At the core of our Milky Way galaxy lies a black hole. Like all black holes, its gravitational pull is so strong that it swallows anything that ventures too close—even light. It weighs in at four million times the mass of the sun.
But that's nothing compared to what astronomers have discovered at the heart of two galaxies about 300 million light-years away. Those galaxies go by the names NGC 3842 and NGC 4889. And they host the most massive black holes ever observed. Each is about 10 billion times the mass of the sun. That's equivalent to 2,500 of the Milky Way's black holes. The discoveries were announced in the journal Nature. [Nicholas J. McConnell et al., "Two 10-billion-solar-mass black holes at the centres of giant elliptical galaxies"]
Of course, black holes emit no light, and they can't be seen directly. But the astronomers were able to measure the mass of the black holes with a bit of extragalactic detective work. The researchers tracked how the black holes' gravitational pull influenced the motions of nearby stars. It's a bit like the FBI talking to a suspect's neighbors to get information. Word from the neighbors in this case—don't loan the black holes anything. You'll never get it back.
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