Thirty years ago last January, astronomers Aleksander Wolszczan and Dale Frail discovered the first-ever planets beyond the solar system, orbiting pulsar PSR B1257+12. But decades on, only a handful of these extreme objects have been found to have planets, making the first-ever detection even more precious.
In new research presented a the National Astronomy Meeting, graduate researcher Iuliana Nitu showed that less than 0.5 percent of all known pulsars could host Earth-mass planets. Pulsars are a type of neutron stars that form once massive stars go supernova.
"Pulsars are incredibly interesting and exotic objects. 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, from the University of Manchester, said in a statement.
Known planets around pulsars are far from usual. There’s a diamond planet – a former star most likely – orbiting pulsar PSR J1719-1438, for example. So to work out how these peculiar worlds came to be, Nitu’s team undertook the largest search of planets around pulsars to date, studying 800 of them. They looked for worlds up to 100 times the mass of our planet, which orbited the pulsar with a period between 20 days to 17 years.
They had 10 potential detections, with the most likely candidate a system known as PSR J2007+3120, which has probably two planets slightly bigger than Earth – but maybe more – and orbital periods of 1.9 and about 3.6 years.
Based on the full survey, there’s no clear favorite in the type of planet mass or orbital period for a planetary system around a pulsar. But there is something that makes them very different from the Solar System apart from the obvious central member. The orbits of the planet are highly elliptical, different from the close to circular ones of the planets in our neighborhood.
The survey made use of the data collected on pulsars by the Jodrell Bank Observatory over the last 50 years. Pulsars were discovered by Dr. Jocelyn Bell Burnell in 1967 using the Interplanetary Scintillation Array, a radio telescope she helped build.
"[Pulsars] produce signals which sweep the Earth every time they rotate, similarly to a cosmic lighthouse," added Nițu. "These signals can then be picked up by radio telescopes and turned into a lot of amazing science."
Pulsars are fascinating objects in themselves but they are also being used as a galaxy-size gravitational wave observatory.