Astronomers using the 100-meter Robert C. Byrd Green Bank Telescope have discovered an exotic pulsar that has the widest orbit of any around a neutron star.
PSR J1930-1852. Image credit: J. K. Swiggum et al.
About 2,300 pulsars are known to scientists, and only 10% of them are in binary systems. The vast majority of these are found orbiting white dwarfs.
And only a rare few orbit other neutron stars or Sun-like stars. The reason for this paucity of double neutron star systems, scientists believe, is the process by which pulsars and all neutron stars form.
The newly-discovered pulsar, PSR J1930-1852, is part of a binary system, based on the differences in its spin frequency between the original detection and follow-up observations.
Optical telescope surveys revealed no visible companion – which would have been clearly seen if it were a white dwarf star or main sequence star.
“Given the lack of any visible signals and the careful review of the timing of the pulsar, we concluded that the most likely companion was another neutron star,” said Joe Swiggum, a graduate student at West Virginia University in Morgantown.
Further observations revealed that the two neutron stars have the widest separation ever observed in a double neutron star system.
Some pulsars in double neutron star systems are so close to their companion that their orbital paths are comparable to the size of the Sun and they make a full orbit in less than a day.
PSR J1930-1852 has the longest spin period (185 ms) and orbital period (45 days) yet measured among known pulsars in double neutron star systems. Its orbital path spans about 32.3 million miles (52 million km).
“Its orbit is more than twice as large as that of any previously known double neutron star system,” said Swiggum, who is the first author of a paper accepted for publication in the Astrophysical Journal (arXiv.org preprint).
“The pulsar’s parameters give us valuable clues about how a system like this could have formed.”
“Discoveries of outlier systems like PSR J1930-1852 give us a clearer picture of the full range of possibilities in binary evolution.”
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J. K. Swiggum et al. 2015. PSR J1930-1852: a pulsar in the widest known orbit around another neutron star. ApJ, accepted for publication; arXiv: 1503.06276
