Download April 22nd

Survey of the Universe
Tom Burbine
[email protected]
Last HW (due this Wed.)
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Go to http://www.galaxyzoo.org
Register
Classify 100 galaxies
Turn in a sheet of paper with evidence you
classified 100 galaxies
Type II Supernova explosion
Neutron Star
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Neutron stars are usually ~10 kilometers across
But more massive than the Sun
Made almost entirely of neutrons
Electrons and protons have fused together
How do you make a neutron star?
• Remnant of a Supernova
How do we know there are neutron stars?
• The identification of Pulsars
• Pulsars give out pulses of radio waves at precise
intervals
Pulsars
• Pulsars were found at the center of supernovae
remnants
• Fastest pulsars are called millisecond pulsars
Pulsars
• Pulsars were interpreted as rotating neutron stars
• Only neutron stars could rotate that fast
• Strong magnetic fields can beam radiation out
Conservation of Angular Momentum (M x V x R)
If Radius shrinks, Rotation Velocity must increase
• X-ray pulsars – generate pulses of X-ray radiation
• Magnetars – neutron stars with extremely intense
magnetic fields that generate intense bursts of Xray and gamma-ray radiation
Black Hole
• A black hole is a region where nothing can
escape, even light.
Black Hole
• After a supernova if all the outer mass of the star
is not blown off
• The mass falls back on the neutron star
• The gravity causes the neutron star to keep
contracting
http://www.astronomynotes.com/evolutn/remnants.gif
Event Horizon
• Event Horizon is the boundary between the inside
and outside of the Black Hole
• Within the Event Horizon, the escape velocity is
greater than the speed of light
• Nothing can escape once it enters the Event
Horizon
How do calculate the
radius of the Event Horizon?
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It is called the Schwarzschild Radius
Radius = 2GM/c2
This is a variation of the escape velocity formula
Escape velocity = square root (2GMplanet/Rplanet)
Black Hole Sizes
• A Black Hole with the mass of the Earth would
have a radius of ~0.009 meters
• A Black Hole with the mass of the Sun would
have a radius of ~3 kilometers
Anything with mass curves space
Can you see a Black Hole?
No
• Black Holes do not emit any light
• So you must see them indirectly
• You need to see the effects of their gravity
Accretion disk – flat disk of gas or other material
held in orbit around a body before it falls onto the body
Evidence
• The white area is
the core of a Galaxy
• Inside the core there
is a brown spiralshaped disk.
• It weighs a hundred
thousand times as
much as our Sun.
http://helios.augustana.edu/~dr/img/ngc4261.jpg
Evidence
• Because it is rotating we can measure its
radii and speed, and hence determine its
mass.
• This object is about as large as our solar
system, but weighs 1,200,000,000 times as
much as our sun.
• Gravity is about one million times as strong
as on the sun.
• Almost certainly this object is a black hole.
Any Questions?