ALMA observes distant colliding galaxy as it releases gas forming stars

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The Atacama Large Millimeter / submillimeter Array (ALMA) observed a distant galaxy that collided with another galaxy. Scientists have already observed colliding galaxies. What’s unique about this one is that when galaxies collide, the resulting merged galaxy loses its star-forming gas. Astronomers say the galaxy is ejecting almost half of its star-forming gas, and it’s happening at a very rapid rate.
Scientists estimate that the galaxy ejects the equivalent of nearly 10,000 suns of gas per year. Gas injection quickly removes the fuel the galaxy needs to make new stars. It is believed that the gas ejection was triggered when the galaxies collided, and the event could lead astronomers to rethink how galaxies stop giving life to new stars.

Galaxies die when they run out of fuel and stop producing stars. Principal researcher Annagrazia Puglisi says this is the first time astronomers have observed a typical massive star-forming galaxy in the distant universe that is on the verge of dying due to large-scale cold gas ejection . 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 fact that the galaxy releases so much gas, it is also forming stars very quickly at a rate hundreds of times faster than that of stars in the Milky Way. Astronomers say this means the remaining gas will be quickly consumed by the rate of star formation.

ID2299 will no longer form stars in a few tens of millions of years at the rate at which gas will be ejected and consumed by star formation. Scientists determined that the ejection of gas was caused by the collision and fusion of two galaxies due to the association of the ejected gas with a “tidal tail”. A tidal tail is an elongated flow of stars and gas extending through interstellar space, which occurs when two galaxies merge. In general, the tail is too weak to be seen in distant galaxies. However, it is visible in ID2299.

Astronomers believe that winds caused by star formation and black hole activity at the center of massive galaxies are responsible for launching star-forming material into space. However, the new study suggests that galactic mergers may also be responsible for ejecting gas into space.

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