Scientists have combined Euclid’s recently released image of the massive galaxy cluster Abell 2390 with ESA XMM-Newton’s X-ray observation of the same site to showcase the blazing hot gas that fills the space between the galaxies.
Abell 2390 is a giant conglomeration of many galaxies like the Milky Way, located 2.7 billion light-years from Earth. Euclid’s image was obtained from observations in visible and near-infrared light and features more than 50 000 galaxies, thousands of which are part of the cluster. Yet, we cannot directly see most of the mass that makes up this cluster in Euclid’s sparkling view.
A galaxy cluster like Abell 2390 is a gigantic pile of dark matter that makes up about 80% of its total mass. Most of the ‘normal’ matter in the pile is in the form of scorching hot gas, which makes up about 15% of the cluster. The galaxies, which add to only a few percent of the total mass, sit in this pile like raisins in a cake.
The temperature of the gas ranges between 10 to 100 million degrees Celsius. Here, electrons are stripped from the atoms in the gas and become ionised. The sizzling mixture of charged particles produces the X-rays captured by XMM-Newton.
In the image,the X-ray light appears as a blue glow that permeates the expanses between the galaxies. The diffuse light is brighter towards the centre of the cluster, indicating that there the gas becomes hotter and more concentrated.
By mapping where the hot gas is located and studying how it behaves, astronomers learn more about how galaxy clusters grow, and about how galaxies interact and evolve in this dynamic environment.
The gigantic, curved arcs in Euclid’s image are the result of gravitational lensing where the light travelling to us from more distant galaxies is bent and distorted by the matter in the foreground (‘normal’ and dark matter). Euclid uses lensing as a key technique for exploring the dark Universe, indirectly mapping the amount and distribution of dark matter both in galaxy clusters and elsewhere.
XMM-Newton observations of Abell 2390 were taken in 2001 and are available from ESASky. Euclid’s observation of Abell 2390 can be found in ESASky here.