A quasar is an extremely bright galactic nucleus with an active supermassive black hole at its center. When a black hole absorbs surrounding gas and dust, it releases enormous amounts of energy, making quasars some of the brightest objects in the universe. Quasars were observed several hundred million years after the Big Bang, and how these objects could become so bright and massive in such a short cosmic time remains a mystery.

Scientists have suggested that the oldest quasars arose from extremely dense regions of primordial matter, which may have created numerous small galaxies in the quasar environment. But in a new study led by MIT, astronomers observed some ancient quasars that appeared surprisingly lonely in the early universe.

Astronomers used NASA’s James Webb Space Telescope (JWST) to look back more than 13 billion years to examine the cosmic environment of five known ancient quasars. They discovered incredible diversity or “quasar fields” in their environment. Some quasars are found in very populated regions with more than 50 galaxies nearby, as all models predict, while the rest of the quasars appear to be drifting in space with only a few stray galaxies nearby.

These solitary quasars challenge physicists’ understanding of how such bright objects could form so early in the universe, without a significant source of surrounding material to fuel the growth of black holes.

“Contrary to previous beliefs, we found that these quasars, on average, were not located in the highest density regions of the early universe. “Some of them appear to be sitting in the middle of nowhere,” says Anna-Christina Eilers, an associate professor of physics at MIT. “If it looks like they have nothing to eat, that’s “It’s hard to explain how quasars can get so big.”

It is possible that these quasars are not as isolated as they appear, but are surrounded by galaxies that are covered in dense dust and thus hidden from view. Eilers and his colleagues hope to adjust their observations to try to see through such cosmic dust to understand how quasars grew so quickly in the early universe.

Eilers and colleagues report their findings in a published paper. Astrophysical Journal. MIT co-authors include postdoctoral researchers Rohan Naidoo and Minghao Yue; Robert Simko, Francis Friedman Professor of Physics and director of MIT’s Kavli Institute for Astrophysics and Space Studies; and collaborators from institutions such as Leiden University, UC Santa Barbara, ETH Zurich and others.

galactic neighbors

The five newly observed quasars are among the oldest quasars observed to date. Objects over 13 billion years old are believed to have formed 600 to 700 million years after the Big Bang. The supermassive black holes that power quasars are a billion times more massive and a trillion times brighter than the Sun. Because of its extreme brightness, the light from each quasar can extend the age of the universe long enough to reach today’s highly sensitive JWST detectors.

“It’s remarkable that we now have a telescope that can capture light from 13 billion years ago in such detail,” Eilers says. “For the first time, JWST allowed us to look at the environments of these quasars, where they grow, and what their neighborhoods look like.”

The team analyzed images of five ancient quasars taken by JWST between August 2022 and June 2023. Observations of each quasar included multiple “mosaic” images, or partial images of the quasar field; the team effectively brought these together to create a complete picture. The environment of each quasar.

The telescope also took measurements of light at different wavelengths in each quasar’s field; The team then processed these measurements to determine whether a particular object in the field was light from a nearby galaxy and how far the galaxy was from the much brighter central quasar. .

“We found that the only difference between these five quasars is that their environments look very different,” Eilers says. “For example, one quasar has almost 50 galaxies around it, while another has only two galaxies. And both quasars are located at the same size, volume, luminosity, and time of the universe. This was truly amazing to see.”

growth spurts

The difference in quasar fields causes a break in the standard picture of black hole growth and galaxy formation. According to physicists’ best understanding of how the first objects in the universe emerged, the cosmic web of dark matter should have determined the route. Dark matter is an as yet unknown form of matter that interacts with its environment not solely through gravity.

Shortly after the Big Bang, the early universe is thought to have formed dark matter filaments that acted as a kind of gravitational highway, pulling gas and dust along their tendrils. In extremely dense regions of this network, matter can accumulate and form larger objects. And the brightest, most massive proto-objects, such as quasars, may have formed in regions where the network density was highest, giving rise to much smaller galaxies.

“The dark matter cosmic network is a reliable approximation of our cosmological model of the universe and can be explained in detail by numerical simulations,” says co-author Elia Pizzati, a PhD student at Leiden University. “By comparing our observations with these simulations, we can determine where quasars are located in the cosmic web.”

Scientists estimate that quasars must have been growing continuously at very high accretion rates to reach their extreme mass and luminosity during the period when astronomers observed them, less than 1 billion years after the Big Bang.

“The real question we’re trying to answer is how did these billions of solar-mass black holes form when the universe was still very, very young? “It’s still in its infancy,” Eilers says.

The team’s findings may raise more questions than answers. “Lonely” quasars appear to reside in relatively empty regions of space. If physicists’ cosmological models are correct, these barren regions mean little dark matter or source material for the formation of stars and galaxies. So how did extremely bright and massive quasars arise?

“Our results show that we are still missing a big piece of the puzzle of how these supermassive black holes grow,” says Eilers. “If there isn’t enough material around for some quasars to grow continuously, that means there must be another way they can grow, but we haven’t learned that yet.”