A cosmic spider web is unraveled

Long-sought baryonic matter connects two galaxies.Provided by the Max Planck Institute, Garching, Germany
By | Published: May 6, 2008
A bridge of hot gas connects two clusters of galaxies.
Max Planck Institute
May 6, 2008
The composition of the universe still puzzles astronomers. Over 90 percent consists of unknown matter. Just four percent is the normal material of which humans are made — the so-called baryonic matter. Even this small part is not yet completely understood.

A team of astrophysicists from the Max Planck Institute for Extraterrestrial Physics (MPE) and the European Southern Observatory (ESO), and two institutes in the Netherlands have found evidence of the missing baryons in a bridge-like filament connecting two clusters of galaxies.

The Universe is constructed like an oversized spider web. All visible material is arranged along the filamentary structure of the dark matter. On its threads and knots, this web holds gigantic chunks of baryonic matter, which are made of quarks and leptons.

Astronomers knew for a long time that the pieces of the cosmological puzzle must be hidden somewhere. Tracing and capturing this observable component in the universe will help us learn more about dark material.

The missing part of the baryonic matter is thought to be a hot, ultra-thin gas haze of very low density between larger structures. Scientists from SRON Netherlands Institute for Space Research observed the clusters of galaxies Abell 222 and Abell 223, which are connected by a filament.

The gas they found is probably the hottest and densest part of the diffuse gas which constitutes half of the missing baryons in the universe.

This is the first time that scientists have seen the bridge of gas connecting two clusters of galaxies. “So far, we could only see the clusters, the dense knots of the web. Now, we are starting to see the connecting wires of the immense cosmic spider web,” says MPE astrophysicist Aurora Simionescu.