Astronomers observe ripples in the cosmic web

Astronomers have managed to measure ripples in the cosmic web that occurred just two billion years after the Big Bang.

A representation of the technique used to probe the small-scale structure of the cosmic web using light from a rare quasar pair. Bottom right shows spectra containing information about the hydrogen gas the light has encountered, as well as the distance of that gas. Credit: Springel et al. (2005) (cosmic web) / J. Neidel, MPIA

The cosmic web is the name scientists give to the network of filamentary structures thought to contain all the matter in the Universe including planets, stars, galaxies and galaxy clusters. In the farthest reaches of the Universe, a diffuse haze of hydrogen gas exists that is left over from the Big Bang.

This gas fills the cosmic web and accounts for the majority of atoms in the Universe.


Astronomers from the Max Planck Institute for Astronomy (MPIA) have made the first measurements of tiny ripples in this gas 11 billion lightyears away.

They made their measurements using objects called quasars, which are brief bursts of intense light caused by the energy generated as matter falls into a black hole.

While the intergalactic gas the astronomers studied emits no light of its own, they were able to observe it indirectly by measuring how it absorbs light from quasars.

However, quasars last a small fraction of a galaxy’s lifetime and are usually separated from each other by hundreds of millions of lightyears.

This makes them very rare.

A supercomputer simulation showing part of the cosmic web 11.5 billion years ago. The cube is 24 million lightyears on a side.Image: J. Onorbe / MPIA
A supercomputer simulation showing part of the cosmic web 11.5 billion years ago. The cube is 24 million lightyears on a side. Image: J. Onorbe / MPIA

The team were able to take advantage of a rare event: pairs of quasars situated next to each other.

They were then able to measure differences in how these two quasars absorb intergalactic atoms.

“One of the biggest challenges was developing the mathematical and statistical tools to quantify the tiny differences we measure in this new kind of data,” says Alberto Rorai, lead author of the study and post-doctoral researcher at the University of Cambridge.

Using supercomputers that simulate the Universe using the laws of physics, the team input their measurements and found they agreed with the established theories as to how cosmic structures form.

“One reason why these small-scale fluctuations are so interesting is that they encode information about the temperature of gas in the cosmic web just a few billion years after the Big Bang,” says Joseph Hennawi, who leads the research group at MPIA responsible for the measurement.


This information can be used to learn more about what happened during the period just after the Big Bang, and how planets, stars and galaxies eventually formed.