6 billion years ago, two galaxies collided, and their combined force threw a stream of gas hundreds of thousands of light-years away, RT reports.
And over the past few days, a team of scientists, including astronomers at the University of Pittsburgh, reported that this unusual feature provides a possible new explanation for why galaxies have stopped forming stars.
“One of the biggest questions in astronomy is why the largest galaxies die,” said David Seton, PhD in physics and astronomy and a student at the Kenneth P. Dietrich School of Arts and Sciences. “And what we saw is that if you take two galaxies and smash them together, that can actually lead to The gas is ejected from the galaxy itself.
In our part of space, most large galaxies have long since stopped forming new stars.
Only recently have astronomers begun to look far, and therefore farther back, to find dead galaxies and find out how they got this way.
For the first time, astronomers have found an example of the result of the merger of two galaxies, in which the same process of merging slowed the formation of new stars, by removing most of the cold gas reserves from the galaxies.
Cold gas that combines to form stars can escape from galaxies in a number of ways: through black holes or supernovae. A simpler possibility is that galaxies simply calm down when they use up all the raw materials for star formation.
Looking for examples of galaxies that have recently stopped forming stars, the team of scientists used the Sloan Digital Sky Survey in Astronomy (an astronomical survey using redshift spectroscopy to measure the spectra of galaxies), which cataloged millions of galaxies using a telescope at Apache Point Observatory in New Mexico.
Along with observations from the Earth’s Radio Astronomy Network (ALMA), the scientists found a “post-starburst” galaxy seven billion light-years away, which is still showing signs of star-forming fuel.
“So we needed an explanation,” Seton said. “If it contains gas, why don’t stars form?”
Then a second pass using the Hubble Space Telescope revealed a distinctive gas “tail” extending from the galaxy.
From this feature, scientists were able to reconstruct the collision of galaxies and the massive gravitational force that tore the stars apart and released a stream of gas more than two ways from end to end in the Milky Way.
“This was the firearm. We were all shocked with it,” Seaton said. “You can’t see that much gas far from the galaxy.”
The team announced their findings in Astrophysical Journal Letters. Such an extreme meeting of galaxies is rare, Seton explained, but because gravity pulls large objects into dense clusters, such an event is more common than we might expect.
“There are all these big voids in space, but all the big galaxies live in the spaces that all the other big galaxies live in. We expect to see these kinds of big collisions once every 10 billion years or so for a system this big.”
Seton’s role in the project was to determine the galaxy’s size and shape, and he discovered that, other than the tail, a post-merger galaxy looked surprisingly normal.
Once the tail fades in a few hundred million years, it may look just like any other dead galaxy, also suggesting that the process may be more common than it appears, something the team is now pursuing with another survey.
Besides providing clues about how the universe turned out, Seton said such collisions reflect one possibility for the future of our galaxy.
He explained: “If you go to a dark place and look at the night sky, you can see the Andromeda galaxy, which might do exactly this to the Milky Way in five billion years. It helps answer the fundamental question about what will happen to the Milky Way in the future.” .