Dueling supermassive black holes could be behind a galaxy's fading light
A new study may have discovered thecause of a mysterious variation in light emitted by a supermassiveblack hole lurking at the heart of the distant galaxy Markarian 1018(Mrk 1018). Enormous, incredibly powerful black holes are thought topower the cores of many galaxies, including our own Milky Way.
So, why does a black hole, given itsname, shine so brightly? Supermassive black holes are known to havean extremely powerful gravitational pull, which is strong enough todraw any nearby matter towards it. This matter forms what is known asan accretion disk. As matter in the accretion diskspirals inward toward the black hole, it becomes extremely hot,emitting vast quantities of light in the process.
For this reason, supermassive blackholes in active galaxies can number among the most luminous objectsin our universe. However, their light is not always constant, withany number of astronomical events capable of creating dips or surgesin the luminosity of these all-consuming giants.
Astronomers were granted a rare chanceto gain a greater understanding of these variations firsthand thanksto the behavior of Mrk 1018. In the past, the supermassive blackhole at the centre of the galaxy had been observed to brighten, andremain at this level of luminosity while experiencing only tinyfluctuations in output for some 30 years.
However, observations made over thelast five years have seen the level of light from Mrk 1018dramatically fade, returning close to its original pre-brighteningluminosity.
The recent dimming of Mrk 1018 wasobserved by chance as the ESO's Very Large Telescope (VLT) undertook the Close AGN Reference Survey (CARS),the goal of which was to obtain information on 40 galaxies in closeproximity to the Milky Way that boast active cores. Subsequentobservations with the telescope's MUSE instrumenthighlighted the unusual alterations in the appearance of the distantgalaxy.
Thefirst attempts to determine the cause of the reduction in lightoutput by Mrk 1018 were, ultimately, unsuccessful. However,astronomers behind the study were able to rule out the bulkconsumption of a star by the black hole as the cause of thevariations, as such an event would have seen Mrk 1018 slowly declinein brightness, rather than remain consistently bright for around 30years.
Thedata collected by the VLT also suggested that the dimming was not theresult of a cosmic gas cloud passing between Mrk 1018 and Earth,which could have explained the observations by obscuring some of thelight from the black hole.
The data collected by the combinationof these two legendary telescopes led the team to theorize that asecond supermassive black hole may be choking off the supply ofmaterial to Mrk 1018. This fits with Markarian 1018's original formation as the result of a galactic merger. Therefore, it is possible that thetwo black holes that once sat at the center of the two galaxies arenow are disrupting each other's feeding patterns, and in so doing,causing a dimming in the output of light from Mrk 1018.
Further observations of Mrk 1018 andsimilar systems will be undertaken in an attempt to better understandthe feeding dynamics of supermassive black holes.