Astronomers Solve Quasar Mystery: Sequence Explained by Ratio

Quasars are supermassive black holes located at the center of distant, massive galaxies. Now, scientists have solved a particular quasar mystery that has puzzled astronomers for over 20 years. They've found out how the most observed quasar phenomena can be unified with two simple quantities: one that describes how efficiently the hole is being fed, and the other that reflects the viewing orientation of the astronomer.

Quasars are some of the most luminous beacons in the sky, emitting light across the entire electromagnetic spectrum by accreting matter into their gravitationally inescapable centers. These comic features display a wide range of outward appearances when viewed by astronomers, though, and reflect the diversity in the conditions of the regions close to their centers. Despite this variety, quasars have a surprising amount of regularity in their physical properties. Now, researchers have found what unifies these properties into this main sequence.

The scientists examined 20,000 quasars from the Sloan Digital Sky Survey and then combined the findings with several novel statistical tests. In the end, the researchers found that one particular property related to the accretion of the hole, called the Eddington ratio, is the driving force behind the so-called main sequence.

The Eddington ratio describes the efficiency of matter fueling the black hole, the competition between the gravitational force pulling matter inward and the luminosity driving radiation outward. This push and pull between gravity and luminosity has long been suspected to be the primary driver behind the so-called main sequence.

Now, scientists have found that this is indeed the case. It turns out that the Eddington ratio is the reason why quasars are unified into this main sequence.

"Our findings have profound implications for quasar research," said Yue Shen, one of the researchers, in a news release. "This simple unification scheme presents a pathway to better understand how supermassive black holes accrete matter and interplay with their environments."

The findings are published in the journal Nature.