Stephen Hawking's Universe Black Holes and Beyond After WWII, Radio
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Stephen Hawking’s Universe Black Holes and Beyond After WWII, radio astronomy advanced Some galaxies emitted radio waves Strong radio emitters did not have catastrophic events 3C273 was a boring star…in Virgo But emitted radio waves Spectroscopy of this star showed a shift in pattern of colors Moving away will result in ‘longer’ wavelengths, looking redder than it should Emitting a strange spectrum: same spacing as hydrogen, but not yellow like hydrogen gas emission was usually—shifted 16% Could be explained by it moving away from us very rapidly Also it seemed to be VERY far away, therefore it must be extremely bright Radio star: quasi-stellar radio sources—QUASARs Extremely powerful source—greatly more powerful than the entire Milky Way galaxy Hawking started studying these in graduate school Perhaps an explanation would be gravitational collapse Einstein’s theory has prediction that large amount of matter would have gravity that results in infinite collapse…catastrophic gravitational collapse that cuts it off from the rest of the universe. Einstein did not believe it was possible, although his theory predicted it. Oppenheimer convinced Wheeler that this collapse was possible. Wheeler is a great physicist of the 20th century. Witnessed the development of the atomic bomb. 1963 controversy of collapsing stars rekindled by discovery of quasars. The concept was inspirational to Wheeler, as it was predicted by the theory. Einstein had no confidence that the ‘objects’ were real, just an artifact of the general theory of relativity. Gravitational completely collapsed objects…too long a name: Wheeler called them Black Holes—gravity is so great that light cannot escape. Some thought the idea of a black hole was ludicrous, but Hawking was not one of them. Many people thought that they explained some of the anomalies of the universe. The number of black holes may be related to what happens in the explosion that occurs at the end of the lifespan of the end of massive stars. Research at the Lawrence Livermore National Laboratory in California includes one of the first supercomputers. Allowed nearly unimaginable calculations to be performed. They became available for investigation of astronomical theory after no longer required for development of atomic bombs. The research indicated that the collapse of a large star would result in continual collapse, not reach a condensed equilibrium. A ‘black hole’…but how can you detect it if nothing can get out of it?? Science fiction writers seized upon the hypothesis—it was a very exciting concept. Benford’s fiction is convincing because he is a physicist. Realized that there may be a black hole at the center of our galaxy, millions of times more massive than our Sun…billions of Sun’s mass? Perhaps. As it draws in more matter by gravity, its mass increases, so its gravity increases, so it can draw in more things from further away. What ‘happens’ in a black hole? Roger Penrose mathematician wrote paper with son Lionel that mimicked Escher’s drawing of impossible objects. Penrose conceived that gravitational collapse would break the known laws of physics. Would the central region reach infinite density: not self-consistent with the theory. Described as a ‘singularity’: a point of infinite density. Matter would exit the known universe— Hawking’s thesis concluded that in black holes, space and time come to an end. Zeldovich was applying Einstein’s theory Quasars are most violent explosion short of the big bang. How do you see a black hole? It is a powerful gravitational influence. If one of a pair of stars is a black hole, it will suck gas from the visible one. Friction of the gases being drawn to it will result in glowing of these atoms. Magnetic fields drawn into the black hole become elongated into galactic jet, visible at extreme distances. If you find two jets, and only one has a visible star, then you have found a black hole. Galactic jets had been observed, but not actual proof of the existence of the black holes. As the black hole is gathering material it would glow brightly at first and then quiet down Wait for a while until it ‘gets’ most of the stuff around it, and not glow so brightly. If you see the visible star orbiting a ‘blank’ spot, you have found the black hole. There can be unique explanations for individual objects, however the black hole hypothesis explains a wide range of objects: a single simple explanation. Do black holes power the brightest objects in the universe: quasars? Perhaps those we see in the distance past of the universe have remnants in our neighborhood. Centers of large galaxies don’t glow because they have gathered all the material near them, and are no longer actively absorbing material. Large galaxies have development of black hole in their center. Friction of the material drawn into the black hole would cause it to glow, and brightest at the center where velocities are greatest. Shines extremely brightly, through the entire universe. From the far past (because it takes time for light to reach us…billions of years ago) we see very distance quasars. The center of the Milky Way was never in the quasar league—only the mass of a million Suns, not billions of Suns. Hawking states that material can escape a black hole, because the velocities of the particles in it are random, and some have speeds great enough to escape it. But the radiation released will be random and reveal no useful information. SETI (search for extra terrestrial intelligence)believes that the galaxy is filled with intelligent life. But there has been no information about any found in over 30 years of searching. Theories of time travel and worm holes from our universe into another invoke black holes as mechanisms. The physics of black holes imply there might be other ways to communicate. So we on Earth may not be able to receive the communication that other civilizations may be using. Although many are cautious to not discount the possibility, because sometimes the unimaginable becomes believable. .