A mystery for physicists is now almost twice as big. Astronomers have already found black holes that are heavier than should be possible, given their age, and a new discovery is even bigger. The object in question is at least 4,000 times as massive as the black hole at the center of the Milky Way, and growing faster than any black hole we have ever seen before.
Black holes gain mass from the inflow of material attracted by their gravitational pull. However, any black hole has a size-dependent limit on its rate of growth, which should theoretically never be exceeded.
This makes puzzling certain black holes so distant we are seeing them as they were only 2 billion years after the Big Bang. Yet these objects are so massive that even if they formed immediately after the birth of the universe, and grew at the maximum rate possible, they would need to have started off with masses thousands of times that of the Sun to have reached the size we see.
Dr Christian Wolf of the Australian National University told IFLScience this is a weighty problem for physics, because the largest supernovas produce black holes of up to 50 solar masses. Either these holes must have started with a far larger mass than we can explain, or grow much faster than we think is possible.
Wolf heads a team that has announced in Publications of the Astronomical Society of Australia (preprint on ArXiv.org) the discovery of J215728.21-360215.1, a black hole growing so fast it must, according to existing theories, be 20 billion times the mass of the Sun. “This black hole is growing so rapidly that it’s shining thousands of times more brightly than an entire galaxy,” Wolf said in an emailed statement. “If we had this monster sitting at the center of our Milky Way galaxy, it would appear 10 times brighter than a full Moon.” It's rate of growth, half a solar mass every day, almost doubles the previous record.
More massive black holes have been found, but all are old enough to not need explaining. Previously identified anomalies of similar age to J215728.21-360215.1 are 10 and 12 billion solar masses.
Wolf told IFLScience we have yet to confirm J215728.21-360215.1's mass precisely, although time has been booked on a telescope capable of measuring the speed with which gas is orbiting it, which will reveal its mass. Its rate of growth, however, was more easily determined from its quasar's brightness.
J215728.21-360215.1 was discovered as a by-product of Gaia's study of stellar movements. Distant quasars that look like red dwarfs because their light has been so Doppler shifted were identified. Wolf hopes further searching will reveal these over-sized black holes' frequency, and therefore; “The scale of the problem we have to explain.”