{{Short description|Galaxy in constellation Coma Berenices}} {{infobox galaxy |name = Dragonfly 44 |image =Df44-BW-high-contrast.png |caption = Hubble Space Telescope view of the galaxy Dragonfly 44 |appmag_v = 21 mags; or 19.4 mags<ref name=" Dokkum1May2015">{{cite journal |author=Van Dokkum, Pieter |display-authors=etal |title=Spectroscopic confirmation of the existence of large, diffuse galaxies in the coma cluster |date=1 May 2015|journal=[[Astrophysical Journal|The Astrophysical Journal Letters]] |doi=10.1088/2041-8205/804/1/L26 |volume=804 |issue=1 |page=L26|arxiv = 1504.03320 |bibcode = 2015ApJ...804L..26V |s2cid=54664026 }}</ref> |ra = {{RA|13|00|58.0}}<ref name=Dokkum/> |dec = {{DEC|+26|58|35}}<ref name=Dokkum/> |epoch = J2000 |appmag_b = 22 |absmag_v = -16.1 mag<ref name="Dokkum1May2015" /> |group_cluster = [[Coma Cluster]] |dist_ly = ~100 Mpc (~330 Mly) |h_radial_v = 6280 ± 120 km/s |z = ~0.023 |mass = ~1.6{{e|11}} |size_v = 10 x 35 arcsec |constellation name = [[Coma Berenices]] |names = [[Sloan Digital Sky Survey|SDSS]] [http://skyserver.sdss.org/dr8/en/tools/explore/obj.asp?id=1237667442975048507 J130057.98+265839.6], ''' SDSS [http://skyserver.sdss.org/dr8/en/tools/explore/obj.asp?id=1237667442975048508 J130058.17+265836.1]''', SDSS [http://skyserver.sdss.org/dr8/en/tools/explore/obj.asp?id=1237667442975048506 J130058.21+265829.3] }}
'''Dragonfly 44''' is an [[ultra diffuse galaxy]] in the [[Coma Cluster]].<ref name=Dokkum>{{cite journal |author=Van Dokkum, Pieter |display-authors=etal |title=Forty-Seven Milky Way-sized, Extremely Diffuse Galaxies in the Coma-Cluster |date=7 January 2015|journal=The Astrophysical Journal Letters |volume=798 |issue=2 |pages=L45 |doi=10.1088/2041-8205/798/2/L45|arxiv = 1410.8141 |bibcode = 2015ApJ...798L..45V |s2cid=119279968 }}</ref><ref name=Phys.org-2015-05-14>{{cite web|url=http://phys.org/news/2015-05-scientists-fluffiest-galaxies.html|title=Scientists discover the fluffiest galaxies|date=14 May 2015|publisher=[[phys.org]]}}</ref><ref name="Dokkum1May2015" /><ref name=DF_1>{{cite web| title=Dragonfly 44: Ultra-Diffuse Galaxy Made Mostly of Dark Matter| url=http://www.sci-news.com/astronomy/dragonfly-44-ultra-diffuse-galaxy-dark-matter-04135.html| publisher=Sci.News| date=25 August 2016| access-date=21 January 2024}}</ref> This galaxy is well-known because observations of the [[velocity dispersion]] in 2016 suggested a mass of about one trillion [[solar mass]]es, about the same as the [[Milky Way]]. This mass was consistent with a count of about 90 and 70 [[globular clusters]] observed around Dragonfly 44 in two different studies.
Later, spatially resolved [[kinematics]] measured a mass of about 160 billion [[solar mass]]es, six times less than early mass measurements and one order of magnitude less than the [[Milky Way|Milky Way's]] mass.<ref>{{Cite journal|title=Spatially Resolved Stellar Kinematics of the Ultra-diffuse Galaxy Dragonfly 44. I. Observations, Kinematics, and Cold Dark Matter Halo Fits, Peter van Dokkum et al. 2019|journal=The Astrophysical Journal|year=2019|language=en|volume=880|doi=10.3847/1538-4357/ab2914|arxiv=1904.04838|last1=Van Dokkum|first1=Pieter|last2=Wasserman|first2=Asher|last3=Danieli|first3=Shany|last4=Abraham|first4=Roberto|last5=Brodie|first5=Jean|last6=Conroy|first6=Charlie|last7=Forbes|first7=Duncan A.|last8=Martin|first8=Christopher|last9=Matuszewski|first9=Matt|last10=Romanowsky|first10=Aaron J.|last11=Villaume|first11=Alexa|issue=2|page=91|s2cid=119185644 |doi-access=free }}</ref> The most recent work found 20 [[globular cluster]]s around the galaxy, which is consistent with the current mass measurement.<ref>{{Cite journal|title="The number of globular clusters around the iconic UDG DF44 is as expected for dwarf galaxies", Saifollahi et al. 2020|journal=Monthly Notices of the Royal Astronomical Society|doi=10.1093/mnras/staa3016|arxiv=2006.14630|s2cid=220127887|last1 = Saifollahi|first1 = Teymoor|last2 = Trujillo|first2 = Ignacio|last3 = Beasley|first3 = Michael A.|last4 = Peletier|first4 = Reynier F.|last5 = Knapen|first5 = Johan H.|year = 2020|volume = 502|issue = 4|pages = 5921–5934| doi-access=free }}</ref><ref name=PZ_1>{{cite web| title=The puzzle of the strange galaxy made of 99.99% dark matter is solved| url=https://www.iac.es/en/outreach/news/puzzle-strange-galaxy-made-9999-dark-matter-solved| publisher=[[Instituto de Astrofísica de Canarias]]| date=13 October 2020| access-date=21 January 2024}}</ref> The lack of [[X-ray]] emission from the galaxy and its surroundings also shows that the number of [[globular cluster]]s cannot be as many as was claimed before.<ref>{{Cite journal|title="The American Astronomical Society, find out more The Institute of Physics, find out more The Archetypal Ultra-diffuse Galaxy, Dragonfly 44, Is not a Dark Milky Way", Bogdan 2020|journal=The Astrophysical Journal Letters|doi=10.3847/2041-8213/abb886|arxiv=2009.07846|s2cid=221761669|last1=Bogdan|first1=Akos|year=2020 |doi-access=free }}</ref>
The galaxy emits only 1% of the light emitted by the Milky Way.<ref>{{cite news|last1=Crosswell|first1=Ken|date=26 July 2016|title=The Milky Way's dark twin revealed|publisher=[[Nature (journal)|Nature]] News|url=http://www.nature.com/news/the-milky-way-s-dark-twin-revealed-1.20333|access-date=30 July 2016}}</ref> The galaxy was discovered with the [[Dragonfly Telephoto Array]].<ref name=" WashPost-2016-08-25">{{cite news|author=Rachel Feltman|date=25 August 2016|title=A new class of galaxy has been discovered, one made almost entirely of dark matter|newspaper=[[The Washington Post]]|url=https://www.washingtonpost.com/news/speaking-of-science/wp/2016/08/25/a-new-class-of-galaxy-has-been-discovered-one-made-almost-entirely-of-dark-matter/}}</ref>
== Early study == To determine the amount of [[dark matter]] in this galaxy, in 2016, astronomers used the DEIMOS instrument installed on [[Keck II]] to measure the velocities of stars for 33.5 hours for six nights so they could determine the galaxy's mass. The scientists then used the Gemini Multi-Object Spectrograph on the 8-m [[Gemini North]] telescope to reveal a halo of spherical clusters of stars around the galaxy's core.<ref name=GM_1>{{cite web| title=A galaxy made of 99.9% dark matter| author=Byrd, D.| url=https://earthsky.org/space/dragonfly-44-dark-matter-galaxy-2016| publisher=EarthSky Communications| date=30 August 2016| access-date=21 January 2024}}</ref> Following this observation, in August 2016, astronomers reported that this galaxy might be [[Dark galaxy|made almost entirely]] of dark matter.<ref name="AJL-20160825">{{cite journal |author=Van Dokkum, Pieter |display-authors=etal |title=A High Stellar Velocity Dispersion and ~100 Globular Clusters For The Ultra-Diffuse Galaxy Dragonfly 44 |date=25 August 2016 |journal=[[The Astrophysical Journal Letters]] |doi=10.3847/2041-8205/828/1/L6 |volume=828 |issue=1 |page=L6|arxiv = 1606.06291 |bibcode = 2016ApJ...828L...6V |s2cid=1275440 |url=http://scholarworks.sjsu.edu/physics_astron_pub/174 |doi-access=free }}</ref><ref name="NS-20160825">{{cite web |last=Hall |first=Shannon |title=Ghost galaxy is 99.99 per cent dark matter with almost no stars |url=https://www.newscientist.com/article/2102584-ghost-galaxy-is-99-99-per-cent-dark-matter-with-almost-no-stars/ |date=25 August 2016 |work=[[New Scientist]] |access-date=27 August 2016 }}</ref><ref name="WP-20160826">{{cite news |last=Feltman |first=Rachael |title=A new class of galaxy has been discovered, one made almost entirely of dark matter |url=https://www.washingtonpost.com/news/speaking-of-science/wp/2016/08/25/a-new-class-of-galaxy-has-been-discovered-one-made-almost-entirely-of-dark-matter |date=26 August 2016 |newspaper=[[The Washington Post]] |access-date=26 August 2016}}</ref>
== See also == * {{annotated link|Globular cluster}} * {{annotated link|Low surface brightness galaxy}} (LSB galaxy) * {{annotated link|NGC 1052-DF2}} – a galaxy thought to contain almost no dark matter. * {{annotated link|Type-cD galaxy}} or ''c-Diffuse'' galaxy type * {{annotated link|Type-D galaxy}} or ''Diffuse''-type galaxy * {{annotated link|Ultra-diffuse galaxy}} * {{annotated link|Dark matter halo}} * {{annotated link|DGSAT I}}
== References == {{reflist}}
== External links == * {{Commons category-inline}}
{{Stars of Coma Berenices}}
{{portal bar |Astronomy|Space}}
{{DEFAULTSORT:Dragonfly 44}} [[Category:Coma Cluster]] [[Category:Coma Berenices]] [[Category:Observational astronomy]] [[Category:Dark galaxies]]