The first ever exoplanets were discovered 30 years ago around a rapidly rotating star called a pulsar. Now astronomers have revealed that these planets may be incredibly rare. The new work will be presented tomorrow (Tuesday 12 July) at the National Astronomy Meeting (NAM 2022) by Iuliana Nițu, a PhD student at the University of Manchester. The processes that cause the formation and survival of planets around pulsars are currently unknown. A survey of 800 pulsars over the past 50 years by the Jodrell Bank Observatory has revealed that this first detected exoplanet system may be extremely unusual: less than 0.5% of all known pulsars could host Earth-mass planets.
Pulsars are a type of neutron star, the densest stars in the universe, born during powerful explosions at the end of a typical star’s life. They are exceptionally stable, rapidly rotating and have incredibly strong magnetic fields. Pulsars emit beams of bright radio radiation from their magnetic poles, which seem to pulsate as the star rotates.”[Pulsars] produce signals that sweep the Earth every time they rotate, much like a cosmic beacon,” says Nițu. “These signals can then be picked up by radio telescopes and turned into a lot of amazing science.”
In 1992, the first ever exoplanets orbiting a pulsar named PSR B1257+12 were discovered. The planetary system is now known to host at least three planets of similar mass to the rocky planets in our solar system. Since then, several pulsars have been found to host planets. However, the extremely violent conditions surrounding the birth and life of pulsars make “normal” planet formation unlikely, and many of these detected planets are exotic objects (such as planets made mostly of diamond) unlike those we know in our solar system.
A team of astronomers from the University of Manchester has carried out the largest ever search for planets orbiting pulsars. In particular, the team looked for signals that indicate the presence of planetary companions with masses up to 100 times that of Earth and orbital periods between 20 days and 17 years. Of the 10 potential detections, the most promising system is PSR J2007+3120, with the possibility of hosting at least two planets, with masses several times larger than Earth, and orbital periods of 1.9 and ~3.6 years.
The results of the work do not indicate any bias for specific planetary masses or orbital periods in pulsar systems. However, the results provide information about the shape of these planets’ orbits: unlike the near-circular orbits found in our Solar System, these planets would orbit their stars in highly elliptical orbits. This suggests that the formation process of pulsar-planet systems is significantly different from traditional star-planet systems. Nițu says about the motivation of his research: “Pulsars are incredibly interesting and exotic objects. Exactly 30 years ago, the first extrasolar planets were discovered around a pulsar, but we still do not understand how these planets can form and survive in such extreme conditions. To find out how are these planets common and what they look like is a crucial step towards that.”
Source Reference: Materials provided by Royal Astronomical Society. Note: Content may be edited for style and length. https://ras.ac.uk/
