Nice Nature paper coming out tomorrow by Jay Strader et al
on a pair of flat spectrum ultra-faint radio sources in the core of M22.
The sources are consistent with being ~ 20 solar mass black holes, accreting at a low rate from, well, something.
Best candidates yet in the Milky Way globulars.
M22 has a somewhat unusual structure (massive fluffy core) in a way that several authors have suggested might be a signature of black holes remnants in the cluster, and it is the closest of the dozen or so clusters which are most like that. So easiest to see in M22. At that, it is a nice tour de force by the eVLA in picking up the sources, those suckers are faint!
“Simulations have indicated that these black holes would fall toward the center of the cluster, then begin a violent gravitational dance with each other, in which all of them or perhaps all but a single one would be thrown completely out of the cluster.
“There is supposed to be only one survivor possible,” said Jay Strader, of Michigan State University and the Harvard-Smithsonian Center for Astrophysics. “Finding two black holes, instead of one, in this globular cluster definitely changes the picture,” he said.”
To be fair, we did say that there could be 0, 1 OR 2 black holes left at the end, but not quite like this, except with low probability…
Also, if this is the tip of the iceberg for the black hole population, then there ought to be 10-100 black holes in there, which is hard to understand, makes for a dynamically crowded system.
There is an interesting point made in the supplemental information that M22 is unusual in that there is [Fe/H] variation in this cluster, and they suggest that maybe it is the product of the collision of two globulars with different age and composition. If true, it could help in producing such things.