Ancient galaxy slowly starved by its black hole
Astronomers have uncovered one of the universe's earliest "dead" galaxies, where a supermassive black hole at its core halted star formation not through a dramatic outburst but via repeated cycles of gas heating and ejection a process likened to death by a thousand cuts.
The study, published on January 11 in Nature Astronomy, drew on observations from the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA) to analyze a galaxy labeled GS-10578, affectionately known as "Pablo's galaxy" after the astronomer who first studied it in detail. This massive galaxy existed roughly three billion years after the Big Bang, boasting a stellar mass equivalent to about 200 billion suns an impressive scale for such an early epoch. Most of its stars formed between 12.5 and 11.5 billion years ago, yet star formation ceased around 400 million years ago, despite ample raw material remaining.
Researchers from the University of Cambridge led the effort, dedicating nearly seven hours of ALMA time to hunt for carbon monoxide, a tracer of the cold hydrogen gas crucial for birthing new stars. They detected almost none. "The surprise was in the absence," said co-lead author Dr. Jan Scholtz from Cambridge's Cavendish Laboratory and Kavli Institute for Cosmology. "Even with one of ALMA's deepest observations for this galaxy type, cold gas was virtually gone, pointing to a gradual starvation rather than a single catastrophic blow."
JWST spectroscopy exposed powerful outflows of neutral gas from the central black hole, racing outward at 400 kilometers per second and expelling material equivalent to 60 solar masses annually. At that pace, the galaxy's remaining fuel would deplete in just 16 to 220 million years far quicker than the typical billion-year timeline for similar systems. "The galaxy appears as a serene rotating disk," noted co-lead author Dr. Francesco D'Eugenio from the Kavli Institute. "No major disruptive merger is evident, yet star formation stopped 400 million years ago while the black hole reactivated."
These findings shed light on the surprisingly abundant massive, mature-looking galaxies that JWST has revealed in the early universe objects previously undetected. "Before JWST, we didn't know they existed in such numbers," Scholtz added. "This quenching mechanism explains how they burn bright but fade fast." The Cambridge team has secured an extra 6.5 hours of JWST time to probe warmer hydrogen gas, potentially unveiling more about how black holes enforce stellar silence.
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