Astronomers observe difficult to track down stellar light surrounding ancient quasars

MIT astronomers have observed the difficult to catch (elusive) starlight surrounding some of the earliest quasars in the cosmos. The distant signals, which trace back over 13 billion years to the cosmos’s infancy, are offering clues to how the earliest black holes and galaxies evolved.

Quasars are the blazing cores of active galaxies, which host an insatiable supermassive black hole (SMBH) at their core. Most galaxies host a central black hole that may sporadically feast on gas and stellar debris, generating a short-lived burst of light in the form of a glowing ring as material swirls in toward the black hole.Quasars, on the contrary, can consume colossal amounts of matter over much longer expanses of time, generating an exceptionally bright and long-lasting ring—so bright, actually, that quasars are amongst the most luminous objects in the cosmos.

Quasars are so bright, they outshine the rest of the galaxy in which they exist. But the MIT team was successful for the first time to observe the far fainter light from stars in the host galaxies of three ancient quasars.Based on this elusive stellar light, the scientists estimated the mass of each host galaxy, in comparison to the mass of its central SMBH. They found that for these quasars, the central black holes were much more colossal comparative to their host galaxies, in comparison to their modern counterparts.

The findings, published yesterday in The Astrophysical Journal, may shed light on how the earliest SMBH became so colossal despite having a comparatively short amount of cosmic time in which to grow. Specifically, those earliest monster black holes might have sprouted from more colossal “seeds” than more modern black holes did.

“After the universe came into existence, there were seed black holes that then consumed material and grew in a very short time,” states study author Minghao Yue (a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research). “One of the big questions is to understand how those monster black holes could grow so big, so fast.”

“These black holes are billions of times more massive than the sun, at a time when the universe is still in its infancy,” states study author Anna-Christina Eilers (assistant professor of physics at MIT). “Our results imply that in the early universe, supermassive black holes might have gained their mass before their host galaxies did, and the initial black hole seeds could have been more massive than today.”