A distant galaxy dies as astronomers watch

(CNN) Galaxies die when the stars that live in them stop forming. Now, for the first time, astronomers have witnessed this phenomenon in a distant galaxy.

Scientists were able to glimpse a galaxy as it ejected almost half of the gas it uses to form stars. They captured this rare observation using the Atacama Large Millimeter/submillimeter Array of telescopes in Chile.

The light from this galaxy, known as ID2299, has taken about nine billion years to reach Earth. That means astronomers are essentially observing how it appeared when the universe was only 4.5 billion years old (it's now an estimated 14 billion years old).

The ID2299 galaxy is losing 10,000 suns-worth of gas per year, which is diminishing the fuel it needs to form stars by removing 46% of the galaxy's total cold gas so far.

But the galaxy is still quickly forming stars at a rate that is hundreds of times faster than our own Milky Way, which will use up the rest of the gas in the galaxy. This will effectively cause ID2299 to die in a few tens of million years.

The study published Monday in the journal Nature Astronomy.

"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," said Annagrazia Puglisi, lead study researcher and postdoctoral research associate from Durham University in the UK and the Saclay Nuclear Research Centre in France, in a statement.

A possible collision

It's possible that this galaxy's demise was caused by a collision with another galaxy, which eventually merged to create ID2299.

The telling evidence that a collision may have led to a loss of gas is a tidal tail, which is a long stream of gas and stars that extend out into space after two galaxies come together in a collision.

Typically, these tidal tails are too faint to be seen in such distant galaxies, but the astronomers were able to observe the bright tail as it was extending out into space.

If a merger led to this galaxy's loss of gas, astronomers may need to reconsider theories on the end of star formation in galaxies. Previously, scientists have believed that the winds created by the formation of stars, combined with active black holes at the centers of giant galaxies, sent the material needed to form stars hurtling out into space and ending star formation.

"Our study suggests that gas ejections can be produced by mergers and that winds and tidal tails can appear very similar," said Emanuele Daddi, study coauthor and astronomer at the Saclay Nuclear Research Centre in France. "This might lead us to revise our understanding of how galaxies 'die.' "

Perhaps the best part about this discovery is that it was made while the astronomers were working on a different survey of cold gas in distant galaxies. They only observed ID2299 for a few minutes, but it was enough to capture the tidal tail.

Future observations of the galaxy could reveal more about the gas being ejected from the galaxy.

"ALMA has shed new light on the mechanisms that can halt the formation of stars in distant galaxies. Witnessing such a massive disruption event adds an important piece to the complex puzzle of galaxy evolution," said Chiara Circosta, study coauthor and researcher at the University College London, in a statement.