A2261-BCG

A2261-BCG is a supergiant elliptical galaxy in the galaxy cluster Abell 2261. One of the largest galaxies known, A2261-BCG is estimated to have an isophotal diameter of about, roughly 6 times larger than the Milky Way. It is the brightest and most massive galaxy in the cluster, and has one of the largest galactic cores ever observed, spanning over 10,000 light-years.
The cD elliptical galaxy, located at from Earth, is also well known as a radio source. Its core is highly populated by a dense number of old stars, but is mysteriously diffuse, giving it a large core.

Possible supermassive black hole

On September 10, 2012, using Hubble Space Telescope's Wide Field Camera 3, A2261-BCG was not found to contain an active supermassive black hole of at least at its center. This is maybe due to a black hole merger that created gravity waves, rippling in the fabric of space, or two central black holes orbiting each other, with one of them native to the galaxy while the second black hole may have been added from a smaller former galaxy that A2261-BCG may have gobbled up. Furthermore, since a supermassive black hole will only be visible while it is accreting, a supermassive black hole can be nearly invisible, except in its effects on stellar orbits. This implies that either A2261-BGC has a central black hole that is accreting at a low level or has a mass rather below.
Despite the lack of evidence, several studies derived mass estimates for a possible central black hole, such as about between or between, which would make it one of the most massive black holes.