Transcript Lecture 8

240,000 mi
It takes light just over
one second to travel from
the moon to the earth
The simplest atom is hydrogen.
Its nucleus is a single proton.
And one distant electron moves around it
• An atom is nearly entirely empty space.
A scale model has
the electron at the outside of Miller Park,
the nucleus a marble at its center
.
electron
proton
neutrino
neutron
neutrino
neutron
Fusion of hydrogen to helium
4 electrons
4 protons
Fusion of hydrogen to helium
4 electrons
4 protons
Fusion of hydrogen to helium
4 electrons
4 protons
Fusion of hydrogen to helium
4 electrons
4 protons
Fusion of hydrogen to helium
4 electrons
4 protons
Fusion of hydrogen to helium
4 electrons
4 protons
Fusion of hydrogen to helium
4 electrons
4 protons
Fusion of hydrogen to helium
4 electrons
4 protons
Fusion of hydrogen to helium
4 electrons
2 neutrons
2 protons
Fusion of hydrogen to helium
4 electrons
2 neutrons
2 protons
Fusion of hydrogen to helium
4 electrons
2 neutrons
2 protons
Fusion of hydrogen to helium
4 electrons
2 neutrons
2 protons
Fusion of hydrogen to helium
4 electrons
2 neutrons
2 protons
Fusion of hydrogen to helium
4 electrons
2 neutrons
2 protons
Fusion of hydrogen to helium
(Helium nucleus)
Fusion of hydrogen to helium
Fusion of hydrogen to helium
Fusion of hydrogen to helium
Fusion of hydrogen to helium
Fusion of hydrogen to helium
Fusion of hydrogen to helium
Chandrasekhar at
about the time he
found that an
upper limit on
the mass of white
dwarfs was set
by the upper
limit c on the
speed at which
electrons can
travel.
Matter is supported against gravity by its pressure.
Recall that the pressure of a collection of particles
depends on their speed.
What is left behind?
Lev Landau
Neutron stars
Immediately after the neutron was discovered in
1930, Landau suggested the possibility that the
pressure in the cores of stars might push the
electrons onto their protons to make a core entirely
of neutrons.
proton
electron
Neutron stars
Immediately after the neutron was discovered in
1930, Landau suggested the possibility that the
pressure in the cores of stars might push the
electrons onto their protons to make a core entirely
of neutrons.
proton
electron
Neutron stars
Immediately after the neutron was discovered in
1930, Landau suggested the possibility that the
pressure in the cores of stars might push the
electrons onto their protons to make a core entirely
of neutrons.
neutron
neutrino
•If all of the electrons of the Sun were pulled onto
their nuclei to form neutrons, the Sun would shrink
by nearly 100,000 times, from 700,000 km to about
10 km
.
•If all of the electrons of the Sun were pulled onto
their nuclei to form neutrons, the Sun would shrink
by nearly 100,000 times, from 700,000 km to about
10 km
.
•If all of the electrons of the Sun were pulled onto
their nuclei to form neutrons, the Sun would shrink
by nearly 100,000 times, from 700,000 km to about
10 km
.
•If all of the electrons of the Sun were pulled onto
their nuclei to form neutrons, the Sun would shrink
by nearly 100,000 times, from 700,000 km to about
10 km
.
•If all of the electrons of the Sun were pulled onto
their nuclei to form neutrons, the Sun would shrink
by nearly 100,000 times, from 700,000 km to about
10 km
.
“With all due humility, we propose . . .”
Walter Baade
Fritz Zwicky
that supernovae represent the transition from
ordinary stars to neutron stars, which represent
their final stage.”
Walter Baade
Fritz Zwicky
A neutron star is about 1/1000 that size
Neutron Stars
•Radius about 10 km
•Density over 1 billion tons per teaspoon
•Mass about 1.5 Msun
•A neutron star is a giant atomic nucleus, made
almost entirely of neutrons, held together by gravity
•Flashes of light seen as pole passes our line of sight
(like the light from a searchlight beam sweeping
past you)
•Neutron stars seen in this way are called pulsars
Jocelyn Bell, at about the
time she discovered the
first neutron stars.
To get full screen, need this already
open.
Neutron star
spinning about 5
times /second
Neutron star
spinning 642
times /second
300,000 km/s
It’s not just a good idea.
It’s the law.
The speed of light, 300,000 km/s (or 186,000 mph), is
really the speed of information.
It is the maximum speed at which anything can travel,
matter or energy or simply a wave of curvature of
space itself.
No change in one place can alter what happens
somewhere else more quickly than this speed limit
allows.
Because of the limit on the speed of information,
a charge moving up and down creates a wave in the
electric field that moves outward at the speed of
information, 300,000 km/s.
Because of the limit on the speed of information,
a charge moving up and down creates a wave in the
electric field that moves outward at the speed of
information, 300,000 km/s.
Because of the limit on the speed of information,
a charge moving up and down creates a wave in the
electric field that moves outward at the speed of
information, 300,000 km/s.
Because of the limit on the speed of information,
a charge moving up and down creates a wave in the
electric field that moves outward at the speed of
information, 300,000 km/s.
Because of the limit on the speed of information,
a charge moving up and down creates a wave in the
electric field that moves outward at the speed of
information, 300,000 km/s.
This speed limit
is the reason light exists
When a charge moves, the information that it is at a
new position travels outward at 300,000 km/s.
electric field
After one second
After 1 second, the electric field has changed only
within a distance 1 light-second from the charge.
After 2 seconds, the electric field has changed
within a distance 2 light-seconds from the charge.
After 3 seconds, the electric field has changed
within a distance 3 light-seconds from the charge.
Escape velocity
from Earth:
from
Sun:
7 mi/second
500 mi/second
from neutron star: 60,000 mi/second
John Michell 1784
First published suggestion
of existence of black stars
“supposing light to be
attracted by the same
force in proportion to its
vis inertiae, all light
emitted from such a body
would be made to return
towards it, by its own
proper gravity”
Pierre Simon Laplace
1799
“Proof of the
theorem, that the
attractive force of
a heavenly body
could be so large,
that light could
not flow out of it.”
No Exit:
Everything within a few miles of the speck
is pulled by gravity into it.
Star has collapsed to
a speck
This is a black hole –
A region of empty space from which
nothing can escape
Matter falling on a black hole from its
companion in a binary system
Light from the binary system containing
Cygnus X-1, a 7 Msun black hole
Diagram of matter falling onto a giant black
hole
Hubble space telescope photos looking very
much like the giant black hole that we expected
to see
Real black holes (not the Newtonian limit)
Prerequisite: A light cone –
The history of a flash of light
ALLOWED FOR
MASSIVE BODY
ALLOWED FOR LIGHT
NOT ALLOWED
Light cones tip inward as you approach a black hole.
TIME
Inside the event horizon,
the cone is tipped so far that
light rays emitted outward
cannot get out.
DISTANCE FROM CENTER OF STAR
BLACK HOLES
•A black hole is a region of space from which
nothing can escape to the outside
•The boundary of a black holes is called the event
horizon because no events occurring beyond the
horizon can be seen from the outside.
•After a star has collapsed to within a black hole, it
continues to collapse to the size of a speck.
Closeup
Ghez, A. M., Klein, B. L., Morris, M., and Becklin, E. E.
ApJ, 509, 678 (1998)
High Proper Motions in the Vicinity of Sgr A*:
Unambiguous Evidence for a Massive Central Black Hole
“These observations reveal stars
moving at apparent speed as high as
12,000 km/sec (~4% the speed of
light!) whose orbits imply the
presence of 4 million M e of dark
matter interior to a radius of about 6
light hours ”
Andrea Ghez
Strong evidence
for giant black
holes in the
centers of nearly
all galaxies
The gravity waves from a pair of
neutron stars that spiral together
The dawn of gravitational-wave astronomy
LIGO, TAMA, GEO, VIRGO, . . .
LIGO’s two detectors:
4km interferometers
at Hanford , WA
Livingston, LA
Postdocs, faculty,
research scientists at
UWM working on
detection of
gravitational waves
Students involved in research on gravitational waves
and relativistic astrophysics
einstein@home: Download a screensaver to let
LIGO add your computer to >100,000 others
searching current data for gravitational waves
from bumps on rotating neutron stars.
Google “einstein at home”
or go to
einstein.phys.uwm.edu