PSR J1614−2230

Pulsars were discovered in 1967 by Jocelyn Bell and her adviser Antony Hewish using the Interplanetary Scintillation Array. Franco Pacini and Thomas Gold quickly put forth the idea that pulsars are highly magnetized rotating neutron stars, which form as a result of a supernova at the end of the life of stars more massive than about . The radiation emitted by pulsars is caused by interaction of the plasma surrounding the neutron star with its rapidly rotating magnetic field. This interaction leads to emission "in the pattern of a rotating beacon," as emission escapes along the magnetic poles of the neutron star. The "rotating beacon" property of pulsars arises from the misalignment of their magnetic poles with their rotational poles. Historically, pulsars have been discovered at radio wavelengths where emission is strong, but space telescopes that operate in the gamma ray wavelengths have also discovered pulsars. ==Observations==

The Energetic Gamma-Ray Experiment Telescope (EGRET) identified a half dozen known pulsars at gamma ray wavelengths. Many of the sources it detected had no known counterparts at other wavelengths. In order to see whether any of these sources were pulsars, Fronefield Crawford et al. used the Parkes telescope to conduct a survey of the EGRET sources located in the plane of the Milky Way that lacked a known counterpart. In the search, they discovered PSR J1614–2230, and concluded that it might be a counterpart to a gamma ray source near the same location. The radio observations revealed that PSR J1614–2230 had a companion, likely a white dwarf. The observed orbital parameters of the system indicated a minimum companion mass of , and an orbital period of 8.6866 days. Paul Demorest et al. used the Green Bank Telescope at the National Radio Astronomy Observatory to observe the system through a complete 8.68661942256 day orbit, recording the pulse arrival times from PSR J1614–2230 over this period. After accounting for factors that would alter pulse arrival times from exactly matching its period of 3.150807655690673 milliseconds, including the orbital parameters of the binary system, the spin of the pulsar, and the motion of the system, Demorest et al. determined the delay in the arrival of pulses that resulted from the pulse having to travel past the companion to PSR J1614–2230 on its way to Earth. This delay is a consequence of general relativity known as the Shapiro delay, and the magnitude of the delay is dependent upon the mass of the white dwarf companion. The best fit companion mass was . Knowing the companion mass and orbital elements then provided enough information to determine the mass of PSR J1614–2230 to be . The measurement was later improved based on observations of the pulses over several years. ==Significance==

The conditions in neutron stars are very different from those encountered on Earth, as a result of the high density and gravity of neutron stars; their masses are of order the mass of a star, but they have sizes around in radius, which is comparable to the size of the center of large cities such as London. ==Notes==