Pulsars and neutron stars/Neutron star properties

Neutron star masses
A catalogue of pulsar and companion masses is available. Below we list the pulsar masses for systems in which the mass is well determined:

Neutron star radii
It is very difficult to make a direct determination of a neutron star radius. One method is to study X-ray bursters - these are neutron stars that are still accreting material from a companion in a close orbit. It is thought that they can build up layers of material on their surface until it reaches a critical mass at which point it undergoes a thermonuclear explosion causing a burst of emission from the surface. From a knowledge of the distance to the neutron star it is possible to estimate the radius of the neutron star. Results are obtained of around 9.6 to 11km (see e.g., Fujimoto & Gottwald 1989). More recently model spectra of neutron star atmospheres is used to fit the thermal X-ray spectra of neutron stars. Suleimanov et al. (2015) obtain radii of around 12km.

Types of neutron stars
There is a large zoology of different types of neutron star. They can be differentiated between radio loud and radio quiet sources. Some are rotationally-powered whilst others are accretion-powered. There are now sources that switch between the different types. For instance, Papitto et al. discuss a neutron star (IGR J18245-2452; PSR J1824-2452I located in the globular cluster M28) which accretes matter and angular momentum from its companion star (this system is a low-mass X-ray binary; LMXB). During this stage, bright X-ray emission is observed. However, the rate of mass transfer can decrease and a radio millisecond pulsar switches on - in this state the emission is powered by the neutron star's rotating magnetic field.

Types of neutron star include:


 * radio pulsars
 * recycled pulsars
 * millisecond pulsars
 * magnetar
 * soft gamma ray repeater
 * anomalous X-ray pulsar
 * Low-mass X-ray binaries (LMXB)
 * Intermediate-mass X-ray binaries (IMXB)
 * High-mass X-ray binaries (HMXB)
 * Accretion powered pulsar