For the first time ever, astronomers are witnessing a galaxy’s ‘death’ as its happening – ThePrint

An artist's rendition of the galaxy ID2299, the product of a galactic collision, and some of its gas being ejected by a “tidal tail” as a result of the merger | ESO/M. Kornmesser
An artist’s rendition of the galaxy ID2299, the product of a galactic collision, and some of its gas being ejected by a “tidal tail” as a result of the merger | ESO/M. Kornmesser

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Bengaluru: Astronomers have observed many ‘dead’ galaxies but the process of the death itself hasn’t been observed before — until now.

Using the telescope Atacama Large Millimeter/submillimeter Array (ALMA), astronomers observed a galaxy, nine billion light years away from the Earth, ejecting nearly half of its star-forming gas and losing fuel.

Galaxies begin to ‘die’ when star formation stops inside them or they start losing material that forms stars.

The ID2299 galaxy is currently ejecting material worth about 10,000 suns every year in the form of cold gas ejection. It is estimated that the galaxy is currently removing 46 per cent of the total cold gas it contains.

The galaxy is still forming new stars very rapidly, but since it is also quickly running out of fuel, the remaining gas will be consumed and the galaxy is likely to be dead within a few million years.

“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 researcher of the new study from UK’s Durham University and the Saclay Nuclear Research Centre (CEA-Saclay), France, in a statement.

The findings were published in the journal Nature Astronomy Monday.


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Why ID2299 is ejecting gas

The research team behind the findings believes that the ID2299 galaxy is ejecting monumental amounts of cold gas because of a collision between two galaxies, which eventually merged to form ID2299.

Colliding galaxies are identifiable by their ‘tidal tail’ — elongated streams of gas and stars traced out in interstellar space behind the galaxies.

These tails are harder to spot in distant galaxies but since the researchers caught the bright feature just as it was launching into space, they were able to identify that the gas ejection was a part of the trail.

It was previously believed that black hole activity as well as winds caused by star formation ejected the gases out of galaxies.

“Our study suggests that gas ejections can be produced by mergers and that winds and tidal tails can appear very similar,” said study co-author Emanuele Daddi of CEA-Saclay in the statement.

Daddi believes that retrospective analysis of gas ejections captured could confirm if some of them are in fact tidal tails.

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

The discovery was a serendipitous accident and occurred when the team was inspecting data from a galaxy survey conducted by ALMA to study the properties of cold gas in far away galaxies.


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