Quasars are bright, distant and active supermassive black holes

Scientists unravel mystery behind formation of first quasars in the early universe

The quest to unravel the mystery behind the formation of the first quasars in the early universe has taken a significant step forward.

Since 2003,astrophysicists have been trying to understand the origin of more than 200 quasars – extremely luminous active galactic nuclei – that are powered by supermassive black holes less than a billion years after the Big Bang occurred. 

Now, a team of researchers, including PhD student Nicholas Herrington from the University of Exeter, has discovered the key to this age-old mystery can be found within the natural structure of the cosmic web. 

They found that these early quasars naturally formed in the violent, turbulent conditions of rare reservoirs of gas that were created in the early universe.  

Previous supercomputer simulations have suggested that early quasars could form at the point where cold, powerful streams of gas intersected. Only a dozen of these existed in a volume of space a billion light-years across, but the black hole had to be 100,000 solar masses at birth. Black holes in the present-day universe form from the collapse of massive stars and are usually 10 to 100 solar masses.  

Astrophysicists had long theorized that 10,000 – 100,000 solar-mass stars formed in the early universe but only in exotic, finely-tuned environments like strong ultraviolet backgrounds or supersonic flows between gas and dark matter that had no resemblance to the turbulent clouds in which the first quasars formed. 

In this new research, the team used state-of-the-art supercomputer simulations to show that extreme turbulence, driven by cold accretion streams crashing into the rare reservoirs of gas, birthed two supermassive primordial stars, which quickly collapsed into two 30,000 and 40,000 solar mass black holes.  

Nicholas Herrington said: “The two primordial stars that formed out of this rare gas reservoir, were immersed in infalling material. They engulfed significant fractions of the suns mass every year of their short existence. After roughly 1.5 million years of nuclear burning these two titans became unstable, collapsing in on themselves very rapidly, leaving behind two very massive black holes. It is these types of black holes that are massive enough at birth to be the progenitors of the first quasars in the early universe.” 

Dr Dan Whalen, lead author and from the University of Portsmouth Institute of Cosmology and Gravitation, added:  “Our supercomputer models went back to very early times and found that the cold, dense streams of gas capable of growing a billion solar-mass black hole in just a few hundred million years created their own supermassive stars without any need for unusual environments.  

“The cold streams drove turbulence in the cloud that prevented normal stars from forming until the cloud became so massive it collapsed catastrophically under its own weight, forming two gigantic primordial stars.

“Consequently, the only primordial clouds that could form a quasar just after cosmic dawn -when the first stars in the universe formed - also conveniently created their own massive seeds. This simple, beautiful result not only explains the origin of the first quasars but also their demographics – their numbers at early times.  “ 

The paper The Turbulent Origins of the First Quasars is published in Nature. 

Date: 27 July 2022