Astronomers have found a candidate for ultra-slow neutron stars

(ORDO NEWS) — The object rotates with a period of more than a thousand seconds, which is unusually slow for a 20-kilometer celestial body with a mass greater than that of the Sun.

An international team of astronomers, using observations from the Murchison Radio Telescope Array, has discovered a strange object in our Galaxy – something that emits radio waves with a period of 18.18 minutes. This is not very similar to conventional radio pulsars, in which the frequency of the signal is measured in fractions of a second. In addition, periodically the nature of the signals changes somewhat – for unknown reasons.

The authors of a paper published in Nature suggest that this is an unusual magnetar – a neutron star with a strong magnetic field, but for some reason a large period of rotation around its axis. If confirmed, the discovery could be one of the first to describe bodies of this kind.

In general, the project grew out of the scientific work of a student (one of the authors of the work), who was looking for some outstanding events in the archive data of the Murchison array. Suddenly, he came across 70 rather strong signals from the first half of 2018: they were not like anything described in the scientific literature.

The approximate frequency of the radio signal was 1091 seconds. By all indications, it was similar to the signals from the magnetar. This is the name of a rapidly rotating neutron star, an object with a diameter of only 20 kilometers (that is, much smaller than Moscow), but at the same time more massive than the Sun. An object of such exceptional density is formed during the catastrophic compression of the core of a star that bursts into a supernova.

With a sharp compression, the mass of the nucleus does not change, which is why its rotation accelerates sharply – literally up to hundreds of revolutions per second. The magnetic field of such an object is super-powerful, hence the name “magnetar”.

And the lines of this field in the region of the poles of a neutron star become a natural particle accelerator, and an extremely powerful one at that. As a result of the operation of the “accelerator”, a by-product is formed: electromagnetic radiation, which is produced by particles accelerated by a magnetic field.

The detected object is similar to a magnetar – in all respects, except for one. The period of the radio signal from a magnetar depends on its rotation period: it turns out that the new object has a rotation period of more than a thousand seconds – hundreds of times longer than that of “normal” magnetars.

Astronomers have found a candidate for ultra slow neutron stars 2

Meanwhile, the deceleration of the rotation of neutron stars, according to modern concepts, occurs at rates from one billionth to one ten sextillionth (a figure with 22 zeros) of a second per second of the life of a neutron star. The fastest deceleration occurs in a young neutron star, and over time it falls.

This means that in order to achieve a rotation period of 1091 seconds, the deceleration of the rotation of the detected object should have continued from a trillion to 10 trillion trillion (a figure with 24 zeros) seconds. In years, this is approximately from 30 thousand to 300 quadrillion years – moreover, since the slowdown of rotation in a mature magnetar is slow, in practice this figure cannot be close to 30 thousand years.

The fact that the period of time for such an unprecedented deceleration of rotation must be very long is indirectly indicated by the following: so far, no one has discovered neutron stars emitting with such a huge period. However, as noted in the paper, other explanations in this case are unlikely.

The radio emission of the detected object has a linear rather than circular polarization – its electromagnetic waves oscillate in one plane, not two. The radio emission from the flares of red and white dwarfs has circular polarization, that is, it does not look like the one detected. Yes, and its power should be noticeably less.

Comparing the behavior of radio waves of different lengths emanating from a new source, astronomers have determined that it should be located about 4240 light years from us, in the plane of the galactic disk of the Milky Way. This makes it one of the relatively close candidates for neutron stars.

Previously, astronomers have found something remotely similar: for example, the source of intermittent radio emission GCRT 1745, which had a periodicity of 77 minutes. However, between it and a typical magnetar (radiation frequency no more than 30 seconds) there was too large a gap in the rotation period. The found object seems to fill this gap and may indicate the existence of many other magnetars with rotation periods unusual for astronomers.

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