Editing Hubble Space Telescope (section)

== Scientific results ==
[[File:NASA-HubbleLegacyFieldZoomOut-20190502.webm|thumb|upright=2.7|center|<div align="center">[[Hubble Legacy Field]] (50-second video)</div>]]

=== Key projects ===
In the early 1980s, NASA and STScI convened four panels to discuss key projects. These were projects that were both scientifically important and would require significant telescope time, which would be explicitly dedicated to each project. This guaranteed that these particular projects would be completed early, in case the telescope failed sooner than expected. The panels identified three such projects: 1) a study of the nearby intergalactic medium using quasar [[absorption line]]s to determine the properties of the [[intergalactic medium]] and the gaseous content of galaxies and groups of galaxies;<ref>{{cite journal |last1=Bahcall |first1=J. N. |last2=Bergeron |first2=J. |last3=Boksenberg |first3=A. |last4=Hartig |first4=G. F. |last5=Jannuzi |first5=B. T. |last6=Kirhakos |first6=S. |last7=Sargent |first7=W. L. W. |last8=Savage |first8=B. D. |last9=Schneider |first9=D. P. |display-authors=8 |date=1993 |title=The Hubble Space Telescope Quasar Absorption Line Key Project. I. First Observational Results, Including Lyman-Alpha and Lyman-Limit Systems |journal=The Astrophysical Journal Supplement Series |volume=87 |pages=1–43 |bibcode=1993ApJS...87....1B |doi=10.1086/191797 |doi-access=free}}</ref> 2) a medium deep survey using the Wide Field Camera to take data whenever one of the other instruments was being used<ref>{{cite journal |last1=Ostrander |first1=E. J. |last2=Nichol |first2=R. C. |last3=Ratnatunga |first3=K. U. |author-link3=Kavan Ratnatunga |last4=Griffiths |first4=R. E. |date=1998 |title=The Hubble Space Telescope Medium Deep Survey Cluster Sample: Methodology and Data |journal=The Astronomical Journal |volume=116 |issue=6 |pages=2644–2658 |arxiv=astro-ph/9808304 |bibcode=1998AJ....116.2644O |doi=10.1086/300627 |s2cid=11338445}}</ref> and 3) a project to determine the [[Hubble constant]] within ten percent by reducing the errors, both external and internal, in the calibration of the distance scale.<ref>{{cite web <!-- comments to stop bot from finding doi -->|url=https://www.cfa.harvard.edu/~huchra/hubble/ |title=The Hubble Constant |access-date=January 11, 2011 |author-link1=John Huchra |last=Huchra |first=John |year=2008| volume = <!-- -->| issue = <!-- --> |journal= <!-- --> |pages=<!-- --> |doi = <!-- --> |pmid=<!-- --> |pmc= <!-- --> |s2cid=<!-- -->}}</ref>

=== Important discoveries ===
[[File:Hubble Extreme Deep Field (full resolution).png|thumb|upright=1.4|Hubble Extreme Deep Field image of space in the constellation [[Fornax]]]]

Hubble has helped resolve some long-standing problems in astronomy, while also raising new questions. Some results have required new [[scientific theory|theories]] to explain them.

==== Age and expansion of the universe ====
Among its primary mission targets was to measure distances to [[Cepheid variable]] stars more accurately than ever before, and thus [[Hubble's law#Using Hubble space telescope data|constrain the value]] of the [[Hubble constant]], the measure of the rate at which the universe is expanding, which is also related to its age. Before the launch of HST, estimates of the Hubble constant typically had [[errors and residuals in statistics|errors]] of up to 50%, but Hubble measurements of Cepheid variables in the [[Virgo Cluster]] and other distant galaxy clusters provided a measured value with an accuracy of ±10%, which is consistent with other more accurate measurements made since Hubble's launch using other techniques.<ref>{{cite journal |last1=Freedman |first1=W. L. |last2=Madore |first2=B. F. |last3=Gibson |first3=B.K. |last4=Ferrarese |first4=L. |last5=Kelson |first5=D. D. |last6=Sakai |first6=S. |last7=Mould |first7=J. R. |last8=Kennicutt |first8=R. C. Jr. |display-authors=etal |date=2001 |title=Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant |journal=[[The Astrophysical Journal]] |volume=553 |issue=1 |pages=47–72 |arxiv=astro-ph/0012376 |bibcode=2001ApJ...553...47F |doi=10.1086/320638 |s2cid=119097691}}</ref> The estimated age is now about 13.7&nbsp;billion years, but before the Hubble Telescope, scientists predicted an age ranging from 10 to 20&nbsp;billion years.<ref>{{Cite web |url=http://www.worldsciencefestival.com/2015/04/25-greatest-hubble-telescope-discoveries-past-25-years/ |title=25 of the Greatest Hubble Telescope Discoveries From the Past 25 Years |publisher=World Science Festival |first=Roxanne |last=Palmer |date=April 24, 2015 |access-date=February 23, 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160306180429/http://www.worldsciencefestival.com/2015/04/25-greatest-hubble-telescope-discoveries-past-25-years/ |archive-date=March 6, 2016}}</ref>

While Hubble helped to refine estimates of the age of the universe, it also upended theories about its future. Astronomers from the [[High-z Supernova Search Team]] and the [[Supernova Cosmology Project]] used ground-based telescopes and HST to observe distant [[supernova]]e and uncovered evidence that, far from decelerating under the influence of [[gravity]], the expansion of the universe is instead [[Deceleration parameter|accelerating]]. Three members of these two groups have subsequently been awarded [[Nobel Prize]]s for their discovery.<ref>{{cite book |title=Cosmology |first=Steven |last=Weinberg |publisher=Oxford University Press |date=2008 |isbn=978-0-19-852682-7}}</ref> The cause of this acceleration remains poorly understood;<ref>{{cite journal |last1=Clifton |first1=Timothy |last2=Ferreira |first2=Pedro G. |date=March 23, 2009 |title=Does Dark Energy Really Exist? |url=http://www.scientificamerican.com/article.cfm?id=does-dark-energy-exist |url-status=live |journal=Scientific American |volume=300 |issue=4 |pages=48–55 |bibcode=2009SciAm.300d..48C |doi=10.1038/scientificamerican0409-48 |pmid=19363920 |archive-url=https://web.archive.org/web/20110928054243/http://www.scientificamerican.com/article.cfm?id=does-dark-energy-exist |archive-date=September 28, 2011 |access-date=June 16, 2009}}</ref> the term used for the currently-unknown cause is [[dark energy]], signifying that it is dark (unable to be directly seen and detected) to our current scientific instruments.<ref>{{cite journal |journal=Science |date=June 20, 2003 |volume=300 |pmid=12817137 |issue=5627 |pages=1896–1897 |doi=10.1126/science.300.5627.1896 |title=Dark Energy Tiptoes Toward the Spotlight |first=Charles |last=Seife|s2cid=42463717 }}</ref>

==== Black holes ====
The high-resolution spectra and images provided by the HST have been especially well-suited to establishing the prevalence of [[black hole]]s in the center of nearby galaxies. While it had been hypothesized in the early 1960s that black holes would be found at the centers of some galaxies, and astronomers in the 1980s identified a number of good black hole candidates, work conducted with Hubble shows that black holes are probably common to the centers of all galaxies.<ref>{{cite web |url=http://nssdc.gsfc.nasa.gov/photo_gallery/caption/hst_blkhole.txt |title=Hubble Confirms Existence of Massive Black Hole at Heart of Active Galaxy |publisher=Goddard Space Flight Center |date=May 25, 1994 |access-date=April 26, 2008 |archive-date=September 18, 2011 |archive-url=https://web.archive.org/web/20110918102629/http://nssdc.gsfc.nasa.gov/photo_gallery/caption/hst_blkhole.txt |url-status=live }}</ref> The Hubble programs further established that the masses of the nuclear black holes and properties of the galaxies are closely related.<ref>{{cite journal |last1=Gebhardt |first1=K. |last2=Bender |first2=R. |last3=Bower |first3=G. |last4=Dressler |first4=A. |last5=Faber |first5=S. M. |last6=Filippenko |first6=A. V. |last7=Green |first7=R. |last8=Grillmair |first8=C. |last9=Ho |first9=L. C. |last10=Kormendy |first10=J. |display-authors=4 |date=2000 |title=A Relationship between Nuclear Black Hole Mass and Galaxy Velocity Dispersion |journal=The Astrophysical Journal |volume=539 |issue=1 |pages=L13–L16 |arxiv=astro-ph/0006289 |bibcode=2000ApJ...539L..13G |doi=10.1086/312840 |s2cid=11737403}}</ref><ref>{{cite journal |last1=Ferrarese |first1=Laura |last2=Merritt |first2=David |author2-link=David Merritt |date=2000 |title=A Fundamental Relationship between Supermassive Black Holes and their Host Galaxies |journal=The Astrophysical Journal |volume=539 |issue=1 |pages=L9–L12 |arxiv=astro-ph/0006053 |bibcode=2000ApJ...539L...9F |doi=10.1086/312838 |s2cid=6508110}}</ref>

==== Extending visible wavelength images ====
A unique window on the Universe enabled by Hubble are the [[Hubble Deep Field]], [[Hubble Ultra-Deep Field]], and [[Hubble Extreme Deep Field]] images, which used Hubble's unmatched sensitivity at visible wavelengths to create images of small patches of sky that are the deepest ever obtained at optical wavelengths. The images reveal galaxies billions of light years away, thereby providing information about the early Universe, and have accordingly generated a wealth of scientific papers. The Wide Field Camera{{nbsp}}3 improved the view of these fields in the infrared and ultraviolet, supporting the discovery of some of the most distant objects yet discovered, such as [[MACS0647-JD]].<ref name="heic">{{cite web |date=November 15, 2012 |title=Hubble spots three magnified views of most distant known galaxy |url=http://www.spacetelescope.org/images/heic1217b/ |access-date=April 6, 2022 |work=ESA/Hubble |archive-date=March 1, 2013 |archive-url=https://web.archive.org/web/20130301081845/http://www.spacetelescope.org/images/heic1217b/ |url-status=live }}</ref>

The non-standard object [[SCP 06F6]] was discovered by the Hubble Space Telescope in February 2006.<ref name="nature">{{cite journal |url=http://www.nature.com/news/2008/080919/full/news.2008.1122.html |title=How they wonder what you are |journal=Nature News |date=September 19, 2008 |access-date=November 4, 2012 |last=Brumfiel |first=Geoff |doi=10.1038/news.2008.1122 |archive-date=January 3, 2019 |archive-url=https://web.archive.org/web/20190103052357/http://www.nature.com/news/2008/080919/full/news.2008.1122.html |url-status=live }}</ref><ref name="gans">{{cite journal |author=Gänsicke |first1=B. T. |last2=Levan |first2=A. J. |last3=Marsh |first3=T. R. |last4=Wheatley |first4=P. J. |date=2009 |title=SCP06F6: A carbon-rich extragalactic transient at redshift z~0.14? |journal=The Astrophysical Journal |volume=697 |issue=1 |pages=L129–L132 |arxiv=0809.2562 |bibcode=2009ApJ...697L.129G |doi=10.1088/0004-637X/697/2/L129 |s2cid=14807033}}</ref>

On March 3, 2016, researchers using Hubble data announced the discovery of the farthest confirmed galaxy to date: [[GN-z11]], which Hubble observed as it existed roughly 400 million years after the Big Bang.<ref name="GN-z11">{{cite journal |title=A Remarkably Luminous Galaxy at ''z''=11.1 Measured with ''Hubble Space Telescope'' Grism Spectroscopy |journal=[[The Astrophysical Journal]] |first1=P. A. |last1=Oesch |first2=G. |last2=Brammer |first3=P. |last3=van Dokkum |display-authors=etal |volume=819 |issue=2 |at=129 |date=March 2016 |arxiv=1603.00461 |bibcode=2016ApJ...819..129O |doi=10.3847/0004-637X/819/2/129|s2cid=119262750 |doi-access=free }}</ref> The Hubble observations occurred on February 11, 2015, and April 3, 2015, as part of the [[CANDELS]]/[[GOODS]]-North surveys.<ref>{{cite web |date=March 3, 2016 |title=Hubble Team Breaks Cosmic Distance Record |url=https://hubblesite.org/contents/news-releases/2016/news-2016-07.html |access-date=April 7, 2022 |website=HubbleSite.org |publisher=[[Space Telescope Science Institute]] |id=STScI-2016-07 |archive-date=May 21, 2022 |archive-url=https://web.archive.org/web/20220521162532/https://hubblesite.org/contents/news-releases/2016/news-2016-07.html |url-status=live }}</ref><ref>{{cite news |url=http://news.discovery.com/space/galaxies/hubble-finds-most-distant-oldest-galaxy-ever-160303.htm |title=Hubble Spies Most Distant, Oldest Galaxy Ever |work=[[Discovery News]] |first=Irene |last=Klotz |date=March 3, 2016 |access-date=March 3, 2016 |archive-date=May 11, 2016 |archive-url=https://web.archive.org/web/20160511115454/http://news.discovery.com/space/galaxies/hubble-finds-most-distant-oldest-galaxy-ever-160303.htm |url-status=live }}</ref>

==== Solar System discoveries ====
[[File:Saturn.Aurora.HST.UV-Vis.jpg|thumb|Hubble's STIS UV and ACS visible light combined to reveal Saturn's southern aurora]]
[[File:Jupiter showing SL9 impact sites.jpg|thumb|Brown spots mark [[Comet Shoemaker–Levy 9]] impact sites on [[Jupiter]]'s southern hemisphere. Imaged by Hubble.]]

The collision of [[Comet Shoemaker-Levy 9]] with [[Jupiter]] in 1994 was fortuitously timed for astronomers, coming just a few months after Servicing Mission{{nbsp}}1 had restored Hubble's optical performance. Hubble images of the [[planet]] were sharper than any taken since the passage of ''[[Voyager 2]]'' in 1979, and were crucial in studying the dynamics of the collision of a large comet with Jupiter, an event believed to occur once every few centuries.<ref>{{Cite web |date=July 27, 2021 |title=In Depth {{!}} P/Shoemaker-Levy 9 |url=https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/p-shoemaker-levy-9/in-depth |access-date=April 7, 2022 |website=NASA Solar System Exploration |archive-date=February 2, 2022 |archive-url=https://web.archive.org/web/20220202124627/https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/p-shoemaker-levy-9/in-depth/ |url-status=live }}</ref>

In March 2015, researchers announced that measurements of aurorae around [[Ganymede (moon)|Ganymede]], one of Jupiter's moons, revealed that it has a subsurface ocean. Using Hubble to study the motion of its aurorae, the researchers determined that a large saltwater ocean was helping to suppress the interaction between Jupiter's magnetic field and that of Ganymede. The ocean is estimated to be {{convert|100|km|mi|-1|abbr=on}} deep, trapped beneath a {{convert|150|km|mi|-1|abbr=on}} ice crust.<ref>{{Cite web |date=March 12, 2015 |title=NASA's Hubble Observations Suggest Underground Ocean on Jupiter's Largest Moon |url=http://hubblesite.org/contents/news-releases/2015/news-2015-09 |access-date=April 7, 2022 |website=HubbleSite.org |publisher=[[Space Telescope Science Institute]] |language=en |archive-date=July 15, 2022 |archive-url=https://web.archive.org/web/20220715150224/https://hubblesite.org/contents/news-releases/2015/news-2015-09.html |url-status=live }}</ref><ref name="search_ocean_Ganymede">{{cite journal |title=The search for a subsurface ocean in Ganymede with Hubble Space Telescope observations of its auroral ovals |journal=Journal of Geophysical Research |first1=Joachim |last1=Saur |first2=Stefan |last2=Duling |first3=Lorenz |last3=Roth |first4=Xianzhe |last4=Jia |first5=Darrell F. |last5=Strobel |first6=Paul D. |last6=Feldman |first7=Ulrich R. |last7=Christensen |first8=Kurt D. |last8=Retherford |first9=Melissa A. |last9=McGrath |first10=Fabrizio |last10=Musacchio |first11=Alexandre |last11=Wennmacher |first12=Fritz M. |last12=Neubauer |first13=Sven |last13=Simon |first14=Oliver |last14=Hartkorn |display-authors=4 |volume=120 |issue=3 |date=March 2015 |doi=10.1002/2014JA020778 |bibcode=2015JGRA..120.1715S |pages=1715–1737 |hdl=2027.42/111157 |url=http://kth.diva-portal.org/smash/get/diva2:814598/FULLTEXT01 |doi-access=free |access-date=August 25, 2019 |archive-date=July 20, 2018 |archive-url=https://web.archive.org/web/20180720185410/http://kth.diva-portal.org/smash/get/diva2:814598/FULLTEXT01 |url-status=live |hdl-access=free}}</ref>

HST has also been used to study objects in the outer reaches of the Solar System, including the dwarf planets [[Pluto]],<ref>{{Cite APOD|date=March 11, 1996|title=Hubble Telescope Maps Pluto|access-date=April 26, 2008}}</ref> [[Eris (dwarf planet)|Eris]],<ref>{{Cite web |date=June 14, 2007 |title=Astronomers Measure Mass of Largest Dwarf Planet |url=http://hubblesite.org/contents/news-releases/2007/news-2007-24 |access-date=April 7, 2022 |website=HubbleSite.org |publisher=[[Space Telescope Science Institute]] |language=en |archive-date=December 14, 2023 |archive-url=https://web.archive.org/web/20231214164842/https://hubblesite.org/contents/news-releases/2007/news-2007-24.html |url-status=live }}</ref> and [[90377 Sedna|Sedna]].<ref>{{Cite book |last=Brown |first=Mike |title=How I Killed Pluto and Why It Had It Coming |title-link=How I Killed Pluto and Why It Had It Coming |date=2010 |publisher=Spiegel & Grau |isbn=978-0-385-53108-5 |edition=1st |location=New York |pages=108, 191 |oclc=495271396 |author-link=Mike Brown (astronomer)}}</ref> During June and July 2012, U.S. astronomers using Hubble discovered [[Styx (moon)|Styx]], a tiny fifth moon orbiting Pluto.<ref name="IAUCirc">{{cite journal |last1=Showalter |first1=M. R. |last2=Weaver |first2=H. A. |last3=Stern |first3=S. A. |last4=Steffl |first4=A. J. |last5=Buie |first5=M. W. |last6=Merline |first6=W. J. |last7=Mutchler |first7=M. J. |last8=Soummer |first8=R. |last9=Throop |first9=H. B. |date=2012 |title=New Satellite of (134340) Pluto: S/2012 (134340) 1 |journal=International Astronomical Union Circular |issue=9253 |page=1 |bibcode=2012IAUC.9253....1S}}</ref>

From June to August 2015, Hubble was used to [[New Horizons#KBO Search|search]] for a [[Kuiper belt]] object (KBO) target for the ''[[New Horizons]]'' Kuiper Belt Extended Mission (KEM) when similar searches with ground telescopes failed to find a suitable target.<ref>{{cite web |url=http://www.nasaspaceflight.com/2014/06/hubble-recruited-new-horizons-pluto-target/ |title=Hubble recruited to find New Horizons probe post-Pluto target |work=nasaspaceflight.com |date=June 16, 2014 |access-date=February 1, 2020 |archive-date=June 21, 2019 |archive-url=https://web.archive.org/web/20190621093812/https://www.nasaspaceflight.com/2014/06/hubble-recruited-new-horizons-pluto-target/ |url-status=live }}</ref> This resulted in the discovery of at least five new KBOs, including the eventual KEM target, [[486958 Arrokoth]], that ''New Horizons'' performed a close fly-by of on January 1, 2019.<ref name="NASA-20141015">{{cite web |last1=Brown |first1=Dwayne |last2=Villard |first2=Ray |title=RELEASE 14-281 NASA's Hubble Telescope Finds Potential Kuiper Belt Targets for New Horizons Pluto Mission |url=http://www.nasa.gov/press/2014/october/nasa-s-hubble-telescope-finds-potential-kuiper-belt-targets-for-new-horizons |date=October 15, 2014 |work=NASA |access-date=October 16, 2014 |archive-date=April 6, 2020 |archive-url=https://web.archive.org/web/20200406132923/https://www.nasa.gov/press/2014/october/nasa-s-hubble-telescope-finds-potential-kuiper-belt-targets-for-new-horizons |url-status=live }}</ref><ref>{{cite web |author=Buie, Marc |author-link=Marc W. Buie |title=New Horizons HST KBO Search Results: Status Report |url=http://www.stsci.edu/institute/stuc/oct-2014/New-Horizons.pdf |publisher=[[Space Telescope Science Institute]] |date=October 15, 2014 |page=23 |access-date=February 1, 2020 |archive-date=July 27, 2015 |archive-url=https://wayback.archive-it.org/all/20150727213348/http://www.stsci.edu/institute/stuc/oct-2014/New-Horizons.pdf |url-status=dead }}</ref><ref>{{cite news |last=Corum |first=Jomathan |title=New Horizons Glimpses the Flattened Shape of Ultima Thule |url=https://www.nytimes.com/interactive/2018/12/31/science/new-horizons-ultima-thule-flyby.html |date=February 10, 2019 |work=[[The New York Times]] |access-date=February 1, 2020 |archive-date=December 24, 2021 |archive-url=https://web.archive.org/web/20211224050632/https://www.nytimes.com/interactive/2018/12/31/science/new-horizons-ultima-thule-flyby.html |url-status=live }}</ref>

In April 2022 NASA announced that astronomers were able to use images from HST to determine the size of the nucleus of comet [[C/2014 UN271 (Bernardinelli–Bernstein)]], which is the largest icy comet nucleus ever seen by astronomers. The nucleus of C/2014 UN271 has an estimated mass of 50 trillion tons which is 50 times the mass of other known comets in our solar system.<ref>{{Cite web |last=Jewitt |first=David |date=April 12, 2022 |title=Hubble Confirms Largest Comet Nucleus Ever Seen |url=https://www.nasa.gov/feature/goddard/2022/hubble-confirms-largest-comet-nucleus-ever-seen |url-status=live |access-date=April 13, 2022 |website=NASA.GOV |archive-url=https://web.archive.org/web/20220414102506/https://www.nasa.gov/feature/goddard/2022/hubble-confirms-largest-comet-nucleus-ever-seen/ |archive-date=April 14, 2022 }}</ref>

[[File:Hubble and ALMA image of MACS J1149.5+2223.jpg|thumb|Hubble and ALMA image of [[MACS J1149.5+2223]]<ref>{{cite web |title=ALMA and VLT Find Evidence for Stars Forming Just 250 Million Years After Big Bang |url=https://www.eso.org/public/news/eso1815/ |website=eso.org |access-date=May 18, 2018 |archive-date=May 16, 2018 |archive-url=https://web.archive.org/web/20180516233203/http://www.eso.org/public/news/eso1815/ |url-status=live }}</ref>]]

==== Supernova reappearance ====
On December 11, 2015, Hubble captured an image of the first-ever predicted reappearance of a supernova, dubbed "[[SN Refsdal|Refsdal]]", which was calculated using different mass models of a galaxy cluster whose gravity is [[General relativity|warping]] the supernova's light. The supernova was previously seen in November 2014 behind galaxy cluster [[MACS J1149.5+2223]] as part of Hubble's Frontier Fields program. The light from the cluster took roughly five billion years to reach Earth, while the light from the supernova behind it took five billion more years than that, as measured by their respective [[redshift]]s. Because of the gravitational effect of the galaxy cluster, four images of the supernova appeared instead of one, an example of an [[Einstein Cross|Einstein cross]]. Based on early lens models, a fifth image was predicted to reappear by the end of 2015.<ref>{{cite journal |last1=Diego |first1=J. M. |last2=Broadhurst |first2=T. |last3=Chen |first3=C. |last4=Lim |first4=J. |last5=Zitrin |first5=A. |last6=Chan |first6=B. |last7=Coe |first7=D. |last8=Ford |first8=H. C. |last9=Lam |first9=D. |last10=Zheng |first10=W. |year=2016 |title=A Free-Form Prediction for the Reappearance of Supernova Refsdal in the Hubble Frontier Fields Cluster MACSJ1149.5+2223 |journal=Monthly Notices of the Royal Astronomical Society |volume=456 |issue=1 |pages=356–365 |arxiv=1504.05953 |bibcode=2016MNRAS.456..356D |doi=10.1093/mnras/stv2638|doi-access=free }}</ref> Refsdal reappeared as predicted in 2015.<ref>{{Cite journal |last1=Kelly |first1=P. L. |last2=Rodney |first2=S. A. |last3=Treu |first3=T. |last4=Strolger |first4=L.-G. |last5=Foley |first5=R. J. |last6=Jha |first6=S. W. |last7=Selsing |first7=J. |last8=Brammer |first8=G. |last9=Bradač |first9=M. |last10=Cenko |first10=S. B. |last11=Graur |first11=O. |date=February 23, 2016 |title=Deja Vu All Over Again: The Reappearance of Supernova Refsdal |journal=The Astrophysical Journal |volume=819 |issue=1 |pages=L8 |arxiv=1512.04654 |bibcode=2016ApJ...819L...8K |doi=10.3847/2041-8205/819/1/L8 |hdl=1885/153586 |s2cid=32126257 |doi-access=free }}</ref>

==== Mass and size of Milky Way ====
In March 2019, observations from Hubble and data from the European Space Agency's [[Gaia (spacecraft)|Gaia]] space observatory were combined to determine that the mass of the [[Milky Way Galaxy]] is approximately 1.5&nbsp;trillion times the mass of the Sun, a value intermediate between prior estimates.<ref>{{Cite journal |last1=Watkins |first1=Laura L. |last2=van der Marel |first2=Roeland P. |last3=Sohn |first3=Sangmo Tony |last4=Wyn Evans |first4=N. |date=March 12, 2019 |title=Evidence for an Intermediate-mass Milky Way from Gaia DR2 Halo Globular Cluster Motions |journal=The Astrophysical Journal |volume=873 |issue=2 |pages=118 |arxiv=1804.11348 |bibcode=2019ApJ...873..118W |doi=10.3847/1538-4357/ab089f |s2cid=85463973 |doi-access=free }}</ref>

==== Other discoveries ====
Other discoveries made with Hubble data include proto-planetary disks ([[proplyd]]s) in the [[Orion Nebula]];<ref>{{cite web |date=June 13, 1994 |title=Hubble Confirms Abundance of Protoplanetary Disks around Newborn Stars |url=https://hubblesite.org/contents/news-releases/1994/news-1994-24.html |access-date=April 7, 2022 |website=HubbleSite.org |publisher=[[Space Telescope Science Institute]] |archive-date=April 7, 2022 |archive-url=https://web.archive.org/web/20220407155227/https://hubblesite.org/contents/news-releases/1994/news-1994-24.html |url-status=live }}</ref> evidence for the presence of [[extrasolar planet]]s around Sun-like stars;<ref>{{cite web |url=http://www.nasa.gov/mission_pages/hubble/exoplanet_transit.html |title=Hubble Finds Extrasolar Planets Far Across Galaxy |publisher=NASA |date=October 4, 2006 |access-date=April 26, 2008 |archive-date=August 23, 2011 |archive-url=https://web.archive.org/web/20110823093611/http://www.nasa.gov/mission_pages/hubble/exoplanet_transit.html |url-status=live }}</ref> and the optical counterparts of the still-mysterious [[gamma-ray burst]]s.<ref>{{cite web |url=https://science.nasa.gov/newhome/headlines/ast26mar99_1.htm |title=Autopsy of an Explosion |publisher=NASA |date=March 26, 1999 |access-date=April 26, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080415053228/https://science.nasa.gov/newhome/headlines/ast26mar99_1.htm |archive-date=April 15, 2008}}</ref> Using [[gravitational lens]]ing, Hubble observed a galaxy designated [[MACS 2129-1]] approximately 10 billion light-years from Earth. MACS 2129-1 subverted expectations about galaxies in which new star formation had ceased, a significant result for understanding the formation of [[Elliptical galaxy|elliptical galaxies]].<ref>{{cite journal |last1=Toft |first1=Sune |last2=Zabl |first2=Johannes |last3=Richard |first3=Johan |last4=Gallazzi |first4=Anna |last5=Zibetti |first5=Stefano |last6=Prescott |first6=Moire |last7=Grillo |first7=Claudio |last8=Man |first8=Allison W. S. |last9=Lee |first9=Nicholas Y. |last10=Gómez-Guijarro |first10=Carlos |last11=Stockmann |first11=Mikkel |year=2017 |title=A massive, dead disk galaxy in the early Universe |journal=Nature |volume=546 |issue=7659 |pages=510–513 |arxiv=1706.07030 |bibcode=2017Natur.546..510T |doi=10.1038/nature22388 |pmc=6485677 |pmid=28640271 |first13=Charles L. |last13=Steinhardt |first12=Georgios |last12=Magdis}}</ref>

In 2022 Hubble detected the light of the farthest individual star ever seen to date. The star, [[WHL0137-LS]] (nicknamed ''Earendel''), existed within the first billion years after the big bang. It will be observed by NASA's James Webb Space Telescope to confirm Earendel is indeed a star.<ref>{{Cite web |url=https://www.nasa.gov/feature/goddard/2022/record-broken-hubble-spots-farthest-star-ever-seen |title=Record Broken: Hubble Spots Farthest Star Ever Seen |date=March 29, 2022 |access-date=March 31, 2022 |archive-date=March 30, 2022 |archive-url=https://web.archive.org/web/20220330215951/https://www.nasa.gov/feature/goddard/2022/record-broken-hubble-spots-farthest-star-ever-seen/ |url-status=live }}</ref>

=== Impact on astronomy ===
[[File:Hubble Probes the Early Universe.jpg|thumb|upright=2.4|alt=Depiction of progress in the detection of the early Universe|Evolution of detecting the [[Timeline of the Big Bang|early Universe]]]]
[[File:Hs-2009-25-e-full.jpg|thumb|upright=1.2|Some of the Carina nebula by WFC3]]

Many objective measures show the positive impact of Hubble data on astronomy. As of 2025, over 22,000 [[Scientific paper|papers]] based on Hubble data have been published in peer-reviewed journals,<ref>{{cite web |url=http://archive.stsci.edu/hst/bibliography/pubstat.html |title=HST Publication Statistics |publisher=STScI |access-date=December 26, 2017 |archive-date=May 14, 2019 |archive-url=https://web.archive.org/web/20190514172346/http://archive.stsci.edu/hst/bibliography/pubstat.html |url-status=live }}</ref> and countless more have appeared in conference [[proceedings]]. Looking at papers several years after their publication, about one-third of all astronomy papers have no [[citation]]s, while only two percent of papers based on Hubble data have no citations. On average, a paper based on Hubble data receives about twice as many citations as papers based on non-Hubble data. Of the 200 papers published each year that receive the most citations, about 10% are based on Hubble data.<ref>{{cite journal |url=http://www.stsci.edu/%7Ewebdocs/STScINewsletter/2003/spring_03.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.stsci.edu/%7Ewebdocs/STScINewsletter/2003/spring_03.pdf |archive-date=October 9, 2022 |url-status=live |title=Hubble Science Metrics |journal=Newsletter |publisher=Space Telescope Science Institute |first1=Georges |last1=Meylan |first2=Juan |last2=Madrid |first3=Duccio |last3=Macchetto |volume=20 |issue=2 |date=Spring 2003}}</ref>

Although the HST has clearly helped astronomical research, its financial cost has been large. A study on the relative astronomical benefits of different sizes of telescopes found that while papers based on HST data generate 15 times as many citations as a {{convert|4|m|ft|abbr=on|adj=on}} ground-based telescope such as the [[William Herschel Telescope]], the HST costs about 100 times as much to build and maintain.<ref>{{cite journal |author=Benn |first1=C. R. |last2=Sánchez |first2=S. F. |date=2001 |title=Scientific Impact of Large Telescopes |journal=Publications of the Astronomical Society of the Pacific |volume=113 |issue=781 |pages=385–396 |arxiv=astro-ph/0010304 |bibcode=2001PASP..113..385B |doi=10.1086/319325 |s2cid=204931773}}</ref>

Deciding between building ground- versus space-based telescopes is complex. Even before Hubble was launched, specialized ground-based techniques such as [[aperture masking interferometry]] had obtained higher-resolution optical and infrared images than Hubble would achieve, though restricted to targets about 10<sup>8</sup> times brighter than the faintest targets observed by Hubble.<ref>{{cite journal |author=Haniff |first1=C. A. |last2=Mackay |first2=C. D. |last3=Titterington |first3=D. J. |last4=Sivia |first4=D. |last5=Baldwin |first5=J. E. |display-authors=4 |date=August 1987 |title=The first images from optical aperture synthesis |journal=[[Nature (journal)|Nature]] |volume=328 |issue=6132 |pages=694–696 |bibcode=1987Natur.328..694H |doi=10.1038/328694a0 |s2cid=4281897}}</ref><ref>{{cite journal |author=Buscher |first1=D. F. |last2=Baldwin |first2=J. E. |last3=Warner |first3=P. J. |last4=Haniff |first4=C. A. |date=July 1990 |title=Detection of a bright feature on the surface of Betelgeuse |journal=Monthly Notices of the Royal Astronomical Society |volume=245 |page=7 |bibcode=1990MNRAS.245P...7B}}</ref> Since then, advances in [[adaptive optics]] have extended the high-resolution imaging capabilities of ground-based telescopes to the infrared imaging of faint objects. The usefulness of adaptive optics versus HST observations depends strongly on the particular details of the research questions being asked. In the visible bands, adaptive optics can correct only a relatively small field of view, whereas HST can conduct high-resolution optical imaging over a wider field.<ref name=":3">{{Cite journal |last=Williams |first=Robert |date=April 1, 2020 |title=Hubble telescope 30 years in orbit: personal reflections |url=https://iopscience.iop.org/article/10.1088/1674-4527/20/4/44 |journal=Research in Astronomy and Astrophysics |volume=20 |issue=4 |pages=044 |doi=10.1088/1674-4527/20/4/44 |arxiv=2004.12132 |bibcode=2020RAA....20...44W |s2cid=218517143 |access-date=April 7, 2022 |archive-date=April 7, 2022 |archive-url=https://web.archive.org/web/20220407051942/https://iopscience.iop.org/article/10.1088/1674-4527/20/4/44 |url-status=live }}</ref> Moreover, Hubble can image more faint objects, since ground-based telescopes are affected by the background of scattered light created by the Earth's atmosphere.<ref name=":4">{{Cite web |last=Max |first=Claire |author-link=Claire Ellen Max |date=2001 |title=Introduction to Adaptive Optics and its History |url=https://cfao.ucolick.org/EO/resourcesnew/History_AO_Max.pdf |access-date=April 7, 2022 |website=Center for Adaptive Optics |archive-date=April 12, 2022 |archive-url=https://web.archive.org/web/20220412003424/https://cfao.ucolick.org/EO/resourcesnew/History_AO_Max.pdf |url-status=live }}</ref>

=== Impact on aerospace engineering ===
In addition to its scientific results, Hubble has also made significant contributions to [[aerospace engineering]], in particular the performance of systems in low Earth orbit (LEO). These insights result from Hubble's long lifetime on orbit, extensive instrumentation, and return of assemblies to the Earth where they can be studied in detail. In particular, Hubble has contributed to studies of the behavior of [[Carbon fiber reinforced polymer|graphite composite]] structures in vacuum, optical contamination from residual gas and human servicing, [[radiation damage]] to electronics and sensors, and the long term behavior of [[multi-layer insulation]].<ref>{{cite journal |title=Experience with the Hubble Space Telescope: 20 years of an archetype |journal=Optical Engineering |first=Matthew D. |last=Lallo |volume=51 |issue=1 |at=011011 |date=January 2012 |doi=10.1117/1.OE.51.1.011011 |bibcode=2012OptEn..51a1011L |arxiv=1203.0002|s2cid=15722152 }}</ref> One lesson learned was that gyroscopes assembled using pressurized oxygen to deliver suspension fluid were prone to failure due to electric wire corrosion. Gyroscopes are now assembled using pressurized nitrogen.<ref name="Gyros" /> Another is that optical surfaces in LEO can have surprisingly long lifetimes; Hubble was only expected to last 15 years before the mirror became unusable, but after 14 years there was no measureable degradation.<ref name=NAS2005/> Finally, Hubble servicing missions, particularly those that serviced components not designed for in-space maintenance, have contributed towards the development of new tools and techniques for on-orbit repair.<ref>{{cite web |url=https://www.nasa.gov/mission_pages/hubble/servicing/SM4/main/SM4_Essentials.html |title=Servicing Mission 4 Essentials |publisher=NASA |date=September 15, 2008 |access-date=December 14, 2020 |archive-date=May 3, 2019 |archive-url=https://web.archive.org/web/20190503051034/https://www.nasa.gov/mission_pages/hubble/servicing/SM4/main/SM4_Essentials.html |url-status=live }}</ref>