November 05, 2016

Pulsar - Neutron Star

Lighting up the sky at night, sparkling and shining as they do, stars are hot balls of glowing plasma held together by their own gravity. They crush themselves continuously with immense pressure and temperature causing gravitational friction and other fusion reactions to take place. Atoms of hydrogen fuse with helium to release an enormous amount of energy in the form of gamma rays that are trapped within each of the stars that we are able to see. As they try to be pushed outward, absorbed by another atom and emit radiation, such that the photons from their core leap off their surface becoming visible light photons as they lose their energy. Thus enabling our eyes to look out for those white spots brightening the darkest of our nights’ skies, returning beauty to the eyes of the beholder. This particular thesis holds its own vital role when one considers learning about neutron stars. Neutron stars are the collapsed core of a large star. They are the smallest and densest stars known to exist. They result from the supernova explosion of a massive star, composed almost entirely of neutrons that are subatomic particles with no net electrical charge and mass slightly more than that of protons. These stars, however, collapse further by neutron degeneracy pressure explained by Pauli’s exclusion principle. If the remnant has too great a density, something which occurs in excess of an upper limit of the size of neutron stars of solar masses 2-3, it will continue collapsing thus to form the ever known black hole. Coming to our core point, pulsars are highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. Neutron stars are very dense and have short regular rotational periods. This produces a very precise interval between pulses that range roughly from milliseconds to seconds for an individual pulsar. The precise periods of pulsars make them very useful tools, eg: atomic clocks, extrasolar planets found outside around a pulsar (PSR B1257+12). These pulsed radio waves are emitted from neutron stars are thought to be caused by particle acceleration near their magnetic poles, which need not be aligned with the rotational axis of the neutron star. Emission of electrons is caused due to large electrostatic fields near their magnetic poles as these electrons accelerated along the field lines, then causing polarized curvature radiation. High energy photons interact with low energy photons and the magnetic field for electron-positron pair production, which through electron-positron annihilation leads to further high energy photons. If the axis of rotation of the neutron star is different from the magnetic axis, external viewers will only see these beams of radiation whenever the magnetic axis point towards them during the neutron star rotation. This rotation slows down over time as electromagnetic power is emitted. When a pulsar's spin period slows down sufficiently, the radio pulsar mechanism is believed to turn off (the so-called "death line"). This turn-off seems to take place after about 10–100 million years, which means of all the neutron stars born in the 13.6 billion years of age of the universe, around 99% no longer pulsate. Therefore, periodic pulses are observed, at the same rate as the rotation of the neutron star. This theory behind its turn off and formations is still considered to be in its infancy, but yet to be discovered to innovate the specific thoughts over their pulsed radiations and binary systems.
There are different types of pulsars:
  • Rotation-powered pulsars, Acceleration-powered pulsars, Magnetars
  • X-ray pulsars, Millisecond pulsars (the process of accretion causing transfer of angular momentum to the neutron star to recycle it as a rotationally powered pulsar)
  • Disrupted recycled pulsar ( 2 massive stars born close together from the same cloud of gas, where the more massive star explodes leaving behind a neutron star, if the second star still remains the same then the binary system survives. Which later has it mass sucked up by the neutron star as it slowly loses energy.

More on: “recycled” and “disrupted recycled” pulsar; If the second star that was mentioned above spins the neutron star up reducing its magnetic field then the neutron star is said to be recycled as it returns to a quickly spinning state, producing supernova and hence another neutron star. If this second star fails to disrupt binary, then double neutron star binary is formed, left with no companion, turning into a disrupted recycled pulsar. Of interest to the study of the state of the matter in a neutron star are the glitches observed in the rotation velocity of the neutron star. This velocity is decreasing slowly but steadily, except by sudden variations. One model put forward to explain these glitches is that they are the result of "starquakes" that adjust the crust of the neutron star. Models, where the glitch is due to a decoupling of the possibly superconducting interior of the star, have also been advanced. In both cases, the star's moment of inertia changes, but its angular momentum does not, resulting in a change in rotation rate.
Applications involve Maps, Precise clocks, Probes of the interstellar medium, Probes of space-time, Gravitational-wave detectors, etc.

Whatsapp Button works on Mobile Device only