Astronomers detect ancient solitary quasars with obscure origins

A quasar is the extremely bright core of a galaxy with an active supermassive black hole at its center. When the black hole attracts surrounding gas and dust, it emits an enormous amount of energy, making quasars one of the brightest objects in the universe. Quasars were observed a few 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 proposed that the first quasars arose from regions that were too dense with primordial matter, which would also have produced many smaller galaxies in the quasars’ environment. But in a new study led by MIT, astronomers observed ancient quasars that appear surprisingly alone in the early universe.

Astronomers used NASA’s James Webb Space Telescope (JWST) to travel back in time, more than 13 billion years, to study the cosmic environment of five known ancient quasars. They discovered a surprising variety in their neighborhoods, or “quasar fields.” While some quasars reside in highly populated fields with more than 50 neighboring galaxies, as all models predict, the remaining quasars appear to drift in the void, with only a few galaxies wandering nearby.

These solitary quasars challenge physicists’ understanding of how such luminous objects could have formed so early in the universe, without a significant source of surrounding matter to fuel the growth of their black holes.

“Contrary to what was previously thought, on average we find that these quasars are not necessarily in the densest regions of the early universe. Some of them seem to be in the middle of nowhere,” explains Anna-Christina Eilers, research assistant professor. physics at MIT. “It is difficult to explain how these quasars could have grown so large if they appear to have nothing to feed on.”

It is possible that these quasars are not as solitary as they appear, but rather are surrounded by galaxies that are heavily shrouded in dust and therefore hidden from view. Eilers and his colleagues hope to adjust their observations to try to see through such cosmic dust, to understand how quasars became so large and fast in the early universe.

Eilers and colleagues report their findings in a paper in The Astrophysics Journal. MIT co-authors include postdocs Rohan Naidu and Minghao Yue; Robert Simcoe, Francis Friedman Professor of Physics and director of the Kavli Institute for Astrophysics and Space Research at MIT; and collaborators from institutions including Leiden University, University of California Santa Barbara, ETH Zurich and elsewhere.

Galactic Neighbors

The five newly observed quasars are among the oldest quasars observed to date. More than 13 billion years old, these objects were formed between 600 and 700 million years after the Big Bang. The supermassive black holes that power quasars are a billion times more massive than the Sun and more than a trillion times more luminous. Because of their extreme luminosity, light from each quasar is able to travel across the age of the universe, far enough to reach the highly sensitive detectors at JWST today.

“It’s just phenomenal that we now have a telescope that can capture light from 13 billion years ago in such detail,” says Eilers. “For the first time, JWST allowed us to observe the environment of these quasars, where they grew up and what their neighborhood looked like.”

The team analyzed images of the five ancient quasars taken by JWST between August 2022 and June 2023. Observations of each quasar included several “mosaic” images, or partial views of the quasar field, which the team efficiently stitched together to produce a complete picture. of the surrounding neighborhood of each quasar.

The telescope also took measurements of light in multiple wavelengths in each quasar’s field, which the team then processed to determine whether a given object in the field was light from a nearby galaxy and how far away. lies a much brighter central quasar galaxy.

“We found that the only difference between these five quasars is that their environments are very different,” says Eilers. “For example, one quasar is surrounded by almost 50 galaxies, while another has only two. And both quasars have the same size, volume, luminosity and duration as the universe . It was really surprising to see.”

Growth spurts

The disparity in quasar fields introduces a distortion into the standard picture of black hole growth and galaxy formation. According to physicists’ best understanding of how the first objects in the universe emerged, a cosmic web of dark matter should have set the course. Dark matter is a still unknown form of matter that only interacts with its environment through gravity.

Shortly after the Big Bang, the early universe is thought to have formed filaments of dark matter that acted as a kind of gravitational highway, drawing gas and dust along its tendrils. In regions of this web that are too dense, matter would have accumulated to form more massive objects. And the first brightest and most massive objects, such as quasars, would have formed in the densest regions of the web, which would also have produced many more smaller galaxies.

“The cosmic dark matter network is a strong prediction of our cosmological model of the universe, and it can be described in detail using numerical simulations,” explains co-author Elia Pizzati, a graduate student at the University from Leiden. “By comparing our observations to these simulations, we can determine where quasars are located in the cosmic web.”

Scientists estimate that quasars would have had to grow continuously with very high accretion rates to reach the extreme mass and luminosities at the time astronomers observed them, less than a billion years after the Big Bang.

“The main question we’re trying to answer is: How do these billion-solar-mass black holes form at a time when the universe is still very, very young? It’s still in its infancy “, explains Eilers.

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

“Our results show that an important piece of the puzzle regarding the growth of these supermassive black holes is still missing,” says Eilers. “If there isn’t enough material for some quasars to grow continuously, that means there must be another way of growth, which we haven’t found yet.”

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news in MIT research, innovation and education.