PSR J0952–0607 is a massive millisecond pulsar in a binary system, located between 3,200–5,700 light-years (970–1,740 pc) from Earth in the constellation Sextans.

[8]: 2  Because of its optimal location away from the crowded Galactic Center and its pulsar-like[12]: 8  gamma-ray emission peak at 1.4 GeV, it was deemed a prime millisecond pulsar candidate for follow-up.

[8]: 3  Optical observations by the 2.54-meter Isaac Newton Telescope on La Palma detected and confirmed the pulsar's companion at a faint apparent magnitude of 23 in January 2017.

[3]: 8  The companion does not appear to eclipse the pulsar,[8]: 1 [3]: 12  indicating that its orbit is oriented nearly face-on with an inclination of 60° with respect to the plane perpendicular to Earth's line of sight.

[3]: 4 The companion was likely a former star that had been reduced to the size of a large gas giant planet or brown dwarf,[7][3]: 12  with a present-day mass of 0.032±0.002 M☉ or 34±2 MJ according to radial velocity measurements.

[4]: 1, 4 [2]: 1  As a result of bloating, the companion attains a low density likely around 10 g/cm3 (with significant uncertainty due to the system's unknown distance from Earth),[2]: 11  making it susceptible to tidal deformation by the pulsar.

[8][6] Assuming a standard neutron star radius of 10 km (6.2 mi),[3]: 11  the equator of PSR J0952–0607 rotates at a tangential velocity over 44,400 km/s (27,600 mi/s)—about 14% the speed of light.