Tham khảo tài liệu 'intro to differential geometry and general relativity - s. warner episode 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 3. Calculate the Riemann coordinates of curvature tensor Rabcd at the event horizon. r 2M. 16. White Dwarfs Neutron Stars and Black Holes Guest Lecture by Gregory C. Levine I Introduction In this section we will look at the physical mechanisms responsible for the formation compact stellar objects. Compact objects such as white dwarf stars neutron stars and ultimately black holes represent the final state of a star s evolution. Stars are born in gaseous nebulae in which clouds of hydrogen coalesce becoming highly compressed and heated through the gravitational interaction. At a temperature of about 107 K a nuclear reaction begins converting hydrogen into the next heavier element helium and releasing a large quantity of electromagnetic energy light . The helium accumulates at the center of the star and eventually becomes compressed and heated enough 108 K to initiate nuclear fusion of helium into heavier elements. So far the star is held in near-equilibrium by the countervailing forces of gravity which compresses the star and pressure from the vast electromagnetic energy produced during nuclear fusion which tends to make it expand. However as the star burns hotter and ignites heavier elements which accumulate in the core electromagnetic pressure becomes less and less effective against gravitational collapse. In most stars this becomes a serious problem when the core has reached the carbon rich phase but the temperature is still insufficient to fuse carbon into iron. Even if a star has reached sufficient temperature to create iron no other nuclear fusion reactions producing heavier elements are exothermic and the star has exhausted its nuclear fuel. Without electromagnetic energy to hold the core up one would think that the core would become unstable and begin to collapse---but another mechanism intervenes. II The Electron Gas But there is another force that holds the core up now we will turn to a study of this force and how the balance between this force and gravity
