The science of the solar system is linked to colossal collisions.

 A new study reveals a deep connection between some of the universe's largest, most energetic events and much smaller, weaker ones powered by our own Sun.

Colossal collisions linked to solar system science
Colossal collisions linked to solar system science. Credit: Image of Abell 2146

A new study reveals a deep connection between some of the universe's largest, most energetic events and much smaller, weaker ones powered by our own Sun.

The findings are the result of a long observation of Abell 2146, a pair of colliding galaxy clusters located about 2.8 billion light-years from Earth, with NASA's Chandra X-ray Observatory. Helen Russell of the University of Nottingham's School of Physics and Astronomy led the new study.

Galaxy clusters are among the largest structures in the universe, containing hundreds of galaxies as well as massive amounts of hot gas and dark matter. Collisions between galaxy clusters release massive amounts of energy unprecedented since the Big Bang and provide scientists with physics laboratories not available on Earth.

Chandra X-ray data (purple) shows hot gas in this composite image of Abell 2146, while Subaru Telescope optical data shows galaxies (red and white). One cluster (labeled #2) is moving in the direction shown, towards the bottom left, and plowing through the other cluster (#1). As it collides with the hot gas in the other cluster, the former produces a shock wave similar to a sonic boom produced by a supersonic jet.

The shock wave is approximately 1.6 million light-years long and is best seen in an X-ray image that has been processed to emphasize sharp features. The central core of hot gas in cluster #2, as well as the tail of gas it has left behind, are also labeled. Behind the collision, a second shock wave of comparable size can be seen. This type of feature, known as an "upstream shock," results from the complex interplay of stripped gas from the infalling cluster and the surrounding cluster gas. Each cluster's brightest and most massive galaxy is also labeled.

Collisional shocks, such as those produced by a supersonic jet, involve direct collisions between particles. Gas particles in the Earth's atmosphere near sea level typically travel only about 4 millionths of an inch before colliding with another particle.

Direct collisions between particles occur too rarely in galaxy clusters and the solar wind (streams of particles blown away from the Sun) to produce shock waves because the gas is so diffuse and has such a low density. In galaxy clusters, for example, particles must typically travel 30,000 to 50,000 light-years before colliding. The shocks in these cosmic environments, on the other hand, are "collisionless," caused by interactions between charged particles and magnetic fields.

Chandra observed Abell 2146 for approximately 23 days, yielding the most detailed X-ray image of shock fronts in a galaxy cluster yet obtained. Abell 2146's two shock fronts are among the brightest and clearest shock fronts known in galaxy clusters.

'I first detected these shock fronts in an earlier, brief Chandra observation when I was a Ph.D. student,' Helen said. It was an exciting discovery and an incredible journey to this deep, legacy observation that revealed the detailed shock structure.'

Russell and her colleagues studied the gas temperature behind the shock waves in Abell 2146 using this powerful data. They demonstrated that electrons were primarily heated by shock compression of gas, a phenomenon similar to that seen in the solar wind. The rest of the heating was caused by particle collisions. Because the gas is so diffuse, the additional heating occurred gradually over 200 million years.

Chandra produces such sharp images that it can actually measure how much random gas motions blur a shock front that should be much narrower based on theory. They measure random gas motions of around 650,000 miles per hour for this cluster.

Collisionless shock waves are useful in a variety of other fields of study. For example, radiation produced by solar wind shocks can have a negative impact on spacecraft operations as well as human safety in space.


Materials provided by the University of Nottingham. Note: Content may be edited for style and length.


H R Russell, P E J Nulsen, D Caprioli, U Chadayammuri, A C Fabian, M W Kunz, B R McNamara, J S Sanders, A Richard-Laferrière, M Beleznay, R E A Canning, J Hlavacek-Larrondo, L J King. The structure of cluster merger shocks: Turbulent width and the electron heating timescale. Monthly Notices of the Royal Astronomical Society, 2022; DOI: 10.1093/mnras/stac1055


Font Size
lines height