AST 105 1st Edition Lecture 14Outline of Previous Lecture I. Super NovaII. Neutron Stars III. Pulsar’sIV. Binary Neutron Star SystemsV. X-ray Bursters Outline Of Current Lecture I. Super GiantsII. Special Relativity a. 2 postulatesb. Postulate consequencesIII. General Relativity IV. Gravitational Red ShiftV. Black Holesa. How Black Holes formb. Details of i. Schwarzschild Super giants, which arise from main-sequence stars (w/ 8Msun < Mass < 25 Msun), form neutron stars (after the supernova).In the neutron star, the neutron degeneracy pressure balances the gravitational attraction.As long as the mass of the neutron star < 3 Msun, the degeneracy pressure can repulse the force of gravity.But if mass > 3 Msun, gravity wins and neutron star collapses to form a black hole.To understand Black Holes, we need Einstein’s theory of relativity (1905). Special Relativity - 2 postulates laws of physics are the same in every non-accelerating frame (inertial frames) speed of light (is a finite value) the same in all non-acceleratingframes no instantaneous action - these 2 postulates give rise to consequences - time dilation moving clocks slow down - length contraction moving objects get smaller - E=mc2 Mass energy equivalence (Mass and energy are the same thing)- The fast that time is now a function of the motion means that space and time cannot be considered as 2 separate concepts we call them as one: space-timeGeneral Relativity - here, the principle of relativity is extended to accelerating frames- postulate: there is no difference between a person on the earth and a person in a rocket accelerating at g both will feel the same downward force g=acceleration of gravity - what general theory predicts is that matter (or energy) warps the surrounding space- any massive body bends the space inward- consequence: light form a distant star will bend as it passes by the sun not only does matter curve, or warp space, it also slows down time “clocks run slower near massive objects”Gravitation Redshift- shift of wavelength as light leaves the surface of a massive object - another prediction of GR in perihelion of mercury’s orbit around the sun Black Holes- how they form: start with mass >25 Msun Iron core mass exceeds Chandrasekhar limit (1.4 Msun) EDP falls, core collapses Black hole so dense that space is warped so as to close the black hole off from the rest of the universe - Nothing can escape Not even light - Masses of black holes are basically unlimited up to 109 Msun - Stephan Hawking: during Big Bang small Black holes could have formed Primordial Black Holes- If isolated, will lose mass over time (theory)- Schwarzschild Size of black hole-
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