Neutron Stars

Predicted in 1930’s, but thought unobservable.

Compress matter hard enough that protons absorb electrons to become neutrons.

Solid ball of neutrons – a giant atomic nucleus bound by gravity. Supported by degeneracy.

nucleus: =1.2*10^14 gm cm^-3

R=1.5*10^-13 cm

m=1.7*10-24 gm

mass: 1.4 Msun=2.8*10^33 gm

Therefore, volume: 2.3*10^19 cm^3, and radius=1.8*10^6cm = 18 km

Formed in supernova and elsewhere ?

Lots of these just sitting around in the galaxy.

Look like dark rocks

Mass must be less than 2.1 Msun



Pressure is immense



Discovery in 1968

Unobservable, as they have no atmosphere

In hindsight, they should have realized this was false, neutron stars have large B field.

Therefore 10^10 Bsun ~10^12 gauss

Will be rotating rapidly

Electron at surface

if 10 rotations per second

v=10 * 2pR cm s^-1 = 1.2*10^8 cm s^-1=0.004c

E + 0.0004 * 10^12 = 0

E= 4* 10^9 e=4.8 * 10^-12

F=eE=1 dyne

Fe >> Fg therefore rips particles from surface

This magnetosphere emits radio radiation from charged particles getting thrown around

We don’t see all pulsars because we miss their beams

Crab Pulsar Shows

Slows down because radiation supplies energy

Glitches speed up suddenly – "star quakes"

Neutron stars – X-ray mass transfer


Binary Pulsars

companion collapsed also

Laboratory for general relativity

gravitational radiation will cause system to spiral in

Recent studies – first proof of gravitiational waves.


Mass Tansfer Binaries

What happens when stars get close together and one is a collapsed object? A lot!

From Keplers law:

P ~ R3/2

When stars get close enough to touch an orbit takes 3 hours to a few days…

Formation of an accretion disk

Two things run the mass transfer: giant radius and mass loss, spiral together.