Astronomers have discovered ancient quasars that seem unexpectedly isolated in the early universe. This observation raises questions about how such incredibly bright objects could have emerged so early, given the lack of additional matter nearby to support their development.
A quasar is essentially the extremely luminous core of a galaxy, which contains an active supermassive black hole at its center. As the black hole consumes surrounding gas and dust, it emits a vast amount of energy, making quasars some of the brightest entities in the cosmos. Quasars have been detected dating back to only a few hundred million years after the Big Bang, and it remains unclear how they could attain such brightness and mass in a relatively brief span of cosmic time.
Scientists have suggested that the earliest quasars developed from regions with absurdly dense primordial matter, which would have also led to the formation of several smaller galaxies in their vicinity. However, a new study led by MIT reveals that some ancient quasars seem to be surprisingly isolated in the early universe.
Using NASA’s James Webb Space Telescope (JWST), the astronomers looked back over 13 billion years to investigate the surroundings of five ancient quasars. They observed an unexpected variety in their environments, referred to as “quasar fields.” While some quasars are found amidst densely packed fields with over 50 neighboring galaxies—as all models anticipate—others appear to be floating in voids with only a few distant galaxies nearby.
These solitary quasars pose a challenge to physicists trying to understand how such brilliant entities could have formed so early, without a significant amount of surrounding matter to support the growth of their black holes.
“In contrast to what was previously thought, our findings indicate that, on average, these quasars do not necessarily reside in the densest regions of the early universe. Some appear to be situated in almost empty spaces,” comments Anna-Christina Eilers, an assistant professor of physics at MIT. “It’s quite perplexing to figure out how these quasars could have grown so massive if they seem to lack a significant source of nourishment.”
There remains the possibility that these quasars might not be as isolated as they seem but could be surrounded by galaxies that are heavily obscured by dust and thus invisible to our current observations. Eilers and her team aim to refine their observations to penetrate this cosmic dust and gain insight into how quasars became so large so quickly in the early universe.
The results of Eilers and her team’s study are published in the latest issue of the Astrophysical Journal. The research was co-authored by MIT postdocs Rohan Naidu and Minghao Yue, along with Robert Simcoe, the Francis Friedman Professor of Physics and director of MIT’s Kavli Institute for Astrophysics and Space Research, as well as collaborators from institutions such as Leiden University, the University of California at Santa Barbara, ETH Zurich, and others.
Galactic neighbors
The five quasars studied are among the oldest observed, dating back over 13 billion years. They are believed to have formed between 600 and 700 million years post-Big Bang. The supermassive black holes powering these quasars are a billion times more massive than our Sun and more than a trillion times brighter. Their extreme brightness allows their light to travel across the universe to be detected by JWST today.
“It’s remarkable that we now possess a telescope capable of capturing light from 13 billion years ago with such incredible detail,” Eilers expresses. “For the first time, JWST allows us to examine the environments of these quasars, uncovering details about where they formed and what their surroundings were like.”
The research team analyzed images of the five quasars captured by JWST between August 2022 and June 2023. Each quasar’s observations consisted of multiple partial views or “mosaic” images, which the team combined to create comprehensive images of their surrounding neighborhoods.
The telescope also took measurements of light across different wavelengths in each quasar’s field. The team processed this data to identify whether a particular object was light from a neighboring galaxy and determined the distance of each galaxy from the significantly brighter quasar.
“We discovered that the only significant difference among these five quasars is the appearance of their environments,” Eilers notes. “For instance, one quasar has nearly 50 nearby galaxies, while another has just two. All five quasars share similar sizes, luminosities, and cosmic timeframes, so it was astonishing to see such a disparity.”
Growth spurts
The variation in quasar environments presents a challenge to the conventional understanding of black hole growth and galaxy formation. Physicists believe that the emergence of the universe’s earliest objects is influenced by a cosmic web of dark matter. Dark matter is a not yet fully understood type of matter that interacts with the universe only through gravitational effects.
After the Big Bang, the early universe is thought to have formed dark matter filaments that acted as gravitational channels, attracting gas and dust along their paths. In regions of high density within this web, matter would have coalesced into larger formations, leading to the development of the brightest and most massive early objects, such as quasars, alongside many smaller galaxies.
“The cosmic web of dark matter is a key prediction from our cosmological model of the universe, and it can be detailed through numerical simulations,” explains co-author Elia Pizzati, a graduate student at Leiden University. “By comparing our observations to these simulations, we can pinpoint where quasars are situated within the cosmic web.”
Estimates suggest that quasars would need to consistently accrete matter at very high rates to achieve their extreme mass and brightness by the time they were observed, which is less than 1 billion years after the Big Bang.
“The pressing question we’re aiming to answer is how these billion-solar-mass black holes formed when the universe was still in its early stages,” Eilers remarks.
The team’s discoveries may lead to more inquiries than resolutions. The “lonely” quasars seem to occupy relatively sparse areas of space. If physicists’ cosmological theories hold true, these empty regions imply minimal dark matter or insufficient starting material for the creation of stars and galaxies. How then did such bright and massive quasars come into existence?
“Our findings indicate that there’s still a crucial element of the puzzle missing regarding how these supermassive black holes grow,” Eilers concludes. “If there isn’t enough material in the vicinity for these quasars to steadily grow, it suggests there must be another mechanism at play, which we have yet to uncover.”
This research received partial funding from the European Research Council.
