Astronomers have identified that the young galaxy GS-10578, also known as "Pablo's Galaxy," experienced a gradual cessation of star formation due to its central supermassive black hole. This process is described as a cosmic "death by a thousand cuts."
Observations and Discoveries
The James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA) were utilized to study GS-10578. The light from this galaxy took approximately 11 billion years to reach Earth, allowing astronomers to observe it as it existed roughly 3 billion years after the Big Bang. GS-10578 is exceptionally massive for an early galaxy, containing mass equivalent to about 200 billion suns.
The majority of stars in GS-10578 formed between 12.5 billion and 11.5 billion years ago. However, the galaxy ceased star formation and depleted its supply of cold gas, which is necessary for star birth, despite its relatively young age. The cessation of star formation and transition to quiescence is considered the "death" of a galaxy.
Initial JWST observations indicated that the supermassive black hole at the galaxy's core was expelling vast quantities of gas at speeds up to 2.2 million miles per hour (3.5 million km/h). This velocity is sufficient for the star-forming material to escape the galaxy's gravitational pull.
Further observations using ALMA, which involved searching for carbon monoxide to trace cold hydrogen gas, yielded no detections. This absence of cold gas suggests a lack of star-forming fuel. Jan Scholtz from Cambridge University commented that "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."
Rate of Gas Loss and Implications
An additional 6.5 hours of JWST observations revealed that GS-10578 is losing approximately 60 solar masses of gas annually. At this rate, the galaxy's star-forming fuel could have been exhausted within 16 to 220 million years, a significantly shorter timeframe compared to the typical estimate of a billion years for similar galaxies.
Francesco D'Eugenio of the Kavli Institute for Cosmology noted that "The galaxy looks like a calm, rotating disc." This suggests that a major, disruptive merger with another galaxy did not cause its cessation of star formation. The galaxy stopped forming stars 400 million years ago, with the black hole remaining active.
The research team reconstructed the star formation history of GS-10578, finding that the black hole prevented fresh gas from falling back into the galaxy, thus stopping the replenishment of star-forming fuel. They determined that the black hole did not expel all its gas at once but underwent repeated cycles of gas expulsion. D'Eugenio added that "repeated episodes likely kept the fuel from coming back."
These findings may provide insights into why the JWST has identified numerous old-looking galaxies in the early universe. Scholtz stated, "You don't need a single cataclysm to stop a galaxy forming stars, just keep the fresh fuel from coming in." He further suggested that this starvation effect might be the reason these galaxies "live fast and die young."
Astronomers plan further ALMA/JWST observations of GS-10578 to investigate the mechanism through which the supermassive black hole prematurely depleted the galaxy's star-forming material.