James Webb Space Telescope finds Strange "Little Red Dots" That Challenge Our Understanding of Early Cosmic Evolution

 

A Little Red Dot galaxy (center) in false color.

James Webb Space Telescope finds Strange "Little Red Dots" That Challenge Our Understanding of Early Cosmic Evolution

COSMOS-Web reveals mysterious galaxy populations powered by unexpectedly massive black holes in the infant universe

When the James Webb Space Telescope began peering into the most distant reaches of the cosmos, astronomers expected to find small, relatively simple galaxies from the universe's youth. Instead, the telescope's largest survey has revealed a population of mysterious objects that are forcing scientists to reconsider fundamental assumptions about how the early universe evolved.

The COSMOS-Web survey is now complete, combining JWST and Hubble infrared data to create the largest, deepest view of the Universe ever acquired with JWST. Spanning 0.54 deg² NIRCam imaging survey in four filters over 255 hours of telescope time, this ambitious project has catalogued nearly 800,000 galaxies across cosmic time, fundamentally transforming our understanding of early galaxy formation.

The Mystery of the Little Red Dots

Among COSMOS-Web's most intriguing discoveries are what astronomers have dubbed "little red dots" (LRDs) — numerous red objects that appear small on the sky scattered throughout images of the early universe. These enigmatic objects, which emerge in large numbers around 600 million years after the big bang and undergo a rapid decline in quantity around 1.5 billion years after the big bang, appear to be unlike any galaxies observed in the modern cosmos.

Their distinctive redness isn't merely a matter of redshifting; rather it indicates they were emitting large amounts of light at longer, redder wavelengths. More puzzling still is their extreme compactness: a typical LRD has an approximate radius of no more than 500 light-years, while for some of them it can be smaller than 150 light-years. Our own Milky Way galaxy, in the modern-day "local" universe, is more than 100 times bigger!

Solving the "Universe-Breaking" Problem

When JWST first detected these bright, distant galaxies, breathless headlines proclaimed that observations of distant galaxies were "breaking theories of cosmic evolution". If all their light came from stars alone, these galaxies would have assembled stellar masses so quickly that existing models of cosmic evolution couldn't explain them.

However, recent research has revealed the solution to this apparent paradox. The team behind this research found the majority of the ancient galaxies in their sample — which existed earlier than 1.5 billion years after the Big Bang — seem to host rapidly feeding, or "accreting," supermassive black holes.

A team of astronomers recently compiled one of the largest samples of LRDs to date, nearly all of which existed during the first 1.5 billion years after the big bang. They found that a large fraction of the LRDs in their sample showed signs of containing growing supermassive black holes.

Supermassive Black Holes in Miniature Galaxies

The supermassive black holes lurking within these little red dots are extraordinary by any measure. In the modern universe, for galaxies close to our own Milky Way, supermassive black holes tend to have masses equal to around 0.01% of the stellar mass of their host galaxy. But in the early universe LRDs, researchers statistically calculated that supermassive black holes in some of the early galaxies seen by JWST have masses of 10% of their galaxies' stellar mass.

This represents a stunning departure from modern cosmic architecture. The odd red bodies, scientists say, hide stars that models suggest are "too old" to have lived during early cosmic times and black holes that measure up to thousands of times larger than the supermassive black hole at the heart of the Milky Way.

Each LRD appears to host a rapidly growing black hole embedded in a dense cloud of ionized gas. This cloud is thick enough to absorb most of the X-ray and radio emissions that are typically seen in active black holes, which explains why LRDs remain relatively "quiet" in those wavelengths.

Revolutionary Insights into Galaxy Evolution

Beyond the mystery of little red dots, COSMOS-Web is providing unprecedented insights into how galaxies and dark matter halos co-evolved throughout cosmic history. The survey's three primary science goals are systematically revealing new aspects of cosmic evolution:

Mapping Cosmic Reionization: COSMOS-Web will revolutionize our understanding of reionization's spatial distribution, environments, and drivers at early stages by detecting thousands of galaxies in the epoch of reionization (6<z<11) and map reionization's spatial distribution.

Tracing Massive Galaxy Evolution: The survey is identifying hundreds of rare quiescent galaxies at early epochs, helping scientists understand how galaxies must have formed their stars at incredible rates (≫100 M⊙ yr−1 at very early times) and then abruptly shut down the production of stars well within the Universe's first billion years.

Linking Dark Matter to Visible Matter: COSMOS-Web provides some of the first systematic quantification of the integrated star formation efficiency from JWST, down to the earliest ages of the Universe, revealing how efficiently galaxies converted their available gas into stars throughout cosmic time.

A New Population of Hidden Black Holes

The survey has also uncovered a hidden population of supermassive black holes in the early universe that have never been seen before. These newly discovered objects appear to bridge the gap between classical bright quasars and the enigmatic little red dots.

These newly discovered "hidden" quasars are as bright as classical quasars, but the level of dust obscuring their light resembles what astronomers have found in the case of Little Red Dots. This discovery suggests that there may be a continuous spectrum of early black hole-powered systems, from heavily obscured little red dots to brilliant unobscured quasars.

Implications for Cosmic History

The discoveries from COSMOS-Web are fundamentally altering our understanding of how the universe evolved from its earliest epochs. If supermassive black holes were already forming when the universe was just a few hundred million years old, they could have played a significant role in the early heating and ionization of the cosmos, influencing the development of the first galaxies.

The research suggests that the physical mechanisms that suppress galaxy growth start to take place at z ∼ 5.5 on a global scale, at least out to masses that we can probe in the COSMOS-Web volume. This is likely due to the onset of negative AGN feedback at these redshifts.

Looking Forward

In a tantalizing mystery, outside of their ancient relic light picked up by JWST, there seems to be no trace of them in today's universe. Why did they vanish? Or what did they morph into? These questions represent some of the most compelling puzzles in modern astronomy.

Future JWST observations will continue to push the limits of our knowledge, searching for even earlier and fainter LRDs. As astronomers continue to analyze the wealth of data from COSMOS-Web, we can expect even more revelations about the universe's most formative period.

The survey represents a triumph of international collaboration, involving more than 100 scientists across multiple countries and building on decades of observations in the COSMOS field. The deep imaging comes with a catalog (the "COSMOS2025" catalog), which contains photometry, structural measurements, redshifts, and physical parameters for nearly 800,000 galaxies, providing an unprecedented resource for understanding cosmic evolution.

COSMOS-Web has demonstrated that the early universe was far more complex and dynamic than previously imagined, populated by exotic objects that challenge our fundamental understanding of how galaxies, black holes, and the cosmic web itself came to be.

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Sources and Citations

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2. Casey, C. M., Kartaltepe, J. S., et al. "COSMOS-Web: An Overview of the JWST Cosmic Origins Survey." The Astrophysical Journal, 954, 31 (2023). arXiv:2211.07865. https://arxiv.org/abs/2211.07865
3. Franco, M., et al. "Unveiling the distant Universe: Characterizing z≥9 Galaxies in the first epoch of COSMOS-Web." The Astrophysical Journal, 973, 23 (2024).
4. Gentile, F., et al. "Not-so-little Red Dots: Two Massive and Dusty Starbursts at z ∼ 5–7 Pushing the Limits of Star Formation Discovered by JWST in the COSMOS-Web Survey." The Astrophysical Journal, 973, 2 (2024).
5. Kocevski, D., et al. "Newfound Galaxy Class May Indicate Early Black Hole Growth, Webb Finds." NASA Science, January 14, 2025. https://science.nasa.gov/missions/webb/newfound-galaxy-class-may-indicate-early-black-hole-growth-webb-finds/
6. Matthee, J., et al. "Little Red Dots: an abundant population of faint AGN at z~5 revealed by the EIGER and FRESCO JWST surveys." arXiv:2306.05448 (2023). https://arxiv.org/abs/2306.05448
7. Rusakov, V., et al. "JWST's little red dots: an emerging population of young, low-mass AGN cocooned in dense ionized gas." arXiv preprint arXiv:2503.16595 (2025).
8. Shuntov, M., et al. "COSMOS-Web: Stellar mass assembly in relation to dark matter halos across 0.2 < z < 12 of cosmic history." Astronomy & Astrophysics, 695, 20 (2025). https://www.aanda.org/articles/aa/full_html/2025/03/aa52570-24/aa52570-24.html
9. Tanaka, M., et al. "The MBH–M∗ Relation up to z ∼ 2 through Decomposition of COSMOS-Web NIRCam Images." The Astrophysical Journal, 979, 215 (2025).
10. Van Dokkum, P., et al. "A massive compact quiescent galaxy at z = 2 with a complete Einstein ring in JWST imaging." Nature Astronomy, 8, 119 (2024).

Primary Survey Information

• COSMOS-Web Official Website: https://cosmos.astro.caltech.edu/page/cosmosweb
• COSMOS Survey Homepage: https://cosmos.astro.caltech.edu/
• JWST Mission Page: https://science.nasa.gov/mission/webb/