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Astronomers observe the death of a distant galaxy for the first time

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Astronomers have, for the first time, witnessed the death of a distant galaxy, which they describe as a "truly extreme event." 

When all of the stars in a galaxy die, and new ones are no longer forming, the galaxy itself ceases to exist. This occurs when all of the galaxy's gas is ejected, making it impossible for new stars to form.

According to a study published Monday in the journal Nature Astronomy, scientists were "thrilled" to be able to capture this rare phenomenon recently using the Atacama Large Millimeter/submilimeter Array of telescopes in Chile.

It has taken about nine billion years for the light from the starburst galaxy ID2299 to reach Earth. So, when astronomers happened to observe it by chance, they witnessed the universe as it appeared at just 4.5 billion years old. 

Astronomers say that ID2299 is losing 10,000 suns worth of gas each year — rapidly depleting fuel needed to form new stars. This startling release of gas appears to be the result of two galaxies violently colliding and merging together to create ID2299. 

The galaxy is also currently forming stars at a rate hundreds of times faster than the Milky Way — using up the rest of its precious gas supply. Because of this, ID2299 is expected to die relatively soon, in just a few tens of thousands of years. 

This artist's impression of ID2299 shows the galaxy, the product of a galactic collision, and some of its gas being ejected by a "tidal tail" as a result of the merger. New observations made with ALMA have captured the earliest stages of this ejection, before the gas reached the very large scales depicted in this artist's impression. European Southern Observatory

"This is the first time we have observed a typical massive star-forming galaxy in the distant universe about to 'die' because of a massive cold gas ejection," lead author Annagrazia Puglisi said in a statement

Astronomers believe the phenomenon is the result of galaxies merging because they were able to witness a rare "tidal tail," usually too faint to see in distant galaxies. This elongated stream of stars and gas, astronomers suggest, is the direct result of the galactic merger. 

They only observed the galaxy for a few minutes, but it was enough to spot the elusive tidal tail. 

"Our study suggests that gas ejections can be produced by mergers and that winds and tidal tails can appear very similar," says study co-author Emanuele Daddi. "This might lead us to revise our understanding of how galaxies 'die.'"

If the astronomers are correct that the merger led to the massive loss of gas, they will need to reconsider prior theories on how galaxies form and evolve — and how they die. Other theories have suggested that wind from active black holes or intense star formations are responsible for such deaths.

"Studying this single case unveiled the possibility that this type of event might not be unusual at all and that many galaxies suffered from this 'gravitational gas removal', including misinterpreted past observations," said co-author Dr. Jeremy Fensch.

"This might have huge consequences on our understanding of what actually shapes the evolution of galaxies."

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