PSR J0348+0432

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Lore & Background

The first radio pulsar was 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 10 times the mass of the Sun. 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.

In Their Own Story

In 2007, the Green Bank Telescope underwent track repair, and was unable to track for several months. An international team of astronomers was nevertheless able to record the data from the antenna, letting the Earth do the job of moving the beam of the telescope across the sky, a process known as a drift scan survey. They found a total of 35 new pulsars, including 7 new millisecond pulsars and PSR J0348+0432. In 2011 the white dwarf companion to the pulsar was observed with the FORS2 spectrograph of the European Southern Observatory's Very Large Telescope, in Chile. These data were combined with radio observations to determine the mass of the white dwarf and the pulsar. Radio timing of the pulsar with the 305-metre radio telescope at the Arecibo Observatory and the Effelsberg 100-metre Radio Telescope soon also detected the orbital decay of the system due to the emission of gravitational waves. This matched the rate predicted by general relativity.

Reader's Guide

The combination of a large neutron-star mass, low white-dwarf mass (mass ratio ~ 1:11.7) and short orbital period (2 hours and 27 minutes) allows astronomers to test general relativity in a regime of extreme gravitational fields, where it had never been tested before. The result also has implications for the direct detection of gravitational waves and for understanding of stellar evolution. The measured mass of 2.01±0.04 M☉ puts an empirical lower bound on the value of the Tolman–Oppenheimer–Volkoff limit. PSR J0348+0432 is also a candidate for a hyperon star, a massive neutron star containing hyperons.

Did You Know?

• PSR J0348+0432 was discovered in 2007 during a drift-scan survey using the Green Bank Telescope while its track was under repair.
• Its mass of 2.01±0.04 M☉ is slightly higher than, but statistically indistinguishable from, the mass of PSR J1614−2230.
• The orbital decay of this system due to gravitational-wave emission matches the rate predicted by general relativity.
• The white dwarf companion was observed in 2011 with the FORS2 spectrograph on the Very Large Telescope in Chile.
• PSR J0348+0432 is a candidate for a hyperon star, a massive neutron star containing hyperons.