double quasar

Intergalactic gas and ripples in the cosmic web

The most barren regions known are the far-flung corners of intergalactic space. In these vast expanses between the galaxies there is just one solitary atom per cubic meter – a diffuse haze of hydrogen gas left over from the Big Bang. On the largest scales, this 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 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. The results appear in the journal Science.

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Double Vision

This new Hubble image shows two bright objects, seemingly identical. In fact, only one object exists — the double image comes from the effect of gravitational lensing. The pair of images form a double quasar known as QSO 0957+561, also called the “Twin Quasar,” which lies just under 14 billion light-years from Earth. Quasars represent the intensely powerful centers of distant galaxies. The huge galaxy YGKOW G1 lies roughly 4 billion light-years from Earth, directly between us and QSO 0957+561. This galaxy possesses a mass so great that it bends the light from objects lying behind it. In this case, it also allows us to see the quasar twice. Einstein’s theory of general relativity first suggested this phenomenon could arise.

Image Credit: ESA/Hubble & NASA