New findings show that Earth-sized planets may be even less likely to survive the violent end-of-life conditions of some stars than previously thought. That means the first exoplanet discovered outside the solar system 30 years ago could be a lot stranger than we thought.
Discovered in 1992 by astronomers Alex Wolszczan and Dale Frail, planet PSR B1257+12B has Earth-like mass and orbits an exotic dead star dubbed Pulsar. The discovery was followed by the revelation that the planet is accompanied by at least two other worlds. Orbiting pulsar PSR B1257+12, these other planets are also similar in size to the rocky worlds of the solar system.
However, the largest study ever of pulsars and their planets has shown that these dead stars rarely have Earth-like companions. That’s what this system does NASA describes (opens in new tab) a rarity as a “cemetery” after the supernova that generated PSR B1257+1.
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And conditions in the system, 2,300 light-years from Earth, aren’t getting any more hospitable. The pulsar at its heart spins every 6.22 milliseconds, or about 161 times per second, bombarding its planets with an intense beam of deadly radiation that can be seen from Earth.
It’s no wonder the pulsar was nicknamed the “Lich” after a powerful and evil undead creature of the same name in fantasy.
A survey of 800 pulsars over the past 50 years by researchers at the UK’s Jodrell Bank Observatory found that only 0.5% of pulsars host Earth-like mass planets. The explorers’ results have been published (opens in new tab) in the Monthly Notices of the Royal Astronomical Society.
The discovery deepens the mystery of how planets can survive around pulsars, which like all neutron stars are formed when massive stars reach the end of nuclear fusion and the external pressure supporting them against gravitational collapse ceases.
The resulting collapse creates a massive supernova explosion, often powerful enough to outshine every star in the galaxy that hosts it. In the end, a neutron star of similar mass to the sun stays within a radius similar to that of a city on Earth. Neutron stars are made of the densest known matter in the universe: just a teaspoon of that matter would weigh 8 trillion pounds (3.6 trillion kilograms).
Pulsars are a special type of neutron star that emit bright radio wave radiation due to their rapid rotation and strong magnetic fields.
“[Pulsars] Generate signals that sweep the Earth with each spin, much like a cosmic lighthouse,” says Iuliana-Camelia Nițu, a PhD student at the University of Manchester said in a statement (opens in new tab). “These signals can then be picked up by radio telescopes and turned into a lot of amazing science.”
While many pulsars harbor exotic worlds unlike anything found in the solar system, the violent conditions surrounding pulsar birth and survival seem to make the formation of Earth-like planets around them unlikely.
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Nițu was part of a team of astronomers from the University of Manchester that conducted the largest search to date for planets near pulsars, focusing on planets with masses up to 100 times that of Earth and orbital periods ranging from 20 days to 17 years.
They made ten potential discoveries of such worlds, with the system most likely to host exoplanets of this type being PSR J2007+3120. The team believes this pulsar, located 17,000 light-years from Earth, could host two planets with masses a few times Earth’s and orbital periods ranging from 1.9 to about 3.6 years.
The astronomers did not find enough information to say that planets around pulsars have similar masses and orbital periods, but they seem to have something else in common: the exoplanets around the pulsars studied appear to have highly elliptical orbits, in contrast to the near-circular orbits of planets in the solar system.
This could indicate that whatever planets form around pulsars, these processes are different from the mechanism that led to the formation of planets in the Solar System.
“Pulsars are incredibly interesting and exotic objects. Exactly 30 years ago, the first extrasolar planets were discovered around a pulsar, but we have yet to understand how these planets can form and survive in such extreme conditions,” said Nițu in a expression (opens in new tab). “Finding out how common these are and what they look like is a critical step in that direction.”
tea research (opens in new tab) will be presented at the National Astronomy Meeting (NAM 2022) on July 12.
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