... tely compact state 13.7 billion years ago. The initial conditions are not known, but less than a second after the beginning, temperatures were trillions of degrees Celsius and the primordial universe was much smaller than an atom. It has been expandi ...

... late K or M spectral type. They range in in mass from a low of 0.075 solar masses to about 50% of the Sun and have a surface temperatures of less than 4,000 K. Red dwarfs are by far the most common type of star in the Milky Way, at least in the neigh ...

Black holes normally reveal themselves in astronomy because they are surrounded by discs of gas, heated to high temperatures, stolen from nearby stars. The X-rays emitted from these accretion discs give away the black hole although it cannot itself b...

... ing off a vast accretion disc - a donut-shaped gas cloud. The gas in the disc spirals around and is heated to extremely high temperatures by friction, before falling into the hole. In some cases, magnetic fields thread the disc, and lead to the forma ...