Pulsars and neutron stars/Neutron star properties
Introduction
editNeutron star masses
editA catalogue of pulsar and companion masses is available. Below we list the pulsar masses for systems in which the mass is well determined:
| Pulsar | Mass (solar masses) |
|---|---|
| J0337+1715 | 1.4378(13) |
| J0348+0432 | 2.01(4) |
| J0437-4715 | 1.44(7) |
| J0453+1559 | 1.559(5) |
| J0621+1001 | 1.53 +0.10-0.20 |
| J0737-3039A | 1.3381(7) |
| J0737-3039B | 1.2489(7) |
| J0751+1807 | 1.26(14) |
| J1012+5307 | 1.64(22) |
| J1141-6545 | 1.27(1) |
| B1534+12 | 1.3330(4) |
| J1614-2230 | 1.97(4) |
| J1713+0747 | 1.31(11) |
| J1738+0333 | 1.47+0.07-0.06 |
| J1756-2251 | 1.341(7) |
| J1802-2124 | 1.24(11) |
| J1807-2500B | 1.3655(21) |
| B1855+09 | 1.58+10-13 |
| J1903+0327 | 1.667(21) |
| J1906+0746 | 1.291(11) |
| J1909-3744 | 1.47(3) |
| J1910-5958A | 1.3(2) |
| B1913+16 | 1.4398(2) |
| B2127+11C | 1.358(10) |
| J2222-0137 | 1.20(14) |
| B2303+46 | 1.24-1.44 |
Neutron star radii
editIt 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.
The neutron star interior
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Types of neutron stars
editThere 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
- recycled pulsars
- Low-mass X-ray binaries (LMXB)
- Intermediate-mass X-ray binaries (IMXB)
- High-mass X-ray binaries (HMXB)
- Accretion powered pulsar