Early Universe Black Holes May Be Smaller Than Previously Thought

Astronomers may have significantly overestimated the size of supermassive black holes in the early universe. New research suggests these celestial objects are far less massive than previously believed, potentially solving a paradox that challenged existing models of how the universe evolved.

Led by Alessandro Trinca of the Italian National Institute for Astrophysics (INAF), the study analyzed 14 supermassive black holes observed by the James Webb Space Telescope (JWST). The team focused on objects that were "X-ray-silent," meaning they were not detected by NASA's Chandra X-ray Observatory. According to the research published in the June 19, 2026, edition of the journal Astronomy & Astrophysics, these black holes are relatively small compared to previous estimates that placed them in the tens or hundreds of millions of solar masses.

The Growth Paradox

For years, the James Webb Space Telescope has identified "overmassive" black holes that appeared too large relative to their host galaxies. Under current cosmological models, these objects should not have had enough time to reach such immense sizes within the first billion years after the Big Bang. Their existence defied the Eddington limit, which is the theoretical maximum rate at which a black hole can consume matter before the resulting radiation pushes incoming gas away.

Trinca's team proposes that these black holes are not actually giants, but are instead smaller objects undergoing "super-Eddington" accretion. In this state, the black holes feed at an extreme rate, which allows them to mimic the spectral signatures of much larger black holes while remaining physically smaller. Trinca noted that while a non-detection of X-rays might seem uninformative, in this instance, the absence of those emissions provided a strong constraint that helped define the physical picture more clearly than detections alone.

Implications for Cosmology

If these black holes are indeed smaller, it removes the need for extreme, uninterrupted growth histories that currently defy the laws of physics. This finding aligns the mass of early black holes more closely with their host galaxies, suggesting that growth occurs in rapid, episodic bursts rather than a steady, impossible climb. This provides a more plausible timeline for the evolution of the early universe and suggests that the "overmassive" problem may have been an illusion caused by the way these objects feed.

What's Next

While the core finding resolves a major tension in early-universe physics, researchers will continue to monitor these X-ray-silent objects to confirm the super-Eddington model. Future observations will focus on whether this episodic growth pattern is universal for all early supermassive black holes or if some truly anomalous giants still exist.