Lecture31_LB.doc - black hole, however, it all takes place...

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Black Holes   continued Now, in a black hole, the gravitational field is so strong that space is curved back around  on itself.   Light that is emitted by a black hole must lose energy in escaping a black hole, thus the  light from such a photon becomes  redshifted . Time must also slow as one approaches the event horizon of a black hole.  One may think  of this as light having to traverse a longer path in the curvature around the black hole.  At  the event horizon, time stops for a distant observer. If we could see something falling into a black hole, it would seem to slow down as it  approached the event horizon, the light from the object becoming redder and redder,  while the image becomes frozen (since it takes an infinite amount of time for a distant  observer to see the object cross the event horizon).  Sitting on the object falling into the 
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Unformatted text preview: black hole, however, it all takes place quite quickly. All information is lost for something falling into a black hole. No communication of any kind can ever take place across the event horizon. More implications: Because gravity can bend light (by bending the space around it), gravity acts in the same way a lens does. However, a gravitational lens has a different equivalent geometry than an ordinary lens has. We so in fact see evidence of gravitational lenses in space by seeing the distorted images distant quasars and galaxies. In fact, gravitational lensing is so prevalent that it is a useful too for astronomers in measuring the mass of distant objects. It is one of the very few ways that mass can be directly measured besides Kepler’s third law....
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This note was uploaded on 03/02/2011 for the course ASTRO 10 taught by Professor Norm during the Spring '06 term at Berkeley.

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