Blinking like cosmic beacons on a coastline 13 billion light-years from Earth, quasars are some of the oldest and brightest relics of the early universe that astronomers can detect today.
Quasars are short for “quasi-stellar radio sources,” which are massive black holes that shine as brightly as galaxies and are millions to billions of times more massive than Earth’s Sun. Today, quasars exist at the centers of many large galaxies. But thanks to their exceptional luminosity, quasars have been tracked far across space-time, roughly 200 identified as having formed during the first billion years of our universe’s history.
How could such massive objects have formed so early when galaxies were sparse and giant stars exceptionally rare? That question has plagued researchers for more than two decades since the first quasars were identified—and now, a new study published July 6 in the journal Nature (opens in a new tab) may provide the long-sought answer.
Using a computer simulation, the researchers modeled star formation in the early universe, focusing on one of the rare junctions where two streams of cold, turbulent gas met. While streams of star-forming gas today criss-cross the universe as cosmic interstates, natural “clouds” or reservoirs where the two streams met were extremely rare during the first billion years after the Big Bang, making them tempting but elusive areas of study.
In the simulation, two large “clumps” of star-forming gas accumulated at the center of these streams over millions of years. But to the team’s surprise, these clumps never coalesced into normal-sized stars, as previous models of the early universe predicted.
“The cold currents created turbulence in the [gas] cloud that prevented normal stars from forming until the cloud became so massive that it catastrophically collapsed under its own weight to form two gigantic primordial stars,” study co-author Daniel Whalen, associate professor of cosmology at the University of Portsmouth in England, he said in a statement (opens in a new tab). “One [star] was 30,000 solar masses and the other 40,000.”
Previous studies have estimated that a quasar must measure anywhere from 10,000 to 100,000 solar masses at birth. If so, the study authors wrote that the two massive primordial stars from the new simulation could be viable “seeds” for the first quasars in the universe.
It’s possible that both prominent stars could have collapsed into black holes almost immediately and then continued to absorb gas as they grew into the supermassive quasars that scientists discovered in the early universe. As the monstrous black holes continue to grow, they could even merge, releasing a stream of space-time waves known as gravitational waves, the researchers wrote. It is possible that scientists could even detect these waves with unique observatories in the coming decades, potentially confirming the simulation results.
If confirmed, the research would overturn decades of speculation about the formation of stars in the early universe. Previous studies have suggested that giant primordial stars only form in extreme environments, where external forces such as ultraviolet radiation can prevent smaller stars from forming. However, this new simulation shows that such exotic settings may not be necessary. Quasar seeds could develop naturally where rare streams of the cold gas meet.