This image, taken by NASA’s James Webb Space Telescope, shows an ancient quasar (circled in red) with fewer than expected neighbouring galaxies (bright blobs), challenging physicists’ understanding of how the first quasars and supermassive black holes formed. Credit: Christina Eilers/EIGER team.

The quasars appear to have few cosmic neighbours, raising questions about how they first emerged more than 13 billion years ago.

A quasar is the extremely bright core of a galaxy that hosts an active supermassive black hole at its centre. As the black hole draws in surrounding gas and dust, it blasts out an enormous amount of energy, making quasars some of the brightest objects in the Universe.

Quasars have been observed as early as a few hundred million years after the Big Bang, and it’s been a mystery as to how these objects could have grown so bright and massive in such a short amount of cosmic time.

Scientists have proposed that the earliest quasars sprang from overly dense regions of primordial matter, which would also have produced many smaller galaxies in the quasars’ environment. But in a new MIT-led study, astronomers observed some ancient quasars that appear to be surprisingly alone in the early Universe. 

The astronomers used NASA’s James Webb Space Telescope (JWST) to peer back in time, more than 13 billion years, to study the cosmic surroundings of five known ancient quasars.

They found a surprising variety in their neighbourhoods, or ‘quasar fields’. While some quasars reside in very crowded fields with more than 50 neighbouring galaxies, as all models predict, the remaining quasars appear to drift in voids, with only a few stray galaxies in their vicinity.

These lonely quasars are challenging physicists’ understanding of how such luminous objects could have formed so early on in the Universe, without a significant source of surrounding matter to fuel their black hole growth.

Anna-Christina Eilers, assistant professor of physics at MIT, said: “Contrary to previous belief, we find on average, these quasars are not necessarily in those highest-density regions of the early Universe. Some of them seem to be sitting in the middle of nowhere.

“It’s difficult to explain how these quasars could have grown so big if they appear to have nothing to feed from.”

There is a possibility that these quasars may not be as solitary as they appear, but are instead surrounded by galaxies that are heavily shrouded in dust and therefore hidden from view.

Eilers and her colleagues hope to tune their observations to try and see through any such cosmic dust, in order to understand how quasars grew so big, so fast, in the early Universe. 

Galactic neighbours

The five newly observed quasars are among the oldest quasars observed to date.

More than 13 billion years old, the objects are thought to have formed between 600 to 700 million years after the Big Bang.

The supermassive black holes powering the quasars are a billion times more massive than the Sun, and more than a trillion times brighter.

Due to their extreme luminosity, the light from each quasar is able to travel over the age of the Universe, far enough to reach JWST’s highly sensitive detectors today. 

Eilers said: “It’s just phenomenal that we now have a telescope that can capture light from 13 billion years ago in so much detail.

“For the first time, JWST enabled us to look at the environment of these quasars, where they grew up, and what their neighbourhood was like.”

The team analysed images of the five ancient quasars taken by JWST between August 2022 and June 2023. The observations of each quasar comprised multiple ‘mosaic’ images, or partial views of the quasar’s field, which the team effectively stitched together to produce a complete picture of each quasar’s surrounding neighbourhood. 

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

Eilers advised: “We found that the only difference between these five quasars is that their environments look so different. For instance, one quasar has almost 50 galaxies around it, while another has just two.

“And both quasars are within the same size, volume, brightness, and time of the Universe. That was really surprising to see.”

Growth spurts

The disparity in quasar fields introduces a kink 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, a cosmic web of dark matter should have set the course.

Dark matter is an as-yet-unknown form of matter that has no other interactions with its surroundings other than through gravity. 

Shortly after the Big Bang, the early Universe is thought to have formed filaments of dark matter that acted as a sort of gravitational road, attracting gas and dust along its tendrils.

In overly dense regions of this web, matter would have accumulated to form more massive objects.

And the brightest, most massive early objects, such as quasars, would have formed in the web’s highest-density regions, which would have also churned out many more, smaller galaxies. 

Co-author Elia Pizzati, a graduate student at Leiden University, said: “The cosmic web of dark matter is a solid prediction of our cosmological model of the Universe, and it can be described in detail using numerical simulations.

“By comparing our observations to these simulations, we can determine where in the cosmic web quasars are located.” 

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

Eilers said: “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 really, really young? It’s still in its infancy.” 

The team’s findings may raise more questions than answers. The ‘lonely’ quasars appear to live in relatively empty regions of space.

If the physicists’ cosmological models are correct, these barren regions signify very little dark matter, or starting material for brewing up stars and galaxies.

How, then, did extremely bright and massive quasars come to be? 

Eilers said: “Our results show that there’s still a significant piece of the puzzle missing of how these supermassive black holes grow.

“If there’s not enough material around for some quasars to be able to grow continuously, that means there must be some other way that they can grow, that we have yet to figure out.”

The report is published in the Astrophysical Journal.