Small Galaxy Packs Black Hole Whopper

NGC 1277 is embedded in the nearby Perseus galaxy cluster -- the small galaxy in the center of this image. Compared to all the other galaxies around it, NGC 1277 is very compact and flat. Click to enlarge this image. David W. Hogg, Michael Blanton, and the SDSS Collaboration
David W. Hogg, Michael Blanton, and the SDSS Collaboration

The black hole behemoth is 17 billion times the mass of the sun. Astronomers have no clue why it's so big.

Astronomers have found a super-super-massive black hole comprising a whopping and unprecedented 59 percent of the mass of stars in the central bulge of its host galaxy, a discovery that adds a new twist to the mysterious relationship between a galaxy and its black hole.

The black hole inside the small, compact galaxy known as NGC 1277, located about 250 million light years away in the constellation Perseus, weighs in at 17 billion times the mass of the sun.

In comparison, the supermassive black hole at the heart of our Milky Way galaxy is equal to the mass of about 4 million suns.

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Typically, black holes account for 0.1 percent of a galaxy's stellar bulge. Until now, the galaxy with the proportionally largest black hole was NCG 4486B, which has a black hole accounting for 11 percent of the combined mass of the central stars.

How 1277's black hole came to be so large is mystery.

"We didn't expect these systems to exist at all, but because the stars move so incredibly fast in the centers of these objects, we know these big black holes exist in these small galaxies," astronomer Remco van den Bosch, with the Max Planck Institute for Astronomy in Germany, wrote in an email to Discovery News.

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"Now that we have found that these crazy kind of galaxies exist, we want to know how they form and how (un-)common they are," he wrote.

However the galaxy and its black hole came to cohabitate, they've been together and in relative peace for a long, long time.

The galaxy has a flat disk, indicating its stars are, and have been, relatively undisturbed for eons. If the black hole had been feeding, the flux of infalling material would have triggered new star formation, van den Bosch said.

"This black hole -- and galaxy -- must have formed in its final form fairly quickly after the big bang. We do not have any information on whether the black hole formed before the galaxy, but most likely it happened at the same time," van den Bosch wrote.

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"Somehow, the black hole could grow without forming much stars in the galaxy. We want to know if the black hole, or perhaps the stars, played an active role in it," he said.

NGC 1277 might not be alone. Astronomers are studying about a half-dozen more similar galaxies that may harbor disproportionately large black holes.

"It would likely mean that these oddball galaxies follow a different evolutionary path than the typical galaxy," astronomer Karl Gebhardt, at the University of Texas in Austin, told Discovery News.

"It could also mean that we have to modify some of the basic ideas for how black holes and their galaxies evolve," he said.

The research is published in this week's Nature.