Quasars don’t last long—so how do they get so massive?

Quasars represent some of the most luminous and energetic phenomena in the universe. These distant powerhouses are driven by supermassive black holes—colossal gravitational engines with masses millions to billions of times that of our sun—which actively devour surrounding matter at incredible rates.

As gas, dust, and stellar material spiral inward through an accretion disk superheated to millions of degrees, this matter releases tremendous energy across the electromagnetic spectrum before crossing the event horizon. The resulting emissions can outshine entire galaxies despite originating from a region no larger than our solar system.

The discovery of billion-solar-mass black holes in distant quasars challenges conventional growth models in astrophysics. Scientists have observed these supermassive black holes (SMBHs) at redshifts beyond z≳6, when the universe was less than a billion years old—theoretically insufficient time for them to reach such enormous masses through standard Eddington-limited accretion from stellar-mass seeds.

Eddington-limited accretion represents the maximum rate at which matter can fall into a black hole while maintaining balance between gravitational pull and radiation pressure.

Making matters more puzzling, recent measurements of quasar proximity zones (regions of increased light transmission in the intergalactic medium) and spectral features suggest these early quasars have surprisingly short active lifetimes of less than a million years.

A team led by Dominika Ďurovčíková from the MIT Kavli Institute for Astrophysics and Space Research has been exploring alternative growth mechanisms including episodic super-Eddington accretion, black hole mergers, and jet-assisted growth to explain how these cosmic giants achieved such rapid development in the early universe. The team examined young quasars at redshift z~6 using observations from the Very Large Telescope’s Multi-Unit Spectroscopic Explorer (MUSE).

The researchers specifically targeted quasars with unusually small proximity zones, which suggest extremely short active lifetimes of less than 1 million years—some as brief as 1,000 years. By searching for extended Lyman-alpha nebulae (vast, glowing clouds of hydrogen gas) around these quasars, the team aimed to determine whether these objects are truly in their early accretion phases (which would be indicated by small or absent nebulae) or if their small proximity zones might instead be caused by directional obscuration effects hiding more extensive nebular emission.

Their findings, posted to the arXiv preprint server, add compelling evidence that these distant quasars have only recently ignited their engines of intense accretion, revealing supermassive black holes caught in the earliest moments of their active feeding phases.

This observation profoundly challenges conventional models of supermassive black hole growth, as it suggests these cosmic behemoths somehow reached their enormous masses through mechanisms that defy our current understanding of steady, gradual accumulation processes in the early universe.