x-ray-astronomy

Galaxy clusters are the largest structures held together by their own gravity: hundreds to thousands of galaxies, a vast reservoir of X-ray-bright gas, and a dark matter halo that outweighs everything else. They also work as natural telescopes, bending and magnifying light from the early universe.

X-ray binaries are binary star systems where a neutron star or black hole pulls gas from a companion star, converting gravitational energy into X-rays with an efficiency that dwarfs nuclear fusion. They are among the brightest X-ray sources in the sky and natural laboratories for extreme physics.