Using the James Webb Space Telescope (JWST), astronomers have observed a supermassive black hole in the early universe starving a galaxy to death. Amazingly, this “starvation” seems to have happened very quickly, with gas winds blowing at speeds of up to 2 million miles per hour.
A galaxy is considered “dead” or “quiescent” when star formation stops. This can happen when it runs out of dense clouds of gas and dust – the building blocks of stars. Scientists have long suspected that a galaxy could “die” prematurely by being “cleaned up” by a supermassive black hole at its center.
The JWST observations are the first definitive detection of such an effect, suggesting that starving a galaxy could actually suppress star birth. The discovery was announced by a team led by scientists from the University of Cambridge, who studied an early galaxy officially named GS-10578 but nicknamed “Pablo’s Galaxy” after the team member who proposed observing it in detail.
The Pavaro Galaxy is located about 11.5 billion light years away, meaning it is being observed as it appeared just 2.3 billion years after the Big Bang.
“We knew from previous observations that this galaxy is in an extinct state – given its size, not many stars have formed and we think there is a link between the black hole and the end of star formation,” said team member Francesco D’Eugenio from the Kavli Institute for Cosmology at the University of Cambridge. It said in a statement“But until JWST we weren’t able to study this galaxy in enough detail to confirm this connection, and we didn’t know whether this disappearance was temporary or permanent.”
Related: How could a supermassive black hole “starve” a galaxy and stop star formation?
With a mass 200 billion times that of the Sun and roughly the size of the Milky Way, the galaxy produced most of its stars between 12.5 and 11.5 billion years ago, making it unusually large for this time in the early universe.
“It’s intriguing to see such a massive dead galaxy at this time in the universe, because in the early stages most galaxies are forming lots of stars,” said team member Roberto Maiorino, also of the Kavli Institute for Cosmology. “If it had enough time to grow to such a massive size, it’s likely that the process that stopped star formation happened relatively quickly.”
Using the JWST, the team determined that the supermassive black hole at the center of the Pablo galaxy is pushing out tons of gas at a whopping 2.2 million miles per hour — 1,500 times faster than the top speed of a Lockheed Martin F-16 fighter jet.
The gas’s speed is important because it’s fast enough to overcome the gravitational effects of Pablo’s galaxy and escape the galaxy forever.
Many galaxies with incoming or “accreting” supermassive black holes have rapid winds of gas blowing out of them, but their masses are usually quite small. JWST discovered a new component of Pablo’s galactic wind that other telescopes have missed around other active galaxies.
This dense gas component is so cold and dense that it barely emits any light, making it undetectable by other telescopes. JWST’s incredible sensitivity allowed it to detect this outflow of dense gas because it blocks light from the galaxy behind it.
The team found that the mass of the gas outflow from Pablo’s galaxy is greater than the gas needed to form the basis for new star formation — enough to indicate that the galaxy’s supermassive black hole is suppressing star birth in this distant, early galaxy.
“We’ve found the culprit,” DeEugenio said. “A black hole is killing this galaxy, rendering it dormant by cutting off its source of ‘food’ needed to form new stars.”
The JWST observations support previous models of galactic evolution and the role of supermassive black holes in quenching star birth, but they also yielded some surprises.
Previous theoretical models predicted that the end of star formation would bring chaos and turbulence to a galaxy, potentially destroying its shape, but the fact that Pablo’s stars still appear to be moving in an orderly fashion suggests this may not necessarily be the case.
The team now plans to follow up JWST’s observations of Pablo with a survey using the Atacama Large Millimeter/submillimeter Array (ALMA), a collection of 66 radio telescopes in northern Chile. This could reveal whether Pablo still has cold, dense gas and how its supermassive black hole is affecting its surroundings.
“We knew that black holes have a profound effect on galaxies, and that it’s probably common for them to halt star formation, but until JWST we’d never been able to see this directly,” Maiorino concluded. “This is another sign that JWST is a major step forward in our ability to study the early universe and its evolution.”
The team’s research was published Monday (September 16) in the journal Nature Astronomy.
