Imagine if the tallest skyscraper in Kalamazoo, Michigan, towered over any in New York City. That's akin to the puzzle confronting astronomers who have spotted one of the largest black holes ever found—anchoring a galaxy smaller than our Milky Way.
"This is totally not what I was looking for," says astronomer Remco van den Bosch of the Max Planck Institute for Astronomy in Heidelberg, Germany. "I was expecting to find really big black holes in really big galaxies."
Most large galaxies harbor giant black holes at their centers. The Milky Way's central black hole, for example, weighs 4 million times as much as the sun. But such black holes usually obey a standard correlation: The heavier the galaxy's central bulge of stars, the heavier the black hole. In particular, the mass of a galaxy's bulge is about a thousand times that of its black hole.
But it seems that NGC 1277, a compact galaxy 230 million light-years away, never got the memo. van den Bosch's team found that the stars near this galaxy's center are whirling around an enormous mass. As the researchers report online today in Nature, NGC 1277 sports a black hole that is 4000 times more massive than the Milky Way's and a whopping 17 billion times as massive as the sun. In fact, more than half of the bulge mass of NGC 1277—59%—is in its black hole, far more than the expected 0.1%. If this black hole occupied the center of our solar system, it would engulf all the planets and extend nearly 10 times farther out than Pluto's orbit.
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