X-ray Pulsar
Neutron starDense ball of neutrons that remains at the core of a star after a supernova explosion has destroyed the rest of a star with mass 8-18 (?) Msun. A neutron star has mass ~2-3 Msun, density ~1014 g/cm3, and is supported by neutron degeneracy pressure. Typical neutron stars are 10-20 with a powerful magnetic field in an X-ray binaryClose binary system where a neutron star (or rarely a black hole) accretes matter from what is usually a main sequence star (left). X-ray binaries are some of the most luminous X-ray sources in the sky. X-rays are produced as material from the companion star is drawn to the compact. Gas accreted from the companion starSelf-luminous object held together by its own self-gravity. Often refers to those objects which generate energy from nuclear reactions occurring at their cores, but may also be applied to stellar remnants such as neutron stars. is channeled to the magnetic poles
of the neutronCharge-neutral hadron with a mass of 1.6748 x 10 kg, equivalent to 939.573 MeV, and an intrinsic angular momentum, or spin, of ½ (in units of h/2π). The neutron is a nucleon, one of the two basic constituents of all atomic nuclei (apart from H, which consists of a single star and forms X-ray emitting hot spots which move into and out of view as the neutron star spins, giving rise to regular X-ray pulses. The pulsation periods of X-ray pulsars range from 1.6 ms to >10 minutes in length. Long period X-ray pulsars have particularly strong magnetic fields that decrease their rotation rates through torques exerted on its magnetosphereRegion around an astronomical object in which phenomena are dominated or organized by its magnetic field. A schematic diagram of the features of Earth's magnetosphere is shown..
Image source: http://lheawww.gsfc.nasa.gov/users/white/xrb/xrb.html.
Unlike radio pulsars, which are all spinning down due to energy losses in the form of relativistic particles and magnetic dipole radiation, some X-ray pulsars have been found to be spinning up; whereas, others have relatively stable spin rates or show erratic behavior (alternating periods of spin-up and spin-down). The variations in the spin rate arise because the pulsar can gain, lose or maintain its angular momentum depending on how the accreting material is transferred to the neutron star. They can have persistent mass transfer from Roche-lobe overflow, episodes of mass accretionAccumulation of smaller objects into progressively larger bodies in the solar nebula leading to the eventual formation of asteroids, planetesimals and planets. The earliest accretion of the smallest particles was due to Van der Waals and electromagnetic forces. Further accretion continued by relatively low-velocity collisions of smaller bodies in the (possibly due to an eccentric orbitThe elliptical path of one body around another, typically the path of a small body around a much larger body. However, depending on the mass distribution of the objects, they may rotate around an empty spot in space • The Moon orbits around the Earth. • The Earth orbits around that takes the neutron star close to the companion near periastron), or can be powered by stellar windFast continuous outflow of material (p+, e–, and atoms of heavier metals) ejected from stars. Stellar winds are characterized by speeds of 20–2,000 km/sec. The causes, ejection rates and speeds of stellar winds vary with the mass of the star. In relatively cool, low-mass stars, such as the Sun, the accretion. In contrast, a solitary radio
pulsar can only lose angular momentum through radiation of energy.
