14 DAY TRIAL // There are many peculiar types of objects in the Universe, but a quasar tends to overcome most of them in terms of weirdness. Scientists describe it as the highly-active area around a supermassive black hole that is capable of gobbling up matter from its surroundings at a frantic rate, while at the same time emitting large amounts of light. This is all well and good, but for many years researchers had no idea as to how these impressive structures formed. Now, new studies appear to suggest that they are the direct result of galactic mergers, when two galaxies “cannibalize” each other, Space reports.
Naturally, there is no way of knowing this for sure, given the fact that we could never observe a galactic collision from start to finish. These processes take millions of years to happen, and observing them is impractical. But we do have supercomputers, capable of simulating the past and the future of a system in which two galaxies are colliding based only on minimal amounts of data. It's through this type of methods that astronomers were finally able to hypothesize that mergers may be directly responsible for the formation of quasars – some of the brightest structures in the Cosmos.
Small- and average-sized black holes never become quasars. Only the largest of the behemoths develop the impressive disk of matter around them, allowing them to grow very fast, while releasing vast amounts of radiation in nearly all wavelength ranges of the electromagnetic spectrum. These emissions are caused by the large amount of heat that is caused by the friction of matter before it falls through the event horizon. Because they are always “hungry,” quasars only develop within galaxies that have a sufficiently-bulky core to allow for the structure to feed for a long time.
A new study proposes that the quasars may have found a way around this limitation, by developing at the core of a galactic merger, between two gas-rich galaxies. This idea was first proposed in 1988, by astronomer David Sanders, from the University of Hawaii. It was only now that, together with UH colleagues led by expert Ezequiel Treister, he had a chance to test the idea. Data from the Chandra, Spitzer and Hubble space telescopes were used to look at various quasars in several wavelength ranges, including optical light, X-ray and infrared.
“We made a simple model in which every galaxy merger generates a quasar that is first obscured and then un-obscured. The agreement is just remarkable. That does indicate that pretty much every galaxy merger generates a quasar. When the Milky Way collides with Andromeda, if at that time there's enough gas available, that gas will probably end up in the center around the black hole, making a quasar,” says Treister.