Mayall II

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.

Mayall II
Hubble Telescope image of Mayall II
Observation data (J2000 epoch)
Constellation	Andromeda
Right ascension	00h 32m 46.51s[1]
Declination	+39° 34′ 39.7″[1]
Distance	2.52 ± 0.14 Mly (770 ± 40 kpc)
Apparent magnitude (V)	+13.81[1]
Physical characteristics
Mass	1×107[2] M☉ (2×1037 kg)
Radius	21.2 ± 1.0 ly (6.5 ± 0.3 pc) (Half light radius rh) and tidal radius 263.2 ± 12.7 ly (80.7 ± 3.9 pc)[3]
Estimated age	~ 12 Gyr[2]
Other designations	SKHB 1, HBK 0-1[1]
See also: Globular cluster, List of globular clusters

It is located 130,000 light-years (40 kpc)^[3] from the Andromeda Galaxy's galactic core, and is the brightest^[3] (by absolute magnitude) globular cluster in the Local Group, with an absolute visual magnitude of −10.94 and the luminosity of 2 million Suns.^[4] 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 (~ 2×10⁴ M_⊙) black hole.^[3]

It was first identified as a possible globular cluster by American astronomers Nicholas Mayall and Olin J. Eggen in 1953 using a Palomar 48-inch (1.2 m) Schmidt plate exposed in 1948.^[3]

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.^[3][5]

Origin of names

• Mayall II is named after Nicholas U. Mayall, who, with Olin J. Eggen, discovered it in 1953.
• SKHB 1 is named for Wallace L. W. Sargent, Charles T. Kowal, F. D. A. Hartwick and Sidney van den Bergh. They also named it G1 in 1977.
• HBK 0-1 is named for John Huchra, J. P. Brodie and S. M. Kent in 1991.^[4]

See also

• Astronomy portal

• Messier 54
• Omega Centauri
• Mayall's Object