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Chinese Astronomers Discover New Millisecond Pulsar Using FAST
Recent observations by the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) have led to the discovery of a new millisecond pulsar, designated PSR J2129-1210O. This discovery is significant as prior searches overlooked this pulsar due to its spin period aligning closely with the harmonics of the better-known pulsar PSR J2129+1210A.
The findings were detailed in a study released on April 23 on the arXiv pre-print server.
Pulsars are neutron stars characterized by their rapid rotation and emission of electromagnetic radiation. Millisecond pulsars (MSPs), which have rotation periods of less than 30 milliseconds, are particularly noteworthy for their extreme speeds.
A common theory about the formation of pulsars suggests that they originate in binary star systems. In these systems, the more massive star evolves into a neutron star that gains speed by accreting matter from its companion star.
NGC 7078, known as Messier 15 or M15, is a globular cluster renowned for its population of pulsars. Situated approximately 35,700 light years away, M15 is considered one of the oldest clusters, and simulations predict it hosts a greater number of pulsars compared to other clusters observed by FAST.
The observational campaign targeting this cluster was conducted by a research team led by Yinfeng Dai from Guizhou University, spanning from November 2019 to February 2024.
The team identified a pulsar with a spin period of roughly 11.07 milliseconds, subsequently naming it PSR J2129-1210O, or M15O. This pulsar evaded detection in earlier surveys primarily because its spin period is close to the 10th harmonic of PSR J2129+1210A (M15A).
“If the period of a new pulsar overlaps or is similar to that of a known pulsar, alongside similar dispersion measure (DM) values due to the cluster’s concentrated DM distribution, conventional algorithms may struggle to accurately separate the signals. This can lead to missed discoveries,” the researchers noted.
The study indicates that M15O has a dispersion measure of about 67.44 pc/cm³. It is positioned 0.37 arcseconds from the center of the pulsar cluster and 0.81 arcseconds from M15A, making it the nearest known pulsar to the optical center of M15.
In addition to M15O, the FAST observations uncovered two other pulsars, identified as PSR J2129+1210M and PSR J2129+1210N (M15M and M15N). Details regarding these pulsars will be presented in an upcoming publication by the researchers.
More information: Yinfeng Dai et al, The FAST Discovery of a Millisecond Pulsar Hidden in the Harmonics of PSR J2129+1210A (M15A), arXiv (2025). DOI: 10.48550/arxiv.2504.16872
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phys.org