(ORDO NEWS) — In the early 1990s, planetary history was created. In 1992, two astronomers, Alexander Volshchan and Dale Fraile, published an article in the journal Nature announcing the discovery of the very first planets outside the solar system.
These two extrasolar planets, or exoplanets, immediately intrigued. These were rocky worlds, 4.3 and 3.9 times the mass of the Earth, orbiting a type of dead star known as a millisecond pulsar called PSR B1257+12, or Lich for short (Lich is a powerful living dead being in folklore).
In 1994, a third exoplanet, with a mass of 0.2 times that of Earth, was confirmed to orbit a pulsar. Now, an analysis of hundreds of pulsars has shown that such exoplanets are incredibly rare almost disappearing.
Pulsars are quite rare; only about 3,320 are known in the Milky Way at the time of writing. Of these, astronomers now say less than 0.5 percent likely have rocky, Earth-like worlds in orbit. There are 16 pulsars in total.
Millisecond pulsars are even rarer, with about 550 known pulsars in the Milky Way. This makes the very first discoveries of exoplanets by mankind amazing as hell.
All dead stars are charming, but pulsars add a bit of interest to the interesting factor.
They are a kind of neutron star; it is the core of a dead star that has reached the end of its atomic fusion lifetime, ejected most of its outer material, and collapsed into an object whose density is second only to black holes.
Neutron stars can be about 2.3 times the mass of the Sun and are packed into a sphere only 20 kilometers (12 miles) in diameter.
A pulsar is a rotating neutron star from which rays of radiation emanate. poles. Its orientation is such that as the pulsar rotates, its beams pass by the Earth, giving the impression that the star is pulsing. Think of a really dense space beacon.
And because some pulsars spin extremely fast on the millisecond scale these light pulses also occur on the millisecond scale. To better understand what this means, you can listen to the pulsar’s pulses converted to sound here.
It’s a pretty extreme environment. They may have exoplanets; since the discovery of Lich and his worlds, several other exoplanet-bearing pulsars have been discovered.
However, most of these planets are giants, and those that aren’t can get a little weird, like a superdense world thought to be the remnants of a white dwarf eaten by a pulsar.
A team of astronomers led by Juliana Nitsu from the University of Manchester in the UK wanted to find out how common pulsar planets are. They conducted a study of 800 pulsars monitored by the Jodrell Bank Observatory in the UK, looking for spikes in pulse timing that could indicate the presence of exoplanets in their orbits.
“Pulsars are incredibly interesting and exotic objects. “Nitsu said.
“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. they are, and the way they look is a crucial step towards that.”
Their search parameters were tuned to find worlds with masses ranging from 1 percent that of the Moon to 100 times the mass of the Earth, with orbital periods ranging from 20 days to 17 years.
These search parameters would reveal the larger of the Lich’s two worlds, Poltergeist and Phoebetor, which have orbital periods of 66 and 98 days respectively.
The team found that two-thirds of the pulsars in their sample are extremely unlikely to have exoplanets much heavier than Earth, and less than 0.5 percent likely contain exoplanets in the Poltergeist and Phobetor mass ranges.
The presence of exoplanets like the smaller exoplanet in the Lich system, Draugr. , is a bit harder to measure.
Draug, with its low mass and 25-day orbit, will not be detected in 95 percent of the team’s samples, as it will get lost in the noise. It is not clear how many pulsars such tiny worlds can contain; or even whether it is possible for these worlds to exist outside of a multi-planetary system.
Of the 800 pulsars, 15 showed periodic signals that can be attributed to exoplanets. However, the team believes that most of them can be attributed to the magnetosphere of the pulsar. One pulsar in particular, PSR J2007+3120, looked like a promising candidate for future exoplanet studies.
This means that only 0.5 percent of pulsars could have Earth-like worlds, the team concluded. meaning that the chances of us hitting a distant planet with a rare millisecond pulsar for a star is pretty low.
The team also found that pulsar systems are not prone to any range of exoplanet sizes or masses. However, any such exoplanets around a pulsar would have extremely elliptical orbits.
This is in stark contrast to the near-circular orbits seen in the solar system and suggests that, however they formed, the process was different from that which creates planets around small stars just beginning their lives.
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