Supermassive black holes grew faster than thought, study finds

The black hole at the center of our galaxy weighs as much as 4.5 million suns. Across the universe, in a galaxy called M87 some six million light-years away, sits another one that tips the scales at around 5 billion suns. The gap between these two numbers has long puzzled astronomers: How did the universe find time to build objects so vastly different in size, especially when the oldest ones formed billions of years ago?

A new study suggests the answer may be simpler than expected—these cosmic monsters grew faster than anyone realized. Using novel computer modeling, researchers led by Joseph Simon, a postdoctoral researcher at the University of Colorado Boulder, analyzed data from hundreds of thousands of galaxies to estimate the masses of supermassive black holes across cosmic history. What they found was unexpected: the early universe contained far more massive black holes than current theories predicted, and they appear to have reached their enormous sizes without requiring the vast stretches of time scientists had assumed necessary.

The challenge has always been one of measurement and time. Astronomers have precise readings for the supermassive black holes nearest to us—the one in our own Milky Way, and a handful of others in nearby galaxies. But for distant galaxies, seen as they existed billions of years ago, direct measurement is impossible. "We just have to guess," Simon explained. The guessing has led to a persistent puzzle: observations kept turning up unexpectedly large black holes in the young universe, objects that shouldn't exist if growth required the conventional timeline.

Simon's approach bypassed the measurement problem by working backward. He gathered information about hundreds of thousands of galaxies across cosmic distances, then used that data to calculate what masses their central black holes must possess. Computer simulations then predicted the gravitational waves these objects would generate—the ripples in space-time that Einstein's theory predicts are created when massive objects accelerate. This method gave him a distribution of black hole masses stretching back roughly four billion years, a window into the universe's middle age.

The results challenged the existing framework. The data revealed that large galaxies and their supermassive black holes were far more common in the early universe than models had suggested. More importantly, the findings imply these objects did not require as much time to grow as previously theorized. The implication is profound: either black holes merge and accumulate mass more efficiently than thought, or the processes driving their growth operate differently than current models assume.

This matters because supermassive black holes are not merely cosmic curiosities. They sit at the hearts of most galaxies and exert tremendous influence over how those galaxies evolve. Understanding how quickly black holes grow is therefore central to understanding how galaxies form and how the universe itself has changed over billions of years. Simon's work also feeds into a larger effort called the North American Nanohertz Observatory for Gravitational Waves, which hunts for a steady background hum of gravitational waves produced by merging black holes throughout cosmic history. To interpret that signal, researchers need accurate estimates of black hole masses across time.

The next phase of this research will push even farther back, examining black holes in more distant galaxies and thus seeing them as they existed even earlier in the universe's history. Simon hopes that peering deeper into the cosmic past will illuminate fundamental questions about galaxy formation and the universe's evolutionary arc. The work represents a shift in how astronomers think about black hole growth—not as a slow, time-constrained process, but as something that may have unfolded far more rapidly than the standard models allow.