About a year after launching into orbit around the Sun, the James Webb Space Telescope began imaging an abundance of little red dots, which scientists called, um, “little red dots.” I know—not only is the name highly unimaginative, it also conveys a false impression of insignificance. In reality, these little red dots almost “broke” modern cosmology.
Astronomers have assembled one of the largest surveys of little red dots (LRDs) ever made, and theorize that a large portion of these mysterious space objects are galaxies with supermassive black holes. Their results, presented during the 245th meeting of the American Astronomical Society in Maryland and accepted for future publication in The Astrophysical Journal, could resolve the “universe-breaking problem.”
“We’re confounded by this new population of objects that Webb has found. We don’t see analogs of them at lower redshifts, which is why we haven’t seen them prior to Webb,” Dale Kocevski of Colby College in Waterville, who led the study, said in a Space Telescope Science Institute statement.
Redshift happens when the universe’s expansion stretches light waves, increasing their wavelengths. This makes them appear more red because they “shift” closer to the red part of the light spectrum. That’s partially why little red dots are—you guessed it—red. Essentially, lower redshifts correspond to closer distances in space.
“There’s a substantial amount of work being done to try to determine the nature of these little red dots and whether their light is dominated by accreting [growing by accumulating matter] black holes,” Kocevski added. Kocevski and his team’s research was published in a September preprint article on arXiv.
Nearly all the LRDs in their survey existed during the universe’s first 1.5 billion years. How do we know about objects that existed billions of years ago? It’s because light takes time to travel. When we observe celestial bodies, we’re seeing them not as they are today, but as they were when their light first began its journey to Earth. For example, it takes eight minutes and twenty seconds for the Sun’s light to travel to our planet. That means we see the Sun as it was eight minutes and twenty seconds ago. The same goes for objects much farther away from us. In fact, the farther away they are, the higher their redshift, and the further “back in time” we can see.
Don’t worry, there won’t be a quiz at the end.
The team’s research indicated that a large portion of the LRDs in question existed between 600 million and 1.5 billion years after the Big Bang. They also found evidence that many of them had orbiting gas traveling at about 2 million miles per hour (around 3.2 million kilometers per hour). Based on this evidence, the researchers suggest that LRDs could be active galactic nuclei (AGN): extremely luminous and growing supermassive black holes.
“The most exciting thing for me is the redshift distributions. These really red, high-redshift sources basically stop existing at a certain point after the big bang,” said Steven Finkelstein from the University of Texas at Austin, who also participated in the research. “If they are growing black holes, and we think at least 70 percent of them are, this hints at an era of obscured black hole growth in the early universe.”
It would also “fix” the cosmology that the JWST “broke” when it first identified the LRDs. The possibility of stars emitting that kind of light within this context contradicted widely-accepted cosmological theories, leading some scholars to suggest that cosmology was “broken.” Light emitted by AGNs, however, fits with those theories.
“This is how you solve the universe-breaking problem,” said Anthony Taylor from the University of Texas at Austin, a co-author of the forthcoming study.
While the universe-breaking problem might be solved, however, many questions about LRDs remain.
“There’s always two or more potential ways to explain the confounding properties of little red dots,” said Kocevski. “It’s a continuous exchange between models and observations, finding a balance between what aligns well between the two and what conflicts.”
Ultimately, the take-aways from the study are two: don’t judge an astronomical phenomenon by its name, and even universe-breaking problems can eventually be fixed.