Imagine a galaxy meeting a tragic fate through a slow, relentless process—this is the story of Pablo's Galaxy, which astronomers have identified as a victim of its own supermassive black hole. This discovery highlights an intriguing cosmic phenomenon often described as a “death by a thousand cuts.”
Utilizing the advanced capabilities of the James Webb Space Telescope (JWST) alongside the Atacama Large Millimeter/submillimeter Array (ALMA), researchers have been able to delve into the life story of this unfortunate galaxy, officially designated GS-10578 and affectionately called "Pablo's Galaxy" in tribute to the first astronomer who extensively examined it. The light we now observe from this galaxy has traveled approximately 11 billion years to reach us, allowing scientists to witness its existence just 3 billion years after the Big Bang. Notably, this early galaxy boasts a mass equivalent to around 200 billion suns, making it exceptionally large for its age.
The research team initially released findings about Pablo's Galaxy in September 2024, focusing solely on observations made with the JWST. They discovered that the supermassive black hole at its center is expelling vast amounts of gas at staggering speeds of up to 2.2 million miles per hour (or 3.5 million kilometers per hour). Such velocities are significant enough to enable star-forming gas to escape the galaxy’s gravitational pull entirely.
To deepen their investigation, the researchers utilized ALMA—an array consisting of 66 radio telescopes situated in Chile's Atacama Desert—for an additional seven hours to search for carbon monoxide, a vital indicator that could help trace the presence of cold hydrogen gas essential for star formation. However, the absence of such gas during their observations proved to be insightful in itself.
Jan Scholtz, a member of the team from Cambridge University, remarked, "What surprised us was how much you can learn by not seeing something. 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."
In addition, another 6.5 hours of observations using the JWST indicated that Pablo's Galaxy is losing the equivalent of about 60 solar masses of gas annually. At this rate, the galaxy could deplete its star-forming fuel within a timeframe ranging from 16 million to 220 million years. While this may seem like a lengthy duration, it's important to note that astronomers typically estimate that it can take up to a billion years for a galaxy similar to Pablo's to exhaust its star formation fuel.
Francesco D'Eugenio, co-leader of the research team from the Kavli Institute for Cosmology, explained, "The galaxy looks like a calm, rotating disc, which indicates that it did not undergo a major merger with another galaxy. Yet it ceased forming stars 400 million years ago while its black hole remains active.
The team's analysis traced the star formation history of Pablo's Galaxy, revealing that the black hole has been pushing gas outward, effectively preventing fresh supplies from returning to the galaxy and replenishing its resources for star formation. They found that the supermassive black hole did not expel all its gas in one go; instead, it experienced cycles of gas ejection over time.
D'Eugenio further elaborated, "So the current black hole activity and the outbursts of gas we observed didn't cause the shutdown; rather, repeated episodes likely inhibited the inflow of new fuel."
These findings offer valuable insights into why the JWST has been identifying numerous galaxies appearing older than expected from the early universe. Scholtz noted, "You don't need a single cataclysm to halt a galaxy's star formation; simply preventing fresh fuel from entering is sufficient. Before Webb, such instances were virtually unheard of. Now we understand they are more prevalent than previously thought, and this starvation effect may explain why these galaxies have short lifespans.
With the successful collaboration of ALMA and JWST established, astronomers are eager to conduct more observations of Pablo's Galaxy to uncover further details about the mechanisms employed by the supermassive black hole that led to this galaxy's premature decline.
The team's research findings were published on November 25 in the journal Nature Astronomy, contributing to our understanding of cosmic marvels and the intricate dynamics at play in galaxies across the universe.
