Inside the galaxy known as NGC 1600 there is a black hole 17 billion times more massive than our Sun. It’s been heralded as the largest black hole ever discovered. While that can be debated, it is certainly among the very largest. It’s also unusual because it doesn’t lie in a dense region of galaxies, but a fairly deserted region. Just how such a large black hole could have formed there isn’t entirely clear.
Since black holes grow in mass by capturing nearby matter, one would expect large black holes to be located in regions that are fairly dense with matter. This is similar to expecting skyscrapers to be located in dense cities, as Jens Thomas (lead author of a new paper on the discovery) puts it. But NGC 1600 is a fairly diffuse elliptical galaxy, and it’s pretty isolated from any nearby galaxies. Finding such a massive black hole in NGC 1600 is like finding a skyscraper in the middle of remote farmland.
Since this black hole is in a diffuse region of the cosmos, it likely won’t grow much beyond its current mass. It’s also likely that the black hole gained its mass much earlier in the Universe, which has implications for just how supermassive black holes formed in the early Universe.
Paper: Jens Thomas, et al. A 17-billion-solar-mass black hole in a group galaxy with a diffuse core. Nature (2016) doi:10.1038/nature17197