Galaxy cluster
= Galaxy cluster
{wiki}
A <galaxy cluster> is a gravitationally bound collection of <galaxies>, diffuse gas and <dark matter>. Much of its ordinary matter can reside in hot intracluster gas, visible through <thermal bremsstrahlung> and the <Sunyaev-Zeldovich effect>. The two signals weight the electron density differently, making the cluster useful both as a structure-formation probe and, with a geometrical model, as a distance indicator.