>

On October 10, 2018, Chandra entered safe mode operations, due to a gyroscope glitch. NASA reported that all science instruments were safe.<ref name="cnet20181012">{{cite news |url=https://www.cnet.com/news/another-nasa-space-telescope-chandra-x-ray-observatory-just-went-into-safe-mode/ |title=Another NASA space telescope just went into safe mode |work=CNET |first=Amanda |last=Kooser |date=October 12, 2018 |access-date=October 14, 2018 }}</ref><ref>{{cite web |url=https://www.nasa.gov/feature/chandra-enters-safe-mode-investigation-underway |title=Chandra Enters Safe Mode; Investigation Underway |publisher=NASA |editor-first=Brian |editor-last=Dunbar |date=October 12, 2018 |access-date=October 14, 2018 |archive-date=November 11, 2022 |archive-url=https://web.archive.org/web/20221111213927/https://www.nasa.gov/feature/chandra-enters-safe-mode-investigation-underway/ }}</ref> Within days, the 3-second error in data from one gyro was understood, and plans were made to return Chandra to full service. The gyroscope that experienced the glitch was placed in reserve and is otherwise healthy.<ref>{{cite web |url=http://chandra.si.edu/press/18_releases/press_101518.html |title=Chandra Operations Resume after Cause of Safe Mode Identified |publisher=NASA/[[Smithsonian]] |first1=Felicia |last1=Chou |first2=Molly |last2=Porter |first3=Megan |last3=Watzke |date=October 24, 2018 |access-date=June 19, 2024 }}</ref>

In March 2024, Congress decided to reduce funding for NASA and its missions.
This may lead to the premature end of this mission.<ref>{{cite news |url=https://www.space.com/chandra-x-ray-observatory-nasa-fy2025-budget |title=The Chandra X-ray spacecraft may soon go dark, threatening a great deal of astronomy |work=Space.com |first=Monisha |last=Ravisetti |date=March 23, 2024 |access-date=June 13, 2023 }}</ref>
In June 2024, Senators urged NASA to reconsider the cuts to Chandra, which was accepted.<ref>{{cite news|url=https://spacenews.com/congressional-letter-asks-nasa-to-rescind-chandra-cuts/ |title=Congressional letter asks NASA to rescind Chandra cuts |work=Spacenews.com |first=Jeff |last=Foust |date=June 13, 2024 |access-date=June 13, 2024 }}</ref>

==Example discoveries==
[[File:STS-93 crew.jpg|thumb|Crew of STS-93 with a scale model]]
The data gathered by Chandra has greatly advanced the field of [[X-ray astronomy]]. Here are some examples of discoveries supported by observations from Chandra:
* The [[First light (astronomy)|first light]] image, of [[supernova remnant]] [[Cassiopeia A]], gave astronomers their first glimpse of the [[compact object]] at the center of the remnant, probably a neutron star or black hole.<ref>{{cite web |last=Hall |first=Alan |title=Chandra Sees Its 'First Light' |url=https://www.scientificamerican.com/article/chandra-sees-its-first-li/ |access-date=September 27, 2023 |website=Scientific American }}</ref><ref>{{cite journal |title=The Compact Central Object in Cassiopeia A: A Neutron Star with Hot Polar Caps or a Black Hole? |journal=[[The Astrophysical Journal]] |last1=Pavlov |first1=G. G. |last2=Zavlin |first2=V. E. |last3=Aschenbach |first3=B. |last4=Trumper |first4=J. |last5=Sanwal |first5=D. |volume=531 |issue=1 |pages=L53–L56 |date=2000 |arxiv=astro-ph/9912024 |doi=10.1086/312521 |pmid=10673413 |bibcode=2000ApJ...531L..53P |s2cid=16849221 }}</ref>
* In the [[Crab Nebula]], another supernova remnant, Chandra showed a never-before-seen ring around the central [[pulsar]] and jets that had only been partially seen by earlier telescopes.<ref>{{cite journal |title=Discovery of Spatial and Spectral Structure in the X-Ray Emission from the Crab Nebula |journal=[[The Astrophysical Journal]] |last1=Weisskopf |first1=M. C. |last2=Hester |first2=J. J. |last3=Tennant |first3=A. F. |last4=Elsner |first4=R. F. |last5=Schulz |first5=N. S. |last6=Marshall |first6=H. L. |last7=Karovska |first7=M. |last8=Nichols |first8=J. S. |last9=Swartz |first9=D. A. |last10=Kolodziejczak |first10=J. J. |last11=O'Dell |first11=S. L. |display-authors=9 |volume=536 |issue=2 |pages=L81–L84 |date=2000 |arxiv=astro-ph/0003216 |doi=10.1086/312733 |pmid=10859123 |bibcode=2000ApJ...536L..81W|s2cid=14879330 }}</ref>
* The first X-ray emission was seen from the [[supermassive black hole]], [[Sagittarius A*]], at the [[Galactic Center|center]] of the [[Milky Way]].<ref>{{cite journal |title=Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre |journal=[[Nature (journal)|Nature]] |first1=F. K. |last1=Baganoff |first2=M. W. |last2=Bautz |first3=W. N. |last3=Brandt |first4=G. |last4=Chartas |first5=E. D. |last5=Feigelson |first6=G. P. |last6=Garmire |first7=Y. |last7=Maeda |first8=M. |last8=Morris |first9=G. R. |last9=Ricker |first10=L. K. |last10=Townsley |first11=F. |last11=Walter |display-authors=9 |volume=413 |issue=6851 |pages=45–48 |date=2001 |arxiv=astro-ph/0109367 |doi=10.1038/35092510 |pmid=11544519 |bibcode=2001Natur.413...45B|s2cid=2298716 }}</ref>
* Chandra confirmed that X-rays in [[O-type stars]] are generated through plasma shocks embedded in their wind.<ref>{{cite journal |title=Chandra Discovers a Very High Density X-Ray Plasma on the O Star ζ Orionis |journal=[[The Astrophysical Journal]] |last1=Waldron |first1=Wayne L. |last2=Cassinelli |first2=Joseph P. |volume=548 |issue=1 |pages=L45-L48 |date=2001 |arxiv=astro-ph/0012190 |doi=10.1086/318926 |bibcode=2001ApJ...548L..45W }}</ref>
* Chandra found much more cool [[gas]] than expected spiraling into the center of the [[Andromeda Galaxy]].
* Pressure fronts were observed in detail for the first time in [[Abell 2142]], where [[galaxy cluster|clusters]] of galaxies are merging.
* The earliest images in X-rays of the [[shock wave]] of a [[supernova]] were taken of [[SN 1987A]].
* Chandra showed for the first time the shadow of a small [[galaxy]] as it is being cannibalized by a larger one, in an image of [[Perseus A]].
* A new type of black hole was discovered in galaxy [[Messier 82|M82]], mid-mass objects purported to be the missing link between [[Stellar black hole|stellar-sized black holes]] and [[super massive black holes]].<ref>{{cite journal |title=Hot Plasma and Black Hole Binaries in Starburst Galaxy M82 |journal=[[Science (journal)|Science]] |first1=R. E. |last1=Griffiths |first2=A. |last2=Ptak |first3=E. D. |last3=Feigelson |first4=G. |last4=Garmire |first5=L. |last5=Townsley |first6=W. N. |last6=Brandt |first7=R. |last7=Sambruna |first8=J. N. |last8=Bregman |volume=290 |issue=5495 |pages=1325–1328 |date=2000 |doi=10.1126/science.290.5495.1325 |pmid=11082054 |bibcode=2000Sci...290.1325G }}</ref>
* X-ray [[emission line]]s were associated for the first time with a [[gamma-ray burst]], [[Beethoven Burst]] GRB 991216.<ref>{{cite journal |title=Observation of X-ray lines from a gamma-ray burst (GRB991216): evidence of moving ejecta from the progenitor |journal=[[Science (journal)|Science]] |first1=L. |last1=Piro |first2=G. |last2=Garmire |first3=M. |last3=Garcia |first4=G. |last4=Stratta |first5=E. |last5=Costa |first6=M. |last6=Feroci |first7=P. |last7=Meszaros |first8=M. |last8=Vietri |first9=H. |last9=Bradt |first10=D. |last10=Frail |first11=F. |last11=Frontera |first12=J. |last12=Halpern |first13=J. |last13=Heise |first14=K. |last14=Hurley |first15=N. |last15=Kawai |first16=R. M. |last16=Kippen |first17=F. |last17=Marshall |first18=T. |last18=Murakami |first19=V. V. |last19=Sokolov |first20=T. |last20=Takeshima |first21=A. |last21=Yoshida |display-authors=9 |volume=290 |issue=5493 |pages=955–958 |date=2000 |arxiv=astro-ph/0011337 |doi=10.1126/science.290.5493.955 |pmid=11062121 |bibcode=2000Sci...290..955P|s2cid=35190896 }}</ref>
* High school students, using Chandra data, [[CXOU J061705.3+222127|discovered]] a neutron star in supernova remnant [[IC 443]].<ref>{{cite press release |url=http://quest.nasa.gov/dso/news/press_release/12-11-00.txt |title=Students Using NASA and NSF Data Make Stellar Discovery; Win Science Team Competition |publisher=NASA |id=Release 00-195 |date=December 12, 2000 |archive-url=https://web.archive.org/web/20130510130847/http://quest.nasa.gov/dso/news/press_release/12-11-00.txt |archive-date=May 10, 2013 }}</ref>
* Observations by Chandra and [[BeppoSAX]] suggest that gamma-ray bursts occur in [[star-forming region]]s.
* Chandra data suggested that [[RX J1856.5-3754]] and [[3C58]], previously thought to be pulsars, might be even denser objects: [[quark star]]s. These results are still debated.
* Sound waves from violent activity around a [[super massive black hole]] were observed in the [[Perseus Cluster]] (2003).
* [[File:Chandra X-ray Observatory image of the brown dwarf TWA 5B.jpg|thumb|CXO image of the brown dwarf TWA 5B]]TWA 5B, a [[brown dwarf]], was seen orbiting a [[binary star|binary]] system of Sun-like [[star]]s.
* Nearly all stars on the [[main sequence]] are X-ray emitters.<ref>Schmitt & Liefke, 2004</ref>
* The X-ray shadow of [[Titan (moon)|Titan]] was seen when it [[Astronomical transit|transited]] the Crab Nebula.
* X-ray emissions from materials falling from a [[protoplanetary disc]] into a star.<ref>{{cite journal |title=An X-ray outburst from the rapidly accreting young star that illuminates McNeil's nebula |journal=[[Nature (journal)|Nature]] |first1=J. H. |last1=Kastner |first2=M. |last2=Richmond |first3=N. |last3=Grosso |first4=D. A. |last4=Weintraub |first5=T. |last5=Simon |first6=A. |last6=Frank |first7=K. |last7=Hamaguchi |first8=H. |last8=Ozawa |first9=A. |last9=Henden |volume=430 |issue=6998 |pages=429–431 |date=2004 |arxiv=astro-ph/0408332 |doi=10.1038/nature02747 |pmid=15269761 |bibcode=2004Natur.430..429K|s2cid=1186552 }}</ref>
* [[Hubble constant]] measured to be 76.9&nbsp;km/s/[[Parsec|Mpc]] using [[Sunyaev-Zel'dovich effect]].<ref>{{cite journal |title=Determination of the Cosmic Distance Scale from Sunyaev-Zel'dovich Effect and Chandra X-Ray Measurements of High-Redshift Galaxy Clusters |last1=Bonamente |first1=Massimiliano |last2=Joy |first2=Marshall |last3=LaRoque |first3=Samuel |last4=Carlstrom |first4=John |last5=Reese |first5=Erik |last6=Dawson |first6=Kyle |date=August 10, 2006 |journal=The Astrophysical Journal |volume=647 |issue=1 |pages=25–54 |doi=10.1086/505291 |arxiv=astro-ph/0512349 |bibcode=2006ApJ...647...25B |s2cid=15723115 }}</ref>
* 2006 Chandra found strong evidence that dark matter exists by observing super cluster collision.<ref>{{cite journal |title=A Direct Empirical Proof of the Existence of Dark Matter |last1=Clowe |first1=Douglas |last2=Bradač |first2=Maruša |last3=Gonzalez |first3=Anthony |last4=Markevitch |first4=Maxim |last5=Randall |first5=Scott |last6=Jones |first6=Christine |last7=Zaritsky |first7=Dennis |date=August 30, 2006 |journal=The Astrophysical Journal |volume=648 |issue=2 |pages=L109–L113 |doi=10.1086/508162 |arxiv=astro-ph/0608407 |bibcode=2006ApJ...648L.109C |doi-access=free }}</ref>
* 2006 X-ray emitting loops, rings and filaments discovered around a [[super massive black hole]] within [[Messier 87]] imply the presence of pressure waves, shock waves and sound waves. The evolution of [[Messier 87]] may have been dramatically affected.<ref>{{cite press release |last1=Roy |first1=Steve |last2=Watzke |first2=Megan |url=http://chandra.harvard.edu/press/06_releases/press_100506.html |title=Chandra Reviews Black Hole Musical: Epic But Off-Key |publisher=Center for Astrophysics {{!}} Harvard & Smithsonian |date=October 2006}}</ref>
* Observations of the [[Bullet cluster]] put limits on the cross-section of the self-interaction of [[dark matter]].<ref>{{cite conference |title=Recent and Future Observations in the X-ray and Gamma-ray Bands: Chandra, Suzaku, GLAST, and NuSTAR |conference=Astrophysical Sources of High Energy Particles and Radiation. June 20–24, 2005. Torun, Poland. |series=AIP Conference Proceedings |first=Greg |last=Madejski |volume=801 |page=21 |date=2005 |doi=10.1063/1.2141828 |arxiv=astro-ph/0512012 }}</ref>
* "The Hand of God" photograph of [[PSR B1509-58]].
* Jupiter's x-rays coming from poles, not auroral ring.<ref>{{cite news |url=https://science.nasa.gov/science-news/science-at-nasa/2002/07mar_jupiterpuzzle/ |title=Puzzling X-rays from Jupiter |publisher=NASA |date=March 7, 2002 |access-date=July 12, 2022 }}</ref>
* A large halo of hot gas was found surrounding the Milky Way.<ref>{{cite web |first1=J. D. |last1=Harrington |first2=Janet |last2=Anderson |first3=Peter |last3=Edmonds |date=September 24, 2012 |url=http://www.nasa.gov/mission_pages/chandra/news/H-12-331.html |title=NASA's Chandra Shows Milky Way is Surrounded by Halo of Hot Gas |publisher=NASA }}</ref>
* Extremely dense and luminous dwarf galaxy [[M60-UCD1]] observed.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/chandra/multimedia/m60-dense-galaxy.html |title=M60-UCD1: An Ultra-Compact Dwarf Galaxy |publisher=NASA |date=September 24, 2013}}</ref>
* On January 5, 2015, NASA reported that CXO observed an [[X-ray]] flare 400 times brighter than usual, a record-breaker, from [[Sagittarius A*]], the [[supermassive black hole]] in the center of the [[Milky Way|Milky Way galaxy]]. The unusual event may have been caused by the breaking apart of an [[asteroid]] falling into the black hole or by the entanglement of [[magnetic field lines]] within gas flowing into Sagittarius A*, according to astronomers.<ref name="NASA-20150105">{{cite web |last1=Chou |first1=Felicia |last2=Anderson |first2=Janet |last3=Watzke |first3=Megan |title=RELEASE 15-001 - NASA's Chandra Detects Record-Breaking Outburst from Milky Way's Black Hole |url=http://www.nasa.gov/press/2015/january/nasa-s-chandra-detects-record-breaking-outburst-from-milky-way-s-black-hole/ |date=January 5, 2015 |work=[[NASA]] |access-date=January 6, 2015}}</ref>
* In September 2016, it was announced that Chandra had detected X-ray emissions from [[Pluto]], the first detection of X-rays from a [[Kuiper belt]] object. Chandra had made the observations in 2014 and 2015, supporting the ''[[New Horizons]]'' spacecraft for its July 2015 encounter.<ref>{{cite web |url=http://www.jhuapl.edu/newscenter/pressreleases/2016/160914.asp |title=X-Ray Detection Sheds New Light on Pluto |publisher=[[Applied Physics Laboratory]] |date=September 14, 2016 |archive-url=https://web.archive.org/web/20161017110547/http://jhuapl.edu/newscenter/pressreleases/2016/160914.asp |archive-date=October 17, 2016 }}</ref>
* In September 2020, Chandra reportedly may have made an observation of an [[exoplanet]] in the [[Whirlpool Galaxy]], which would be the first planet discovered beyond the Milky Way.<ref>{{Cite news |first=Paul |last=Rincon |date=October 25, 2021 |title=Signs of first planet found outside our galaxy |work=BBC News |url=https://www.bbc.com/news/science-environment-59044650 |archive-url=https://web.archive.org/web/20211025214850/https://www.bbc.com/news/science-environment-59044650 |archive-date=October 25, 2021 |url-status=live }}</ref><ref>{{cite news |last=Crane |first=Leah |title=Astronomers May Have Found the First Planet in Another Galaxy |url=https://www.newscientist.com/article/2255431-astronomers-may-have-found-the-first-planet-in-another-galaxy/ |date=September 23, 2020 |work=[[New Scientist]] |access-date=September 25, 2020 }}</ref><ref>{{cite arXiv |last=Di Stefano |first=R. |display-authors=et al. |title=M51-ULS-1b: The First Candidate for a Planet in an External Galaxy |eprint=2009.08987 |date=September 18, 2020 |class=astro-ph.HE }}</ref>
* In April 2021, NASA announced findings from the observatory in a tweet saying "Uranus gives off X-rays, astronomers find". The discovery would have "intriguing implications for understanding Uranus" if it is confirmed that the X-rays originate from the planet and are not emitted by the Sun.<ref>{{cite web |last=Mohon |first=Lee |date=March 30, 2021 |title=First X-rays from Uranus Discovered |url=http://www.nasa.gov/mission_pages/chandra/images/first-x-rays-from-uranus-discovered.html |archive-date=July 25, 2022 |archive-url=https://web.archive.org/web/20220725172011/https://www.nasa.gov/mission_pages/chandra/images/first-x-rays-from-uranus-discovered.html |publisher=NASA }}</ref>

==Technical description==
[[File:Chandra X-ray space observatory Obs assemb2 300.jpg|thumb|Assembly of the telescope]]
[[File:Chandra telescope mirror assembled Hrma7 300.jpg|thumb|The main mirror of AXAF (Chandra)]]
[[File:Chandra X-ray space observatory - HRCfront-150.jpg|thumb|HRC flight unit of Chandra]]

Unlike [[optical]] telescopes which possess simple aluminized [[Parabolic reflector|parabolic]] surfaces (mirrors), X-ray telescopes generally use a [[Wolter telescope]] consisting of nested cylindrical [[paraboloid]] and [[hyperboloid]] surfaces coated with [[iridium]] or [[gold]]. X-ray [[photon]]s would be absorbed by normal mirror surfaces, so mirrors with a low grazing angle are necessary to reflect them. Chandra uses four pairs of nested mirrors, together with their support structure, called the [[High Resolution Mirror Assembly]] (HRMA); the mirror substrate is 2&nbsp;cm-thick glass, with the reflecting surface a 33&nbsp;nm iridium coating, and the diameters are 65&nbsp;cm, 87&nbsp;cm, 99&nbsp;cm and 123&nbsp;cm.<ref>{{cite web |url=http://cxc.harvard.edu/cal/Hrma/users_guide/hrma-notes.pdf |title=The HRMA User's Guide |publisher=Chandra X-ray Center |first1=T. J. |last1=Gaetz |first2=Diab |last2=Jerius |date=January 28, 2005 |archive-url=https://web.archive.org/web/20060210070532/http://cxc.harvard.edu/cal/Hrma/users_guide/hrma-notes.pdf |archive-date=February 10, 2006}}</ref> The thick substrate and particularly careful polishing allowed a very precise optical surface, which is responsible for Chandra's unmatched resolution: between 80% and 95% of the incoming X-ray energy is focused into a one-[[arcsecond]] circle. However, the thickness of the substrate limits the proportion of the aperture which is filled, leading to the low collecting area compared to [[XMM-Newton]].

Chandra's highly [[ellipse|elliptical]] orbit allows it to observe continuously for up to 55 hours of its 65-hour [[orbital period]]. At its furthest orbital point from Earth, Chandra is one of the most distant Earth-orbiting satellites. This orbit takes it beyond the geostationary satellites and beyond the outer [[Van Allen belt]].<ref>{{cite web |last1=Gott |first1=J. Richard |last2=Juric |first2=Mario |date=2006 |url=http://www.astro.princeton.edu/universe/ |title=Logarithmic Map of the Universe |publisher=Princeton University }}</ref>

With an [[angular resolution]] of 0.5 [[arcsecond]] (2.4 μrad), Chandra possesses a resolution over 1000 times better than that of the first orbiting X-ray telescope.

CXO uses mechanical [[gyroscope]]s,<ref>{{cite web |url=http://jwst.nasa.gov/faq_scientists.html |title=Technical Frequently Asked Questions (FAQ) |series=James Webb Space Telescope |publisher=NASA |access-date=December 14, 2016 }}</ref> which are sensors that help determine what direction the telescope is pointed.<ref name="chandra-spacecraft">{{cite web |url=http://chandra.harvard.edu/about/spacecraft.html |title=Spacecraft: Motion, Heat, and Energy |series=Chandra X-ray Observatory |publisher=NASA |date=March 17, 2014 |access-date=December 14, 2016 }}</ref> Other navigation and orientation systems on board CXO include an aspect camera, Earth and [[Sun sensor]]s, and [[reaction wheel]]s. It also has two sets of thrusters, one for movement and another for offloading momentum.<ref name="chandra-spacecraft" />

==Instruments==
The Science Instrument Module (SIM) holds the two focal plane instruments, the [[Advanced CCD Imaging Spectrometer]] (ACIS) and the [[High Resolution Camera]] (HRC), moving whichever is called for into position during an observation.

ACIS consists of 10 [[Charge-coupled device|CCD]] chips and provides images as well as [[spectroscopy|spectral]] information of the object observed. It operates in the [[photon energy]] range of 0.2–10 [[keV]]. The HRC has two [[micro-channel plate]] components and images over the range of 0.1–10&nbsp;keV. It also has a time resolution of 16 [[microsecond]]s. Both of these instruments can be used on their own or in conjunction with one of the observatory's two [[Diffraction grating|transmission gratings]].

The transmission gratings, which swing into the optical path behind the mirrors, provide Chandra with high resolution spectroscopy. The [http://space.mit.edu/HETG/ High Energy Transmission Grating Spectrometer] (HETGS) works over 0.4–10&nbsp;keV and has a [[spectral resolution]] of 60–1000. The [[Low Energy Transmission Grating Spectrometer]] (LETGS) has a range of 0.09–3&nbsp;keV and a resolution of 40–2000.

Summary:<ref>{{cite web |url=http://chandra.si.edu/about/science_instruments.html |title=Science Instruments |publisher=Center for Astrophysics {{!}} Harvard & Smithsonian |access-date=November 17, 2016 }}</ref>
* High Resolution Camera (HRC)
* [[Advanced CCD Imaging Spectrometer]] (ACIS)
* High Energy Transmission Grating Spectrometer (HETGS)
* Low Energy Transmission Grating Spectrometer (LETGS)

==Gallery==
[[File:Chandra-spacecraft labeled-en.jpg|thumb|left|400px|Labeled diagram of CXO]]
[[File:Animation of Chandra X-ray Observatory orbit.gif|thumb|center|300px|Animation of Chandra X-ray Observatory{{'s}} orbit around Earth from August 7, 1999<br>{{legend2|magenta|Chandra}}{{·}}{{legend2|RoyalBlue|[[Earth]]}}]]
{{Clear}}
<gallery>
File:PIA21061-Pluto-DwarfPlanet-XRays-20160914.jpg|X-Rays of [[Pluto]]
File:Jupiter X-ray Aurora Chandra.jpg|[[Jupiter]] in X-ray light
File:Tycho xrayonly.jpg|[[Tycho Supernova]] remnant in X-ray light
File:Sn2006gy CHANDRA x-ray.jpg|[[SN 2006gy]] (upper right) and parent galaxy [[NGC 1260]]
File:CXO orbit 20140107.png|CXO orbit as of January 7, 2014
File:M31 Core in X-rays.jpg|M31 Core in X-ray light
File:PSR B1509-58 full.jpg|[[PSR B1509-58]] – red, green and blue/max energy
File:14-296-GalaxyClusters-PerseusVirgo-ChandraXRay-20141027.jpg|[[Turbulence]] may prevent [[galaxy cluster]]s from cooling.
File:X-RayFlare-BlackHole-MilkyWay-20140105.jpg|Bright [[X-ray]] flare from [[Sagittarius A*]], [[supermassive black hole]] in the [[Milky Way]]<ref name="NASA-20150105" />
File:NASA-SNR0519690-ChandraXRayObservatory-20150122.jpg|SNR 0519–69.0 – remains of an exploding star in the [[Large Magellanic Cloud]]
File:NASA-2015IYL-MultiPix-ChandraXRayObservatory-20150122.jpg|Images released to celebrate the [[International Year of Light|International Year of Light 2015]]
File:Chandra X-ray View of Orion.jpg|[[Trapezium Cluster|Cluster]] of [[star formation|newly formed stars]] in [[Orion Nebula]]
File:GKPersei-MiniSuperNova-20150316.jpg|[[GK Persei]]: Nova of 1901
File:15-137-CircinusX1-XRayLightRings-NeutronStar-Chandra-20150624.jpg|X-ray light rings from a [[neutron star]] in [[Circinus X-1]]
File:Chandra image of Cygnus X-1.jpg|[[Cygnus X-1]], the first strong black hole discovered
File:ESO-Chandra Deep Field-phot-02a-03-hires.jpg|Image of the [[Chandra Deep Field South]] estimated by [[Kimberly Arcand]] as showing 5000 black holes
</gallery>

==See also==
{{Portal|Astronomy|Spaceflight}}
* [[AGILE (satellite)]], an Italian orbital X-ray telescope
* [[Great Observatories program]]
* [[List of deep fields]]
* [[List of space telescopes]]
* [[List of X-ray space telescopes]]
* [[Lynx X-ray Observatory]], possible successor
* [[NuSTAR]]
* [[Suzaku (satellite)|Suzaku]], a sister satellite originating from AXAF-S (spectrometer)
* [[X-ray astronomy]]

==References==
{{Reflist}}

==Further reading==
* {{cite journal |last1=Swartz |first1=Douglas A. |last2=Wolk |first2=Scott J. |last3=Fruscione |first3=Antonella |title=Chandra's First Decade of Discovery |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=107 |issue=16 |pages=7127–7134 |date=April 20, 2010 |doi=10.1073/pnas.0914464107 |pmid=20406906 |pmc=2867717 |bibcode=2010PNAS..107.7127S |doi-access=free }}

==External links==
{{Commons category|Chandra X-ray Observatory}}
* [http://www.nasa.gov/chandra Chandra X-ray Observatory] at NASA.gov
* [http://chandra.harvard.edu/ Chandra X-ray Observatory] at Harvard.edu
* [https://cxc.harvard.edu/ Chandra X-Ray Center (CXC)] at Harvard.edu
* [https://www.youtube.com/user/cxcpub/ Chandra X-ray Observatory] at YouTube
* [http://www.astronomycast.com/missions/192-chandra-x-ray-observatory/ Chandra podcast (2010)] by [[Astronomy Cast]]

{{Space observatories}}
{{Orbital launches in 1999}}
{{TRW}}
{{Smithsonian Institution}}
{{Authority control}}

{{DEFAULTSORT:Chandra X-Ray Observatory}}
[[Category:Chandra X-ray Observatory| ]]
[[Category:Great Observatories program]]
[[Category:Northrop Grumman spacecraft]]
[[Category:Satellites orbiting Earth]]
[[Category:Space telescopes]]
[[Category:Space telescopes orbiting Earth]]
[[Category:Spacecraft launched by the Space Shuttle]]
[[Category:Spacecraft launched in 1999]]
[[Category:TRW Inc.]]
[[Category:X-ray telescopes]]