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Light captured from early stars: high-energy radiation reveals founding stellar generations.

Light from the universe's very first stars still lingers in space. Now astronomers have a new way to catch it- distant, ultrabright galaxies that expose relict photons in a blaze of gamma rays.

But it's not just these earliest photons that are snared; light from every star that ever shined can be caught. "We now have constraints on the total number of stars that ever formed," astronomer Volker Bromm of the University of Texas at Austin says of the new way to see old light, described online November 1 in Science.

Studying these stellar fingerprints will help astronomers learn more about the universe's earliest years. Now roughly 13.7 billion years old, the universe is thought to have switched on the first stars about 400 million years after the Big Bang.

Astrophysicist Marco Ajello of Stanford and his colleagues used the orbiting Fermi Large Area Telescope to study distant blazars, a type of bright, active galaxy. Blazars are powered by supermassive black holes that shoot enormous jets toward Earth. The jets include gamma rays that can interact with photons from early stars.

Photons colliding with a blazar's gamma rays are converted into electrons and their antimatter particles, positrons. The transition produces a dimming effect, with the amount of dimming corresponding to the quantity of photons between Earth and the blazar.

Ajello and his colleagues used 150 blazars to parse early photons from the rest of the cosmic melee. So far, the researchers have managed to peer at the shimmering universe as it appeared when it was just 4 billion years old. The team plans to follow up with blazars at greater distances and earlier ages.

The new results suggest that early stars may have formed a bit more slowly than previously thought, were primarily made of hydrogen, and lived fast and died young. "The first stars were in general more massive--up to hundreds of times as massive as the sun--hotter, brighter and more short-lived," Ajello says.


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Title Annotation:Atom & Cosmos
Author:Drake, Nadia
Publication:Science News
Article Type:Brief article
Geographic Code:1USA
Date:Dec 15, 2012
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