About a year after it was launched into orbit around the Sun, the James Webb Space Telescope began to take pictures of many small red dots that scientists called “little red dots.” I know that this name is not only unimaginative, but also gives the false impression that they are insignificant. In fact, these little red dots have almost “broken” modern cosmology.
Astronomers have assembled one of the largest studies of small red dots (LRDs) ever done and suggest that a significant proportion of these mysterious cosmic 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 solve the “universe tearing apart problem”.
“We are confused by this new population of objects that Webb has found. We don’t see their lower redshift counterparts, which is why we didn’t see them before Webb,” said Dale Koczewski of Colby College in Waterville, who led the study, in a statement from the Space Telescope Science Institute.
Redshift occurs when the expansion of the Universe stretches light waves, increasing their length. This makes them appear redder as they “shift” closer to the red part of the light spectrum. This is partly why small red dots are – you guessed it – red. Essentially, smaller redshifts correspond to closer distances in space.
“There’s a lot of work going on to try to determine the nature of these little red dots and to see if their light is dominant in accretionary [growing through the accumulation of matter] black holes,” Kochevsky added. The study by Kochevsky and his team was published in a September preprint article on arXiv.
Almost all of the LRDs in their study existed during the first 1.5 billion years of the Universe’s existence. 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 don’t see them as they are today, but as they were when their light first began its journey to Earth. For example, the light of the Sun reaches our planet in eight minutes and twenty seconds. This means that we see the Sun as it was eight minutes and twenty seconds ago. The same goes for objects that are much further away from us. In fact, the further away they are, the greater their redshift, and the further “back in time” we can see.
The team’s study found that a large proportion 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 were orbiting gas at speeds of about 2 million miles per hour (about 3.2 million kilometers per hour). Based on this evidence, the researchers suggest that the LRDs could be active galactic nuclei (AGNs): extremely luminous supermassive black holes that are growing.
“The most interesting thing for me is the distribution of redshifts. These really redshifted, high redshift sources basically cease to exist at some point after the Big Bang,” said Steven Finkelstein of the University of Texas at Austin, who also participated in the study. “If they are accreting black holes, and we believe that at least 70 percent of them are, this hints at an era of accreting black holes in the early Universe.”
This will also “fix” the cosmology that JWST “broke” when it first detected the LRD. The possibility of stars emitting such light in this context contradicted conventional cosmological theories, leading some scientists to suggest that cosmology had been “broken.” However, the light emitted by supernovae fits into these theories.
“This is how you can solve the problem of the tearing of the universe,” said Anthony Taylor of the University of Texas at Austin, co-author of the upcoming study.
While the universe tearing problem may be solved, many questions about LRD remain open.
“There are always two or more potential ways to explain the confusing properties of small red dots,” says Kochevsky. “It’s a continuous exchange between models and observations, finding a balance between what fits well and what conflicts.”
Ultimately, two conclusions can be drawn from the study: don’t judge an astronomical phenomenon by its name, and even problems that disrupt the universe can eventually be solved.
