Astronomers have identified one of the universe’s oldest ‘dead’ galaxies, revealing that a supermassive black hole can slowly starve a galaxy rather than destroy it outright. The discovery, led by researchers from the University of Cambridge, utilized data from the James Webb Space Telescope (JWST) and the Atacama Large Millimeter Array (ALMA) to study a galaxy from the early universe, approximately three billion years post-Big Bang.
The galaxy, known as GS-10578 but affectionately dubbed ‘Pablo’s Galaxy’ after its first detailed observer, is unusually massive for such an early cosmic period. It boasts a mass about 200 billion times that of our Sun, with the majority of its stars forming between 12.5 and 11.5 billion years ago. Despite its youthful age, Pablo’s Galaxy ceased star formation due to a near-complete lack of cold gas, essential for star creation.
The Role of the Supermassive Black Hole
At the heart of this cosmic mystery is the galaxy’s supermassive black hole. Unlike a singular catastrophic event, the black hole has been slowly suffocating the galaxy in a process described as ‘death by a thousand cuts.’ By repeatedly heating the gas within and around the galaxy, the black hole prevents the influx of fresh gas, gradually stifling star formation. These findings were published in the journal Nature Astronomy.
Researchers dedicated nearly seven hours to observing the galaxy with ALMA, in hopes of detecting carbon monoxide, a tracer of cold hydrogen gas. Their efforts yielded no results.
“What surprised us was how much you can learn by not seeing something,” said Dr. Jan Scholtz, co-first author from Cambridge’s Cavendish Laboratory and Kavli Institute for Cosmology. “Even with one of ALMA’s deepest observations of this kind of galaxy, there was essentially no cold gas left. It points to a slow starvation rather than a single dramatic death blow.”
Insights from JWST Spectroscopy
Meanwhile, JWST spectroscopy uncovered powerful winds of neutral gas streaming from the galaxy’s supermassive black hole at 400 kilometers per second, expelling 60 solar masses of gas annually. This rapid depletion suggests the galaxy’s remaining fuel was exhausted in as little as 16 to 220 million years, much faster than the typical billion-year timescale for similar galaxies.
Dr. Francesco D’Eugenio, co-first author and also affiliated with the Kavli Institute for Cosmology, noted,
“The galaxy looks like a calm, rotating disc. 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.”
Understanding the Starvation Process
By reconstructing the galaxy’s star-formation history, the researchers concluded that the galaxy evolved with net-zero inflow, meaning fresh gas never replenished its reserves. Rather than expelling all its gas in one dramatic event, the black hole seems to have heated or expelled incoming material over multiple cycles, thwarting the galaxy’s ability to rejuvenate itself.
Dr. Scholtz explained,
“You don’t need a single cataclysm to stop a galaxy forming stars, just keep the fresh fuel from coming in.”
This insight helps explain the growing population of massive, surprisingly mature galaxies observed by Webb in the early universe. “Before Webb, these were unheard of,” Scholtz added. “Now we know they’re more common than we thought – and this starvation effect may be why they live fast and die young.”
Future Research and Implications
The study underscores the advantages of combining ALMA’s ultra-deep radio observations with JWST’s infrared spectra. Future research will aim to observe more galaxies like this one to determine if slow starvation, rather than violent blowouts, is typical for early-universe galaxies. The Cambridge team has secured an additional 6.5 hours of JWST time using the MIRI instrument, which will focus on the warmer hydrogen gas to further elucidate the mechanisms by which the supermassive black hole inhibits star formation.
This research received support from 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 a collaboration involving ESO (representing its member states), NSF (USA), NINS (Japan), NRC (Canada), NSTC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The James Webb Space Telescope is a joint effort between NASA, ESA, and the Canadian Space Agency (CSA).
