Astronomers Map a Three-Star System Where the Outer Star Takes 73.5 Years to Orbit

Astronomers have identified the gamma-ray pulsar PSR J0435+3233 as a member of a three-star system and worked out both of its orbits. Z. L. Yang of the Chinese Academy of Sciences and colleagues report that the pulsar circles a helium white dwarf once every 8.0 days, while a Sun-like star loops around that close pair once every 73.5 years. The paper was published online Oct. 8, 2026, in The Astrophysical Journal Letters.

Yang and colleagues present the system as a target for detailed observation across radio, optical and gamma-ray wavelengths, and for tracing how a triple-star system that formed together evolves. They expect it to end up as a neutron star with two white dwarfs. Their paper is open access.

The orbits came out of one combined fit: 16.7 years of gamma-ray pulse timing from the pulsar, nearly five years of radio timing, the slow drift of the inner orbit, the delay in the pulses as they pass close to the white dwarf, and positions from the Gaia star-mapping mission. The inner orbit is almost perfectly circular; the outer one is strongly elongated.

What the fit does not settle is how the two orbits are tilted against each other. In one solution they are close to perpendicular, about 85 degrees apart; in the other the tilt is about 54 degrees. The pulsar's mass comes out at 1.16 times the Sun's under the first geometry and 1.34 under the second. The white dwarf falls between a quarter and a third of the Sun's mass either way, and the outer star close to the Sun's own.

A pulsar in a three-star system is not new. PSR J0337+1715, a pulsar orbited by two white dwarfs, has been studied for more than a decade. What Yang's team adds is a full orbital and mass solution for this one.

The outer star is a G-type subgiant, a Sun-like star that has started to swell with age. The team places the system about 6,800 light-years from Earth.