Astronomers see galaxy starting to die

Astronomers have seen a distant galaxy starting to die in what could be a major breakthrough in our understanding of the cosmos.

Galaxies begin to “die” when they stop forming stars. Astronomers have observed a vast array of such dead galaxies scattered through the universe – but have been unable to say exactly why it happens.

Now astronomers have got a clear view at such a spectacular event, and hope that it could shed light on the process that leads galaxies to die out.

The galaxy observed is losing some 10,000 Suns-worth of gas each year, meaning that it is running out of fuel to make new stars. It has now lost nearly half of that gas, and because it is still creating stars at a rate hundreds of times faster than our own Milky Way, it will use up the remains in jus ta few tens of millions of years, and will die out as it does.

Because the galaxy is 9 billion light-years away, astronomers are actually looking at events that happened in the universe’s relative youth, when the cosmos was only 4.5 billion years old.

Astronomers think that the dramatic death was caused by a collision with another galaxy, potentially changing our understanding of how the events can happen.

As the two galaxies collided, they joined to create the one observed by astronomers and named ID2299. The evidence for the collision was found in the form of a “tidal tail” – a long stream of stars and gas that extend out into interstellar space.

Such clues are usually too dim to be seen in distant galaxies. But the researchers caught it, by accident, just as it was being launched out and so were able to identify it.

Galaxies’ deaths come about when their star-forming material is flung out into space, leaving it without the material needed to make new stars. Until now, most astronomers have believed that happens as a result of the winds that erupt when stars form, and the black holes that sit at the centre of the galaxy.

The new research indicates, however, that such collisions can kill them, too.

The new paper also suggests that those two events can be easily mixed up: when gas ejections are caused by mergers and leave behind tidal tails, they can look similar to those deaths caused by winds. As such, previous research that appeared to be pointing to winds could actually have been observing tidal tails all along, the researchers said, and previous work may need to be re-evaluated.

The research is reported in a new paper, ‘A titanic interstellar medium ejection from a massive starburst galaxy at z=1.4’, published in Nature Astronomy.