Image illustrating neutron star

Scientists have discovered a strange neutron star spinning extremely slowly

Neutron stars are the dense remnants of the supernova explosion of a massive star. As the neutron star rotates, it can produce radio wave beams that race across the sky, producing regular flashes like cosmic lighthouses. Scientists have known more than 3000 neutron stars in our Milky Way.

An international team of scientists led by members of the ERC-funded MeerTRAP (More Transients and Pulsars) group in The University of Manchester– has discovered a strange radio-emitting neutron star, spinning extremely slowly, completing one revolution every 76 seconds. The discovery of this strange rotating star is unlike anything seen so far.

Scientists reported that it is a unique discovery because it belongs to the graveyard of neutron stars, where they expect no radio emission at all.

Scientists named the neutron star PSR J0901-4046, which shows features of pulsars, (ultra-long period) magnetarseven fast radio bursts† The emitted radio energy suggests a pulsar origin, the pulses with chaotic subpulse components and the polarization of the pulses are reminiscent of magnetars.

The discovery was made using the MeerKAT radio telescope in South Africa. The MeerTRAP instrument initially detected a single flash or pulse — while conducting imaging observations — led by another team, ThunderKAT.

Then MeerTRAP and ThunderKAT teamed up to find out where it came from. It was then possible to validate the pulsations and get an accurate position for the source by combining the data from the two teams, allowing for more thorough and sensitive follow-up observations.

dr. Manisha Caleb, formerly of the University of Manchester and now the University of Sydney, who led the study, said: “Amazingly, we detect radio emission from this source only 0.5% of its rotational period. This means that it is very coincidental that the radio beam crosses the Earth. Therefore, it is likely that there are many more of these very slowly rotating sources in the Milky Way, which has important implications for how neutron stars are born and age.”

“Most pulsar studies don’t look for periods that long, so we have no idea how many of these sources there are. In this case, the source was bright enough to detect the single pulses with the MeerTRAP instrument at MeerKAT.”

The spin period of this strange neutron star was more similar to a white dwarf† It remains elusive how long this source has been broadcasting on the radio. It was discovered in a well-studied part of the Milky Way, but radio surveys don’t usually look for long periods or pulses lasting more than tens of milliseconds.

Professor Ben Stappers of the University of Manchester and principal investigator of the MeerTRAP project said: “The radio emission from this neutron star is unlike anything we’ve seen before. We can watch it for about 300 milliseconds, which is much longer than most other radio-emitting neutron stars. There appear to be at least seven different pulse types, some of which exhibit highly periodic structures, which can be interpreted as seismic oscillations from the neutron star. These pulses can give us a vital insight into the nature of the emission mechanism for these sources.”

dr. Ian Heywood of the ThunderKAT team and the University of Oxford, who contributed to this study, said“The sensitivity that MeerKAT offers, combined with the advanced search possible with MeerTRAP and the ability to capture simultaneous images of the sky, made this discovery possible. It took an eagle eye to spot it for something that might have been a real source because it looked so unusual!”

This new finding strengthens the case for a new type of radio transients known as ultra-long-period neutron stars, implying a link between the evolution of highly magnetic neutron stars, ultra-long-period magnetars, and fast radio bursts.

Magazine reference:

  1. Caleb, M., Heywood, I., Rajwade, K. et al. Discovery of a radio-emitting neutron star with an ultra-long spin period of 76 s. Nat Astron (2022). DOI: 10.1038/s41550-022-01688-x

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