Active galaxies are among the universe's brightest celestial objects. Scientists believe that a supermassive black hole lies at the center of these galaxies.
The dense center accumulates gas and dust onto the black hole. This results in the release of a massive amount of gravitational energy, including x-rays and gamma rays, making the accretion disk surrounding the black hole shine brightly.
One of these active galaxies is Markarian 1018, a Seyfert type of galaxy in the Cetus constellation. It is located 555 million light-years from Earth.
Although located millions of light-years away, scientists are able to study active galaxies because of their luminosity. Some of these change dramatically after a decade. In the case of Markarian 1018, however, the changes are drastic.
When it was first observed, it was a dim galaxy. In the 1980s, it was categorized as a Seyfert type, a very bright galaxy. With the use of the European Southern Observatory's Very Large Telescope, NASA's Chandra X-ray Observatory, and the Hubble Space Telescope, scientists observed in 2015 that Markarian reverted to its original category.
Before, scientists thought that the dimming is caused by a black hole that pulls in and consumes a single star. Another theory is that intervening gas dims the view of this galaxy.
Based on the latest studies, however, astronomers believe that Markarian has a black hole binary system. The accretion disk of the black hole was slowly fading because it is being starved of gas and dust, probably because of the presence of another black hole.
This makes sense given that Markarian was born when two galaxies with their own massive black holes merged.
"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," said Rebecca McElroy, a Ph.D. student at the University of Sydney and lead author of one of the two studies detailing the findings.
