RAS: Astronomers find evidence of cosmic climate change

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RAS: Astronomers find evidence of cosmic climate change

Post by bystander » Tue Nov 02, 2010 2:56 pm

Astronomers find evidence of cosmic climate change
Royal Astronomical Society | 02 Nov 2010
A team of astronomers has found evidence that the universe may have gone through a warming trend early in its history. They measured the temperature of the gas that lies in between galaxies, and found a clear indication that it had increased steadily over the period from when the universe was one tenth to one quarter of its current age. This cosmic climate change is most likely caused by the huge amount of energy output from young, active galaxies during this epoch. The researchers publish their results in a forthcoming paper in the journal Monthly Notices of the Royal Astronomical Society.

"Early in the history of the universe, the vast majority of matter was not in stars or galaxies", University of Cambridge astronomer George Becker explains. "Instead, it was spread out in a very thin gas that filled up all of space." The team, led by Becker, was able to measure the temperature of this gas using the light from distant objects called quasars. "The gas, which lies between us and the quasar, adds a series of imprints to the light from these extremely bright objects," Becker continues, "and by analyzing how those imprints partly block the background light from the quasars, we can infer many of the properties of the absorbing gas, such as where it is, what it's made of, and what its temperature is."

The quasar light the astronomers were studying was more than ten billion years old by the time it reached Earth, and had travelled through vast tracts of the universe. Each intergalactic gas cloud the light passed through during this journey left its own mark, and the accumulated effect can be used as a fossil record of temperature in the early universe. "Just as Earth's climate can be studied from ice cores and tree rings," says Becker, "the quasar light contains a record of the climate history of the cosmos.
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The warming trend is believed to run counter to normal cosmic climate patterns. Normally the universe is expected to cool down over time. As the cosmos expands, the gas should get colder, much like gas escaping from an aerosol can. To create the observed rise in temperature, something substantial must have been heating the gas.
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One of the lightest and most abundant elements in these intergalactic clouds, helium, played a vital role in the heating process. Ultraviolet light (from quasars) stripped the electrons from a helium atom, freeing the electrons to collide with other atoms and heat up the gas. Once the supply of fresh helium was exhausted, the universe started to cool down again. Astronomers believe this probably occurred after the cosmos was one quarter of its present age.
Detection of Extended He II Reionization in the Temperature Evolution of the Intergalactic Medium - GD Decker et al

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