[6][7] Stellar encounters are not very common in the disk of the Milky Way, where the Sun is, but in the dense core of globular clusters, they occur frequently.

About half a billion years ago, the newly captured star began to expand into a red giant (see stellar evolution).

It is believed that as the pulsar's red giant companion expanded, it filled and then exceeded its Roche lobe, so that its surface layers started being transferred onto the neutron star.

The infalling matter 'spun up' the neutron star, due to the transfer of angular momentum, and for a few hundred million years, the stars formed a low-mass X-ray binary, as the infalling matter was heated to temperatures high enough to glow in X-rays.

Mass transfer came to an end when the surface layers of the mass-losing star were depleted, and the core slowly shrunk to a white dwarf.

In the early 1990s, a group of astronomers led by Donald Backer, who were 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.

On July 10, 2003, the detection of the white dwarf and confirmation of its predicted properties were announced by a team led by Steinn Sigurdsson, using observations from the Hubble Space Telescope.

This designation doesn't appear in the SIMBAD database, and more modern naming conventions use a separated lettering system where lower-case letters to refer to planets and upper-case letters to designate stars (e.g. Gliese 667 Cc is the 'c' planet orbiting Gliese 667C, which is the 'C' star of a triple system), making PSR B1620-26 b the designation for a planet orbiting both stars of the PSR B1620-26 system.