A slow dance lasting up to 10 million years between a super-massive black hole and a smaller one culminates in a violent outflow of energy, possibly powering the bright light known as a quasar, a Yale researcher and her collaborator have found.
"Ours is the first detailed calculation of how the merger of these two super-massive black holes proceeds," says Priyamvada Natarajan, assistant professor of astronomy. "This second phase, the merger, takes a few million years. And then there is a huge outflow of gas, and the quasar shines very brightly. It's a violent, very high energy event."
She and Philip Armitage, lead author of the article to be published in a forthcoming issue of the Astrophysical Journal Letters, and assistant professor at the University of Colorado, arrived at their conclusion via a theoretical, numerical calculation conducted on a supercomputer. The calculation allows the researchers to understand how the configuration would change over time.
Every galaxy has a massive black hole at its center that is more than one million times the mass of the sun. The black hole is detected, and its size determined, by the gravitational effect it has on the stars moving nearby. The larger the black hole, the stronger the pull of gravity and the faster the stars move.
A black hole gobbles up gas from what is known as an accretion disc, which is the disc of material that is spiraling around the black hole. En route to the black hole, the gas from the disc emits X-rays as its inner edge disappears into the gravitational field of the hole.
Energy released as gas falls into the black hole powers quasars, quasi-stellar objects that are very bright and inhabit extremely distant galaxies. What is not known, and what the researchers attempted to deduce, is how the quasars are likely to be turned on and off as a consequence of the merger of two super-massive black holes.
Once the two super-massive black holes become embedded in the accretion disc, they sit quietly at first, and then slowly their orbit shrinks, causing them to move closer together, Natarajan says.
"What is interesting during this phase is the critical separation stage when the black holes get close enough and all the gas trapped between them immediately rushes to the more massive black hole, leading to a brief increase in brightness coupled with an energetic outflow of gas at very high speeds," she says.
Natarajan says the next step in the research is to try to understand the final "hiss" when there is an outflow of energy following the merger of the black holes. "Our model predicts that both of those phenomena should happen simultaneously with the final merger of the black hole," she says.
-- By Jacqueline Weaver
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