Neutron Stars & Black Holes
(Chapter 11)
APOD
Student Learning Objective
Indentify
properties of
Neutron Stars
&
Black Holes
NASA
What is a neutron star?
A Neutron Star is a collapsed core remnant.
Mass Limit: < 3 Msun
Radii: 10-30 km
High Mass Star Core
Neutron Core
SN explosions leave
core remnants that
collapse more than a
White Dwarf
 Electrons and protons
combine into neutrons
 Degenerate neutron
pressure stops the
collapse
Neutron Core Remnant
Neutron Star RCW 103
2,000 year-old-remnant
10,000 light years
from Earth
Neutron star near center
rotates once every 6.7 hours
Image Credit: Chandra
Neutron Stars
• Hot
• Spin Rapidly
• Super High Density
• Strong Magnetic Field
A neutron star the size of a sugar cube
would weigh 100 million tons on Earth!
Practice
1) What causes the neutron star to be very hot?
2) Why does a neutron star spin rapidly?
3) What makes the magnetic field of a neutron
star particularly strong?
4) Is a neutron star a star?
 Neutron stars in binary systems emit x-rays.
High Energy Object = High Energy Photons (x-rays)
How are neutron stars found?
Pulses of x-rays are seen if x-ray beams sweep across
our path. (Pulsars)
X-rays appear to pulse on and off.
Periods = 0.00156 – 8.51 seconds
Crab Pulsar “On”
Crab Pulsar “Off”
Practice
1) Why is not possible for
a pulsar to be a
pulsating star?
2) What conditions are
necessary for a neutron
star to be detected?
3) Can a Neutron star
become a Nova?
4) What would be
surrounding and
associated with, a
young neutron star?
Supernova Remnant & Neutron Star
APOD
The Pulsar
Powered Crab
APOD
What is a black hole?
A Black Hole is a collapsed core remnant.
 A SN explosion leaves a core remnant that collapses
more than a White Dwarf or Neutron star.
 There is too much mass for anything to stop the
collapse.
Highest Mass Star Core
Curvature of Space-time
Concentrated Mass  Extreme Curvature
Practice
If our Sun was replaced by a black hole of equal mass,
what would happen to the orbits of the planets? Would
the planets be sucked into the black hole? Explain.
Black Holes
• Gravity wins against all types of pressure
• Core collapses to a singularity
• Gravity is concentrated
• Light is trapped
Black holes can be millions of times the
mass of the Sun.
Evidence suggests galaxy NGC 5408 has a black
hole with about 2,000 solar masses NASA
According to special relativity, nothing can
travel faster than light.
If light cannot escape a black hole, then
nothing can!
Vesc (Earth) = 11 km/s
Vesc (Sun) = 600 km/s
Vesc (Black Hole) = 3 x 108 m/s
Approaching a Black Hole
 Traveler perceives "normal" time and length.
Observer perceives time slowing down and length
contracting.
Time Dilation – time slows down
Event Horizon
Matter that crosses the event horizon cannot escape.
The Scharzchild Radius (boundary) is determined
by mass.
Our Sun
Current Radius
696,000 km
Scharzschild Radius
3 km
X-Rays Indicate Star Ripped Up by Black Hole
APOD
Practice
1) Which type of Supernova may produce a
black hole?
2) Why doesn’t electron degenerate pressure or
neutron pressure stop the core remnant from
collapsing to a singularity?
3) Should we expect black holes to be rotating?
More Practice
4) What exactly is a black hole? Is it a hole?
5) Would it be infinitely dark or infinitely bright if you
were able to cross the event horizon? Why?
Black Holes may emit x-rays and affect stellar
motions.
 Stellar motions are erratic
 Accretion disk emits x-rays
Turbulence  Gas Heats  Emits x-rays
Cygnus X-1
1st Black Hole observed
7 Msun
1/4 size of Earth
Centaurus A (an active black hole)
Animation of Stellar Motions
Black hole evidence in the center of our galaxy
The rotation of a black hole drags space-time around
with it. (ergo-sphere)
Matter ripped apart
Ejected matter takes black hole energy
Rotation of Space Time
What happens when black holes collide?
Black holes
merge.
Gravity waves
travel across
space.
Are Wormholes Real?
Wormholes
In 1935, Albert Einstein and Nathan Rosen realized that general
relativity allows the existence of “bridges,” originally called
Einstein-Rosen bridges.
A wormhole is a theoretical connection between
two extreme curvatures of space.
Calculations indicate a wormhole could be
maintained using “Negative Energy”.