Massive black hole lurks in lightweight galaxy

A black hole roughly 7 billion times as massive as the sun lurks in a relatively lightweight far-flung galaxy, researchers report in the July 10 Science.

This dark behemoth is a whopping one-eighth of the mass of all the stars in CID-947, a galaxy in the constellation Sextans whose light takes about 11.8 billion years to reach Earth. Most supermassive black holes in the local universe top out at around one-two-hundredth of the mass of their host galaxies.  

The black hole pulled in all this mass within just 2 billion years after the Big Bang, which challenges a long-standing idea that supermassive black holes and the galaxies they inhabit evolve in lockstep. For CID-947 and similar galaxies that will eventually become quite massive, the central black hole comes first and the galaxy slowly builds around it, Benny Trakhtenbrot, an astrophysicist at ETH Zurich in Switzerland, and colleagues suggest. They weighed the black hole by measuring how quickly its gravity whipped gas around the center of CID-947.

Trakhtenbrot and colleagues also found that CID-947 churns out about 400 new suns a year; the Milky Way, by comparison, builds only a few. Some theories indicate that a rapidly growing black hole would blast out energy that suppresses star formation throughout a galaxy. This galaxy, however, forms stars prodigiously despite its black hole’s ferocious growth spurt.