Quasars are super-massive black holes that live at the centre of distant massive galaxies.
They shine as the most luminous beacons in the sky across the entire electromagnetic spectrum by rapidly accreting matter into their gravitationally inescapable centres.
New research from The Carnegie Institution for Science's Hubble Fellow Yue Shen and Luis Ho of the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University solves a quasar mystery that astronomers have been puzzling over for 20 years.
Quasars display a broad range of outward appearances when viewed by astronomers, reflecting the diversity in the conditions of the regions close to their centres.
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But despite this variety, quasars have a surprising amount of regularity in their quantifiable physical properties, which follow well-defined trends (referred to as the "main sequence" of quasars) discovered more than 20 years ago.
Shen and Ho solved a two-decade puzzle in quasar research: What unifies these properties into this main sequence?
The Eddington ratio describes the efficiency of matter fuelling 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, and their work at long last confirms this hypothesis.
"And better black hole mass measurements will benefit a variety of applications in understanding the cosmic growth of super-massive black holes and their place in galaxy formation," Ho added.
The study was published in the journal Nature.