A binary pulsar in a 53-minute orbit

Abstract

Spider pulsars are neutron stars that have a companion star in a close orbit. The companion star sheds material to the neutron star, spinning it up to millisecond rotation periods, while the orbit shortens to hours. The companion is eventually ablated and destroyed by the pulsar wind and radiation1,2. Spider pulsars are key for studying the evolutionary link between accreting X-ray pulsars and isolated millisecond pulsars, pulsar irradiation effects and the birth of massive neutron stars3–6. Black widow pulsars in extremely compact orbits (as short as 62 minutes7) have companions with masses much smaller than 0.1 M⊙. They may have evolved from redback pulsars with companion masses of about 0.1–0.4 M⊙ and orbital periods of less than 1 day8. If this is true, then there should be a population of millisecond pulsars with moderate-mass companions and very short orbital periods9, but, hitherto, no such system was known. Here we report radio observations of the binary millisecond pulsar PSR J1953+1844 (M71E) that show it to have an orbital period of 53.3 minutes and a companion with a mass of around 0.07 M⊙. It is a faint X-ray source and located 2.5 arcminutes from the centre of the globular cluster M71.

PSR J1953+1844 Probably Being the Descendant of an Ultracompact X-Ray Binary

“…The follow-up timing observations have revealed that M71E has an orbit period of 53 minutes (Pan et al 2023). Its short orbit period of 53 minutes breaks the previous record for the orbit period of 75 minutes for PSR J1653-0158 (Nieder et al 2020); no eclipses and significant orbital period changes have been detected yet (Pan et al 2023). The nature of this system is not well understood yet.…”

“…The nature of this system is not well understood yet. This system was interpreted as an intermediate between redbacks and black widows by Pan et al (2023). Based on a low mass function of 2.3 × 10 −7 M e and the strikingly short orbital period in the range of UCXB orbital periods, here we discuss an alternative evolution scenario for this binary system, namely that it is a newly evolved descendant of a UCXB, as a complementary theory to Pan et al (2023).…”

“…Recently a binary pulsar PSR J1953+1844 (i.e., M71E, because it is probably located in the globular cluster M71) was discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST; Nan 2006;Nan et al 2011) during the FAST Galactic Plane Pulsar Snapshot (GPPS) survey (Han et al 2021). The follow-up timing observations have revealed that M71E has an orbit period of 53 minutes (Pan et al 2023). Its short orbit period of 53 minutes breaks the previous record for the orbit period of 75 minutes for PSR J1653-0158 (Nieder et al 2020); no eclipses and significant orbital period changes have been detected yet (Pan et al 2023).…”

“…This system was interpreted as an intermediate between redbacks and black widows by Pan et al (2023). Based on a low mass function of 2.3 × 10 −7 M e and the strikingly short orbital period in the range of UCXB orbital periods, here we discuss an alternative evolution scenario for this binary system, namely that it is a newly evolved descendant of a UCXB, as a complementary theory to Pan et al (2023). We discuss in this Letter the evolution and fate of this binary system, and suggest that the companion of M71E is a hydrogen-poor star with a mass of ∼0.01 M e .…”

Optical Identification of the Shortest-period Spider Pulsar System M71E

“…By analyzing the pulsar timing data from the Five-hundredmeter Aperture Spherical radio Telescope (FAST), Pan et al (2023;hereafter Pan23) find that M71E (aka, PSR J1953 +1844, discovered by Han et al 2021 in the field of GC M71) is an extraordinary noneclipsing spider pulsar, which has a record-breaking short orbital period of P = 53.3 minutes and a very small mass function of 2.3 × 10 −7 M e . Pan23ʼs analysis favors a stripped dwarf companion with M c = 0.047-0.097 M e , estimated by imposing mass-radius relations for brown dwarfs (BDs)/low-mass dwarfs (Burrows et al 1993) and restricting its radius within the Roche lobe radius (Eggleton 1983).…”