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Giant black hole too big for its galaxy

Ancient giant Astronomers have discovered a monster black hole that has grown surprisingly way out of proportion to its ancient galaxy.

The supermassive black hole contains an amazing 10 per cent of its galaxy's overall mass, over 20 times more than usual.

The new findings, reported in the journal Science, contradict existing models about how the growth of supermassive black holes are closely linked to the growth of their host galaxy

"This is really unexpected and was found in a really small survey, so it can't be that rare, unless we're just extraordinarily fortunate," says one of the study's authors, Professor Megan Urry of Yale University in New Haven.

"It's only one result and we shouldn't extrapolate, but if it were true then it would say that black holes grow substantially before the galaxies around them do."

Most if not all galaxies are thought to contain supermassive black holes in their centres.

The international team of reseachers discovered the supermassive black hole in a distant galaxy called CID-947 that formed about 2 billion years after the Big Bang.

The researchers found CID-947 contains a supermassive black hole over 6.9 billion times the mass of our Sun, a tenth of the galaxy's overall mass.

However, most supermassive black holes in the nearby universe seem to consistently have between about 0.2 to 0.5 per cent of the mass of their host galaxies.

Powerful X-rays

The findings, which suggest black holes and galaxies don't always coevolve in-synch, challenge existing models of galaxy formation.

Astronomers think the link between the mass of a galaxy and the mass of its supermassive black hole is associated with amount of matter consumed by the black hole.

Material falling onto a black hole is heated by friction and intense gravitational forces, producing huge amounts of X-ray energy. The more material falling in, the bigger the black hole gets and the more energy it produces.

The energy generated by a feeding black hole has enough power to blow away gas and dust, preventing more material from falling into the black hole, and so shutting down the feeding process.

But this energy also heats up and disrupts the galaxy's star forming molecular clouds, restricting or even preventing them from making new stars.

"So this tight relation between black hole mass and the mass of the host galaxy implied some kind of evolutionary link that perhaps they formed some sort of a feedback that would regulate the amount of mass that fell into the black hole, and the amount of stars that form in the galaxy," says Urry.

If that feedback is the controlling mechanism, you would expect the mass of the black hole and the mass of the galaxy to more or less track each other continuously through cosmic time.

Yet the black hole in this galaxy, which is 12 billion light-years away, is out of proportion to those seen in more recent galaxies, says Urry.

"It's as if the black hole grew quite rapidly early on, and the galaxy is going to take another 12 billion years to catch up," says Urry.

"This is potentially quite an interesting signpost pointing in the direction to look for more of these."