Holmberg 15A (abbreviated to Holm 15A) is a supergiant
elliptical galaxy and the
central dominant galaxy of the
Abell 85 galaxy cluster in the
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
Cetus, about 700 million light-years from Earth.
[ ] It was discovered by
Erik Holmberg.
It became well known when it was reported to have the largest core ever observed in a galaxy, spanning some 15,000 light years,
however this was subsequently refuted.
Supermassive black hole
It has been postulated that the primary component of the galactic core is a
supermassive black hole with a mass of 40 billion
solar mass
The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
es (),
although no direct measurement has yet been made. Previous estimates by Lauer ''et al.'' have jointed a mass value as high as 310 billion
using the
gamma ray point break radius method. Kormendy and Bender gave a value of 260 billion in a 2009 paper. Lower estimates were given by Kormendy and Ho ''et al.'' in 2013 at 2.1 and 9.2 billion .
The paper by Lopez-Cruz ''et al.'' stated:
"Therefore, we conservatively suggest that Holm 15A hosts an SMBH with a mass of ~1 ." Kormendy and Ho ''et al'' derived these equations using the
M–sigma relation
The M–sigma (or ''M''–''σ'') relation is an empirical correlation between the stellar velocity dispersion ''σ'' of a galaxy bulge and the mass M of the supermassive black hole at its center.
The ''M''–''σ'' relation was first presented i ...
and the size of the outer bulge of the galaxy, which are indirect estimates. Rusli ''et al'' derived a value of 170 billion 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 , 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".
This makes it one of the
most massive black holes ever discovered, with it being classified as an
ultramassive black hole
A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical obj ...
.
See also
*
List of galaxies
References
* Measures SMBH mass as .
Supermassive black holes
Cetus (constellation)
Elliptical galaxies
002501
Astronomical objects discovered in 1937
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