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Why do galaxies stop making stars? An enormous collision in space provides new clues

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Six billion years back, two galaxies were colliding, their combined forces hurling a blast of gas thousands of light years away. Reported this week by way of a team including Pitt astronomers, that unusual feature offers a new possible reason why galaxies stop forming stars.

“One of the primary questions in astronomy is the reason why the largest galaxies are dead,” said David Setton, a sixth-year physics and astronomy Ph.D. student in the Kenneth P. Dietrich School of Arts and Sciences. “What we saw is that should you take two galaxies and smash them together, that may actually rip gas from the galaxy itself.”

In the section of space we inhabit, most large galaxies have way back when stopped making new stars. Only recently have astronomers started looking further awayand thus farther back timewith the various tools to get recently dead galaxies and work out how they got this way.

The that coalesces to create stars may escape from galaxies by several means, impressed by black holes or supernovae. And there’s a straight simpler possibility, that galaxies simply quiet down when they’ve consumed all of the for creating stars.

Searching for types of galaxies that recently shut down , the team of researchers used the Sloan Digital Sky Survey, which includes cataloged an incredible number of galaxies with a telescope at Apache Point Observatory in New Mexico. Alongside observations from the ground-based radio astronomy network ALMA, the researchers found this type of “post-starburst” galaxy seven billion away that still showed signs of available star-forming fuel. “So then we needed a conclusion,” said Setton. “If it has gas, exactly why is it not forming stars?”

Another pass with the Hubble Space Telescope then revealed the distinctive “tail” of gas extending from the galaxy. From that feature, like forensic examiners working by way of a telescope, the researchers could actually reconstruct the galaxies’ collision and the tremendous gravitational force that tore apart stars and flung a blast of gas a distance a lot more than two Milky Ways laid end-to-end.

“That has been the smoking gun,” said Setton. “We were all so struck because of it. You merely don’t see anywhere near this much gas this a long way away from the galaxy.”

The team, including Pitt Physics and Astronomy Associate Professor Rachel Bezanson and alum Margaret Verrico (A&S ’21) alongside colleagues at Texas A&M University and many other institutions, reported their results in the Astrophysical Journal Letters on Aug. 30.

This extreme meeting of galaxies is probable rare, Setton said, but because gravity pulls large objects into dense groups, this event is more prevalent than you may anticipate. “You can find each one of these big voids in space, but all the biggest reside in the spaces where all the other big live,” he said. “You anticipate to see these kinds of big collisions once every 10 billion years roughly for something this massive.”

Setton’s role on the project was to look for the galaxy’s decoration, and he found that apart from the tail, the post-merger galaxy looked surprisingly normal. After the tail fades in a couple of hundred million years, it could look exactly like any dead galaxyfurther suggesting that the procedure may be more prevalent than it seems, something the team is following up now with another survey.

Alongside providing clues for the way the universe became just how it really is, Setton said such collisions reflects one possibility for future years of our very own galaxy.

“In the event that you go execute a dark place and appearance up at the night time sky, you can view the Andromeda Galaxy, which in five billion years might do exactly this to your Milky Way,” Setton said. “It’s helping answer the essential question of after that eventually the Milky Way in the foreseeable future.”

More info: Justin S. Spilker et al, Star Formation Suppression by Tidal Removal of Cold Molecular Gas from an Intermediate-redshift Massive Post-starburst Galaxy, The Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac75ea

Citation: Why do galaxies stop making stars? An enormous collision in space provides new clues (2022, September 3) retrieved 4 September 2022 from

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