By using the 64-m Parkes radio telescope, a team of scientists have discovered two new exotic millisecond pulsars in the globular cluster 47Tucanae (NGC 104), 16,700 light years away from Earth.
Currently, there are 25 confirmed pulsars in 47Tucanae, a global cluster that ontains at least 500,000 stars — the second most populated cluster in our galaxy. All of them were discovered by reprocessing archival observations from the Parkes radio telescope (Parkes, New South Wales, Australia), a telescope as part of the Australia Telescope National Facility (ATNF) network of radio telescopes.
The new pulsars, named PSRs J0024−7204aa and J0024−7204ab, are millisecond pulsars — rapidly rotating neutron stars — with a high spin frequency, much higher than those of the galactic population. PSRs J0024−7204aa has a pulse frequency higher than any other pulsars currently known in the cluster and ranks 12th amongst all the currently known pulsars.
Astronomers think that millisecond pulsars are related to low-mass X-ray double systems. The high-energy X-rays in these systems are emitted by the collision between the accretion disk of matter of a companion star and particles racing away from the pulsar at exuberant speeds.However, the newly pulsar J0024−7204aa is unlikely to be in a fast binary system as there is no evidence that is accelerating. The second pulsar is weaker and fainter and only occasionally observable in scientists data. Its associated and situated in the central region of 47Tucanae, having a proper motion consistent with the global proper motion of the cluster, as astronomers reported.
One of the primary goals of modern day pulsar astronomy is to discover an exotic system with a millisecond pulsar in orbit around a black hole. Evolutionary models suggest that such a system is only likely to form in globular cluster where is high stellar interaction rates. Such system, if exists, is considered “an authentic holy grail” for testing Einstein’s theory of gravity.
The two new discoveries add to the growing population of pulsars in globular clusters. Such pulsars are weak and hard to detect. However, in the near future, much more sensitive telescopes, such as MeerKAT and the Square Kilometer Array (SKA), will be operating and will be able to make regular observations of these new pulsars.