PSR B1620-26

PSR B1620-26 is a white dwarf companion in orbit around a millisecond pulsar, (PSR 1620-26) located within the globular cluster M4 (NGC 6121). Measurements using the pulsar timing method indicate that the white dwarf is orbited by three massive planets.1, 2


Distance 12,400 light-years (3.8 kpc)
Period 11 milliseconds (= 90 rev/s)

  a b c
Mass (Jupiter = 1) 1.2 3.4 6.7
Semimajor axis ~10 30 64
Orbital period (years) 61.8 129 389
Eccentricity 0.0 0.2 0.5



1. Rasio, F. A. "New Evidence for a Planet or Brown Dwarf in Orbit Around PSR M1620-26." In A. Olinto et al., eds., Proceedings of the Texas Symposium on Relativistic Astrophysics, Annals of the New York Academy of Science (1998).
2. Thorsett, S., Arzoumanian, Z., Camilo, F., and Lyne, A. "The Triple Pulsar System PSR B1620-26 in M4," Astrophysical Journal (submitted 1999).