PSR J1719-1438 is a millisecond pulsar with a spin period of 5.8 ms located about 4,000 ly from Earth in the direction of Serpens Cauda,[1][4] one minute from the border with Ophiuchus.

It orbits the pulsar with a period of 2 hours 10 minutes and 37 seconds, at a distance of around 600,000 km (0.89 solar radii).

Calculations show the companion has a minimum density of 23 grams per cubic centimeter and is probably an ultra-low-mass carbon–oxygen white dwarf.

[1] Because the companion to PSR J1719-1438 is planet-sized, made primarily of carbon (with an unknown amount of oxygen), and very dense, it may be similar to a large diamond.

[4][5][6] It has been suggested in 2012 that PSR J1719-1438 b may not be the remnant of a white dwarf, but a lump of quark matter with a size of just 1 kilometer and the mass of Jupiter,[7] that would have been born in the collision and merger of two previous quark stars, part of the ejected matter ending orbiting the merger remnant we see as the pulsar PSR J1719-1438.