AST201 week 3

black hole origin

black - no light can escape

hole - captures idea that a black hole is like a hole in the observable universe

event horizon

boundary between inside of black hole and the universe outside

spacetime

space and time are not distinct, but bound up together as a four-diamensional

size of black hole

measures a radius for the circle if the black hole was flat

Schwarschild radius

the radius of the event horizon

collapsing stellar core

becomes a black hole at the moment it shrinks to a size smaller than its Schwarschild radius

black hole properties

mass, electric charge, angular momentum

singularity

the point of the black hole which ultimately will crush everything into an infinitely tiny and dense point

supermassive black hole

much weaker title force and hence its non lethal

V orbital

high enough velocity that its able to orbit

V circular

special velocity that gives you a circular velocity

minimum speed to orbit

V = V orbital

elliptical orbits

V orbital < V < V circular

V circular < V < V escape

circular orbit

V = V circular

escape “orbit”

V ≥ V escape

escape speed from earth

40,000 km/h (11 km/s)

squeeze the earth

the escape speed would increase

escape speed of c or higher

this object is a black hole

escape speed depends on

linearly on body’s mass

inversely (squared) with distance from the body

attempt to orbit above the escape speed

objects will fly off into space and never return (unless acted on by another force)

attempt to orbit below the escape speed

objects can end up on elliptical orbits, circular orbits, or crash into the surface

black holes are a

* bottomless pit in spacetime
* simplest object in the universe (dont omit light)

event horizon is like

a border between countries

there is no physical object at the event horizon of a black hole

schwarzchild radius equation

R Schwarzchild = 2GM / c^2

black holes are not

cosmic vacuum cleaners

what escapes a black hole’s event horizon

NOTHING

what evidence do we have that black holes actually exist?

* look for objects that appear to be orbiting an invisible object
* look for a small dark thing that is producing a lot of radiation

stellar mass black holes form when

very large stars die in huge explosions called “supernovae”

“supermassive black hole”

* much more massive kind of black hole, only found at the centres of galaxies
* the one at the centre of our galaxy is 4 million times the mass of the sun

primordial black holes

a black hole the size of an atom or smaller, would have formed just after the Big Bang, no one has ever seen one