Using China’s Five-hundred-meter Aperture Spherical radio Telescope (FAST), astronomers have discovered three new pulsars in an ancient Galactic globular cluster known as Messier 15. Two of them have been long-period pulsars, while the remaining one rotates thus. so fast that it is classified as a millisecond pulsar. The finding was reported in a paper published on December 11 on the pre-print server arXiv.
Pulsars are highly magnetic, spinning neutron stars that emit a beam of electromagnetic radiation. The fastest rotating pulsars, with rotation periods of less than 30 milliseconds, are known as millisecond pulsars (MSPs). Astronomers believe it formed in a binary system when the larger component initially became a neutron star that was then spun off by accretion of matter from the secondary star.
Located about 35,700 light years from Earth, Messier 15 (also known as NGC 7078) is a core-collapsed GC with a radius of about 88 light years and an estimated mass of 560,000 solar masses. It is one of the oldest (about 12 billion years) and poorest Galactic GCs (with a metallicity of approximately 2.25), and one of the densest GCs in our galaxy.
Previous observations of Messier 15 detected nine pulsars and the first was identified in 1989. According to simulations, Messier 15 is possibly one of the GCs with the highest number of pulsars. So a group of astronomers led by Yuxiao Wu of Chongqing University of Posts and Telecommunications in China, decided to conduct a pulsar search in this cluster using FAST.
The newly discovered pulsars received the names PSR J2129 + 1210J, PSR J2129 + 1210K and PSR J2129 + 1210L. The observations found that PSR J2129 + 1210J is an MSP, while the other two are long-period pulsars.
According to the study, PSR J2129+1210J is an isolated pulsar with a spin period of approximately 11.84 milliseconds and its dispersion measure calculated to be 66.68 pc/cm3. As for PSR J2129+1210K, it has a spin period of about 1.93 seconds and a dispersion scale of 68.01 pc/csm3.
With a spin period of 3.96 seconds, PSR J2129+1210L is the longest spinning pulsar in a GC known to date. The dispersion measure of this pulsar was found to be approximately 67.1 pc/cm3.
The researchers noted that the exact position of PSR J2129 + 1210K and PSR J2129 + 1210L remains unknown, but they are probably not too far from the core of Messier 15. Therefore, more observations are needed to find their exact location, which helps determine whether they are young or recycled pulsars.
Yuxiao Wu et al, Three Pulsars Discovered in the Globular Cluster M15 (NGC 7078) with FAST, arXiv (2023). DOI: 10.48550/arxiv.2312.06067
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Citation: FAST detects three new pulsars in an old globular cluster (2023, December 20) retrieved 21 December 2023 from https://phys.org/news/2023-12-fast-pulsars-globular -cluster.html
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