The first ever exoplanets were discovered 30 years ago around a rapidly spinning star, called a pulsar. Now, astronomers have revealed that these planets may be extremely 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 planets to form and survive around pulsars are currently unknown. A survey of 800 pulsars followed by the Jodrell Bank Observatory over the past 50 years has revealed that the first discovered exoplanet system may be extremely uncommon: less than 0.5% of all known pulsars could host Earth-mass planets.
Pulsars are a type of neutron star, the densest star in the universe, born during powerful explosions at the end of a typical star’s life. It is exceptionally stable, spins quickly, and has incredibly strong magnetic fields. Pulsars emit beams of bright radio emission from their magnetic poles that appear to pulsate as the star rotates.
“[Pulsars] “It produces signals that sweep the Earth every time it rotates, similar to a cosmic lighthouse,” says Nițu. “These signals can then be picked up by radio telescopes and turned into a lot of amazing science.”
In 1992, the first exoplanets were discovered orbiting a pulsar called PSR B1257 + 12. It is now known that the planetary system hosts at least three planets similar in mass to the rocky planets of our solar system. Since then, a handful of pulsars have been found to host planets. However, the extremely violent conditions surrounding the birth and life of pulsars make “normal” planet formation improbable, and many of these discovered planets are exotic objects (such as planets made mostly of diamond) unlike those we know in our solar system.
A team of astronomers at the University of Manchester has conducted the largest search for planets orbiting pulsars to date. In particular, the team looked for signs of planetary companions with masses up to 100 times the mass of Earth, and orbital time periods between 20 days and 17 years. Of the ten possible discoveries, the most promising is the PSR system J2007 + 3120 with the potential to host at least two planets, with masses a few times greater than that of Earth, and with orbital periods of 1.9 and ~3.6 years.
The results of the work indicate that there is no bias for specific planetary masses or orbital periods in pulsar systems. However, the results give information about the shape of the orbits of these planets: unlike the semicircular orbits found in our solar system, these planets will orbit their stars on highly elliptical paths. This indicates that the formation process of pulsar planetary systems is very different from that of traditional stellar planetary systems.
Nițu discusses the motivation behind her research, saying, “Pulsars are incredibly strange and interesting objects. Exactly 30 years ago, the first extrasolar planets were discovered around a pulsar, but we do not yet understand how these planets can form and live in. Such planets Extreme conditions. Finding out how common they are, and what they look like is a crucial step toward that.”
Astronomers survey 800 pulsars to see if any of them have planets
Presented by the Royal Astronomical Society
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