Pulsars and Neutron Stars

Just learned in tutorial #5 & Monday's class: "Quantum Pressure" in white dwarfs & the Chandrasekar limit for white dwarfs (~1.5 solar mass). 

What happens to cores of stars that are MORE MASSIVE THAN THAT? 

We learned before spring break: Super nova. Protons --> Neutrons + Neutrinos + anti-electrons. So core becomes mostly neutrons. 

Pauli exclusion principle for neutrons: Neutrons don't "want" to be too close to each other. 

Radius of neutron stars of 1.5 solar mass - roughly the distance from Lewisburg to I-80. (1000 times smaller than WD's).

Quantum pressure holds against gravity for cores of up to ~ 2 solar mass.

That's the Chandrasekar limit for neutron stars.

What's beyond that? Probably black holes (next week).

Are there any neutron stars? 
(Lots of WD were observed from orbital considerations. No neutron stars were discovered that way.)

Pulsar discovery: 
1967, Jocelynn Bell, Cambridge, Grad. student, observed a RADIO SIGNAL, regular 1.3 sec. interval,
const. direction in the sky. Different hight of each pulse.
What can it be?
Show an AM radio signal. Looks similar! 
Is it ET?

Dubbed LGM. Many more found, unrelated. Now associated with Neutron stars. Why?

1. Incredibly accurate intervals - probably rotations. White dwarf (earth size) spins around once in a second - pieces fly off because of inertia. Not white dwarfs.

2. Neutron stars should form in supernovae. The crab nebula is a supernova observed in 1054 AD. We now see a pulsar at the center of this explosions.This pulsar emits regular light too!

How do pulsars work?

The lighthouse effect: Use two fleshlight, spin.