Chinese astronomers find evolving triple-star system with pulsar that challenges spin-up theory
Chinese astronomers, using the FAST radio telescope, identified a triple-star system, J0435+3233, containing a pulsar spinning once every 3.2 milliseconds, a white dwarf and a Sun-like star, according to a paper in The Astrophysical Journal Letters. A separate team led by Prof. WANG Na of the Xinjiang Astronomical Observatory reported in Nature Astronomy that the pulsar's spin-down rate is two orders of magnitude higher than any other known millisecond pulsar in the Galaxy, which the team said challenges the classical accretion-driven formation theory.
Bottom line — The system's outer star orbits every 73.5 years, and the pulsar's spin period is increasing about one nanosecond a year.
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The Chinese-led paper says the outer star was identified by combining FAST radio data with archived infrared, optical and gamma-ray data, and that the system is likely to end as a neutron star with two white dwarfs.
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Global Times reports the findings as a joint Chinese-European confirmation, though the article text does not detail the European contribution.
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According to the Nature Astronomy summary from the Xinjiang Astronomical Observatory, the pulsar sits well above the Eddington spin-up line, which the team says is not explained by the standard recycling process.
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The researchers suggest super-Eddington accretion onto a strongly magnetized neutron star, or accretion-induced collapse of a magnetized white dwarf, as possible explanations, a view the team presents as speculative.
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The Astrophysical Journal Letters paper notes that a second, independent group led by P. Freire reached similar results while the Chinese team was preparing its submission.
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The paper says the system was probably formed from three stars born together, with the pulsar progenitor around 20 solar masses, though these masses are presented as an illustrative scenario rather than a measurement.