A research team at the National Astronomical Observatories of the Chinese Academy of Sciences, using China's FAST radio telescope, has confirmed that the millisecond pulsar PSR J0435+3233 belongs to an evolving, primordial triple-star system. It is the second confirmed pulsar triple system known to humanity and the first still in an evolutionary stage. The findings were published in The Astrophysical Journal Letters on October 9, 2026.
The system contains three bodies: a millisecond pulsar, a white dwarf, and a sun-like star still undergoing nuclear evolution. The pulsar and the white dwarf form an inner binary, orbiting each other in a nearly circular orbit every eight days. The outer, sun-like companion loops around that close pair once every 73.5 years along an eccentric orbit with an eccentricity of 0.6. The pulsar spins extraordinarily fast, with a period of only 3.2 milliseconds, or roughly 312 rotations per second.
FAST's drift-scan survey first detected this pulsar on June 8, 2020. A follow-up team then monitored it with FAST for roughly five years, collecting 192 measurements. Researchers found the pulsar's spin period increasing by one nanosecond per year, about two orders of magnitude more than typical millisecond pulsars. That anomaly was traced to external gravitational acceleration, revealing the third companion. The team also used 18 years of Fermi satellite gamma-ray data, comprising 160 effective photons, to pinpoint the optical companion.
In Liu Cixin's The Three-Body Problem, three suns move chaotically, plunging a civilization into unpredictable extremes. The real system, by contrast, was born from the same nebula as a primordial "triplet" and follows a stable, hierarchical orbit. Researcher Jinlin Han noted the system will likely end up as a neutron star orbited by two white dwarfs.
While the Chinese team worked, a European team of scientists from Germany, the Netherlands, France, and the United Kingdom independently analyzed similar archival data and reached the same conclusion. The Chinese team's orbital parameters were more precise by an order of magnitude, thanks to its treatment of three-body gravity and relativistic effects, and it determined the masses of all three bodies using FAST and Fermi data. Researchers say the system provides a natural laboratory for testing the strong equivalence principle and other fundamental gravity theories.
Located in the Galactic field rather than a dense cluster, the system lies roughly 7,000 light years from Earth. FAST has discovered more than 1,000 pulsars since it began operations. Researchers say follow-up observations across radio, optical, and gamma-ray wavelengths will trace the full evolutionary path of this rare triple.