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Intergalactic gas and ripples in the cosmic web

04.05.2017
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Now, a team of astronomers, including UC Santa Barbara physicist Joseph Hennawi, have made the first measurements of small-scale ripples in this primeval hydrogen gas using rare double quasars. Although the regions of cosmic web they studied lie nearly 11 billion light years away, they were able to measure variations in its structure on scales 100,000 times smaller, comparable to the size of a single galaxy. Appear in results of The the journal Science .Intergalactic gas is so tenuous that it emits no light of its own. Instead astronomers study it indirectly by observing how it selectively absorbs the light coming from faraway sources known as quasars. Quasars constitute a brief hyperluminous phase of the galactic life cycle powered by matter falling into a galaxy's central supermassive black hole. Acting like cosmic lighthouses, they are bright, distant beacons that allow astronomers to study intergalactic atoms residing between the location of the quasar and Earth. But because these hyperluminous episodes last only a tiny fraction of a galaxy's lifetime, quasars are correspondingly rare and are typically separated from each other by hundreds of millions of light years.In order to probe the cosmic web on much smaller length scales, the astronomers exploited a fortuitous cosmic coincidence: They identified exceedingly rare pairs of quasars and measured subtle differences in the absorption of intergalactic atoms along the two sightlines. «Pairs of quasars are like needles in a haystack,» explained Hennawi, associate professor in UCSB's Department of Physics. Hennawi pioneered the application of algorithms from " machine learning" — a brand of artificial intelligence — to efficiently locate quasar pairs in the massive amounts of data produced by digital imaging surveys of the night sky. «In order to find them, we combed through images of billions of celestial objects millions of times fainter than what the naked eye can see.»

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Автор: Roland Baker

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