Theory even light no mass is affected by gravity li

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Unformatted text preview: observable universe & can never return once you enter a black hole. EE8086 EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 29 Event Event Horizon extremely distorted near black hole path of light through space is bent of light through space is bent Matter/light cannot climb out once within a bo boundary known as the event horizon. kno as the event horizon tidal forces are tremendous near event horizon object would be “spaghettified” would be spaghettified EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 30 Schwarzchild radius -- Event Horizon Boundary between inside of black between inside of black hole & the universe. boundary at which escape velocity at which escape velocity equals speed of light spherical (escape velocity depends (escape velocity depends on distance from centre) point of no return for objects entering black hole Defined by a sphere of radius Rs around black hole. also defines the size of black hole Schwarzchild radius, Rs, is given by Rs = 3M (Rs in km, M in Msun) 3M black hole with the mass of the Sun, Rs = 3 km 10 black hole with 10Msun , Rs = 30 km 30 EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 31 EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 32 Properties Properties of a Black Hole Properties of a Black Hole A collapsing stellar core becomes a black hole when it shrinks to a size smaller than the Schwarzschild radius Stellar core disappears within its own event horizon own event horizon. Black hole at a distance exerts gravity according to hole at distance gra according to Newton’s Law. hidden from view contains all the mass & exerts full all the mass exerts full gravity of the mass planets’ orbits l the same if a 1Msun black hole replace our Sun th if 1M black hole does not suck in everything around it! All matter crushed to an infinitely matter crushed to an infinitely tiny & dense point singularity. Gravity increases from Newton’s predictions only at 3Rs 3R distance from black hole. very EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 33 Light near a Black Hole EE8086 – Astronomy: Stars, Galaxies & Cosmology Page 34 Close Encounter with a Black Hole Light is trapped due to effects of general relativity: spacetime is severely warped within event horizon. Time slows down near a black hole. Consider a probe approaching the approaching the event horizon. Light coming from a coming from region close to a black hole is bent (if not hole is bent (if not radial) & red-shifted. probe to clock ticks more slowly & light from probe is red-shifted the mother ship, probe takes forever to reach event horizon probe eventually disappear as light is red-shifted beyond radio & time on clock stops Light can orbit a black hole at a radius of 1.5Rs. EE8086 – Astronomy: Stars, Galaxies & Cosmology difficult to fall into by accident in the universe! To the probe, light from the mother ship is blue-shifted. Page 35 EE8086 – Astronomy: Stars, Galaxies & Cosm...
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This document was uploaded on 11/25/2013.

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