A supermassive black hole that is bigger relative to its host galaxy than any measured before could be the fossil of a burned-out quasar that existed at the dawn of time. These black-hole-powered beacons were once among the brightest objects in the universe, and it is a mystery how they got so large and powerful so soon after the big bang.
Remco van den Bosch at the Max Planck Institute for Astronomy in Heidelberg, Germany, and colleagues looked at the galaxy NGC 1277 with the Hubble Space Telescope and the Hobby-Eberly telescope in Texas. They found that stars move slowly in the galaxy's outer regions, but gyrate rapidly around the inner core.
That suggests gravity is strong in the galaxy's middle, implying that the central black hole is extremely massive. Based on stellar motion, the team calculates that the hole is 17 billion times the mass of our sun. Such a whopper wouldn't seem out of place in a galaxy hundreds of times the size of NGC 1277, but it is an oddity in a galaxy that is fairly small.
Until now, galaxies were thought to have central black holes that are in proportion to their size. Usually a supermassive black hole would have a mass only a tenth of a per cent that of the galaxy's central bulge, the oldest part of a galaxy, believed to form at the same time as the hole. But in NGC 1277, the hole is 59 per cent of the bulge mass, or 14 per cent of the mass of all the galaxy's stars.
Jackpot galaxy
"Remco's team has gone after some atypical galaxies, and it looks like they hit the jackpot," says Nicholas McConnell at the University of California, Berkeley. "This discovery throws a big wrench in the idea that supermassive black hole growth and galaxy growth are tightly connected throughout the universe."
Theories say the monsters swell by consuming matter in their host galaxies. But it is unclear how NGC 1277 had enough gas for its black hole to grow so big without the rest of the galaxy also forming lots of stars, says McConnell.
"I think this object is interesting and unusual," says Martin Rees of the University of Cambridge, who was one of the first to suggest that quasars were powered by black holes. Rees questions, however, whether the black hole is quite as big as the team calculates.
If the result stands, the black hole may be a pristine remnant of an ancient quasar, says van den Bosch. NGC 1277's stars are all old and its shape indicates it has not collided with other galaxies, so it may preserve a record of why the super-quasars grew so fast in the early universe.
The team now plan to look at five more galaxies that are superficially similar to NGC 1277, to see if they also harbour slumbering giants.
Journal reference: Nature, DOI: 10.1038/nature11592
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