Download Document

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project

Document related concepts

Ursa Major wikipedia , lookup

International Ultraviolet Explorer wikipedia , lookup

Observational astronomy wikipedia , lookup

CoRoT wikipedia , lookup

Hipparcos wikipedia , lookup

Lyra wikipedia , lookup

Aquarius (constellation) wikipedia , lookup

Dyson sphere wikipedia , lookup

Gamma-ray burst wikipedia , lookup

Corvus (constellation) wikipedia , lookup

Ursa Minor wikipedia , lookup

Astrophysical X-ray source wikipedia , lookup

Cygnus (constellation) wikipedia , lookup

Astronomical spectroscopy wikipedia , lookup

Kerr metric wikipedia , lookup

Black hole wikipedia , lookup

Stellar kinematics wikipedia , lookup

Timeline of astronomy wikipedia , lookup

Hawking radiation wikipedia , lookup

Star formation wikipedia , lookup

P-nuclei wikipedia , lookup

IK Pegasi wikipedia , lookup

R136a1 wikipedia , lookup

Stellar evolution wikipedia , lookup

Transcript
Black Holes and
Neutron Stars
Dead Stars
Copyright – A. Hobart
13
Goals
•
•
•
•
•
What are neutron stars and pulsars?
What are black holes?
What happens near a black hole?
How do we see black holes?
What happens when neutron stars and black holes
are in binaries?
13
Supernova Remnant
• Recall: In the death of a high-mass star, the
core is converted to neutrons and collapses
catastrophically.
• The collapse and rebound creates a supernova.
• But what happens to the neutrons already at the
very center of the core?
• The central core is left behind as a small,
dense, sphere of neutrons  a neutron star.
13
Neutron Stars
• A giant ball of neutrons.
• Mass : at least 1.4 x mass of
the Sun.
• Diameter: 20 km!
• Density: 1018 kg/m3
– A thimble weighs as much as a
mountain
• Day: 1 – 0.001 seconds!
• Magnetic fields as strong as the Sun, but in the
space of a city.
13
Pulsars
• Interstellar
Lighthouses.
• See periodic bursts of
radiation.
• Perfect clocks.
• While every pulsar is
a neutron star, the
opposite isn’t true.
13
Crab Nebula Pulsar
13
Pulsar Motion
• Pulsars born in the
center of supernovae
explosions.
• Non-symmetric
explosions lead to huge
“kick.”
• Large velocity pulsars.
• v = 800 – 1000 km/s!
Guitar Nebula – copyright J.M. Cordes
13
Neutron Degeneracy
• Neutron stars are held up by neutron degeneracy
pressure.
– Recall electron degeneracy pressure for white dwarfs.
– For white dwarfs, maximum mass of 1.4 Msun
• For neutron stars, maximum mass ~3Msun
• What happens if a high-mass star is SO big that its
central core is bigger than this?
• What happens when gravity is stronger than even
neutron degeneracy pressure?
13
Quark Stars
•
•
•
•
Neutrons (and protons) are made of quarks.
Gravity could crush neutrons into free quarks.
Called strange matter (a type of quark).
Astronomers think they may have seen a quark star.
13
13
Density
• Density = mass per volume
• From Red Giant cores to White Dwarfs to Neutron
Stars, density has been increasing.
• As density increases, the force of gravity on the
surface increases.
• The greater the force, the higher the escape
velocity:
– How fast you need to go in order to escape the surface.
• How dense can something get?
• How strong can the force of gravity be?
• What if the escape velocity is faster than light?
13
Black Hole
• When a high-mass star’s core
is greater than ~3 x Msun,
then, when it collapses, the
density becomes so high not
even light can escape!
• The star collapses to form a
Black Hole.
13
13
The Event Horizon
• Event Horizon = black hole “surface”
Object
Earth
Jupiter
Sun
Mass
Radius
cm 
 1M

R EH  3km  
M

300 x Earth
3 mSun 
6 x 1024 kg
300,000 x
Earth
3 km
13
Curved Space
• Einstein related gravity
forces to space curvature.
• Black holes deeply warp
space.
• Everything falls in,
nothing can climb out.
• How does this work?
13
General Relativity
2 Main Postulates:
1. The speed of light is always c.
Thou shalt not add your speed to the speed of light!
13
General Relativity
2. Accelerating reference
frames are
indistinguishable from
a gravitational force.
The Star Tours ride at Disneyland is awesome!
13
Gravity Bends Light
13
Gravitational Lenses
13
distance
time 
c
13
Gravity makes time slow
F
F
S
S
13
Black Holes
• Light is bent by the
gravity of a black
hole.
• The event horizon is
the boundary inside
which light is bent
into the black hole.
• Approaching the
event horizon time
slows down relative
to distant observers.
• Time stops at the event horizon.
13
Orbiting a Black Hole
13
Orbiting a Quark Star
13
Seeing Holes
• Can’t see black hole
itself, but can see matter
falling into a hole.
• Gravitational forces
stretch and rip matter:
heats up.
• Very hot objects emit in
X-rays (interior of Sun)
• Cygnus X-1.
http://www.owlnet.rice.edu/~spac250/steve/ident.html
13
What would be
a good source
of material for a
hungry black
hole?
13
Binaries
• Gravitational tides pull matter off big low density
objects towards small high density objects.
Cygnus X-1
13
Nova and Supernova
• Similar situation with white dwarf-gas giant
pairs.
• White dwarf accretes matter from giant.
• If enough material falls fast enough it will
ignite and fuse on the w.d. surface:
• Nova!
• If enough mass falls onto white dwarf that
Mwd > 1.4 x Msun:
• White dwarf collapses to a neutron star.
• Supernova! (now there are two types)
13
Binary Pulsars
• Neutron stars
can also be in
binaries.
• General
Relativity
says they will
eventually
spiral into
one another.
• Result: g-ray
bursts:
• Most violent explosions in the universe.
13