Observed Neutron-Star Properties

Abstract

The Galaxy contains at least 10^{9 ± 1} neutron stars which are thought to be born in supernova explosions of massive stars, and which we observe as radio pulsars if isolated and as X-ray binaries if attached to a close companion. Their beams are likely to have fan shape. Young radio pulsars are also observed as γ-ray pulsars, perhaps even as ultrahard γ-ray pulsars, and occasionally as infrared, optical, and X-ray pulsars. Pulsars die after 10^{6.7 ± 0.3} years, probably due to flux alignment (with the spin axis).

Binary neutron stars are probably spun down by the wind of their companion — generating cosmic rays — until an accretion disk forms which confines the corotating magnetosphere and reverses the spindown, though hardly to the msec regime. One then sees an X-ray source which may flicker (down to several msec intervals, perhaps because of inverse-Compton losses of relativistic pair plasma) and pulse if a significant amount of matter accretes onto the polar caps. Non-pulsing X-ray sources can emit X-ray bursts, explained by nuclear-chemical explosions (type 1) or spasmodic accretion (type 2), and show enhanced variability in a preferred frequency interval (=QPO). Even γ-ray bursts may be emitted by (old) neutron stars.

The jet sources Sco X-l, SS 433, and Cyg X-3 and the black-hole candidates — headed by Cyg X-1 and A 0620–00 — may likewise be binary neutron stars.

All observed neutron stars appear to be strongly magnetized, with dipole moments BR³ := µ = 10^{3 0 . 8 ± 0.5} G cm³ except for the (eight) msec pulsars whose moments may be 10^{3 ± 1} times weaker. Their surface temperatures are ≤ l0^5.8 K after a few 10² yr, cooler than expected for conductive plus radiative cooling.

Supernova shells are initially almost spherical, or barrel-shaped; when older than 10⁴ years they can look exotic, like CTB 80, IC 433, the flying duck, and others.

Perhaps all of them contain a neutron star near their center.