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Unformatted text preview: observable universe & can never return
once you enter a black hole.
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
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
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
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
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
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
event horizon. Light coming from a
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.
- Fall '13