A VORACIOUSLY FEEDING black hole creates a ‘wind’ that pushes its own ‘food’ of dust and gas out of reach, astronomers using the Gemini North telescope in Hawai’i have found.
They think this is the process that turned actively feeding black holes—common in the early universe—into the quiescent ones found in galaxies today.
“It looks like they’ve found the ‘off switch’ for black holes,” said Professor Joss Bland-Hawthorn of the University of Sydney, who studies galactic winds.
“We’ve long suspected that a negative feedback process like this must be at work, but these Gemini observations are the first clear evidence of outflows that can starve a black hole of fuel.”
The research will be published in the Astrophysical Journal on 10 March.
Astronomers Professor Sylvain Veilleux (University of Maryland, USA) and Dr David Rupke (Rhodes College, Tennessee, USA) studied the galaxy Markarian 231, which lies 600 million light-years away.
Markarian 231 is a ‘train wreck’ resulting from the collision of two galaxies. At its centre is a black hole at least ten million times the mass of the Sun, which is sucking in gas and dust from its immediate surroundings.
Galactic centre boiling over
The black hole in Markarian 231 was known to produce narrow outflows (‘jets’) but the Gemini observations have revealed a broad outflow extending in all directions for at least 8,000 light-years around the galaxy’s core.
More than one physical process is likely to be creating the outflow. One is thought to be the X-rays and gamma rays generated around the black hole, which heat up the gas in the galaxy’s centre until it ‘boils over’.
Gas is streaming away from the galaxy’s centre at speeds of over 1,000 kilometres a second—fast enough to travel from Sydney to Perth in four seconds. The flow is sweeping away huge amounts of gas.
“The fireworks of new star formation and black hole feeding are coming to an end, most likely as a result of this outflow,” Rupke said.
As extreme as Markarian 231 appears, Veilleux says that it is probably not unique. In the early universe galaxies like this “are seen in large numbers and all of them may have gone through shedding events like the one we are witnessing in Markarian 231,” he said.
Australia has a 6.2% share of the international Gemini partnership. Australian astronomers’ access to the Gemini telescopes is managed through the Australian Gemini Office, hosted by the Australian Astronomical Observatory (AAO), Australia’s national optical observatory. The AAO is part of the Commonwealth Department of Innovation, Industry, Science and Research.
Adapted from information issued by AAO. Markarian 231 courtesy NASA / ESA / Hubble Heritage Team / A. Evans. Illustration courtesy Gemini Observatory / AURA / Lynette Cook. Gemini telescope image courtesy Gemini Observatory.
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