Black HolesBlack holes are points in space where there are extreme gravitational attractions that prevent anything, including light, from escaping. The reason for such gravitational attraction is because large amounts of matter are contained in a small space. Stellar black holes form from stars with masses greater than 20 solar masses and can result from gravitational collapse. Gravitational collapse is the result of the star's internal pressure not being able to resist its own gravity. When the star runs out of nuclear fuel and can no longer maintain a high enough temperature, it begins to collapse under its own weight (Seidel 2011). When the star collapses, it causes a supernova that propels the outer layers of the star into space while the core completely collapses under its own weight. If the remaining core exceeds 3 solar masses, no known force can prevent the core from completely collapsing into a black hole (p. 568 Bennett et al. 2013). Since black holes do not emit light and completely absorb light near them. it would seem that they are impossible to detect. Although black holes do not emit light, their effects are detectable. Due to the strong gravitational pull of a black hole, any matter drawn into the black hole accelerates and heats up. This causes the atoms to ionize and when they reach high enough temperatures, they begin to emit X-rays which can be detected and observed from Earth (Netting 2014). Studying binary X-rays is a great way to detect stellar black holes, because binary systems provide enough material to power the black hole's X-ray emissions. Cygnus X-1 is an example of a black hole detected through observation of a binary X-ray ...... middle of paper ...... stripped of its nuclear fuel and lost its outer layers. When a small to medium main sequence star (less than 10 solar masses) begins to run out of fuel in its core, the core begins to collapse where the hydrogen at the edges of the collapsed core can be compressed and heated (Chandra 2012). . The nuclear fusion of this new hydrogen will create a new burst of power that will expand the outer layers of the star; This is called the red giant phase. In the red giant phase, over millions of years, all of the stars' energy reserves are exhausted, leaving behind a hot core that is still surrounded by the enlarged outer layers. The outer layers are eventually expelled by stellar winds which eventually create a planetary nebula and the hot core left behind forms a white dwarf star where the gravitational pull is supported by degeneracy pressure (p. 538 Bennett et al.. 2013).