The galaxy group Abell 959

Most galaxies are grouped into clusters containing from a few to several thousand objects. Our Milky Way, for example, belongs to the local group, a group of about fifty galaxies whose other great member is the Andromeda galaxy about 2.3 million light-years away. Clusters are the gravitational gravitational objects of the universe and form (according to current ideas) in an "upward" way with smaller structures developing first and larger groups gathering later in time. cosmic history.

Astronomers have detected massive clusters of galaxies, some with a mass greater than a hundred Milky Way galaxies, dating back to about three billion years after the big bang, and their stars had yet to form. In today's world, clusters are still formed through hierarchical processes, such as major mergers with neighboring clusters. Astronomers are trying to better understand the formation and evolution of clusters, in part because the details will also help to limit the cosmological parameters and properties of dark matter.

Felipe Andrade-Santos, astronomer of the CfA, was part of a team that studied Abell 959, a cluster of galaxies whose mass is about 3,000 galaxies of the Milky Way and which is about three billion light years away. All important processes for the formation of clusters like Abell 959 dissipate energy through shocks. Processes include, for example, mergers, mass accumulation and phenomena related to their supermassive black hole nuclei. These shocks in turn produce broad-scale diffuse emission characteristics as hot gas electrons are accelerated and radiate, and these structures (known as radio relics) can be studied with radio telescopes. The turbulence of gases in the post-fusion cluster also produces radio functions, called giant radio halos. Abell 959 houses a radio relic more than twelve hundred light-years long and five hundred wide, as well as a giant radio halo.

The scientists analyzed the Abell 959 structures and compared them to an analysis of about eighty other known radio-halo systems in order to test and refine the competing theories of cluster evolution. . They find that the current model of turbulent re-acceleration of electrons is consistent with their results and that, in addition, the new cluster formation simulations are in good agreement with their observations. Their results broadly reinforce our confidence in the formation models of massive galaxy clusters.