Astronomers capture the moment distant galaxy starts to die

·2 min read
The galaxy ID2299 with some of its gas being ejected by a 'tidal tail' after a galactic merger (ESO)
The galaxy ID2299 with some of its gas being ejected by a "tidal tail" after a galactic merger. (ESO)

A huge radio telescope in Chile has captured the moment a distant galaxy starts to die, as it vomits out staggering amounts of gas after a violent collision.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) spotted a galaxy blasting out up to 10,000 suns-worth of gas every Earth year.

The gas is blasting out so quickly that the galaxy will lose its fuel to make new stars - and it could offer important insights into how galaxies die.

The galaxy, ID2299, is so far away that the light from it takes nine billion years to reach us here on Earth – we see it as it was when the Universe was 4.5 billion years old.

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The galaxy will ‘shut down’ in just a few tens of millions of years, the researchers believe – a tiny amount of time in galactic terms.

It is ejecting gas so quickly that it is losing 46% of its total cold gas, and also forming stars very rapidly, hundreds of times faster than the Milky Way.

The gas loss was caused by a collision with another galaxy, the researchers believe, with two galaxies having smashed into one another to form ID2299.

The clue was a ‘tidal tail’ near the ejected gas.

Tidal tails are elongated streams of stars and gas extending into interstellar space that result when two galaxies merge, and they are usually too faint to see in distant galaxies.

The team spotted the relatively bright feature just as it was launching into space, and were able to identify it as a tidal tail.

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Their study, published in Nature Astronomy, suggests a new way that galaxies can eject star-forming fuel into space – sealing their fate.

Previously, astronomers believed that when this happened, it was caused by winds from star formation, or by black holes at the centres of massive galaxies.

Study co-author Emanuele Daddi, of French Alternative Energies and Atomic Energy Commission (CEA) and University Paris-Saclay, said: “Our study suggests that gas ejections can be produced by mergers and that winds and tidal tails can appear very similar.

“This might lead us to revise our understanding of how galaxies ‘die’.”

The find was made by chance while the team studied the properties of cold gas in 100 far-away galaxies.

Chiara Circosta, a researcher at the University College London, said: “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.”

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