An international team of astronomers from France, the Netherlands, Great Britain, South Africa, Australia and Russia have discovered an unusual pulsar with a rotation period of 23.5 seconds, making it the slowest object of its kind known. In addition, it was previously believed that pulsars with such a long rotation period simply could not exist. Details about the opening are described in the preprint published in the arXiv.org repository.
Until now, the rotation periods of all known pulsars have ranged from 1.4 milliseconds (fastest) to 12.1 seconds (slowest). One of the tools for searching for these objects is the giant radio telescope Arecibo, however, the identification of slow pulsars is difficult due to the presence of low-frequency "red" noise. Algorithms used to “clean up” the noise reduce the sensitivity to long-term pulsars, and the duration of observation of one object often does not exceed several minutes. Slowly rotating pulsars are more often detected by emitting high-energy radiation (X-rays), such as magnetars and XDINS (X-ray Dim Isolated Neutron Stars).
PSR J0250 + 5854 was detected using the international radio interferometric facility LOFAR (LOw Frequency ARray, low frequency antenna array) and observed through other telescopes, including the Green Bank Telescope radio telescope and the X-ray space observatories ROSAT and Swift. By the magnitude of the measure of dispersion (DM), which determines the number of electrons refracting radio beams between the observer and the pulsar, scientists have determined the distance to the neutron star, equal to about 1.6 kiloparsecs (more than five thousand light years).
The graph of the dependence of the rotation period of the pulsar and the rate of deceleration of the pulsar shows that PSR J0250 + 5854 is located behind the so-called death line, when the neutron star seems to stop emitting radio emission. One of the hypothetical mechanisms for the emergence of radio waves is the production of particles and antiparticles at the poles of the pulsar, in the vacuum region, where the electric and magnetic fields are not orthogonal and are able to maintain a high potential difference. However, for a sufficiently large rotation period, the potential difference is no longer sufficient for the production of pairs and radio waves.
According to another model, part of the energy released with slowing down the rotation of the pulsar can be “spent” with maximum efficiency on the creation of radio emission. This creates a "valley of death" in which objects such as PSR J0250 + 5854 can still exist, bypassing the traditional death lines. Thus, physicists conclude, there must be many more pulsars with an extremely long rotation period.