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The young galaxy GS-10578 as seen by JWST starved by its supermassive black hole. | Credit: JADES collaboration
Astronomers discovered that a young galaxy was gradually being starved by its central supermassive black hole, in what was effectively a cosmic “death by a thousand cuts”.
The James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA) studied this unfortunate galaxy, known as GS-10578 or by the slightly snappier nickname “Pablo’s Galaxy” in honor of the first astronomer to study it in detail. The light from Pablo’s Galaxy took about 11 billion years to reach us, meaning JWST and ALMA allow astronomers to see it as it was only 3 billion years after the Big Bang. For such an early galaxy, it is exceptionally massive, containing as much mass as about 200 billion suns.
The majority of stars in the Pablo Galaxy appear to have formed between 12.5 billion and 11.5 billion years ago. However, this galaxy appears to have stopped forming stars and exhausted its supply of cold star-forming gas despite its relatively young age. As astronomers define the cessation of star formation and transition to quiescence as the “death” of a galaxy, this means that Pablo’s Galaxy “lived fast and died young.”
The team behind this study released the first results concerning Pablo’s Galaxy back inside September 2024using JWST alone, finding that the supermassive black hole at its core it is pushing away large amounts of gas at speeds as high as 2.2 million miles per hour (3.5 million km/h). That’s fast enough to allow this star-forming matter to completely escape the gravitational influence of the Pablo Galaxy.
With the addition of ALMA, an array of 66 radio telescopes located in the Atacama desert region in northern Chile, the researchers observed the Pablo Galaxy for another seven hours looking for carbon monoxide, which they can use as a way to trace cold hydrogen gas, the stuff that forms stars. However, this search came up empty-handed.
But this in itself was saying.
“What surprised us was how much you can learn by not seeing something,” team member Jan Scholtz from the University of Cambridge in the UK. he said in a statement. “Even with one of ALMA’s deepest observations of this type of galaxy, there was essentially no cold gas left. It points to slow starvation rather than a single dramatic death blow.”
Meanwhile, another 6.5 hours of observations with JWST revealed that the Pablo Galaxy is losing the mass of about 60 suns to gas each year. At that rate, the galaxy’s star-forming fuel could have been exhausted within 16 million to 220 million years. If this seems like an incredibly long period of time, consider that scientists usually estimate that it takes up to a billion years to exhaust their fuel for star formation in such a galaxy.
“The galaxy looks like a calm spinning disk,” said team co-leader Francesco D’Eugenio of the Kavli Institute for Cosmology. “This tells us that it did not suffer a major, disruptive merger with another galaxy. However, it stopped forming stars 400 million years ago, while the black hole became active again.
The team reconstructed the star formation history of the Pablo Galaxy, and found that the fresh gas was prevented by the black hole pushing the gas out from falling back into the galaxy. This prevents star birth “fuel tanks” from being refilled. They also discovered that the supermassive black hole in this young galaxy did not expel all its gas at once, but was experiencing repeated cycles of gas expulsion.
“So the actual black hole activity and gas bursts we observed did not cause the shutdown; instead, repeated episodes likely prevented the fuel from returning,” added D’Eugenio.
The team’s findings may help explain why JWST has been discovering many ancient-looking galaxies in the early universe.
“You don’t need a single cataclysm to stop a galaxy from forming stars, it just keeps fresh fuel from coming in. Before Webb, these were unheard of,” Scholtz said. “Now we know they are more common than we thought – and this effect of starvation may be why they live fast and die young.”
With the effectiveness of the ALMA/JWST telescope tag team established, astronomers hope that further observations of Pablo’s Galaxy can reveal more about the mechanism used by the supermassive black hole to starve this galaxy prematurely.
The team’s research was published on Tuesday (November 25) in the journal Nature Astronomy.