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ASTA02 Lecture Note.docx

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Parandis Khavari

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ASTA02 Lecture Note
Black Holes
-remnants of a supernova
-a region of space time that nothing, not even light, can escape from
-the boundary of a black hole is called the Event Horizon
-a black hole is characterized by an event horizon and a singularity in the centre
-a neutron star more massive than 3M of the sun can collapse into a black hole
-adding mass to the black hole causes the event horizon to increase
-Laplace and Michell in the 18th century argues that a star could be so massive and so
compact that the escape velocity of it is equal to the speed of light or larger
-No hair theorem: black hole is characterized by only 3 main properties: mass, electrical
charge, and angular momentum
-Angular momentum is one of the properties that is conserved
-Loss of information when anything enters a black hole: anything thrown into a black
hole will lose all properties
-What happens to the orbit of the Earth is the sun was replaced by a black hole?
-The Earth will continue in the same orbit, nothing happens in terms of
gravity...but we’re gonna die.
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