The James Webb Space Telescope allowed astronomers to peer into the faraway reaches of the universe like never before, revealing objects that lesser instruments have never glimpsed. Soon after it came online in 2022, Webb observations revealed a population of tiny red objects dubbed little red dots (LRDs). A new study has compiled and analyzed the largest-ever sample of LRDs, and it noted several striking properties, not least of which is that most of these objects contain supermassive black holes. At this point, it appears there is nothing else like LRDs in the observable universe.

The LRDs appeared only in the early universe. While the light from these objects has always been there, other telescopes can't see it. Webb has an enormous primary mirror that allows it to collect more light than other telescopes, but it is also designed to observe the universe in infrared wavelengths. This allows it to peer through clouds of dust and gas to observe the most distant, and therefore oldest, objects in the universe. "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," said lead author Dale Kocevski of Colby College.

In this study, the researchers pulled together data from some of the most ambitious Webb projects, including the Cosmic Evolution Early Release Science (CEERS) survey, the JWST Advanced Deep Extragalactic Survey (JADES), and the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) survey. They also collected spectroscopic data for many of these objects from the Bright Infrared Extragalactic Survey (RUBIES).

The data provided some fascinating insights into the history of Little Red Dots. The oldest of them emerged just 600 million years after the Big Bang, and the youngest appeared 1.5 billion years after the universe came into existence. That's also when the population of LRDs begins to crater -- no objects from later epochs match the properties of LRDs. Even more interesting is what's inside these stellar clusters. About 70% of LRDs studied showed evidence of gas orbiting at more than 2 million miles per hour (1,000 kilometers per second). That strongly suggests we're looking at the accretion disks around supermassive black holes.

Webb's Little Red Dots Credit: NASA, ESA, CSA, STScI, Dale Kocevski, et al.

This is an important step toward understanding the nature of LRDs, but we don't have it all figured out. This work does suggest that some early anxieties about what LRDs meant for cosmology were unfounded. Initially, the high brightness of these objects had scientists fretting that something was very wrong with our understanding of how quickly galaxies could form and grow. However, it now looks like the high brightness is a result of black hole activity. This much at least meshes with current theories.

At the same time, the nature of LRDs is still an open question. Astronomers don't know why these stellar clusters formed enormous black holes so readily, nor why this phenomenon petered out 1.5 billion years after the Big Bang. These objects are also dim in X-rays, which is not the case for black holes at lower redshifts. The team is continuing its work on LRDs, though. By acquiring more mid-infrared spectra from LRDs and studying supermassive black holes with lower redshifts could lead to some answers. For now, Little Red Dots are just a little less mysterious.