What are the mysterious ‘red dots’ seen by the James Webb telescope?
Joel Leja, associate professor of astronomy and astrophysics and Dr. Keiko Miwa Ross Mid-Career Endowed Chair at Penn State University, examines their origin.
Joel Leja is the Dr. Keiko Miwa Ross Mid Career Endowed Faculty Chair and an Associate Professor of astronomy and astrophysics at Penn State University. He researches how galaxies like the Milky Way form over cosmic time, using ground-and space-based telescopes, large cosmic surveys, and supercomputers. He specializes in modeling observations of distant galaxies and in data-intensive methodologies applied to astrophysics. Joel received his Ph.D in Astronomy from Yale University under Dr. Pieter van Dokkum in 2016 and was an NSF Astronomy & Astrophysics Postdoctoral Fellow at the Center for Astrophysics | Harvard and Smithsonian with Dr. Charlie Conroy until 2020. He was named a Clarivate Highly Cited Researcher in 2023 and in 2024 (top 1% of cited researchers in astrophysics), and awarded Yale University’s Brouwer Prize in 2019 for a PhD thesis of unusual merit.
Mysterious ‘Red Dots’ in Early Universe May Be ‘Black Hole Star’ Atmospheres
A core mission goal for the James Webb Space Telescope is to find the first stars, galaxies, and black holes to emerge in the universe. So, right after launch, the James Webb Space Telescope began taking long exposures, staring deep into the distant universe and far back in time. This immediately revealed a big surprise: “little red dots”, mysterious, bright, and tiny objects that appear to live predominantly in the first several billion years of the universe. Astronomers thought the objects were mature galaxies, far more massive and far earlier than we expected. This was problematic for several reasons; the stars would need to be packed in the galaxies with impossible density, and our models of the universe would have to be revised to allow the formation of such massive systems, so early.
Now a few years in, we have better data – and in some little red dots, we can rule out the idea that they shine with many stars. Instead, they appear to be a single block of glowing gas, dense and cool, with immense amounts of matter roiling on their surface. The most straightforward description is something we have termed a “black hole star” – a central, massive black hole, surrounded by a thick ball of dense, cool gas that looks like the atmosphere of a star. It is very abnormal to see a black hole completely suffused with gas, and would likely represent a previously-unknown evolutionary phase of very massive black holes in the early universe.
This is why we do large projects like James Webb – we always hope to observe something shocking, because it means we are going to learn something new. And little red dots have absolutely fit this bill – but we’re just scratching the surface of what we can learn about the origins of the universe.
Read More:
[ads] – A remarkable ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a little red dot at z = 3.5
[Max Planck Gesellschaft] – Are Black Hole Stars real?
[Penn State News] – Mysterious ‘red dots’ in early universe may be ‘black hole star’ atmospheres
