Astronomers detect a new black-widow pulsar
Tomasz Nowakowski
astronomy writer
Sadie Harley
scientific editor
Robert Egan
associate editor
An international team of astronomers reports the discovery of a new "spider" millisecond pulsar, which received designation PSR J1544−2555. The finding was presented in a research paper September 11 on the arXivpre-print server.
The most rapidly rotating pulsars, with rotation periods below 30 milliseconds, are known as millisecond pulsars (MSPs). It is assumed that MSPs are formed in binary systems when the initially more massive component turns into a neutron star that is then spun up due to accretion of matter from the secondary star.
The so-called "spider" pulsars are a unique class of MSPs characterized by eclipses observed in the radio band and containing semi-degenerate companion stars. They are further categorized as "black widows" if the companion has extremely low mass (less than 0.1 solar masses), or "redbacks" if the secondary star is heavier.
Recently, a group of astronomers led by Sergio Belmonte Diaz of the University of Manchester, UK, conducted a search for periodic optical sources in the Fermi-LAT catalog, utilizing the ULTRACAM imaging photometer on the 3.5-m New Technology Telescope at the European Southern Observatory (ESO) in Chile. As a result, they identified a new "black-widow" pulsar.
"In this work, we have presented the discovery of a new black-widow millisecond pulsar, PSR J1544-2555, associated with the Fermi-LAT source 4FGL J1544.2−2554," the researchers wrote in the paper.
The observations found that PSR J1544-2555 contains a neutron star with a spin period of approximately 2.39 milliseconds and a companion star with a radius of about 0.17 solar radii and an estimated mass of 0.095 solar masses. The orbital period of the binary was measured to be some 2.7 hours.
According to the study, PSR J1544-2555, which is estimated to be about 6,500 light years away, has a dispersion measure of 25.8 pc/cm3 and a surface magnetic field strength at a level of 150 million Gauss. It was found that the system showcases orbital period variations and non-thermal emissions that are characteristic of black-widow MSPs.
The observations also allowed the team to detect gamma-ray pulsations of PSR J1544-2555. The gamma-ray luminosity of the system was found to be around 4 decillion erg/s.
Summing up the results, the authors of the paper note that their discovery highlights the importance of the Fermi-LAT catalog in identifying MSP candidates and underscores the effectiveness of optical surveys in detecting variable sources that can be followed up through targeted radio observations.
"This discovery exemplifies the proven capability of the Fermi-LAT catalog in identifying millisecond pulsar candidates and highlights the role of optical surveys in detecting variable sources suitable for radio follow-up," the scientists conclude.
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More information: Sergio Belmonte Diaz et al, Multiwavelength observations of a new black-widow millisecond pulsar PSR J1544-2555, arXiv (2025).
Journal information: arXiv
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