Findings suggest need to reassess ideas about galaxy formation
Science News said:A hefty red, dead galaxy in the early universe appears to have bulked up a bit too fast.
The galaxy, seen as it was when the universe was only 1.65 billion years old, weighs at least three times as much as the Milky Way, but has stopped making stars. Other galaxies at the time tend to be much smaller and continue to churn out stars. How such a monster was made in less than a billion years, then shut down so quickly isn’t clear, says Karl Glazebrook of Swinburne University of Technology in Australia. Finding the behemoth and possibly others like it may mean astronomers will have to rethink how galaxies are built to explain why some grow up fast, while others develop slowly, he and colleagues report in the April 6 Nature.
“The team has found an extreme galaxy, which is exciting,” says Peter Behroozi of the University of California, Berkeley, who was not involved in the study. The data, he says, offer evidence for a population of inactive galaxies early in the universe, which are extremely difficult to observe. Behroozi, however, is not convinced that the discovery warrants a rewrite of the story of galaxy formation just yet. “The galaxy is certainly not typical, but it is consistent with the broad diversity of galaxies coming out of theoretical models,” he says.
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Perhaps the galaxy got so massive by colliding and merging with another galaxy. Such a major merger can stir up and compress gas to high densities, which can trigger intense star formation. These events are typically short bursts, lasting less than 100 million years, compared with the typically billion-year timescales for star formation in normal galaxies. In these merger galaxies, gas gets consumed quickly because stars are forming fast. If the galaxy runs out of gas, star formation stops. Still, if this process happens and these massive galaxies exist, they are expected to be rare, says astronomer Dominik Riechers of Cornell University, who was not involved in the new study.
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