The small red dots in the Webb images turned out to be quasars

Webb n EIGER image of the glowing quasar J1148+5251, an extremely rare active SMBH of 10 billion solar masses (blue box). In the same data set two are visible

In its first year of operation, the James Webb Space Telescope made several significant discoveries. It captured the sharpest images of iconic cosmic structures (such as the Pillars of Creation), transmission spectra of exoplanet atmospheres, and breathtaking views of Jupiter, its largest moons, the rings of Saturn, its largest moon Titan, and the plumes of Enceladus. But in its first year of observations, Webb made an unexpected discovery that could prove groundbreaking: a series of small red dots in a tiny region of the night sky.

These small red dots were discovered as part of the Webb surveys Emission Line Galaxies and Intergalactic Gas in the Epoch of Reionization (EIGER) and Spectroscopically Complete Observations of the First Reionization Epoch (FRESCO). According to a new analysis by an international team of astrophysicists, these points are galactic nuclei containing precursors to supermassive black holes (SMBHs) that existed in the early Universe. The existence of these black holes shortly after the Big Bang may change our understanding of how the first SMBHs formed in our Universe.

The study was led by Jorrit Matti, assistant professor of astrophysics at the Austrian Institute of Science and Technology (ISTA) and ETH Zurich. He was joined by scientists from the MIT Kavli Institute for Astrophysics and Space Research, the Cosmic Dawn Center (DAWN), the National Astronomical Observatory of Japan (NAOJ), the Niels Bohr Institute, the Max Planck Institute for Astronomy (MPIA), the Center for Astrobiology (CAB), and as well as numerous universities and observatories. The results of their work were published in The Astrophysical Journal.

This image shows the area of the sky where record-breaking quasar J0529-4351 was spotted by ESO's Very Large Telescope in Chile.

Scientists have long known that supermassive black holes are at the center of most massive galaxies. And if some of them are in a state of relative rest, like the SMBH located in the center of the Milky Way (Sagittarius A*), then others are extremely active and growing, gaining several solar masses per year. These fast-growing black holes give rise to particularly bright active galactic nuclei (AGNs) – or quasars – that become so bright that they temporarily outshine all the stars in their disk, the brightest of which are known as quasars.

Quasars are among the brightest objects known to astronomers and can be seen at the very edge of our expanding Universe. However, in recent years, astronomers have spotted several quasars and SMBHs in the early Universe, and they turned out to be larger than cosmological models predict. As Matty explained in a recent ISTA press release:

“One of the problems with quasars is that some of them appear to be too massive for the age of the universe at which quasars are observed. We call them 'problem quasars'. Considering that quasars arise from the explosions of massive stars and what we know their maximum growth rate from the general laws of physics, then some of them look like they were growing faster than possible. It's like meeting a five-year-old child who is two meters tall. Something doesn't add up.”

Mati and his team discovered the population of small red dots by studying imagery from the EIGER and FRESCO surveys, large and mid-sized campaigns in Webb's first year in which Mati was involved. The EIGER campaign was specifically designed to search for rare blue supermassive quasars and their environments, rather than to search for quasars in the early Universe. However, Webb's near-infrared camera (NIRCam) can obtain the emission spectra of all objects in the known Universe. These objects were previously observed by Hubble and were mistaken for ordinary galaxies.

Webb's near-infrared view of NGC 604 in the Triangulum galaxy.

But thanks to NIRCam's resolution, the ISTA-led team identified them as SMBHs almost by accident. According to Mathy, this accidental discovery could have profound implications for astronomy and cosmology:

“While not designed for this specific purpose, Webb helped us determine that faint little red dots discovered in the very distant past of the Universe are small versions of extremely massive black holes. These special objects may change our understanding of the origin of black holes. The findings The results may bring us one step closer to answering one of astronomy's greatest dilemmas: According to existing models, some supermassive black holes in the early Universe simply grew “too fast.” So how did they form?”

The team was able to differentiate between galaxies and small quasars because NIRCam detected deep red emission lines (aka Hα spectral lines) that form when hydrogen atoms heat up. They also found that the observed lines had a broad profile, which they used to track the movement of hot hydrogen gas. “The wider the base of the Hα lines, the higher the gas velocity,” says Mathie. “So what these spectra tell us is that we have a very small cloud of gas in front of us that is moving very fast and orbiting something very massive, like a SMBH.”

Equally important are the redshift values they obtained for these SMBGs (Z= 4.2-5.5), which indicate that these objects existed more than 12 billion years ago – about 1 billion years after the Big Bang. They also noticed that these SMBHs were not overly massive like those seen in nearby galaxies today. As Mathie noted:

“While “problem quasars” are blue, extremely bright and reach masses billions of times greater than the mass of the Sun, small red dots are more like “baby quasars.” Their mass ranges from ten to one hundred million solar masses. “In addition, they appear red because they are covered in dust. Dust obscures black holes and colors them red.”

Long exposure photographs taken with a space telescope

Eventually, the flow of hydrogen gas will break through the clouds of dust and gas that surround and hide the massive black holes (“dust cocoons”), and these small SMBHs will evolve into much larger ones. Thus, Mathy and his team proposed that the small red dots are small red versions of giant blue SMBHs in the pre-problem quasar stage. With follow-up observations, astronomers will be able to conduct detailed studies of these small SMBHs, which could lead to a better understanding of how problematic quasars arise.

“Black holes and SMBHs are perhaps the most interesting phenomena in the Universe. It is difficult to explain why they are there, but they are there,” concluded Mathy. “We hope this work will help us lift one of the biggest mysteries about the universe.”