How starbursts stunt galaxy growth
Washington: A new study has tried to find out how there are far fewer galaxies at the most massive end of the galactic scale than expected, which scientists have long sought to explain.
The UMD-led study 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," lead author Alberto Bolatto of the University of Maryland, said.
"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," he said.
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 NGC 253, also known as the Silver Dollar or Sculptor Galaxy.
In starburst galaxies, stars form about 100 times faster than in more normal galaxies like our Milky Way.
NGC 253 -- with its slightly askew orientation-offers astronomers an excellent view of the star formation clusters near the galaxy`s center, clusters that turn out to be the point of departure for material being pushed from the galaxy.
"ALMA is opening a new window for observations of galactic winds," Sylvain Veilleux, also at the University of Maryland and a coauthor on the paper, said.
"Winds have the potential to be incredibly disruptive and carry away a significant fraction of the star-forming material of a galaxy," he said.
The team says their results may help explain the universe`s surprising paucity of high-mass galaxies.
Computer models indicate that old red galaxies, which are far more massive than the Milky Way, should be considerably more common than they are. In their youth, these galaxies likely ejected a large fraction of their gas that would have otherwise formed stars.
The study is published in the journal Nature.
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