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A giant, sleeping galaxy

An international group of astronomers has identified a rare galaxy, known only as XMM-2599, which formed very early in the history of the universe, spawned stars at an extremely fast rate, and then suddenly went quiet. Galaxy XMM-2599 began to form more than 12.8 billion years ago, when the universe was 1 billion years old. Over the following 800 million years, it generated the equivalent of 300 billion stars, and then died—in fact, the galaxy still exists, but it is no longer producing new stars. As a comparison to demonstrate just how fertile XMM-2599 was at that time: the Milky Way, the galaxy that our solar system calls home, began to form 13.5 billion years ago and now has 200 billion stars, including our Sun. At the peak of XMM-2599’s activity, which lasted around 500 million years, it is estimated that 1,000 stars were born per year—the Milky Way produces one star per year (The Astrophysical Journal Letters, February 5). “At that time, very few galaxies had stopped producing stars, and no galaxy had a mass as high as XMM-2599,” astronomer Gillian Wilson of the University of California, Riverside, USA, one of the study’s authors, said in a press statement. According to the researchers, the results challenge our current understanding of how high-mass galaxies formed and evolved in the early universe.