A supermassive black hole in the center of the radio quasar RACS J032021.44-352104.1 (RACS J0320-35 for short) is growing at one of the fastest rates ever recorded, according to an analysis of radio and X-ray data from NASA’s Chandra X-ray Observatory, the Giant Metrewave Radio Telescope, the Australia Telescope Compact Array and the Australian Large Baseline Array.
An artist’s illustration and an X-ray image from Chandra of RACS J0320-35. Image credit: NASA / CXC / INAF-Brera / Ighina et al. / SAO / M. Weiss / N. Wolk.
RACS J0320-35’s black hole weighs about a billion times the mass of the Sun.
The system is located about 12.8 billion light-years from Earth, meaning that astronomers are seeing it only 920 million years after the Universe began.
It is producing more X-rays than any other black hole seen in the first billion years of the Universe.
The black hole is powering what scientists call a quasar, an extremely bright object that outshines entire galaxies.
The power source of this glowing monster is large amounts of matter funneling around and entering the black hole.
While the same team discovered it two years ago, it took observations from Chandra in 2023 to discover what sets RACS J0320-35 apart.
The X-ray data reveal that this black hole appears to be growing at a rate that exceeds the normal limit for these objects.
“It was a bit shocking to see this black hole growing by leaps and bounds,” said Dr. Luca Ighina, an astronomer at the Harvard & Smithsonian’s Center for Astrophysics.
When matter is pulled toward a black hole it is heated and produces intense radiation over a broad spectrum, including X-rays and optical light. This radiation creates pressure on the infalling material.
When the rate of infalling matter reaches a critical value, the radiation pressure balances the black hole’s gravity, and matter cannot normally fall inwards any more rapidly. That maximum is referred to as the Eddington limit.
Scientists think that black holes growing more slowly than the Eddington limit need to be born with masses of about 10,000 solar masses or more so they can reach a billion solar masses within a billion years after the Big Bang — as has been observed in RACS J0320-35.
A black hole with such a high birth mass could directly result from an exotic process: the collapse of a huge cloud of dense gas containing unusually low amounts of elements heavier than helium, conditions that may be extremely rare.
If RACS J0320-35 is indeed growing at a high rate — estimated at 2.4 times the Eddington limit — and has done so for a sustained amount of time, its black hole could have started out in a more conventional way, with a mass less than a hundred solar masses, caused by the implosion of a massive star.
“By knowing the mass of the black hole and working out how quickly it’s growing, we’re able to work backward to estimate how massive it could have been at birth,” said Dr. Alberto Moretti, an astronomer at INAF-Osservatorio Astronomico di Brera.
“With this calculation we can now test different ideas on how black holes are born.”
To figure out how fast this black hole is growing (between 300 and 3,000 Suns per year), the researchers compared theoretical models with X-ray spectrum from Chandra, which gives the amounts of X-rays at different energies.
They found the Chandra spectrum closely matched what they expected from models of a black hole growing faster than the Eddington limit.
The data from optical and infrared light also support the interpretation that this black hole is packing on weight faster than the Eddington limit allows.
“How did the Universe create the first generation of black holes?” said Dr. Thomas of Connor, an astronomer at the Harvard & Smithsonian’s Center for Astrophysics.
“This remains one of the biggest questions in astrophysics and this one object is helping us chase down the answer.”
Another scientific mystery addressed by this result concerns the cause of jets of particles that move away from some black holes at close to the speed of light, as seen in RACS J0320-35.
“Jets like this are rare for quasars, which may mean that the rapid rate of growth of the black hole is somehow contributing to the creation of these jets,” the authors said.
Their paper appears in the Astrophysical Journal.
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Luca Ighina et al. 2025. X-Ray Investigation of Possible Super-Eddington Accretion in a Radio-loud Quasar at z = 6.13. ApJL 990, L56; doi: 10.3847/2041-8213/aded0a
