A 62-minute orbital period black widow binary in a wide hierarchical triple

Burdge, Kevin B.; Marsh, Thomas R.; Fuller, Jim; Bellm, Eric C.; Caiazzo, Ilaria; Chakrabarty, Deepto; Coughlin, Michael W.; De, Kishalay; Dhillon, V. S.; Graham, Matthew J. et al.
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Over a dozen millisecond pulsars are ablating low-mass companions in close binary systems. In the original `black widow', the eight-hour orbital period eclipsing pulsar PSR J1959+2048 (PSR B1957+20)1, high-energy emission originating from the pulsar2 is irradiating and may eventually destroy3 a low-mass companion. These systems are not only physical laboratories that reveal the interesting results of exposing a close companion star to the relativistic energy output of a pulsar, but are also believed to harbour some of the most massive neutron stars4, allowing for robust tests of the neutron star equation of state. Here we report observations of ZTF J1406+1222, a wide hierarchical triple hosting a 62-minute orbital period black widow candidate, the optical flux of which varies by a factor of more than ten. ZTF J1406+1222 pushes the boundaries of evolutionary models5, falling below the 80-minute minimum orbital period of hydrogen-rich systems. The wide tertiary companion is a rare low-metallicity cool subdwarf star, and the system has a Galactic halo orbit consistent with passing near the Galactic Centre, making it a probe of formation channels, neutron star kick physics6 and binary evolution.