CANBERRA, Australia, Aug. 22 (UPI) -- Fewer stars are forming in the universe as time goes by, and Australian astronomers say it's because galaxies are running out of gas -- hydrogen gas.
Astronomer at Australia's Commonwealth Scientific and Industrial Research Organization have used radio telescopes to look at distant galaxies and compare them with nearby ones. The time it takes light to reach Earth from those distant galaxies means astronomers are seeing them as they were between 3 billion and 5 billion years ago.
Galaxies at that stage of the universe's life contained considerably more molecular hydrogen gas than comparable galaxies in the universe now, the research team said in a CSIRO release Monday.
Since stars form from clouds of hydrogen, the less gas there is the fewer stars will form.
Astronomers have known the rate of star formation peaked when the universe was only a few billion years old and has declined ever since.
"Our result helps us understand why the lights are going out," CSIRO astronomer Robert Braun said. "Star formation has used up most of the available molecular hydrogen gas."
Some stars shed gas during various stages of their lives or in dramatic events such as supernova explosions, which returns some gas to space to contribute to further star formation.
"But most of the original gas -- about 70 percent -- remains locked up, having been turned into things such as white dwarfs, neutron stars and planets," Braun said.
