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Galaxies Are Running out of Gas: Why the Lights Are Going out in the Universe

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A CSIRO study has shown why the lights are going out in the Universe. The Universe forms fewer stars than it used to, and a CSIRO study has now shown why: the galaxies are running out of gas.

A star-forming region in a nearby galaxy, imaged by the Hubble Space Telescope

Dr Robert Braun (CSIRO Astronomy and Space Science) and his colleagues used CSIRO’s Mopra radio telescope near Coonabarabran, NSW, to study far-off galaxies and compare them with nearby ones.

Light (and radio waves) from the distant galaxies has taken time to travel to us, so we see the galaxies as they were between three and five billion years ago.

Galaxies at this stage of the Universe’s life appear to contain considerably more molecular hydrogen gas than comparable galaxies in today’s Universe, the research team found.

Stars form from clouds of molecular hydrogen. The less molecular hydrogen there is, the fewer stars will form.

The research team’s paper is in press in Monthly Notices of the Royal Astronomical Society.

Astronomers have known for at least 15 years that the rate of star formation peaked when the Universe was only a few billion years old and has declined steeply ever since.

“Our result helps us understand why the lights are going out,” Dr Braun said.

“Star formation has used up most of the available molecular hydrogen gas.”

After stars form, they shed gas during various stages of their lives, or in dramatic events such as explosions (supernovae).

This returns some gas to space to contribute to further star formation.

“But most of the original gas — about 70% — remains locked up, having been turned into things such as white dwarfs, neutron stars and planets,” Dr Braun said….. Read the rest of this entry »

Written by physicsgg

August 22, 2011 at 7:46 pm