Astronomers have identified one of the oldest “dead” galaxies ever observed, offering new insights into how supermassive black holes can slowly starve galaxies rather than destroy them in a single dramatic event. The galaxy, which was known on prior occasions as GS-10578 but nicknamed “Pablo’s Galaxy” after the astronomer who initially researched it in detail, gives a rare insight into the early universe, just three billion years after the Big Bang theory as indicated by researcher of the study.
University of Cambridge scientists took the lead where the team utilized observations from the James Webb Space Telescope (JWST) as well as the Atacama Large Millimeter Array (ALMA) to look into the structure of the galaxy, star formation history, along with the central black hole activity. Even though it had relatively young age in cosmic terms, Pablo’s Galaxy is massive, that has approximately 200 billion times the mass of the Sun. Most of its stars formed between 12.5 and 11.5 billion years ago, making it a surprisingly mature system for such an early epoch.
Dr. Jan Scholtz, co-first author and researcher at Cambridge’s Cavendish Laboratory and Kavli Institute for Cosmology indicated that what makes this galaxy an interesting case is the fact that it ‘lived fast and died young.’
The team found that the galaxy’s supermassive black hole was key to this slow shutdown. Instead of expelling all gas at once in a violent blowout, the black hole repeatedly heated and pushed gas away over time, preventing fresh gas from replenishing the galaxy’s star-forming reservoir. This “death by a thousand cuts” scenario contrasts with earlier theories in which black holes were thought to destroy galaxies through singular explosive events.
ALMA observations, totaling nearly seven hours, aimed to detect carbon monoxide—a marker of cold hydrogen gas—but revealed essentially none. “What surprised us was how much you can learn by not seeing something,” Scholtz explained. The lack of cold gas strongly indicates a slow starvation process rather than a sudden, violent end to star formation.
JWST spectroscopy revealed powerful winds of neutral gas streaming out of the black hole at speeds of 400 kilometers per second, removing approximately 60 solar masses of gas per year. These rates suggest that the galaxy’s remaining fuel could have been depleted in as little as 16 to 220 million years, a rapid pace compared with the billion-year timescale typical for similar galaxies.
“The galaxy looks like a calm, rotating disc,” said co-first author Dr. Francesco D’Eugenio, also affiliated with the Kavli Institute for Cosmology. “That tells us it didn’t suffer a major, disruptive merger with another galaxy. Yet it stopped forming stars 400 million years ago, while the black hole is yet again active. So the current black hole activity and the outburst of gas we observed didn’t cause the shutdown; instead, repeated episodes likely kept the fuel from coming back.”
By reconstructing Pablo’s Galaxy’s star-formation history, the researchers concluded that it evolved with “net-zero inflow,” meaning fresh gas never refilled its reservoir. This mechanism may explain the growing population of massive, surprisingly old-looking galaxies JWST has revealed in the early universe.
The study highlights the advantages of combining ALMA’s ultra-deep radio observations with JWST’s infrared spectroscopy. The Cambridge team has been awarded an additional 6.5 hours of JWST observing time using the MIRI instrument to examine warmer hydrogen gas, which will help clarify exactly how the black hole shuts down star formation.
This research was supported by the European Union, the European Research Council, the Royal Society, and the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI). ALMA is operated by ESO, NSF, NINS, NRC, NSTC, ASIAA, and KASI in cooperation with Chile, while the James Webb Space Telescope is a collaboration between NASA, ESA, and the Canadian Space Agency.
The discovery of Pablo’s Galaxy demonstrates that not all cosmic deaths are dramatic. Sometimes, the quiet, persistent influence of a black hole is enough to stop a galaxy from forming stars, leaving behind an ancient, massive relic of the early universe.
