Fewer stars born today than in early universe

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

University of Arizona (UA) astronomers have helped solve a mystery surrounding the birth of stars in galaxies that has long puzzled scientists. Cooper and his colleagues used data from an earlier study, in which they had surveyed about 50,000 galaxies, to pick a sample representing an 'average' population of galaxies. They then pointed various telescopes, among them the Hubble and the Spitzer space telescopes and radio telescope arrays in France and California, toward their study objects.

"By observing those galaxies in the infrared spectrum and measuring their radio frequency emissions, we were able to make their cold gas clouds visible," explained Cooper.

"From our study, we now know that typical galaxies in the early universe contained three to ten times more molecular gas than today," said Cooper, "a strong indication that the rate of star formation has slowed because those galaxies have less raw material available compared to when they were younger, and not because there was some change in efficiency with which they make new stars."

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