PSR B1620−26 is a binary star system located at a distance of 3,800 parsecs (12,400 light-years) in the globular cluster of Messier 4 (M4, NGC 6121) in the constellation of Scorpius.

The double system (triple including the substellar companion) is just outside the core of the globular cluster.

In practice, context makes it clear whether the pulsar, the white dwarf, the planet, or the system as a whole is being referred to.

In the early 1990s, a group of astronomers led by Donald Backer, studying what they thought was a binary pulsar, determined that a third object was needed to explain the observed Doppler shifts.

Within a few years, the gravitational effects of the planet on the orbit of the pulsar and white dwarf had been measured, giving an estimate of the mass of the third object that was too small for it to be a star.