Ripples in cosmic web measured using rare double quasars

Physical and Biological Sciences News

Astronomers identified rare pairs of quasars right next to each other on the sky and measured subtle differences in the absorption of intergalactic atoms measured along the two sightlines. This enabled them to detect small-scale fluctuations in primeval hydrogen gas. See larger image. (Credit: J. Onorbe/MPIA)The most barren regions of the universe are the far-flung corners of intergalactic space. In these vast expanses between the galaxies, a diffuse haze of hydrogen gas left over from the Big Bang is spread so thin there's only one atom per cubic meter. On the largest scales, this diffuse material is arranged in a vast network of filamentary structures known as the “cosmic web,” its tangled strands spanning billions of light years and accounting for the majority of atoms in the Universe.
Now a team of astronomers including J. Xavier Prochaska, professor of astronomy and astrophysics at UC Santa Cruz, has made the first measurements of small-scale ripples in this primeval hydrogen gas. 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 a 100,000 times smaller, comparable to the size of a single galaxy. The researchers presented their findings in a paper published April 27 in 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 hyper-luminous phase of the galactic life-cycle, powered by the infall of matter onto a galaxy's central supermassive black hole. They thus act like cosmic lighthouses—bright, distant beacons that allow astronomers to study intergalactic atoms residing between the quasars location and Earth.
Because these hyper-luminous episodes last only a tiny fraction of a galaxy’s lifetime, quasars are correspondingly rare on the sky, and ...

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