The James Webb Space Telescope faced a series of intriguing questions when it launched on Christmas Day 2021. When it finally did, astronomers had a long list of targets that required the kind of detailed observations that only a powerful infrared space telescope could make. One target was an old, massive galaxy that was effectively dead and not forming new stars. The results are in, and an international team of astronomers knows what happened to the dormant galaxy.

The growth and evolution of galaxies is an important area of ​​study in astronomy. How did we get from the Big Bang, when massive galaxies like the Milky Way filled the universe, to today? Astronomers have discovered that supermassive black holes (SMBHs) reside at the hearts of large galaxies and influence their galaxies.

SMBHs form powerful active galactic nuclei (AGN) in the cores of galaxies. As the SMBH pulls material toward itself, material gathers in an accretion disk. The material heats to extremely high temperatures and releases energy across the electromagnetic spectrum, creating AGN that can outshine the rest of the galaxy.

AGN are powerful objects. The theory is that they have the capacity to cut off the supply of cold star-forming gas and significantly slow down the star formation rate (SFR) of their galaxies. They blow winds of star-forming gas out of their galaxies, which slows down the SFR. Astronomers call this quenching, and it is often seen in massive galaxies called quiescent galaxies.

JWST has now observed an ancient massive galaxy called GS-10578 at redshift Z=3.064. It’s called the Pablo Galaxy, and it’s very large for such an early stage in the universe’s evolution: it contains about two billion solar masses.

But the Pablo Galaxy has extinguished, meaning most of its star formation occurred between 12.5 and 11.5 billion years ago. Many local large galaxies are extinguishing, contributing to the theory of AGN extinction.

A team of scientists presents their study of the Pablo galaxy in a new paper titled “A rapidly spinning galaxy after a stellar explosion was quenched by supermassive black hole feedback.” Z=3. The article was published in: Nature Astronomy It is co-authored by Francesco D’Eugenio of the Kavli Institute of Cosmology and the Cavendish Laboratory, University of Cambridge, United Kingdom.

“We found the culprit. The black hole is killing this galaxy and keeping it dormant, cutting off the source of ‘food’ the galaxy needs to form new stars.” Francesco D’Eugenio, Kavli Institute for Cosmology, University of Cambridge, UK

“Local, massive, dormant galaxies remain huge relics of a spectacular but distant past of star formation (SFH) and powerful and rapid extinction that has no analogues today,” the authors write. “The James Webb Space Telescope (JWST) has given us the first image of these monumental galaxies during a long period of rise and fall.”

“Based on previous observations, we knew that this galaxy was in a quenched state: it wasn’t forming many stars given its size, and we expected a link between the black hole and the end of star formation,” said co-author Dr. Francesco D’Eugenio, of Cambridge’s Kavli Institute of Cosmology. “But until Webb, we weren’t able to study this galaxy in sufficient detail to confirm this link, and we didn’t know whether this quenched state was temporary or permanent.”

“In the early universe, most galaxies form many stars, so it’s interesting to see such a large, dead galaxy right now,” said co-author Professor Roberto Maiolino from the Kavli Institute of Cosmology. “If it had had enough time to grow to such a large size, any process that would stop star formation would probably have happened relatively quickly.”

The Pablo Galaxy is sometimes called a “blue nugget”, a class of galaxies thought to have existed only in the early universe. Blue Nuggets are very large and extremely compact, and astronomers believe they are the precursors of today’s dormant galaxies, called “red nuggets”.

The blue nuggets are undergoing “gas-rich compression.” This means that there is a central burst of star formation caused by disk instabilities or gas-rich major mergers. This burst is followed by quenching, leaving behind a red nugget galaxy.

“As we will show, GS-10578 is a red nugget that is currently in the advanced stage of quenching,” the authors write. They explain that it has merged with several low-mass satellite galaxies and “receives strong feedback from its SMBH.”

The researchers say they have direct evidence that AGN feedback can suppress star formation in early galaxies. Previous observations with other telescopes have shown that galaxies have fast flows of gas. This gas is easier to see because it is hot, but they have not provided evidence that SMBHs and AGNs can suppress star formation. This is because the gas is hot and stars form from cold, dense gas.

Pablo’s Galaxy is no different. It ejects a large amount of hot gas, enough to completely leave the galaxy. The SMBH and its AGN expel the gas.

But JWST made a difference in these new observations. It observed a new component of the wind flowing out of the cold gas. The cold gas does not emit light, but JWST is extremely sensitive and can detect it by blocking the light from distant background galaxies. The important thing is that without the cold gas, the galaxy would try to form stars and would disappear.

The amount of gas ejected by the winds driven by AGNs exceeds the amount needed to form new stars.

“We found the culprit,” D’Eugenio said. “The black hole is killing this galaxy and keeping it dormant, cutting off the source of ‘food’ that the galaxy needs to form new stars.”

These are exciting results, but the authors caution that this is just one galaxy. “GS-10578 provides a unique opportunity to study how the largest galaxies in the Universe become and remain dormant,” the authors explain in their study.

“Although we cannot draw general conclusions from a single target, we have shown that the AGN feedback can drive neutral gas outflow at high enough speed and high mass loading to disrupt star formation by removing the cold gas fuel.”

There are also unresolved issues. Other galaxies similar to Pablo’s also suggest that cold gas outflows may be the key to quenching galaxies.

“It is not yet clear how exactly these outflows are coupled to the AGN,” the authors write. They explain that only a census of similar galaxies can tell us whether these powerful outflows of star-forming gas are the primary mechanism causing the quench, or whether the gas emission is only intermittent.

JWST also answered another important question about extinct galaxies. Our theoretical models showed that the cessation of star formation in a galaxy was a turbulent event that violently distorted the shape of the galaxy. Pablo’s galaxy still has the majestic shape of a stationary galaxy’s disk. Its stars move predictably and uniformly.

JWST works exactly as intended. It answers many ancient questions in astronomy, astrophysics, and cosmology when considering the ancient universe.

“We knew that black holes had a big impact on galaxies and could perhaps stop star formation, but we weren’t able to directly confirm that until Webb,” Maiolino said. “This is another way that Webb takes a giant step forward in our ability to study the early universe and its evolution.”