Mayall II

{{Short description|Group of stars in the constellation Andromeda}}

{{Infobox globular cluster

| name = Mayall II

| image = Mayall II (HST-Judy Schmidt-JPG).jpg

| caption = Hubble Telescope image of Mayall II

| epoch = J2000

| class =

| constellation = Andromeda

| ra = {{RA|00|32|46.51}}{{cite simbad

| title = NAME Mayall II

| access-date = 2009-09-13}}

| dec = {{DEC|+39|34|39.7}}

| dist_ly = 2.52 ± 0.14 Mly

| dist_pc = 770 ± 40 kpc

| appmag_v = +13.81

| size_v =

| mass_kg = 2{{e|37}}

| mass_msol = 1{{e|7}}{{cite journal

| bibcode = 2009RAA.....9..641M

| title = RESEARCH PAPER: Old stellar population synthesis: new age and mass estimates for Mayall II = G1

|author1=Ma, Jun |author2=de Grijs, Richard |author3=Fan, Zhou |author4=Rey, Soo-Chang |author5=Wu, Zhen-Yu |author6=Zhou, Xu |author7=Wu, Jiang-Hua |author8=Jiang, Zhao-Ji |author9=Chen, Jian-Sheng |author10=Lee, Kyungsook |author11=Sohn, Sangmo Tony | journal = Research in Astronomy and Astrophysics

| volume = 9

| issue = 6

| pages = 641–652

| date = June 2009

| doi = 10.1088/1674-4527/9/6/003

|arxiv = 0904.0674 |s2cid = 16360116}}

| radius_ly = 21.2 ± 1.0 ly (6.5 ± 0.3 pc) (Half light radius r_h) and tidal radius 263.2 ± 12.7 ly (80.7 ± 3.9 pc){{cite journal

| bibcode = 2007MNRAS.376.1621M

| title = Structural parameters of Mayall II = G1 in M31

| journal = Monthly Notices of the Royal Astronomical Society

| volume = 376

| issue = 4

| pages = 1621–1629

| date = April 2007

| doi = 10.1111/j.1365-2966.2007.11573.x

|author1=Ma, J. |author2=de Grijs, R. |author3=Chen, D. |author4=van den Bergh, S. |author5=Fan, Z. |author6=Wu, Z. |author7=Wu, H. |author8=Zhou, X. |author9=Wu, J. |author10=Jiang, Z. |author11=Chen, J. | doi-access=free |arxiv = astro-ph/0702012 |s2cid = 3591548}}

| v_hb =

| age = ~ 12 Gyr

| notes =

| names = SKHB 1, HBK 0-1

}}

Mayall II, also known as NGC-224-G1, SKHB 1, GSC 2788:2139, HBK 0-1, M31GC J003247+393440 or Andromeda's Cluster, is a globular cluster orbiting M31, the Andromeda Galaxy.

It is located {{convert|130000|ly|kpc|lk=on}} from the Andromeda Galaxy's galactic core, and is the brightest (by absolute magnitude) globular cluster in the Local Group, with an absolute visual magnitude of −10.94 and the luminosity of 2 million Suns. It has an apparent magnitude of 13.81 in V band. Mayall II is considered to have twice the mass of Omega Centauri, and may contain a central, intermediate-mass (~ 2{{e|4}} M_⊙) black hole.

It was first identified as a possible globular cluster by American astronomers Nicholas Mayall and Olin J. Eggen in 1953 using a Palomar {{convert|48|in|m|adj=on}} Schmidt plate exposed in 1948.

Because of the widespread distribution of metallicity, indicating multiple star generations and a large stellar creation period, many contend that it is not a true globular cluster, but is actually the galactic core that remains of a dwarf galaxy consumed by Andromeda.{{cite journal |author1=Meylan, G. |author2=Sarajedini, A. |author3=Jablonka, P. |author4=Djorgovski, S. G. |author5=Bridges, T. |author6=Rich, R. M. | date = August 2001 | bibcode = 2001AJ....122..830M | title = Mayall II=G1 in M31: Giant Globular Cluster or Core of a Dwarf Elliptical Galaxy? | journal = The Astronomical Journal | volume = 122 | issue = 2 | pages = 830–841 | doi = 10.1086/321166 |arxiv = astro-ph/0105013 |s2cid=17778865 }}