UA Science: They Don't Make Stars Like They Used To

Published Feb. 12, 2010 at 8:58 p.m.

A galactic mystery solved by UA astronomers?

Daniel Stolte of University Communications tells us:

• Viewed through the Hubble Space Telescope at visible light (left), a galaxy does not reveal its full secret underlying star formation. Only when observed using a combination of radio emission and infrared wavelengths, the galaxy reveals a massive, rotating disc measuring about 60,000 light years across (right). This disc consists of cold molecular gas and dust, the raw materials from which stars are born. UA astronomers help explain why fewer stars are born today than in the early universe.

University of Arizona astronomers have helped solve a mystery surrounding the birth of stars in galaxies that has long puzzled scientists. Their results are published in the Feb. 11 issue of Nature.

"We have known for more than a decade that in the early universe — three to five billion years after the Big Bang or nine to eleven billion years before today — galaxies churned out new stars at a much faster rate than they do now," said Michael Cooper, a postdoctoral Spitzer fellow at the UA's Steward Observatory.

"What we haven't known is whether this was because they somehow formed stars more efficiently or because more raw material — molecular gas and dust — was available," said his colleague Benjamin Weiner, an assistant astronomer at Steward Observatory and one of the co-authors on the paper.

Compared to the average galaxy today, which produces stars at ratesequaling about 10 times the mass of our sun per year, the rate of star formation in those same galaxies appears to have been up to 10 times higher when they were younger.

In its efforts to find an answer, the scientific community has tended to turn telescopes toward few, rare, very bright objects, mostly because the instruments available did not allow for the study of less extreme, more typical galaxies. By focusing on the rare, bright objects, the results

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