Dennis Overbye in The New York Times:
Don’t get too close. Astronomers are reporting that they have taken the measure of the biggest, baddest black holes yet found in the universe, abyssal yawns 10 times the size of our solar system into which billions of Suns have vanished like a guilty thought. Such holes, they say, might be the gravitational cornerstones of galaxies and clues to the fates of violent quasars, the almost supernaturally powerful explosions in the hearts of young galaxies that dominated the early years of the universe. One of these newly surveyed monsters, which weighs as much as 21 billion Suns, is in an egg-shaped swirl of stars known as NGC 4889, the brightest galaxy in a sprawling cloud of thousands of galaxies about 336 million light-years away in the Coma constellation.
The other black hole, a graveyard for the equivalent of 9.7 billion Suns, more or less, lurks in the center of NGC 3842, a galaxy that anchors another cluster known as Abell 1367, about 331 million light-years away in Leo. “These are the most massive reliably measured black holes ever,” Nicholas J. McConnell, a graduate student at the University of California, Berkeley, said in an e-mail, referring to the new observations. These results are more than just cool and record-setting. Observations with the Hubble Space Telescope over the years have shown that such monster black holes seem to inhabit the centers of all galaxies — the bigger the galaxy, the bigger the black hole. Researchers said the new work could shed light on the role these black holes play in the formation and evolution of galaxies.