“Our first priority was making sure we weren’t fooling ourselves.” -Keith Riles, LIGO team member
When LIGO announced their first discovery of a black hole-black hole merger, it came as a surprise to almost everyone. The shocking part wasn’t that LIGO had seen merging black holes, but that they were discovered to be so massive. At right around ~30 solar masses each, these were black holes that were much larger than expected, forcing astronomers to confront the fact that they didn’t have a good, comprehensive model for how many black holes — and what mass they should be — were in the Universe.
The masses of known binary black hole systems, including the three verified mergers and one merger candidate coming from LIGO. Image credit: LIGO/Caltech/Sonoma State (Aurore Simonnet).
To help this, a trio of researchers from UC Irvine just used the best information we have to simulate galaxy growth and formation, along with stellar evolution, to figure this out. The results they found were that a Milky Way-sized galaxy should have up to 100 million black holes in it, mostly around 10 solar masses each, with a few percent of them being significantly higher in mass. Meanwhile, smaller, lower-mass ...