The Atacama Large Millimeter/submillimeter Array (ALMA) has observed a distant galaxy that has collided with another galaxy. Scientists have observed colliding galaxies before. What’s unique about this one is that as the galaxies collide, the resulting merged galaxy is shedding its star-forming gas. Astronomers say the galaxy is ejecting nearly half of its star-forming gas, and it’s happening at a very fast rate.
Scientists estimate the galaxy is ejecting the equivalent of nearly 10,000 suns worth of gas per year. The gas injection is rapidly removing the fuel the galaxy needs to make new stars. The ejection of gas is believed to have been triggered when the galaxies collided, and the event could lead astronomers to rethink how galaxies stop bringing new stars to life.
Galaxies die when they run out of fuel and stop producing stars. Lead researcher Annagrazia Puglisi says this is the first time astronomers have observed a typical massive star-forming galaxy in the distant universe that is about to die due to cold gas ejection on a massive scale. The distant galaxy is known as ID2299 and is far enough away that it takes 9 billion years for its light to reach us.
From Earth, astronomers see the galaxy as it was when the universe was only 4.5 billion years old. In addition to the galaxy shedding so much gas, it’s also forming stars very quickly at a rate hundreds of times faster than stars form in the Milky Way. Astronomers say that means the remaining gas will be rapidly consumed by the rate of star formation.
ID2299 will no longer form stars in a few tens of millions of years at the rate gas is being ejected and consumed by star formation. Scientists determined the gas ejection was caused by two galaxies colliding and merging due to the association of the ejected gas with a “tidal tail.” A tidal tail is an elongated stream of stars and gas extending into interstellar space, which results when two galaxies merge. Typically the tail is too faint to see in distant galaxies. However, it is visible in ID2299.
Astronomers believe winds caused by star formation and the activity of black holes at the center of massive galaxies are responsible for launching the star-forming material into space. However, the new study suggests galactic mergers can also be responsible for ejecting gas into space.