Monster black hole growing at 2.4 times theoretical limit puzzles scientists

A monster black hole is growing at a rate that defies standard theory, according to new observations. Located about 12.8 billion light-years from Earth, the black hole known as RACS J0320–35 weighs roughly a billion solar masses and appears to be accumulating mass at 2.4 times the Eddington limit, one of the fastest growth rates recorded. Data from NASA's Chandra X-ray Observatory indicate that intense radiation arises as matter—gas, dust and other stellar debris—falls into the black hole’s accretion disk and heats up.

Chandra’s measurements suggest the black hole is feeding on surrounding material at a rate estimated between 300 and 3,000 solar masses per year, making it one of the most rapidly growing black holes observed in the first billion years of the universe. Researchers say the X-ray output from the accretion disk is unusually bright for a black hole at such an early epoch. “It was a bit shocking to see this black hole growing by leaps and bounds,” said Luca Ighina, a study author at the Harvard–Smithsonian Center for Astrophysics in Cambridge, Massachusetts. The object sits at the upper end of the supermassive class, and its observed X-rays outshine those from other known black holes in the universe’s first billion years.

The discovery highlights how quickly black holes can grow in the early universe and raises questions about the mechanisms that can drive sustained, super-Eddington accretion. The Eddington limit is the theoretical threshold at which radiation pressure from infalling matter balances the gravitational pull of the black hole. In most standard models, accretion above that limit would blow away incoming material, curbing growth. Yet RACS J0320–35 seems to defy this constraint, at least for a time, suggesting that under certain conditions accretion can proceed at super-Eddington rates.

Astronomers note that RACS J0320–35’s light comes from a time when the universe was roughly 920 million years old, given that the universe is about 13.8 billion years old. By comparison, the Milky Way’s central black hole, Sagittarius A*, has a mass of about 4.3 million solar masses, far smaller than the billion-solar-mass monster in question. RACS J0320–35’s extreme mass and rapid growth make it a compelling target for understanding how the earliest supermassive black holes formed and evolved.

The black hole was identified about two years ago through X-ray observations from Chandra, NASA’s enduring X-ray observatory now in orbit for more than a quarter of a century. In recent years, researchers have continued to refine measurements and analyses, culminating in a report published in The Astrophysical Journal Letters that documents the unusually high growth rate and its implications for black hole physics.

Looking ahead, scientists say continued, multi-wavelength follow-up will help clarify how such rapid accretion can occur and persist in the early universe. Some teams have proposed there is a substantial chance of observing dramatic black hole events within the next decade, with several estimates suggesting a high probability of at least one such event arising somewhere in the cosmos. While these predictions pertain to a broader class of black holes, they provide important context for the ongoing investigation of RACS J0320–35 and similar systems.

As observations continue, researchers hope to refine models of super-Eddington accretion, jet formation, and the growth pathways that allowed the first supermassive black holes to reach their enormous sizes relatively quickly after the Big Bang.