Holmberg 15A
| Abell 85-Brightest Cluster Galaxy | |
|---|---|
| Observation data (J2000.0 epoch) | |
| Constellation | Cetus |
| Right ascension | 00h 41m 50.5s |
| Declination | −09° 18′ 11″ |
| Redshift | 0.055672 |
| Helio radial velocity | 16690 km/s |
| Galactocentric velocity | 16747 km/s |
| Distance |
704×106 ly (216 Mpc)h−1 0.678 |
| Group or cluster | Abell 85 |
| Type | cD;BrClG |
| Mass | 7×1013 M☉ |
| Size (ly) | 270×103 ly (83 kpc) |
| Number of stars | 5×1012 |
| Apparent dimensions (V) | 1.3 moa |
| Apparent magnitude (V) | 14.7 |
| Other designations | |
| Abell 85-BCG | |
Holmberg 15A is a supergiant elliptical galaxy and the central dominant galaxy of the Abell 85 galaxy cluster in the constellation Cetus, about 700 million light-years from Earth. It was discovered c. 1937 by Erik Holmberg.[1] It is notable for having the largest core ever observed in a galaxy, spanning 15,000 light years.[1]
Supermassive black hole
The primary component of the galactic core is a supermassive black hole with the currently accepted mass value of 10 billion M☉[1] Previous estimates by Lauer et al in equation 26 have jointed a mass value as high as 310 billion M☉[1] using the gamma ray point break radius method. Kormendy and Bender gave a value of 260 billion M☉ in their 3rd equation in a 2009 paper. Lower estimates were given by Kormendy and Ho et al in 2013 in equations 6 and 7 at 2.1 and 9.2 billion M☉, respectively,[1] and the paper by Lopez-Cruz et al[1] stated: "Therefore, we conservatively suggest that Holm 15A hosts an SMBH with M• ∼ 1×1010 M⊙". Kormendy and Ho et al derived these equations using the M-sigma relation and the size of the outer bulge of the galaxy, which are indirect estimates. Rusli et al derived a value of 170 billion M☉ using break radius methodology. In addition, Abell 85 has its velocity dispersion of dark matter halo at ~750 km/s, which could only be explained by a black hole with a mass greater than 150 billion M☉, although Kormendy and Ho et al stated that "dark matter halos are scale-free, and the SMBH-dark matter coevolution is independent from the effects of baryons".[1] This makes it one of the most massive black holes ever discovered.
References
- 1 2 3 4 5 6 7 López-Cruz, O.; Añorve, C.; Birkinshaw, M.; Worrall, D. M.; Ibarra-Medel, H. J.; Barkhouse, W. A.; Torres-Papaqui, J. P.; Motta, V. (2014). "The Brightest Cluster Galaxy in Abell 85: The Largest Core Known So Far". The Astrophysical Journal 795 (2): L31. arXiv:1405.7758. Bibcode:2014ApJ...795L..31L. doi:10.1088/2041-8205/795/2/L31.