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Astronomers Solve 12-Billion-Year-Old Mystery of Stalled Galaxies



An answer to one of the most fundamental questions about our universe has just been revealed by new research published in Nature and led by researchers at the University of Massachusetts Amherst: Why did some of the most massive and ancient galaxies go into hibernation so early in their formation? The reason for this, we now understand, is that they ran out of cold gas.


"The most massive galaxies in our universe formed incredibly early, just after the Big Bang occurred, 14 billion years ago," says Kate Whitaker, an astronomy professor at the University of Massachusetts Amherst. "The most massive galaxies in our universe formed incredibly early, just after the Big Bang occurred, 14 billion years ago." "However, for some reason, they have gone offline. They're no longer forming new stars," says the author. Star formation is one of the most important mechanisms by which galaxies grow, and when they stop forming stars, they are said to have gone quiescent. Astronomers have long suspected that these early, massive galaxies had gone into hibernation, but until now, no one had been able to explain why.


Whitaker's team, which includes Alexandra Pope, associate professor of astronomy, and Christina C. Williams, who received her Ph.D. in astronomy from the University of Massachusetts, devised an innovative pairing of telescopes in order to find the answer. Scientists used the Hubble Space Telescope, which can detect light in the ultraviolet to near-infrared range, including that which we can see with our own eyes, to detect these distant galaxies, which are so far away that we are only now beginning to see the light they emitted 10 billion to 12 billion years ago, when the universe was still in its early stages. In essence, Whitaker's team is delving into the dark recesses of the past.



In addition to appearing young and vigorous, these galaxies should show signs of constant star formation. It turns out that they don't, and Whitaker's team used Hubble images in conjunction with extraordinarily sensitive readings from ALMA, the Atacama Large Millimeter/submillimeter Array, which detects radiation that can't be seen with the naked eye.


ALMA enabled Whitaker's team to search for minute amounts of cold gas, which is the primary source of energy for new star formation. "There was a lot of cold gas in the early universe, so these galaxies, which are 12 billion years old, should have plenty of fuel left in the tank," says the cosmologist. Whitaker and her team, on the other hand, discovered only traces of cold gas at the centers of each galaxy. Therefore, within the first few billion years of the universe's existence, these galaxies either consumed their energy supplies or were ejected from the cosmos, and it is also possible that something is preventing each galaxy's replenishment of cold gas from occurring.


When taken as a whole, the research contributes to rewriting the early history of the universe, allowing us to gain a better understanding of how galaxies evolve. In order to determine how compact the remaining gas is in these quiescent galaxies and why it can only be found in the galaxies' centers, the team will need to conduct additional research.

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