An international team of astronomers has utilized the powerful MeerKAT radio telescope to observe the Galactic globular cluster NGC 6522, leading to the discovery of two previously unknown isolated pulsars within the cluster. This exciting finding was detailed in a paper published on October 5, available on the pre-print server arXiv.
Pulsars are incredibly magnetized, rapidly rotating neutron stars that emit beams of electromagnetic radiation. Astronomers often focus their efforts on globular clusters, as these densely packed groups of stars provide a fertile ground for various astronomical phenomena to occur.
Led by Federico Abbate from the Max Planck Institute for Radio Astronomy in Bonn, Germany, a group of astronomers conducted a targeted search for new pulsars in NGC 6522 as part of the MeerTIME and TRAPUM projects.
NGC 6522 is a core-collapsed Galactic globular cluster located approximately 25,100 light years away, with a mass equivalent to about 300,000 times that of our Sun. It is estimated to be around 12 billion years old, potentially making it the oldest star cluster within the Milky Way.
“In our research, we unveil the discovery of two previously unknown isolated pulsars within NGC 6522, observed using the MeerKAT telescope,” the researchers reported.
The team identified two isolated pulsars and assigned them the names PSR J1803−3002E and PSR J1803−3002F. With these additions, the total count of known pulsars in NGC 6522 now stands at six, and all of them are isolated in nature.
PSR J1803−3002E represents a mildly recycled millisecond pulsar (MSP) with a spin period of around 17.9 milliseconds, found in the vicinity of NGC 6522’s center. Its dispersion measure was determined to be approximately 192.8 pc/cm3.
In contrast, PSR J1803−3002F is a slower pulsar with a spin period of about 148.1 milliseconds, located at a distance of roughly three core radii away from the cluster’s center. The dispersion measure of this pulsar was calculated to be 195.8 pc/cm3.
The researchers highlighted that the spin periods of these newly discovered pulsars are longer than those of the previously known ones. Additionally, they suggested that the characteristic age of PSR J1803−3002F might be smaller than the age of NGC 6522.
This study also pointed out an intriguing finding regarding one of the millisecond pulsars that was previously identified in NGC 6522, denoted as PSR J1803−3002C. It could potentially possess one of the smallest characteristic ages among known millisecond pulsars in globular clusters, estimated at just 132 million years, although further confirmation is required.
The presence of both a slow pulsar and a seemingly young millisecond pulsar, which are rare occurrences within globular clusters, hints at a potential link between their formation and the evolutionary stage of the cluster, as concluded by the authors of the paper.