Transcript Lecture 28 - Empyrean Quest Publishers

Remnant:
< 1.3 MO
1.3 MO<M<3.0 MO
> 3.0 MO
End State: Supporting Pressure:
White Dwarf Electron degeneracy
Neutron Star
Neutron
Black Hole
None
Chandrasekar Limit--white dwarfs form
with remnant under 1.3 Msun.
NOTES:
BLACK HOLES
Laplace (1796) is usually given credit.
John Michell, 13 years earlier (1783), discovered that if matter were concentrated
enough, Newton's Laws would give an escape velocity greater than light. Sun would
be dark if squeezed to a ball 3 km in diameter.
Schwarzschild (~1920) did a calculation which showed Einstein's GTR predicted
that a highly concentrated spherical mass would shrink to a point and have an
event horizon around it beyond which nothing could escape (Vescape> c).
The Schwarzschild radius,
R(event horizon) = 3 km x mass (in solar masses).
Oppenheimer (~1940) demonstrated that a stellar remnant above 3 solar masses
could not be held up by neutron pressure and would collapse further
Penrose (~1968) showed the GTR called for an eventual singularity (point mass)
in the case of mass that large.
John Wheeler gave the 'black hole' its name.
Laplace (1796) is usually given credit.
John Michell, 13 years earlier (1783), discovered
that if matter were concentrated enough, Newton's Laws
would give an escape velocity greater than light.
Sun would be dark if squeezed to a ball 3 km in radius.
Laplace--mathematician
"If the semi-diameter of a sphere of the same
density as the Sun were to exceed that of the Sun
in the proportion of 500 to 1, a body falling from an
infinite height towards it would have acquired at its
surface greater velocity than that of light, and
consequently supposing light to be attracted by
the same force in proportion to its vis inertiae
(inertial mass), with other bodies, all light emitted
from such a body would be made to return
towards it by its own proper gravity."
-John Michell on the concept of black holes
Schwarzschild (~1920) published a calculation which showed
Einstein's GTR predicted that a highly concentrated spherical
mass would shrink to a point and have an event horizon around
it beyond which nothing could escape (Vescape> c).
German astrophysicist Karl
Schwarzschild calculated the
first rigorous solution to the field
equations in Albert Einstein's
theory of general relativity while
serving on the Russian front
during World War 1.
The event horizon:
The Schwarzschild radius,
R(event horizon) = 3 km x mass (in solar masses).
Robert Oppenheimer (~1940) demonstrated that
a stellar remnant above 3 solar masses
could not be held up by neutron pressure
and would collapse further into a black hole.
Should we call it ‘The
Oppenheimer Limit’?
Roger Penrose (~1968) showed the GTR called for an
eventual singularity (point mass)
in the case of mass that large.
Get the point?
He was Stephen Hawking’s
PhD advisor
John Wheeler gave the 'black hole' its name in the late ’60s.
He played a key role in the development of the atom bomb.
We distinguish between
1. Stellar mass black holes < 100 Msun
and
2. Supermassive black holes—bigger than
that.
Confirming a stellar mass black hole requires:
1. A strong x-ray source
2. A inferred mass of over 3 Msun
Stellar mass black holes: only seen when material is
falling in producing an accretion disk. This happens when,
for example, a star (originally bigger than about
5 solar masses) has a companion and draws in material
from the other star. X-rays are produced as the material
heats as it fall in.
Cygnus X-1: first stellar mass black hole discovered by
the Uhuru (means 'freedom' in Swahili) satellite in 1971
Stephen Hawking (~1968) said that black holes radiate!
Black holes are not black!? No proof yet…
With a temperature—it radiates as a black body
And loses the mass equivalent to the energy.
BHs are simple:
they can have only mass, charge, & spin.
This is called The 'no hair' theorem: they can have no
fields along surface, like magnetic fields. Hair on a head
must have a part or swirl, and black holes are too
simple for that.
White hole: time reverse of a black hole.
One way membrane 'out', BH is a one way membrane 'in'.
Novikov (1964) suggested Big Bang might have white holes
(he called them retarded cores--little Bang an example?)
These go off like delayed explosions in fireworks.
Penrose: energy may be extracted
from ergosphere (rotating spacetime) around rotating BH.
Einstein-Rosen Bridge (1930's)--wormhole.
Theory that a closed (massive) universe might have
BH-->WH tunnels connected different places and times.
Wormhole connects black to white hole.
Fall into a BH might not be fatal:
1. If BH is large enough, event horizon is large and provides
little tidal force.
2. If BH is rotating fast enough you could enter wormhole.
3. Wormholes only exist in a massive universe.
4. You must have antigravity material pasted on your spacecraft.
(Kip Thorne)
5. You must be prepared to travel in time or to another
universe without returning.
A rotating black hole’s singularity is like an opening in space-time.
Baby Universes: a closed universe with
1028 Joules of energy in a localized region
can produce a baby universe. Its time is 'imaginary'.
Star Clusters:
Open Clusters: less than 1,000 Population I stars
–young, composed of recycled material with heavy elements.
Not gravitationally bound.
Ex: The Pleiades
and The Hyades.
Globular Clusters: thousands to millions of stars
in a spherical bound group.
Population II stars–old, made of primordial H and He.
From 12-14 billion years old. Stars have small mass.
Globular cluster in Hercules, M13
Cluster age: Determined by where the cluster
is turning off the main sequence–the turnoff point.