Galaxies are considered dead once they stop making new stars. These dead galaxies have run out of gas to make new stars. Without this, they will slowly grow redder as bright blue stars go supernova, leaving behind the smaller, dimmer stars. This will happen to all galaxies but astronomers had never clearly seen the beginning of this process of a galaxy about to die in the very early in the universe, until now. This is a crucial window into galaxy evolution.
In a new paper published in Nature Astronomy, an international team of researchers introduces us to galaxy ID2299. This celestial object is forming stars 550 times faster than the Milky Way, which is known as a starburst galaxy. But this galaxy is also losing gas in an unprecedented way. Every year, it throws the equivalent of 10,000 Suns into intergalactic space, ejected as "tidal tail".
That loss is removing 46 percent of all the cold gas from this galaxy. Between this and the intense star-formation, the galaxy will run out of gas in just a few tens of millions of years. This fact is even more striking considering that the galaxy is going through this event just 4.5 billion years after the Big Bang. That’s just after cosmic high noon, when galaxies were producing stars at incredible rates.
"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 lead author Dr Annagrazia Puglisi, from Durham University in the UK and the Saclay Nuclear Research Centre (CEA-Saclay) in France, in a statement.
The team believes that the cause for this spectacular event is a collision with another galaxy. Galaxy mergers often deliver a new lease of life to galaxies, bringing new gas and the conditions for intense star-formation. This discovery suggests that they could also be fatal as the complex gravitational dance removes gas from the final galaxy.
"Our study suggests that gas ejections can be produced by mergers and that winds and tidal tails can appear very similar," co-author Emanuele Daddi of CEA-Saclay. "This might lead us to revise our understanding of how galaxies 'die'."
These groundbreaking observations were carried out using the Atacama Large Millimeter/submillimeter Array (ALMA), currently the largest radio telescope in the world, but more observations are needed. The team hopes to use ALMA once again to study this galaxy and its gas tail in more detail. They also hope to observe ID2299 in visible light with next-generation instruments such as the Extremely Large Telescope, which is expected to come online in 2025.