New Study Unravels the Mystery of Quasars
By LIDA TUNESI
Quasars have always been mysterious.
Back in the 1950s when astronomers first observed them, they were dubbed “quasi-stellar radio sources” because scientists thought they looked a little star-like. Today we know they are not stars at all; rather, they are sources of light originating from supermassive black holes in the center of galaxies.
The black hole is surrounded by a giant disk of gas and dust that it consumes using its enormous gravitational pull. Friction in this disk creates the huge amounts of light that quasars give off.
But quasars’ behavior still has astronomers scratching their heads. Some quasars are fading while some are getting brighter—all faster than scientists think they should.
A new study is starting to decipher this cosmic mystery. By identifying and studying over 70 changing quasars, the researchers are developing a better idea of what might be causing these changes. A better understanding of quasar behavior could, in turn, help scientists understand the bizarre relationships between black holes and the way galaxies evolve.
Authors on the study, published in Monthly Notices of the Royal Astronomical Society, include Professors D. Barry McKernan and K. E. Saavik Ford, both of Borough of Manhattan Community College and The Graduate Center.
The study suggests that the observed changes are the result of something happening in the quasars’ innermost regions. This rules out the notion that the quasars just looked different because of an external factor like something passing in front of them. The researchers now think the quasars are undergoing significant alterations—more akin to “getting plastic surgery” than “putting on makeup,” explains Ford.
Until now, researchers also haven’t known the exact shape of the disks that surround the supermassive black holes. The new study suggests the disks are closer to a donut shape than being totally flat. The researchers also think the material in the disk is thick, and flows more like molasses than water, Ford says.
The authors postulate that the fading and brightening might be caused by instabilities in this slow-flowing disk. But what the “instabilities” are, exactly, is still unclear—possibly changes in temperature—and the researchers plan on tackling this question next.
Clearing up these mysteries will help answer even larger questions. The amount of disk material that a supermassive black hole eats up seems to be related to the number of stars a galaxy forms, but no one knows why. Do the black holes affect the galaxy, or vice versa? Or is there a third player that affects both? Faster, next-generation sky-surveys and the power of machine learning techniques will help astronomers find and learn from even more of these stellar objects to answer such questions.