BEIJING, Oct. 9 (Xinhua) -- A Chinese research team has found that a pulsar discovered by the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) is part of a primordial triple star system still in the process of evolving, according to a study published Friday in the Astrophysical Journal Letters.
With its extraordinary detection capabilities, FAST has discovered more than 1,000 pulsars. The pulsar in this triple system was detected on June 8, 2020, by the team from National Astronomical Observatories under the Chinese Academy of Sciences (NAOC) using FAST.
After the discovery, a team from the Xinjiang Astronomical Observatory found that the pulsar is orbited by a white dwarf companion. They also found that the pulsar's rotation period is showing an unexpected increase of 1 nanosecond per year, two orders of magnitude higher than similar pulsars.
Following this, NAOC researcher Han Jinlin led researchers from several domestic institutions to analyze the archival data from FAST and other observational facilities. They found that the pulsar has a second companion -- a Sun-like star still evolving, with a mass nearly identical to that of the Sun. These three celestial bodies form a rare triple system.
Based on stellar evolution theory, the team inferred that the triple system originated as "primordial triplets" born from the same gas cloud. The most massive of these stars has already completed its evolution, ended its life in a supernova explosion and become the pulsar observed today by FAST. The second-most massive star has also ended its evolution, becoming the white dwarf that accompanies the pulsar.
The least massive star is relatively far from the other two and was largely unaffected by their early supernova explosions. It is a "living" star, still evolving steadily.
Prior to this discovery, the only known pulsar triple star system was found by the Green Bank Telescope. It consists of a pulsar and two white dwarfs, all three of which have already ended their evolutionary process.
The research team noted that this system shows clear and significant three-body gravitational interactions, making it an excellent natural observational platform for testing fundamental gravitational theories such as the strong equivalence principle.
It also provides a valuable research target for understanding the complex evolutionary mechanisms of triple star systems and for exploring astrophysical processes under extreme conditions.
Located in a naturally deep and round karst depression in southwest China's Guizhou Province, FAST has a reception area equal to 30 standard football fields. As the world's largest single-dish radio telescope, FAST started formal operations in January 2020 and was officially opened to the world in March 2021. ■
