Ch 12-01 Neutron Stars and Pulsars
- Proposal of neutron stars
Chadwick (1932)
Landau (1932)
Baade & Zwicky (1934)
Oppenheimer & Volkoff (1939)
Structure of neutron stars
M ~ M⊙, R ~ 106cm,
Tsurface ~ 106K, ρaverage ~ 1015g/cm3
Pressure of neutron degeneracy against gravity
But, where are neutron stars? Do they really exist?
- Discovery of radio pulsars
The periods of pulsars are very stable and many are measured with 16-digit accuracy.
Pulsars' periods increase very slowly at a rate of about 10-15 sec/sec or so.
Origins of pulsation: orbital motion, oscillation, rotation ?
- Radio pulsars are neutron stars!
[Pulsars are generally believed to be fast rotating, strongly magnetized
neutron stars. The magnetic field is typically about 1012 G at the stellar surface.
This magnetic field is inferred from interpreting pulsar's sipn-down as magnetic dipole braking.
It also provides a platform to explain pulsar's nonthermal electromagnetic emission.
Its origin, however, is not yet clear.]
- High-energy pulsars:
[Some pulsars also emit in higher energy bands. After the launch of
Fermi Space telescope in 2008,
the number of such pulsars increased from 7 to more than 200.
The first figure is taken from D. J. Thompson, 2004, in Cosmic Gamma-Ray Sources, page 149,
and the second from P. A. Caraveo, 2014, Annual Review of Astronomy and Astrophysics, 52, 211.]
- Pulsar glitches:
[Pulsars sometimes sipn up suddenly, that is, their period decreases suddenly at a level of
10-9 ~ 10-6, and then resume their usual spin-down.
This is called pulsar glitches.]
- Binary pulsars:
* (Re-cycled) millisecond pulsars
[Most of millisecond pulsars are in binary systems. Their short spin period is proposed to come
from the spin-up action of material accreted from their companions. This scenario is supported by
the discovery of 'burst oscillation' in some LMXBs
(Strohmayer et al. 1996, Astrophysical Journal 469, L9).
Note that this figure is obsolete now; check an updated figure in the above.]
* Evidence for gravitational waves (PSR B1913+16)
[This Hulse-Taylor pulsar is in a binary system, whose orbital period decreases in a way consistent
with predictions of General Relativity, giving support to the idea of gravitational waves. This figure
is taken from J. M. Weisberg & J. H. Taylor, 2005, ASP Conference Series, 328, 25.]