Some stars live fast, some burn quietly for billions of years, and a rare few find themselves locked in cosmic arrangements that challenge the usual rules of stellar evolution. Astronomers have now identified one such system: a rapidly spinning pulsar accompanied by a white dwarf and a Sun-like subgiant star. The discovery makes PSR J0435+3233 one of only a small number of known millisecond pulsars residing in a triple-star system, states an online report by the American Astronomical Society (AAS) NOVA.
A pulsar spinning at extraordinary speed
According to the report, PSR J0435+3233 was discovered earlier this year using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). It belongs to the millisecond pulsar family, completing a rotation in just 3.2 milliseconds. What immediately set it apart, however, was not simply its speed but how rapidly that spin is slowing.The pulsar is losing rotational speed roughly 100 times faster than typical millisecond pulsars in the Milky Way. Such an unusually rapid slowdown points towards a stronger magnetic field than is normally expected and raises questions about how the object acquired its remarkable characteristics.Initial FAST observations also suggested that the pulsar was orbiting a white dwarf once every eight days. Further observations have now revealed that this compact pairing is only the inner part of a much larger stellar arrangement, the report states.
Three stars, two very different orbits
Researchers led by Zonglin Yang of the National Astronomical Observatories of the Chinese Academy of Sciences combined 4.9 years of FAST observations with 16.7 years of gamma-ray data from NASA’s Fermi Gamma-Ray Space Telescope. Optical and infrared observations from several facilities helped complete the picture.The data confirmed the white-dwarf companion and detected gamma-ray emission associated with the pulsar. More significantly, they uncovered a second companion: a subgiant star with a mass roughly comparable to that of the Sun.The three objects form a hierarchical triple system. The pulsar and white dwarf make up a compact inner binary, while the subgiant circles the pair from much farther away. Its orbit takes about 73.5 years to complete. The two orbital planes are also tilted significantly relative to one another, either almost at right angles or by roughly 54 degrees. Despite the complicated geometry, the system appears dynamically stable over long timescales.
A rare window into stellar evolution
Millisecond pulsars are frequently found with companions. Their extraordinary rotation is generally thought to develop when material from a companion star falls onto the pulsar, transferring angular momentum and effectively spinning it up. Finding one with two stellar companions, however, is considerably rarer.The system is particularly interesting because it exists in isolation rather than inside a dense stellar cluster. That makes it plausible that the three stars formed together, rather than becoming a trio through later gravitational encounters. Its early history was anything but quiet. The most massive star would have exhausted its fuel in less than 10 million years before exploding as a supernova and leaving behind the pulsar. For the remaining system to survive such an event, the explosion’s kick and the amount of mass lost had to fall within a narrow range. Even without a kick, researchers estimate only about a 35% chance that the system would remain gravitationally bound.Its future should be calmer. The distant subgiant will eventually become another white dwarf, undergoing a much gentler transformation. For astronomers, the system offers something even more valuable: a rare natural laboratory for studying how stars interact, evolve and survive together across immense stretches of cosmic time.Image Courtesy: AAS Nova/Kerry Hensley; background image from Thilina Alagiyawanna
