Pulsar planets are extrasolar worlds that are found orbiting pulsars, or rapidly rotating neutron stars. In new research, Iuliana Camelia Nitu, a Ph.D. student at the University of Manchester, and colleagues searched for planetary companions around 800 pulsars monitored at the Jodrell Bank Observatory, with both circular and eccentric orbits of periods between 20 days and 17 years. They found that pulsar planets are extraordinarily uncommon — less than 0.5% of all known pulsars could host Earth-mass planets.
An artist’s impression of the pulsar-planet system PSR B1257+12. Image credit: NASA / JPL-Caltech.
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 emission from their magnetic poles that appear to pulse as the star rotates.
The processes that cause planets to form, and survive, around pulsars are currently unknown.
“Pulsars produce signals which sweep the Earth every time they rotate, similarly to a cosmic lighthouse,” Nitu said.
“These signals can then be picked up by radio telescopes and turned into a lot of amazing science.”
In 1992, the first ever exoplanets were discovered orbiting a pulsar called PSR B1257+12.
The planetary system is now known to host at least three planets similar in mass to the rocky planets in our Solar System.
Since then, a handful of pulsars have been found to host planets.
However, the extremely violent conditions surrounding the births and lives of pulsars make ‘normal’ planet formation unlikely, and many of these detected planets are exotic objects unlike those we know in our Solar System.
Nitu and colleagues performed the largest search for planets orbiting pulsars to date.
In particular, they looked for signals that indicate the presence of planetary companions with masses up to 100 times that of the Earth, and orbital time periods between 20 days and 17 years.
Of the 10 potential detections, the most promising is PSR J2007+3120 with the possibility of hosting at least two planets, with masses a few times bigger than the Earth, and orbital periods of 1.9 and 3.6 years.
The results of the work indicate no bias for particular planet masses or orbital periods in pulsar systems.
However, the results do yield information of the shape of these planets’ orbits: in contrast to the near-circular orbits found in our Solar System, these planets would orbit their stars on highly elliptical paths.
This indicates that the formation process for pulsar-planet systems is vastly different than traditional star-planet systems.
“Pulsars are incredibly interesting and exotic objects,” Nitu said.
“Exactly 30 years ago, the first extra-solar planets were discovered around a pulsar, but we are yet to understand how these planets can form and survive in such extreme conditions.”
“Finding out how common these are, and what they look like is a crucial step towards this.”
Nitu presented the findings today at the 2022 National Astronomy Meeting(NAM 2022).
_____
Iuliana C. Niţu et al. 2022. A search for planetary companions around 800 pulsars from the Jodrell Bank pulsar timing programme. MNRAS 512 (2): 2446-2459; doi: 10.1093/mnras/stac593
Source link: https://www.sci.news/astronomy/pulsar-planets-10986.html
