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Millisecond pulsars (MSPs) are evolved neutron stars with short spin
periods that have gone through a long period of mass transfer in a
low-mass X-ray binary phase. Globular clusters (GCs) - conglomerations
of tens of thousands or millions of stars - are prolific environments
for the formation of MSPs. However, in NGC 6397 - one of the closest
GCs to Earth - only one MSP had been identified until recently. Now
researchers have not only found a second pulsar in our neighboring GC
but have a better idea why other pulsars have "gone missing." Using
the Parkes radio telescope in Australia to observe NGC 6397, Zhang et al.
have reported the discovery of a new 5.78 ms-period MSP, named PSR
J1740-5340B (NGC 6397B), in an eclipsing binary system. This discovery
was confirmed by the MeerKAT radio telescope in South Africa. NGC
6397B is detectable only when the pulsar is on the side of its orbit
closest to the observer. Its measured orbital period of 1.97 days is
the longest among all eclipsing binaries in GCs. This orbital period
is also consistent with that of the previously discovered X-ray source
U18, which was once considered a "hidden MSP." U18 has now been
confirmed by the current research to be NGC 6397B. According to the
researchers, these faint pulsars are hard to pick up in radio bands
either because they are embedded in clouds of plasma or are actively
accreting matter due to their companion stars. (Image credit:
NAOC/ScienceApe)
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