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Discovery of eight new millisecond pulsars

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May 01, 2021, 7:42 am

The investigation of the central regions of globular clusters with the MeerKAT radio telescope in South Africa in search of very weak pulsar signals. A press release from the Max Planck Institute for Radio Astronomy, Bonn.



Image of the globular cluster NGC 6624 with the Hubble Space Telescope. Some of the pulsars in the central area of ​​the globular cluster are highlighted in the inset, including the newly discovered pulsar PSR J1823-3021G marked in red with MeerKAT. The star cluster NGC 6624 is located in the direction of the constellation Sagittarius at a distance of almost 8,000 light years from the sun.
(Image: A. Ridolfi et al./INAF/Hubble Space Telescope)
April 28, 2021 - A group of astronomers under the direction of the Italian National Institute for Astrophysics (INAF) and the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn discovered eight millisecond pulsars with the South African MeerKAT radio telescope are in globular clusters with high star density. Millisecond pulsars are neutron stars and thus the densest known stars that rotate around their axis up to 700 times per second. The results are based on research in two international collaborations, TRAPUM and MeerTIME, and are detailed in an article published today in the journal “Monthly Notices of the Royal Astronomical Society”.

Millisecond pulsars are extremely compact stars composed mainly of neutrons and are among the most extraordinary objects in the universe. They pack a hundred thousand times the mass of the earth into a sphere about 15 miles in diameter and they spin around their axis at a rate of hundreds of revolutions per second. They send out a beam of radio waves that brushes the observer with each rotation, like a beacon on a lighthouse. The formation of these objects is strongly favored in environments of high star density in the centers of globular clusters.

“We aligned the MeerKAT antennas to nine globular clusters and were able to discover new pulsars in six of them,” says first author Alessandro Ridolfi, who works as a post-doc at INAF and MPIfR. Five of these new pulsars each orbit a different star, with one of them, PSR J1823-3021G, proving to be particularly interesting. "Due to its highly elliptical orbit and its massive companion, this system is probably the result of a partner swap: After a close encounter, the original partner was driven away and replaced by a new companion star," Ridolfi continues.

Tasha Gautam, PhD student at the MPIfR in Bonn and co-author of the work, explains: “This special pulsar could have a high mass, more than twice the mass of the sun, but it could also be the first confirmed system that results from a millisecond Composed of pulsar and a neutron star. If this is confirmed by the current additional observations, this millisecond pulsar would represent an excellent test field for new findings in fundamental physics. "

The eight new pulsars are only the tip of the iceberg. In the observations that led to their discovery, only about 40 of the 64 MeerKAT antennas were used and they only focused on the central regions of the globular clusters.

"The MeerKAT radio telescope represents a major technological advance for the research and study of pulsars in the southern skies," says Andrea Possenti from INAF, the coordinator of pulsar observations in globular clusters for the MeerTIME collaboration. “In the next few years MeerKAT is expected to find dozens of new millisecond pulsars and give us a foretaste of what will be possible with the future commissioning of the medium-frequency antennas of the SKA observatory. This will revolutionize many areas of astrophysics, including the study of pulsars. "

Ridolfi, Gautam and Possenti are members of the “TRAnsients and PUlsars with MeerKAT” (TRAPUM) collaboration, a “Large Survey Proposal” for MeerKAT with a comprehensive international collaboration of astronomers who are enthusiastic about the possibilities that MeerKAT opens up to them. For this special work they shared the telescope time with a second “Large Survey Proposal” for MeerKAT, MeerTIME, which MeerKAT uses to examine already known pulsars with previously unattained precision.

This work served the TRAPUM collaboration as a model experiment in order to be able to better plan a full-fledged globular cluster survey to search for new pulsars. Such a screening is currently being carried out using all 64 MeerKAT parabolic mirrors (which further increases sensitivity). It will extend the search to many more globular clusters and also measure their outer regions.

“In previous search programs for pulsars in globular clusters, a number of bizarre and extreme double pulsars have already been discovered. With new instruments such as MeerKAT, we will certainly be able to discover more of these extreme systems that tell us more about the fundamental laws of our universe, ”concludes Paulo Freire, another co-author of the MPIfR.



Fourteen of a total of 64 parabolic mirrors in the MeerKAT radio telescope network in the Karoo semi-desert in South Africa.
(Image: South African Radio Astronomy Observatory (SARAO))
background information
The MeerKAT telescope network operated by the South African Radio Astronomy Observatory (SARAO) is the largest radio telescope in the southern hemisphere and one of two precursor instruments to the Square Kilometer Array Observatory (SKAO), which was built in South Africa. The radio telescope located in the Karoo Desert will soon be expanded by an additional 20 parabolic mirrors ("MeerKAT +"), which will increase the total number of antennas to 84. MeerKAT will later be gradually integrated into the first phase of the SKAO project, the construction of which will begin soon and will last until 2027. The first scientific observations with MeerKAT + could begin as early as 2023, during the test phases of the telescope.

TRAPUM (TRAnsients and PUlsars with MeerKAT) is one of the "Large Survey Proposals" for the operation of the MeerKAT radio telescope. It is an international collaboration led by the University of Manchester and the MPIfR and includes institutions such as INAF, the National Radio Astronomy Observatory (NRAO) and the South African Radio Astronomy Observatory (SARAO).

MeerTIME is also a “Large Survey Proposal” for the operation of MeerKAT. It is led by Swinburne University of Technology and connects several Australian institutions as well as INAF, University of Manchester, MPIfR, NRAO and SARAO.

The research team includes Alessandro Ridolfi, Tasha Gautam, Paulo CC Freire, Scott M. Ransom, Sarah J. Buchner, Andrea Possenti, Vivek Venkatraman Krishnan, Matthew Bailes, Michael Kramer, Benjamin W. Stappers, Federico Abbate, Ewan D. Barr, Marta Burgay, Fernando Camilo, Alessandro Corongiu, Andrew Jameson, Prajval V. Padmanabh, Laila Vleeschower, David J. Champion, Weiwei Chen, Marisa Geyer, Aris Karastergiou, Ramesh Karuppusamy, Aditya Parthasarathy, Daniel J. Reardon, Maciej Serylak, Ryan M. Shannon and Renée Spiewak. Twelve of the authors (Ridolfi, Gautam, Freire, Venkatraman Krishnan, Kramer, Abbate, Barr, Padmanabh, Champion, Chen, Karuppusamy, Parthasarathy) have an affiliation with the MPIfR.

Original publication
Eight new millisecond pulsars from the first MeerKAT globular cluster census
A. Ridolfi et al., Monthly Notices of the Royal Astronomical Society, April 28, 2021
(DOI: 10.1093 / mnras / stab790)

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Source: Max Planck Institute for Radio Astronomy

Author: Raumfahrer.net editors