Extreme pulsars have new exoplanets

(ORDO NEWS) — Astronomers have found another dozen extremely rare exoplanets that orbit neutron pulsar stars: it is still not clear how they appeared in orbit around such extreme objects.

The first exoplanet, discovered in the early 1990s, revolves around a pulsar – a neutron star that sends regular and short radio pulses to Earth. It was a great stroke of luck: planets around pulsars are extremely rare, and it is still not clear how they can appear in such extreme conditions.

This is also indicated by new results obtained by scientists from the University of Manchester. Liliana Nițu will report on them at the National Meeting of Astronomers (NAM 2022), which is taking place these days in the UK. Briefly about the work is reported in the press release of the NAM 2022 organizing committee.

The largest stars turn into black holes at the end of their lives, and those whose mass is not enough for this turn into neutron stars.

These are objects of incredible density: with a mass comparable to the mass of an average star, their diameter can be only a couple of tens of kilometers.

Some of them rotate extremely quickly and throw out powerful and narrow streams of radio emission from the poles. At the moments when such a stream is directed towards the Earth, we see a star in the form of a flash – a periodically ignited pulsar.

PSR 1257+12 also belongs to the pulsars , located 2300 light years from the Sun and flashing at a frequency of about 160 hertz. It was he who, in 1992, managed to detect planets outside the solar system for the first time in history – the first confirmed system of exoplanets B and C.

Today it is known that there are three planets and they all belong to the class of super-Earths, having a rocky surface and several times more mass, than the Earth. However, it is still not clear how they could appear in such an extreme object as a pulsar.

In any case, this is a rarity: of the several thousand exoplanets known today, only about a dozen are in pulsar systems. And only 0.5 percent of pulsars have planets.

A new search for such worlds was carried out by Liliana Nitu and her colleagues, identifying ten possible candidates that can be confirmed by additional observations.

The most interesting of these turned out to be the PSR J2007+3120 pulsar system, which apparently hosts at least two exoplanets. Both of them are several times more massive than the Earth and make a complete revolution around PSR J2007+3120 in 1.9 and 3.6 years.

The search covered possible planets with masses up to 100 Earth and with orbital periods from 20 days to 17 years. At the same time, among the candidates found, it is not possible to single out “preferences” in one direction or another.

The only feature of the planets in pulsars that astronomers noticed was their highly elongated orbits. In the Sun and in the vast majority of other systems, the planets mostly move in circular orbits, while in pulsars they move in highly elliptical orbits. This may help in solving the mystery of their origin.

Today, scientists are considering three hypotheses about the appearance of planets around pulsars. Perhaps such worlds may be the remnants of a nearby neighboring star that died in the same supernova explosion in which the pulsar itself was formed.

In addition, they can be formed from the dust and debris of a neighbor destroyed by the explosion. Finally, pulsars can sometimes catch planets as they pass by, trapping them in their gravity.

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