Starving black hole quickly sends shining galaxy into shadow

A chance observation has uncovered a galaxy flaring brightly before dialling it down again – all in just a few years – because the supermassive black hole in its centre ran out of fuel.

In two papers to be published in Astronomy & Astrophysics, researchers from Europe, the US and Australia tracked the brightening and dimming of the galaxy Markarian 1018 with ground and space telescopes and deduced that its supermassive black hole, which had been feeding voraciously, has fallen on hard times.

Astronomers think most big galaxies, including our Milky Way, house a central supermassive black hole, some of which act strangely – they can get stuck into cold gas, blast hot winds that stunt star growth and sometimes even outgrow their galaxy.

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While black holes are (for the most part) black, matter drawn in by their immense gravitational field can heat, glow and shoot out as bright jets, illuminating the black hole’s host galaxy.

These “active galaxies” aren’t rare, and some do dramatically brighten within a decade – a split second in cosmological terms.

But Markarian 1018 is different. While astronomers have watched it become more luminous since the 1980s, a routine scan of the sky by the Multi Unit Spectroscopic Explorer installed on European Southern Observatory’s Very Large Telescope in Chile found it reverting back to its initial state.

“We were stunned to see such a rare and dramatic change in Markarian 1018,” says Rebecca McElroy from the University of Sydney in Australia and the ARC Centre of Excellence for All Sky Astrophysics, and lead author of the discovery paper.

The astronomers then had to find out what was behind this abrupt U-turn. For this, they turned to the Hubble Space Telescope and Chandra X-Ray Observatory for a closer look.

They report in a second paper that the galaxy’s supermassive black hole was slowly fading because it was being starved of material.

An intriguing possibility, McElroy says, is that there might be two supermassive black holes there. 

“Such a black hole binary system is a distinct possibility in Markarian 1018, as the galaxy is the product of a major merger of two galaxies – each of which likely contained a supermassive black hole in its centre.”