240,000 mi

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

proton

electron

neutron

neutrino

neutron

neutrino

Fusion of hydrogen to helium

4 protons

4 electrons

Fusion of hydrogen to helium

4 protons

4 electrons

Fusion of hydrogen to helium

4 protons

4 electrons

Fusion of hydrogen to helium

4 protons

4 electrons

Fusion of hydrogen to helium

4 protons

4 electrons

Fusion of hydrogen to helium

4 protons

4 electrons

Fusion of hydrogen to helium

4 protons

4 electrons

Fusion of hydrogen to helium

4 protons

4 electrons

Fusion of hydrogen to helium

2 protons

2 neutrons

4 electrons

Fusion of hydrogen to helium

2 protons

2 neutrons

4 electrons

Fusion of hydrogen to helium

2 protons

2 neutrons

4 electrons

Fusion of hydrogen to helium

2 protons

2 neutrons

4 electrons

Fusion of hydrogen to helium

2 protons

2 neutrons

4 electrons

Fusion of hydrogen to helium

2 protons

2 neutrons

4 electrons

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 particlesdepends 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.

neutronneutrino

.

� 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 limitis 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 1 second, the electric field has changed only within a distance 1 light-second from the charge.

After one second

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: 7 mi/second

from Sun: 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.”

Star has collapsed to a speck

No Exit:Everything within a few miles of the speck is pulled by gravity into it.

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.

Inside the event horizon, the cone is tipped so far that light rays emitted outward cannot get out.

TIM

E

DISTANCE FROM CENTER OF STAR

� 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.

BLACK HOLES

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

Andrea Ghez

“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 of dark matter interior to a radius of about 6 light hours ”

M e

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 , WALivingston, 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