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Astronomers explain why outlier galaxies are thin and hyperactive

"A galaxy at its very early stages of life, full of dust and gas, has a very high star formation rate but at the same time it still contains very few stars," said astronomer Claudia Mancuso.

By Brooks Hays
Astronomers explain why outlier galaxies are thin and hyperactive
ALMA observations reveal a handful of thin, young and hyperactive galaxies. Photo by ALMA/NASA/ESA

TRIESTE, Italy, Dec. 13 (UPI) -- New research explains why outlier galaxies are thin and hyperactive, boasting an accelerated rate of star formation. The explanation is rather simple: they're young.

The rates of star formation among most galaxies is closely correlated with the size of galaxies. When plotted on a graph, the galaxies cluster in a compact cloud -- their positioning explained by a simple function.

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Scientists call the visual representation of the relationship between size and star formation the Galaxy Main Sequence. The graph does have outliers, however. Some galaxies are thin, yet still produce new stars at a prodigious rate.

Traditionally, astronomers have explained outliers as the products of galactic mergers and collisions.

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New research, detailed in the Astrophysical Journal, offers an alternative, internal explanation. Outlier galaxies are simply young galaxies, which haven't yet grown to large sizes.

Researchers arrived at their conclusion while working to explain the compact cloud organization unique to the Galaxy Main Sequence graph.

"These two events are simultaneous and interrelated. As the galaxy forms stars and increases its mass in a constant and substantial manner, its black hole grows as well, and does so at an even faster rate," Claudia Mancuso, a researcher at the International School for Advanced Studies in Italy, said in a news release. "At a certain point the black hole becomes so big as to develop an 'energetic wind,' which sweeps away gas and dust from its surrounding environment. Since these are materials that go into forming new stars, the star formation process comes to an abrupt halt."

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The theory that outlier galaxies haven't had time to accrue mass fits neatly with the explanation of the Galaxy Main Sequence pattern.

"A galaxy at its very early stages of life, full of dust and gas, has a very high star formation rate but at the same time it still contains very few stars because it hasn't had the time to form them yet, that's all," Mancuso said.

Initial observations confirm the logic, but scientists say further analysis of the evolution of young galaxies is important.

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"Out theory in fact implies that outlier galaxies, which are young and have very high star formation rates, are still rich in gas, and this will allow us to study them in depth by using the ALMA interferometer," Mancuso concluded.

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