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Starburst wind keeps galaxies 'thin'

A feast and fast sequence explains how large galaxies can keep their mass down.

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Unlike humans, galaxies don't have an obesity problem. In fact there are far fewer galaxies at the most massive end of the galactic scale than expected and scientists have long sought to explain why. A new University of Maryland-led study published in the journal Nature suggests that one answer lies in a kind of feast and fast sequence through which large galaxies can keep their mass down.

Galaxies become more massive by 'consuming' vast clouds of gas and turning them into new stars. The new study shows in unprecedented detail how a burst of star formation in a galaxy can blow most of the remaining star-building gas out to the edge of the galaxy, resulting in a long period of starvation during which few new stars are produced.

"For the first time, we can clearly see massive concentrations of cold molecular gas being jettisoned by expanding shells of intense pressure created by young stars," says lead author Alberto Bolatto of the University of Maryland. "The amount of gas we measure gives us very convincing evidence that some growing galaxies blow out more gas than they take in, slowing star formation down to a crawl."

The team of astronomers used the new Atacama Large Millimeter/submillimeter Array (ALMA), a giant radio telescope in the high desert of northern Chile, to discover billowing columns of cold, dense gas being pushed out of starburst galaxy...

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