Using the MeerKAT radio telescope array, an international team of astronomers has discovered eight new millisecond pulsars. The new objects are located in six globular clusters. This is reported in an article published in the arXiv preprint repository.
Pulsars are highly magnetized rotating 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 (MSP). Astronomers speculate that they form in binary systems when the initially more massive component turns into a neutron star, which then unwinds due to accretion of matter from the secondary star.
The class of extreme binary pulsars with semi-degenerate companion stars is called “spider pulsars”. These objects are further classified as “black widows”.
Now, a team of astronomers led by Alessandro Ridolfi of the Cagliari Observatory, Italy, is reporting the discovery of eight new MSPs. Of these, five are binary systems, and three are weak isolated pulsars. The discovery was made with the 64-dish MeerKAT radio telescope array in South Africa.
Five new MSPs, designated 47 Tuc ac, 47 Tuc ad, NGC 6624G, M62G, and Ter 5, have been discovered in binaries. Objects NGC 6522D, NGC 6624H, and NGC 6752F are faint isolated MSPs. The rotation periods of the new pulsars range from 2.74 to 8.48 ms.
According to the article, 47 Tuc ac (rotation period 2.74 ms) and 47 Tuc ad (rotation period 3.74 ms) are eclipsing “spider pulsars” with low-mass satellites and regular shadowing of their pulsed radiation. 47 Tuc ac turned out to be a “black widow” with an orbital period of about 0.18 days and a minimum satellite mass of about 0.0075 solar masses. Both MSPs are located in globular cluster 47 Tuc, about 15,300 light years from Earth.
NGC 6624G, with a rotation period of 6.09 ms, is a double MSP with a highly eccentric orbit in the cluster NGC 6624. It has an orbital period of 1.54 days and a pulsar mass of about 2.1 solar masses. In this case, the mass of the satellite is only 0.5 Sun. Astronomers speculate that the companion star could be either a massive white dwarf or a neutron star. Another MSP found in this cluster, designated NGC 6624H, is isolated and has a rotation period of approximately 5.13 ms.
M62G is a circular-orbiting double MSP located in the massive M62 cluster, about 22,000 light years away. Its rotation period is about 4.61 ms, its orbital period is about 0.77 days, and the mass of its satellite is estimated to be at least 0.1 solar masses.
The remaining binary MSP, designated Ter 5 an (rotation period 4.8 ms), has a slightly eccentric orbit with the longest orbital period (about 9.62 days). A white dwarf with a minimum mass of 0.43 solar masses is considered a secondary object in this system. The object is part of the globular cluster Ter 5, located in the galaxy’s bulge.
Isolated pulsars NGC 6522D and NGC 6752F have rotation periods of 5.53 ms and 8.48 ms, respectively. NGC 6522D is located in the cluster NGC 6522, which lies about 25,000 light-years away, near the center of our galaxy. As for the slowest rotating object reported in the article, it is located in the collapsed core cluster NGC 6752, about 13,000 light years from Earth.