An international team of researchers has shown that at the core of PSR J2039-5617 (a celestial object), is a rapidly rotating neutron star.
About a sixth of the mass of our sun, a stellar companion is in orbit with the pulsar. This result was shown with the help of using the enormous computing power of the citizen science project Einstein@Home, and novel data analysis methods to track down the neutron star’s faint gamma-ray pulsations in data from NASA’s Fermi Space Telescope.
Slowly but surely this star is being evaporated by the pulsar. The international collaboration also found that the companion’s orbit varies slightly and unpredictably over time. In the future, with the help of Einstein@Home, the researchers hope to find more such systems using their search method.
10 years of precise data is required, in search of rapidly spinning neutron stars (the so-called ‘Spider’ pulsar systems) whose high energy outflows are destroying their binary companion stars. “Black Widows”, or “Redbacks”, species of the spider where the female spider has been seen killing the smaller male spider after mating, the pulsars have been given arachnid names after such species.
Using data from NASA’s Fermi Space Telescope, in an exotic binary system, researchers found a neutron star rotating 377 times a second, the new research published in, Monthly Notices of Astronomical Society, detailing how.
Lending their home computing powers to the efforts of the Fermi Space Telescope’s work, the Einstein@Home project, a network of thousands of civilian volunteers, uniquely boosted the astronomer’s findings.
“It had been suspected for years that there is a pulsar, a rapidly rotating neutron star, at the heart of the source we now know as PSR J2039−5617. But it was only possible to lift the veil and discover the gamma-ray pulsations with the computing power donated by tens of thousands of volunteers to Einstein@Home.”Lars Nieder, a PhD student at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI) in Hannover.
In order to not miss any possible signals, the group’s search required combing very finely through the data. On a single computer core, the search would have taken 500 years to complete. As the computing power required is enormous. Thanks to the resources contributed by Einstein@Home, the search was done in just 2 months.
Since 2014, the celestial object has been known as the source of X – rays, gamma rays, and light. In the absence of clear evidence, nothing could be concluded. But all the evidence obtained, hitherto, hinted at a rapidly rotating neutron star in orbit with a light-weight star being at the heart of the source.
The first step towards solving this riddle was the new observations, taken with the help of optical telescopes, of the stellar companion. A gamma-ray pulsar search would be unfeasible even with the help of Einstein@Home huge computing power if the researchers lacked the precise knowledge about binary systems that the new observations provided.
“For J2039-5617, there are two main processes at work. The pulsar heats up one side of the light-weight companion, which appears brighter and more bluish. Additionally, the companion is distorted by the pulsar’s gravitational pull causing the apparent size of the star to vary over the orbit. These observations allowed the team to get the most precise measurement possible of the binary star’s 5.5-hour orbital period, as well as other properties of the system.”Dr. Colin Clark from Jodrell Bank Centre for Astrophysics, lead author of the study.
Depending on which side of the neutron star’s companion is facing the earth, during an orbital period, the system’s brightness varies.
For a new search of about 10 years of archival observations of NASA’s Fermi Gamma-Ray Space Telescope, with the above information and the precise sky position from Gaia data, the team used the aggregating computing power of the distributed volunteer computing project Einstein@Home. Earlier methods developed for this purpose were improved, to search Fermi data for periodic pulsations in the gamma-ray photons registered by the Large Area Telescope onboard the Space Telescope, they enlisted the help of thousands of volunteers. The volunteers donated idle computing cycles on their computer’s CPUs and GPUs to Einstein@Home.
To detect radio pulsations in archival data from the Parkes radio telescope, the new knowledge of the frequency of gamma-ray pulsations helped.
The pulsar’s radio emission is often eclipsed by material that has been blown off the companion star by its nearby Redback pulsar.
- C J Clark, L Nieder, G Voisin, B Allen, C Aulbert, O Behnke, R P Breton, C Choquet, A Corongiu, V S Dhillon, H B Eggenstein, H Fehrmann, L Guillemot, A K Harding, M R Kennedy, B Machenschalk, T R Marsh, D Mata Sánchez, R P Mignani, J Stringer, Z Wadiasingh, J Wu. Einstein@Home discovery of the gamma-ray millisecond pulsar PSR J2039–5617 confirms its predicted redback nature. Monthly Notices of the Royal Astronomical Society, 2021; 502 (1): 915 DOI: 10.1093/mnras/staa3484