Transcript Black Holes

Black Holes
This one’s green.
I like green.
What happens after a SN?
• Material remaining after a supernova is 3
times more massive than the sun or more
• Pressure is strong enough to collapse the
star beyond the neutron-degeneracy
• Star remnant collapses and vanishes.
Characteristics of a black hole
• Retains only:
– Mass (therefore the gravity)
– Its angular momentum
*** All other characteristics no longer exist!
• concepts like protons, electrons, neutrons,
molecules, compounds etc. no longer apply.
??? I have a headache.
• Escape Speed- speed needed for an object
to escape the gravity of another.
– Bigger mass= bigger grav, then bigger ES
– Smaller radius= bigger grav, then bigger ES
• The escape speed for a black hole is greater
than the speed of light.
• Nothing can exceed the speed of light
(except Bause when he runs towards the
lunch line) SO nothing can escape a BH
• General relativity (Einstein) predicts that in
creating a black hole, matter compresses to
infinite density.
• ALL known laws of physics are invalid.
• Recall Relativity explains the behavior of the
really massive, quantum mechanics explains
the behavior of the really small (subatomic
stuff). A black hole is both REALLY massive
and REALLY small.
Schwarzschild radius
• The radius that matter (any matter, does it
matter?) must be compressed for it to have
an escape speed equal to the speed of light.
• All objects have a SR
– Earth = 1 cm or a grape
– Jupiter = 3 cm or 3 grapes (I’m not creative)
– Sun = 3 km
Event Horizon
• The location around a black hole where the
escape speed EQUALS the speed of light.
• Everything in the EH is lost forever. No
information can be gathered from within.
• Outside of the EH, everything appears to
“slow”… called gravitational redshift
Gravitational Redshift
• Speed of light is CONSTANT through
constant medium.
• In order for light to escape gravity it must
work (use energy). Greater the grav, more
• SO, light will lose energy and shift towards
red portion of electromagnetic spectrum
(longer wavelength)
Gravitational Lens
• Gravity can bend light rays.
• This can allow us to see objects normally
too far for us to see.
• Bause diagram.
All galaxies… ranging from 3 bill. ly to 9
bill ly.
Infalling Matter
• Matter closest to the BH
will be pulled greater,
stretching the matter.
• Eventually pulled apart,
atom by atom.
Does a black hole last forever?
• Nope.
• They can evaporate through Hawking
Radiation (more in your lab).
• Process takes a LONG time. A 5 solar mass
black hole would take 1062 years to
evaporate. So, black holes that have formed,
still exist today.
Supermassive Black Holes
• All elliptical and spiral galaxies seem to
have one in the center. Irregular galaxies
(aka dwarf galaxies) do not.
• A black hole with the mass of millions to
billions of Suns!