'Starving' black hole returns galaxy Mrk 1018 to the shadows

For the second time since it was first observed in 1974, a nearby galaxy with a supermassive black hole at its centre has mysteriously changed – from a dim galaxy to a “Type 1” galaxy until suddenly returning to the shadows.

University of Sydney PhD candidate Rebecca McElroy is the lead author of a new international discovery paper that suggests why: the black hole is being starved of fuel.

Galaxy Markarian 1018 had been on the radar of astronomers since the mid-‘80s and now an international team of scientists has solved the mystery of why the black hole at its centre has again started to “switch off” – one intriguing explanation could be that a second black hole may have fallen into the centre of the galaxy.

Using the European Southern Observatory’s Very Large Telescope along with the NASA/ESA Hubble Space Telescope and NASA’s Chandra X-ray Observatory, the team of scientists have found the black hole is no longer being fed enough fuel to make it shine.

Ms McElroy, a PhD student in the School of Physics at the University of Sydney and the ARC Centre of Excellence for All Sky Astrophysics (CAASTRO), said with the new data from this suite of instruments, the team identified the black hole was slowly fading because it was being starved of accretion material.

“It’s possible that this starvation is because the inflow of fuel is being disrupted,” Ms McElroy said. “This could be because of interactions with a second supermassive black hole.”

Many galaxies are found to have an extremely bright core powered by a supermassive black hole. The cores of these “active galaxies” – some of the brightest objects in the universe – are thought to shine so brightly because hot material is glowing fiercely as it falls into the black hole.

Some of these galaxies have been observed to change dramatically over the course of only 10 years – but the active galaxy in this new study stands out for having changed a second time. A handful of galaxies have been observed to make this full-cycle change, but never before has one been studied in such detail. 

Bernd Husemann of the European Southern Observatory said the team had to work quickly to determine what was causing Mrk 1018’s return to the shadows.

“Future research on the galaxy will allow us to explore the exciting world of starving black holes and changing active galaxies in more detail,” he said.

Since the initial discovery of Mrk 1018’s dimming in 2015, the team has been able to confirm the galaxy’s brightness is further decreasing.

The research is published today in two companion papers, both in the journal Astronomy & Astrophysics.

Details about the discovery are in the Europoean Southern Observatory media statement.