Abell 400 is a galaxy cluster, containing a galaxy (NGC 1128) with two supermassive black holes 3C 75 spiralling towards merger.
These two supermassive black holes are contained in NGC 1128. The galaxy, microwave radio jets, multi-million degree X-ray producing gas and resultant radio source is known as 3C 75. X-ray source 2A 0252+060 (1H 0253+058, XRS 02522+060) may be some additional or other portion of Abell 400.[1]
The black holes are an estimated 25,000 light years apart, and thus will take millions of years to collide. Should the two supermassive black holes merge, they will form a single super-supermassive black hole.