Astronomers Discover Rare Pulsar Triple System with Sun-Like Star
- Astronomers have identified a rapidly spinning pulsar designated PSR J0435+3233 that completes a rotation in 3.2 milliseconds while losing rotational speed roughly 100 times faster than typical millisecond...
- Initial FAST observations suggested that the pulsar was orbiting a white dwarf companion once every eight days in an almost circular orbit.
- The two orbital planes are tilted significantly relative to one another, either almost at right angles or by roughly 54 degrees.
Astronomers have identified a rapidly spinning pulsar designated PSR J0435+3233 that completes a rotation in 3.2 milliseconds while losing rotational speed roughly 100 times faster than typical millisecond pulsars. The discovery stems from observations by the Five-hundred-meter Aperture Spherical radio Telescope, known as FAST. A subsequent study headed by Zonglin Yang of the National Astronomical Observatories of the Chinese Academy of Sciences combined 4.9 years of FAST data with 16.7 years of gamma-ray data from NASA’s Fermi Gamma-Ray Space Telescope.
PSR J0435+3233 Orbits a White Dwarf and a Sun-Like Star
Initial FAST observations suggested that the pulsar was orbiting a white dwarf companion once every eight days in an almost circular orbit. Further analysis revealed a hierarchical triple-star system. The pulsar and the white dwarf form a compact inner binary, while a second companion—a subgiant star with a mass roughly comparable to the Sun—circles the pair from much farther away. As reported by Global Times, the outer star requires an elongated orbit with an eccentricity of about 0.6 to circle the inner pair in roughly 73.5 years.
The two orbital planes are tilted significantly relative to one another, either almost at right angles or by roughly 54 degrees. Despite this complex geometry, the system appears dynamically stable over long timescales. Pointing out systems without planetary companions, Global Times noted that PSR J0435+3233 represents only the second confirmed stellar triple that houses a pulsar. The previously known system, PSR J0337+1715, was discovered using the US Green Bank Telescope and consists of one pulsar and two white dwarfs.
Researchers Trace the Primordial Triple System Evolution
Millisecond pulsars typically develop their extraordinary rotation when material from a companion star falls onto them, transferring angular momentum. Finding one with two stellar companions outside a dense stellar cluster makes it plausible that the three stars formed together rather than through later gravitational encounters. The National Astronomical Observatories described the stellar triple as extremely unique because it contains a still-evolving star rather than solely stellar remnants.
In the formation scenario proposed by researchers, the most massive of the three stars began with about 20 times the Sun’s mass before exhausting its fuel in less than 10 million years and exploding as a supernova. For the remaining system to survive the explosion, the kick and mass loss had to fall within a narrow range, with researchers estimating only about a 35% chance that the system would remain gravitationally bound even without a kick.
Variations in the observed intervals between pulses are driven by the gravitational pull of the distant subgiant, which modifies the motion of the inner pair relative to Earth and explains the unusually large apparent slowdown measured by FAST. The distant subgiant will eventually transform into another white dwarf through a much gentler process. Observatories plan to continue monitoring the system to explore astrophysical processes in extreme environments and map the complex orbital interactions across cosmic time.