UGC 12591

{{Short description| Spiral Galaxy in Pegasus }}

{{Sky|23|25|21.7979|+|28|29|43.281}}

{{Infobox galaxy

| name = UGC 12591

| image = UGC12591 Hubble 4000.jpg

| caption = UGC 12591 imaged by the Hubble Space Telescope

| epoch = J2000

| constellation name = Pegasus

| ra = {{RA|23|25|21.7979}}{{cite web

| website = NASA/IPAC Extragalactic Database

| url = https://ned.ipac.caltech.edu/byname?objname=UGC+12591

| title = NED results for object UGC 12591

| publisher = National Aeronautics and Space Administration / Infrared Processing and Analysis Center

| access-date = 16 April 2017}}

| dec = {{DEC|+28|29|43.281}}

| z = 0.023166

| h_radial_v = 6945 ± 3

| dist_ly = {{cvt|120.880|+/-|18.352|Mpc|Mly|lk=on|order=flip}}

| group_cluster =

| type = S0/a

| size = ~{{convert|83.80|kpc|ly|abbr=on|lk=on|order=flip}} (estimated){{r|ned}}

| mass = {{val|1.9e12}}{{cite journal|last1=Giovanelli|first1=R.|last2=Haynes|first2=M. P.|last3=Rubin|first3=V. C.|last4=Ford|first4=W. K. Jr.|title=UGC 12591 - The most rapidly rotating disk galaxy|journal=The Astrophysical Journal Letters|date=1 February 1986|volume=301|pages=L7–L11|doi=10.1086/184613|bibcode=1986ApJ...301L...7G|issn=0004-637X|doi-access=free}}

| appmag_v =

| appmag_b = 13.90

| absmag_v =

| size_v = {{Val|1.7|×|0.7|u=arcminute}}{{r|ned}}

| notes =

| names = {{odlist | CGCG= 497-015 | MCG= +05-55-015 | PGC= 71392}}

}}

UGC 12591 is a spiral galaxy in the constellation Pegasus. It is located approximately 400 million light-years from Earth. It is the spiral galaxy with the highest known rotational speed of about 500 km/s, almost twice that of the Milky Way galaxy. The high rotational speed means the galaxy must be very massive at the center; the galaxy has a mass estimated at 4 times that of the Milky Way.{{cite web|title=A remarkable galactic hybrid|url=https://www.spacetelescope.org/images/potw1709a/|publisher=ESA/Hubble|access-date=16 April 2017}}

UGC 12591 is relatively isolated; the nearest galaxy{{Which|date=March 2025}} to it is 3.55 million light-years (1.09 Mpc) away. However, its morphology suggests a merger or accretion event in its past: it is somewhat lenticular-like, with a central bulge and dust lanes reminiscent of the Sombrero Galaxy.{{cite journal | doi=10.1093/mnras/stac2683 | title=Hubble Space Telescope Captures UGC 12591: Bulge/Disc properties, star formation and 'missing baryons' census in a very massive and fast-spinning hybrid galaxy | year=2022 | last1=Ray | first1=Shankar | last2=Bagchi | first2=Joydeep | last3=Dhiwar | first3=Suraj | last4=Pandge | first4=M. B. | last5=Mirakhor | first5=Mohammad | last6=Walker | first6=Stephen A. | last7=Mukherjee | first7=Dipanjan | journal=Monthly Notices of the Royal Astronomical Society | volume=517 | issue=1 | pages=99–117 | doi-access=free | bibcode=2022MNRAS.517...99R | arxiv=2203.02885 }}