🔭 A supermassive black hole "killed" its own galaxy

How can a galaxy fade so early in the history of the Universe? Astronomers are particularly intrigued by these massive galaxies which, although young, appear to have stopped all star formation. Behind this apparent tranquility, very active internal processes often lead to their premature demise.

Recently, a team of researchers focused their attention on galaxy GS-10578, nicknamed "Pablo's galaxy" in tribute to the astronomer who studied it in detail. It is located at such a distance that its light has traveled for about 11 billion years to reach us. We therefore see it as it was shortly after the Big Bang, making it a valuable witness to the first cosmic epochs.


To resolve this question, scientists called upon two state-of-the-art instruments: the James Webb Space Telescope (JWST) and the ALMA radio telescope array. While JWST captured detailed images of the galaxy's structure and stellar history, ALMA was used to search for traces of cold gas, essential for the birth of new stars, from the Atacama Desert in Chile.

Despite these efforts, ALMA detected practically nothing in terms of cold gas in Pablo's galaxy. This absence is significant, indicating that the galaxy has exhausted its reserves of raw material for star formation. Jan Scholtz, a team member, believes that this non-detection signals a gradual starvation, as if the galaxy had suffered a series of small losses over time.

The main suspect behind this situation is the supermassive black hole nestled at the galaxy's core. It is actively expelling gas at very high speeds, preventing this material from falling back to fuel star creation. This mechanism works like a slow deprivation, where the black hole regularly interrupts the fuel supply, causing a gradual halt in stellar activity.

Observations indeed show that the black hole has experienced repeated cycles of gas expulsion. Francesco D'Eugenio, co-leader of the study, indicates that this explains why the galaxy stopped forming stars about 400 million years ago, while maintaining a calm appearance. These recurring episodes keep the galaxy in a state of starvation, blocking any influx of gas.

This advance partly explains why JWST has identified many galaxies that appear old in the young Universe. It indicates that comparable processes could be common, contributing to the presence of massive, inactive galaxies at distant epochs. Astronomers already plan to continue observations with the JWST-ALMA duo to examine other cases and refine our view of galactic evolution.