Found less than a billion years after the Big Bang, these massive objects are upending astronomers’ timeline for how early galaxies formed.
These images of Little Red Dots were acquired by the James Webb Space Telescope. Credit: NASA/ESA/CSA/STScI/Dale Kocevski (Colby College)
On Tuesday, at the 245th meeting of the American Astronomical Society, astronomers revisited some recent mysteries. Dale Kocevski, from Colby College in Maine, spoke during a press conference about the Little Red Dots (LRDs) found in data from the James Webb Space Telescope (JWST). These are the same as the “universe-breaking” galaxies first reported roughly two years ago, so called because they are larger than scientists can explain at so early a point in cosmic time — less than a billion years after the Big Bang.
Scientists simply don’t understand how so many stars and so much material can accumulate in so little time. When the news first broke, there were six of the objects. Now, JWST has revealed 341 of them. Kocevski’s update to the LRD investigation has been accepted for publication in The Astrophysical Journal.
Strength in numbers
While the earlier findings were not in question, the sheer number now reported has changed the scientific perspective: These can no longer be thought of as quirks or outliers. Instead, they make up one out of every five to 10 galaxies in the early cosmos, making them routine. That ups the pressure to understand them, and only emphasizes the gathering suspicion that something about how we understand galaxy assembly, at least the ones at the dawn of cosmic time, is incomplete.
Kocevski was able to further probe the brightest of these objects and confirm that most of these — 81 percent of his subset — are active galactic nuclei, or AGN. That means they have central black holes that are actively gobbling material, causing them to heat up and glow even brighter than all their stars can account for.
If most LRDs are AGN, that can explain much of their “universe-breaking” reputation. AGN far outshine normal galaxies, so it could mean they are more moderately sized after all. But even so, the large numbers of them are surprising. There are far more of them — 10 to 100 times more — than other surveys have indicated, whether they are quasars, AGN, or some other form of active black hole.
What’s more, these galaxies only appear in the early universe. They disappear from surveys around a redshift of 4, meaning when the universe was less than 2 billion years old. It’s very likely that they evolve into more typical galaxies — but even that tells us that something strange is happening in those early days to produce these phenomena. The LRD mystery goes hand-in-hand with other findings by JWST that the young universe didn’t unfold the way we thought.
Again, JWST has proven its mettle. With a keener eye to see farther back into cosmic time, scientists are able to rewrite the history of the universe.
