Galaxies Are Being Killed by 'Spectacular and Violent' External Forces

Astronomers may have solved an enduring cosmic mystery by discovering the process that strips galaxies of their star-forming gas, ending the birth of new stars.

The new research presents the clearest evidence yet that the extreme environments in space have a detrimental effect on the gas content of galaxies within them, helping to curtail star formation. Astrophysicists define the cessation of star formation as a galaxy "dying."

Using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope, the researchers studied gas reservoirs in 51 galaxies from the thousands located within the Virgo cluster, 65 million light-years from Earth.

They found an environment so extreme and inhospitable that it can stop entire galaxies from forming stars in a process known as galaxy quenching.

"We know that galaxies are being killed by their environments, and we want to know why," lead author Toby Brown, Plaskett Fellow at the National Research Council of Canada, said in a press release.

Christine Wilson, Distinguished University Professor at McMaster University, Canada, and co-principal investigator on the VERTICO project that made the finding explained why the team chose to focus on galaxies in the Virgo Cluster.

"The Virgo Cluster is a bit unusual in that it has a relatively large population of galaxies that are still forming stars. Many galaxy clusters in the Universe are dominated by red galaxies with little gas and star formation," Wilson said.

"The Virgo Cluster is the most extreme region of the local Universe, filled with million-degree plasma, extreme galaxy speeds, violent interactions between galaxies and their surroundings, a galaxy retirement village, and accordingly, a galaxy graveyard," said Brown.

A paper documenting the results of the project will soon be published in The Astrophysical Journal.

Brown continued by explaining the process of gas stripping discovered by VERTICO and how this can stunt, or shut down star formation—one of the most important physical processes in the universe.

Gas stripping occurs when galaxies are moving so fast through the hot plasma in their cluster that vast quantities of cold molecular gas are stripped away from the galaxy, she said.

"Gas stripping is one of the most spectacular and violent external mechanisms that can shut down star formation in galaxies," said Brown.

"[It's as] though the gas is being swept away by a huge cosmic broom," Brown said. "The exquisite quality of VERTICO's observations allows us to better see and understand such mechanisms."

These observations were made possible with ALMA's 6 band receiver, which is able to make high sensitivity and high resolution observations while not minimizing the observing time.

This allows researchers to capture the necessary amount of data to obtain clues that could solve the mysteries that still surround the effect that a galaxy's environment has on its development. This includes how these environments cause galaxies to "die."

"There have been a lot of questions over the years on whether and how the cluster environment affects the molecular gas in galaxies, and how exactly those environments may contribute to their deaths," Wilson said. "We still have work to do, but I'm confident VERTICO will allow us to answer these questions once and for all."

Galaxies stripped of Gas
(Main) the Virgo cluster traced in carbon monoxide. (Top right) NGC 4567 and NGC 4568 are two of the thousands of galaxies in the Virgo Cluster, located roughly 65 million light-years from Earth. (Bottom Right) Spiral galaxy NGC 4254 is among the thousands of galaxies living and dying by the extreme physical processes in the Virgo Cluster. ALMA/ESO/NAOJ/NRAO/S. Dagnello NRAO/NSF