Such objects are then frozen somewhere along their pre-main sequence contraction phase, continually cooling into compact dark objects. X-ray observations show that these enormous systems of galaxies are filled with colossal clouds of hot gas.
Photons travel through space at the speed of light.
When the changes of energy are small, streams of photons can be described as waves of changing electric and magnetic fields, called electromagnetic waves. Electrons orbit the nucleus of an atom. A white dwarf in a binary system can accrete enough mass that it cannot support its own weight. The star collapses and temperatures become high enough for carbon fusion to occur. The outer, hydrogen-rich, envelope of the star has been driven off by radiation pressure, exposing the hot helium core.