Astronomers using ESO’s Very Large Telescope and NASA’s Chandra and Hubble space telescopes have solved the mystery of a rare change in the behavior of a central black hole of the active galaxy Markarian 1018.
This image from ESO’s Very Large Telescope shows Markarian 1018, a galaxy located approximately 607 million light-years away. The faint loops of light around the galaxy are a result of its interaction and merger with another galaxy in the recent past. Image credit: CARS Survey / ESO.
Many galaxies are found to have an extremely bright core powered by a supermassive black hole. These cores make ‘active galaxies’ some of the brightest objects in the Universe.
They are thought to shine so brightly because hot material is glowing fiercely as it falls into the black hole, a process known as accretion.
This brilliant light can vary hugely between different active galaxies, so astronomers classify them into several types based on the properties of the light they emit.
Some of these galaxies have been observed to change dramatically over the course of only ten years.
However, the active galaxy Markarian 1018 stands out by having changed type a second time, reverting back to its initial classification within the last five years.
“We were stunned to see such a rare and dramatic change in Markarian 1018,” said Rebecca McElroy, from the University of Sydney and the ARC Centre of Excellence for All Sky Astrophysics (CAASTRO).
“The chance observation of the galaxy so soon after it began to fade was an unexpected opportunity to learn what makes these galaxies tick,” added ESO astronomer Dr. Bernd Husemann.
“We were lucky that we detected the event just 3-4 years after the decline started so we could begin monitoring campaigns to study details of the accretion physics of active galaxies that cannot be studied otherwise.”
The team made the most of this opportunity, making it their first priority to pinpoint the process causing Markarian 1018’s brightness to change so wildly.
This could have been caused by any one of a number of astrophysical events, but they could rule out the black hole pulling in and consuming a single star and cast doubt on the possibility of obscuration by intervening gas.
But the true mechanism responsible for Markarian 1018’s surprising variation remained a mystery after the first round of observations.
However, with the new data from Hubble and Chandra space telescopes they were able to solve the mystery – 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. An intriguing possibility is that this could be due to interactions with a second supermassive black hole,” McElroy said.
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 center.
The team’s findings will be published in two papers in the journal Astronomy & Astrophysics.
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R.E. McElroy et al. 2016. The Close AGN Reference Survey: Mrk 1018’s return to the shadows after 30 years as a Seyfert 1. A&A, accepted for publication;
B. Husemann et al. 2016. The Close AGN Reference Survey (CARS): What is causing Mrk 1018’s return to the shadows after 30 years? A&A, accepted for publication;
This article is based on a press-release from the European Southern Observatory.
