Holmberg 15A

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Holmberg 15A
Observation data (J2000.0 epoch)
Right ascension00h 41m 50.5s
Declination−09° 18′ 11″
Helio radial velocity16690 km/s
Galactocentric velocity16747 km/s
Distance704×10^6 ly (216 Mpc)
Group or clusterAbell 85
Apparent magnitude (V)14.7
Mass7×1013 M
Number of stars5×1012
Size270,000 ly (83 kpc)
Apparent size (V)1.3 moa
Other designations
Abell 85-BCG
Image of the galaxy taken by the Gemini Multi Object Spectrograph, showing the galaxy (bright white center) along with many other galaxies in the image.

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.[1] It was discovered c. 1937 by Erik Holmberg.[2] It briefly shot to fame when it was reported to have the largest core ever observed in a galaxy, spanning some 15,000 light years,[2] however this was subsequently refuted.[3][4]

Supermassive black hole[edit]

It has been alleged that the primary component of the galactic core is a supermassive black hole with a mass of 40 billion solar masses (M),[1][2] although no direct measurement has yet been made. Previous estimates by Lauer et al. have jointed a mass value as high as 310 billion M[1][2] using the gamma ray point break radius method. Kormendy and Bender gave a value of 260 billion M in a 2009 paper. Lower estimates were given by Kormendy and Ho et al. in 2013 at 2.1 and 9.2 billion M.[2] The paper by Lopez-Cruz et al. stated:[2] "Therefore, we conservatively suggest that Holm 15A hosts an SMBH with a mass of ∼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".[2] This makes it one of the most massive black holes ever discovered, with it being classified as an ultramassive black hole.[5]


  1. ^ a b c https://www.sciencealert.com/an-absolutely-gargantuan-black-hole-has-been-found-as-massive-as-40-billion-suns
  2. ^ a b c d e f g 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.
  3. ^ Bonfini, Paolo; Dullo, Bililign T.; Graham, Alister W. (2015), Too Big to Be Real? No Depleted Core in Holm 15A
  4. ^ Madrid, Juan P.; Donzelli, Carlos J. (2016), The Abell 85 BCG: A Nucleated, Coreless Galaxy
  5. ^ Tangermann, Victor (August 6, 2019). "Astronomers Just Discovered One Of The Biggest Black Holes Ever". Futurism.com. Retrieved August 7, 2019.
  • K. Mehrgan; J. Thomas; R. Saglia; X. Mazzalay; P. Erwin; R. Bender; M. Kluge; M. Fabricius (24 July 2019). "A 40-billion solar mass black hole in the extreme core of Holm 15A, the central galaxy of Abell 85". arXiv:1907.10608 [astro-ph.GA]. Measures SMBH mass as (40±8)×109 M.