Dueling supermassive black holes could be behind a galaxy's fading light

Image of Mrk 1018 captured by the MUSE instrument mounted on the ESO's Very Large Telescope (VLT)(Credit: ESO/CARS survey)

A new study may have discovered the cause of a mysterious variation in light emitted by a supermassive black hole lurking at the heart of the distant galaxy Markarian 1018 (Mrk 1018). Enormous, incredibly powerful black holes are thought to power the cores of many galaxies, including our own Milky Way.

So, why does a black hole, given its name, shine so brightly? Supermassive black holes are known to have an extremely powerful gravitational pull, which is strong enough to draw any nearby matter towards it. This matter forms what is known as an accretion disk. As matter in the accretion disk spirals inward toward the black hole, it becomes extremely hot, emitting vast quantities of light in the process.

For this reason, supermassive black holes in active galaxies can number among the most luminous objects in our universe. However, their light is not always constant, with any number of astronomical events capable of creating dips or surges in the luminosity of these all-consuming giants.

Astronomers were granted a rare chance to gain a greater understanding of these variations firsthand thanks to the behavior of Mrk 1018. In the past, the supermassive black hole at the centre of the galaxy had been observed to brighten, and remain at this level of luminosity while experiencing only tiny fluctuations in output for some 30 years.

However, observations made over the last five years have seen the level of light from Mrk 1018 dramatically fade, returning close to its original pre-brightening luminosity.

The recent dimming of Mrk 1018 was observed 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 close proximity to the Milky Way that boast active cores. Subsequent observations with the telescope's MUSE instrument highlighted the unusual alterations in the appearance of the distant galaxy.

The first attempts to determine the cause of the reduction in light output by Mrk 1018 were, ultimately, unsuccessful. However, astronomers behind the study were able to rule out the bulk consumption of a star by the black hole as the cause of the variations, as such an event would have seen Mrk 1018 slowly decline in brightness, rather than remain consistently bright for around 30 years.

The data collected by the VLT also suggested that the dimming was not the result of a cosmic gas cloud passing between Mrk 1018 and Earth, which could have explained the observations by obscuring some of the light from the black hole.

Thankfully, this was not the end of the road for astronomers observing the behavior of Mrk 1018. Their studies earned the team observation time with the Hubble and Chandra space telescopes.

The data collected by the combination of these two legendary telescopes led the team to theorize that a second supermassive black hole may be choking off the supply of material to Mrk 1018. This fits with Markarian 1018's original formation as the result of a galactic merger. Therefore, it is possible that the two black holes that once sat at the center of the two galaxies are now 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 and similar systems will be undertaken in an attempt to better understand the feeding dynamics of supermassive black holes.

Source: ESO

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