Holmberg 15A

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 170 billion M_☉, based on the estimate of Rusli et al in his 13th equation using the estimate of its break radius.^[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 beak 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⊙", but these two conclusions are unlikely. 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, compared to Rusli et al value using a more accurate 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 the most massive black hole ever discovered, 30 times the value of the black hole of Messier 87, and 41,500 times the value of the black hole at the center of the Milky Way. Using the Schwarzschild radius formula, this black hole has the diameter of 1 trillion kilometers, more than 190 times the distance from the Sun to Pluto, or with the circumference of 121.3 light-days; about four light-months.

References