When does a galaxy die? According to astronomers, galaxies begin to “die” when they stop forming stars, but until now they had never clearly seen the start of this process in a far-away galaxy. That has changed now.
In a first, using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope facility in northern Chile, astronomers associated with the European Southern Observatory (ESO) witnessed a galaxy ejecting nearly half of its star-forming gas. This essentially means that the galaxy is rapidly losing fuel to make new stars.
The team believes that this spectacular event was triggered by a collision with another galaxy, which could lead astronomers to take a relook at how galaxies stop bringing new stars to life.
The findings of this amazing observation were published in a new paper in the peer-reviewed journal Nature Astronomy on 11 January.
“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,” Annagrazia Puglisi, lead researcher on the new study, from the Durham University, UK, and the Saclay Nuclear Research Centre, France said in an official ESO release. The galaxy, ID2299, is so far away that its light takes some 9 billion years to reach us; we see it when the Universe was just 4.5 billion years old, the release explains.
The gas ejection phenomenon is happening at a rate equivalent to 10,000 Suns per year, removing an astonishing 46% of the total cold gas from ID2299. Since the galaxy is also forming stars very rapidly, hundreds of times faster than our galaxy Milky Way, the remaining gas will be quickly consumed, completely shutting down ID2299 in just a few tens of million years.
The clue that led the astronomers to this discovery is a phenomenon called ‘tidal tails’—elongated streams of stars and gas extending into interstellar space. They occur when two galaxies merge and are usually too faint to capture. However, the team managed to observe the relatively bright feature just as it was launching into space, and were able to identify it as a tidal tail, the release adds.
Previously, astronomers have believed that winds caused by star formation and the black hole activities at the centres of massive galaxies are responsible for releasing star-forming material into space: thus ending a galaxy’s ability to make new stars and eventually die. But this new study suggests that galactic mergers can also be responsible for such events.
Interestingly enough, the galaxy ID2299 was observed by ALMA for only a few minutes. But the observatory, which is the most powerful telescope for observing the cool universe, such as molecular gas and dust, allowed the researchers to gather enough data to detect the galaxy and its ejection tail.