Astronomers observe biggest black holes yet

Our little words — big, huge, massive, monster-sized, gargantuan, colossal — hardly do these justice.

Astronomers have found the two largest black holes yet, with one of them the size of about 9.7 billion Suns, and the other estimated to be a mere 21 billion Suns.

But the discovery isn’t just cool for the wow factor. Their massive size will help scientists figure out how black holes were involved in the formation and evolution of galaxies as well as give hints about the early universe.

At least ten times the size of our solar system, these jumbo-sized black holes each lie at the center of a galaxy — the smaller one in galaxy NGC 3842, which is about 320 million light years away from Earth, and the other in NGC 4889, 336 million light years away.

A team of astronomers led by Nicholas J. McConnell, a graduate student at the University of California, Berkeley, and his advisor, Chung-Pei Ma, weighed the black holes with the use of telescopes in Hawaii, Texas and outer space. They measured the speeds of stars moving closely around them, determining that higher velocities indicated the black hole has more gravity (and more mass) to keep the stars from flying out of orbit.

Their findings will be published in the paper, “Two ten-billion-solar-mass black holes at the centres of giant elliptical galaxies,” Wednesday in Nature.

Understanding how galaxies and black holes form

These newly discovered black holes are abnormally heavy. Black holes smaller than six million Suns have masses that can be predicted based on the central bulge of stars in its galaxy.

But black holes bigger than six billion Suns don’t follow that pattern. The size of these beasts suggest that they evolved differently. For instance, it’s possible that their weight comes from their home galaxies merging with others, while smaller black holes gain mass by absorbing tons of gas from a surrounding spiral galaxy.

Hints about the early universe

These massive black holes could help us understand the early universe, a time when quasars — intensely bright sources of light that are produced when extremely hot matter falls into black holes — are thought to have been active. As The New York Times says:

Where are those quasars now? The new work supports a growing suspicion that those formerly boisterous black holes are among us now, but, having stopped their boisterous growth, are sleeping.

Mr. McConnell said, “Our discovery of extremely massive black holes in the largest present-day galaxies suggests that these galaxies could be the ancient remains of voracious ancestors.”

via: The New York Times, Nature

Illustration: The background image shows the brightest galaxy, NGC 3842, in a rich cluster of galaxies. The black hole is at its center and is surrounded by stars (shown as conceived by an artist in the center). Seven times larger than Pluto’s orbit, the black hole would dwarf our solar system (inset). (Pete Marenfeld)