Chinese, European teams confirm FAST discovery of primordial pulsar triple – Global Times

China’s Five-hundred-meter Aperture Spherical radio Telescope has helped uncover the first known primordial pulsar triple system containing a still-evolving companion star, designated PSR J0435+3233, according to the Global Times. Chinese and European scientists independently confirmed the discovery using shared data from observatories around the world.

Detection and Measurements of PSR J0435+3233

The system was first detected on June 8, 2020, by a National Astronomical Observatories team conducting a drift-scan survey with the telescope known as China’s Sky Eye. The pulsar, a rapidly rotating neutron star, completes one rotation every 3.2 milliseconds. Researchers at the Xinjiang Astronomical Observatory subsequently monitored the object with the telescope for nearly five years, obtaining 192 timing measurements.

An almost circular orbit allows the white dwarf and the pulsar to revolve around their joint center of mass every eight days, as revealed by these measurements. However, the observations presented a puzzle when the pulsar appeared to be slowing down about 100 times faster than comparable millisecond pulsars. Those findings were published in Nature Astronomy in April.

Combined Data Reveals a Third Companion Star

To investigate the unusual slowdown, a research team led by Han Jinlin combined radio measurements from the facility with publicly available optical and infrared data from Gaia, 2MASS, and Pan-STARRS, alongside long-term gamma-ray observations from the Fermi satellite. That analysis revealed a third companion: a star with roughly the mass of the Sun. The Chinese study led by Han was published in The Astrophysical Journal Letters on Friday.

At the same time, a separate group of researchers from the UK, France, the Netherlands, and Germany independently evaluated comparable archival records, arriving at identical conclusions regarding the triple structure of the system. An elongated orbit with an eccentricity of roughly 0.6 enables the outer star to circle the inner pair in approximately 73.5 years, according to calculations by the Chinese team. The unusually large apparent slowdown and altered intervals between observed pulses are caused by its gravitational pull shifting the motion of the inner pair relative to Earth.

Comparison With Known Triple Systems

PSR J0435+3233 stands as just the second verified stellar triple housing a pulsar, leaving aside systems that include planetary companions. The US Green Bank Telescope was used to find the previously known system, PSR J0337+1715, which already comprises one pulsar and a pair of white dwarfs. Astronomers gain an uncommon chance to investigate how such systems develop thanks to the presence of a star that has not yet turned into a stellar remnant.

National Astronomical Observatories described the stellar triple as extremely unique because it contains a still-evolving star. In the proposed formation scenario, the most massive of the three stars began with about 20 times the Sun’s mass and eventually exploded as a supernova, leaving behind the neutron star. Its closer companion, initially several times as massive as the Sun, later became a white dwarf, while the least massive star remains in active stellar evolution.

Three Member System Tests Fundamental Theories of Gravity

The National Astronomical Observatories noted that the outer star is expected to eventually transform into a white dwarf over time, resulting in a pulsar accompanied by two white dwarfs. The discovery was characterized by the observatory as a milestone achieved through multinational collaboration, with research groups in China and other countries building upon each other’s findings and merging multi-wavelength observations.

Stating that the evolving primordial system serves as a precious natural laboratory to put foundational gravity theories—such as the strong equivalence principle—to the test, the National Astronomical Observatories highlighted the distinct and robust gravitational interplay among all three components. Furthermore, the system provides a rare avenue for examining the intricate developmental stages of triple-star arrangements and investigating astrophysical phenomena within harsh settings.

FAST has discovered more than 1,000 pulsars since its completion, including a range of rare systems.