•Remnant of a Type II supernova explosion

• Iron core collapses until neutrons are squeezed tightly together

•During the explosion core remains intact, outer layers explode outward

•10 - 20 km across

•Mass > sun’s mass

•Density: 1 tsp would weigh 100 million tons

•Solid surface• Immense gravity•A 70 kg person on Earth

would weigh 100 billion kg•However you would be

crushed by the gravity

•First discovered in 1967•A pulsating radio source;

many discovered since•Explained by a lighthouse

model•The pulses are usually radio

waves, but may include other EM radiations

Not all pulsars can be detected:

• Improper orientation

•So old that the rate of rotation can not be detected (they slowed down!)

•Occurs when a star and a neutron star orbit each other

•Matter from the giant is drawn off the star and spirals toward the neutron star

•Two types: X-ray bursters and gamma ray bursters

• If the remaining core of a supernova explosion is > 3 solar masses, even neutrons can not stop the collapse

•All the material collapses to a point called singularitysingularity

•Stellar black holes range from 3 - 20 solar masses

•Gravity near a black hole is so large that even light can not escape

•All objects (including Earth) have an escape speed

•The greater the mass, (and the smaller the radius) the greater the escape speed

•The distance from singularity at which the escape speed = light speed is called the Schwarzchild Radius (RSchwarzchild Radius (Rss))

•An imaginary sphere at a distance equal to Rs is called the event horizonevent horizon

•Rs is proportional to mass

•Rs for some common objects:

•Earth = 1 cm• Jupiter = 3 m•Sun = 3 km

What happens to someone falling into a black hole?

•Tidal forces would stretch you out and squeeze you at the same time

•Light emitted red-shifts•Time dilates

•Located at the centers of galaxies and other large objects (globular clusters, quasars)

•Different formation process•Many times more massive!

May be millions of solar masses