Triple system with pulsar discovered in China — South China Morning Post
Chinese astronomers using the FAST radio telescope have discovered a triple star system about 7,000 light-years from Earth. It includes a millisecond pulsar, a white dwarf and a Sun-like star. South China Morning Post reports the discovery.
A stable orbital system
The pulsar rotates more than 300 times per second and completes one orbit around the white dwarf every eight days. The Sun-like star moves around this pair on a more distant orbit, completing it in 73.5 years.
The study by a group led by Han Jinlin of the National Astronomical Observatories in Beijing was published in The Astrophysical Journal Letters. This is only the second known system of this type: in a triple system discovered by a US group in 2014, all three stars were already dead.
Why the pulsar was slowing down
FAST first detected this pulsar in 2020. Over five years of observations, specialists at the Xinjiang Astronomical Observatory established that its rotation was slowing by about 100 times faster than that of similar pulsars. In an April article in Nature Astronomy, they noted that this contradicts the standard theory of the formation of such objects and may indicate the presence of another body in the system.
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The authors of the new study combined FAST data with results from other telescopes, including 18 years of gamma-ray observations by NASA's Fermi telescope. They concluded that the gravity of the Sun-like star causes the pulsar to move back and forth, making its rotation appear slower.
An opportunity to test gravity
Scientists believe that the three stars formed from a single gas cloud, but evolved at different rates due to their different initial masses. The most massive star, about 20 times more massive than the Sun, exploded and left behind a pulsar. Another became a white dwarf, while the least massive star still shines because it is at a sufficient distance from the pair.
Such systems are extremely rare because the explosion that forms a pulsar can destroy the stellar trio. At the same time, they make it possible to test theories of gravity, including the strong equivalence principle in Einstein's theory of gravity. Both research groups also established that the Sun-like star will make its closest approach to the inner pair in 2036, allowing the system's parameters to be measured more precisely.
