New High Frequency Pulsars Discovered
Supernovae are often seen as dramatic endings to the lives of stars. In fact, some of the most fascinating astronomical objects are formed from the ashes of these tremendous events. One such object is a pulsar, a specific variety of neutron star. Neutron stars are formed from normal stars at least 8 times the mass of the Sun. As a sufficiently massive star reaches the end of its normal life, the intense gravitation pull of the dense Iron core causes the star to collapse. This causes the temperature of the core to soar to the point where electrons and protons are forced together to form neutrons. The intense burst of energy produced during this process causes the outer atmosphere of the star to be hurled outwards in a supernova. What remains is a neutron star.
Neutron stars are usually around 20km in diameter, and are extremely dense. They are often spinning very fast, sometimes hundreds of times a second. This is for the same reason that when a figure skater draws in their arms during a spin they rotate faster. Neutron stars can have massive magnetic fields, resulting in highly energetic beams of electromagnetic radiation (such as radio waves or gamma rays) emitted along the axis of the magnetic field. This axis, and therefore the beams emitted, rotate with the star itself. The radiation from the neutron star can only be seen from Earth when the beam is pointing towards us. Since the beam axis is rotating, we observe the neutron star as pulsating. Hence we call this kind of neutron star a pulsar. The first pulsar was discovered in 1967 by Dame Jocelyn Bell Burnell. This discovery later was awarded a Nobel Prize, though somewhat controversially not for Dame Burnell.
This week, a team of astronomers lead by H. T. Cromartie of the University of Virginia, announced the discovery of six new pulsars, all of which have pulse periods of several milliseconds. The fastest pulsar discovered by the team, one of the fastest ever discovered, has a pulse period of 1.99 Milliseconds, meaning it rotates approximately 500 times a second. This particular pulsar is part of a binary system with a white dwarf star, which orbit each other once every 1.6 hours. The team used the 305 meter wide Arecibo radio telescope in Puerto Rico to further analyse 34 candidate gamma ray sources identified by the Large Area Telescope (LAT) instrument aboard NASA’s Fermi spacecraft.
Aside from their fascinating physical characteristics, pulsars are valuable tools for scientific investigation. The rotational speed of pulsars is often very stable, and measurements of their pulse frequency can provide more accurate timing than atomic clocks. The position and timing of pulsars can be used to generate maps. Both Voyager missions contained pulsar maps, which show the position of the Sun relative to 14 pulsars. These maps would allow the position of the human race in space and time to be determined by those who may encounter the Voyager spacecraft in the future.