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Źródło: https://www.bbc.com/future/article/20240522-the-mystery-of-orions-free-floating-giant-twin-planets

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The mysterious pairs of planets we still can't explain

The mysterious pairs of planets we still can't explain

We thought we broadly understoodszeroko rozumiane how planets and stars form. But the discovery of dozens of pairs of young planets in a nearby nebulamgławica threatens to turn that on its headpostawić to na głowie.

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"These things shouldn't exist," says Simon Portegies Zwart, an astrophysicistastrofizyk at Leiden University in the Netherlands. "They go againstprzeciwstawiać się everything we have learned about star and planet formation."

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In the subsequentkolejny months, efforts have been made to try and explain what's going ondzieje się. These planets, called Jupiter Mass Binary ObjectsObiekty Podwójne o Masie Jowisza, or Jumbos, still cannot be fully explained. But we are getting closer to an answer – with crucialkluczowy observations on the horizonna horyzoncie that may solve the mystery once and for allraz na zawsze.

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Each Jumbo pair was separatedoddzielone by distances of as little as 2.8 billion miles (4.5 billion kilometres) – the same distance that separates Neptune and our Sun – or up to nearly 400 times that distance. Each pair appears as twin dots of lightbliźniacze punkty świetlne in the Orion Nebulamgławica and seem to orbit one anotherorbitować wokół siebie nawzajem.

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Jessie Christiansen, an astronomer at the Nasa Exoplanetegzoplaneta Science Institute at the California Institute of Technology, says the discovery set her team of exoplanetegzoplaneta hunters – planets found outside our Solar System – into "crisis" mode. "I was very worried about them at first," she says. "One of our definitions of an exoplanetegzoplaneta is 'a planet that orbits another star'. As soon as these planets came outpojawiły się, I was like, 'Oh my God, binarypodwójny free-floating Jupiter-mass objects. What am I going to do?'"

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Jumbo planets would represent a newly discovered classnowo odkryta klasa below brown dwarfs. McCaughrean and Pearson detecting the hot, infraredpodczerwony glow of about 100 of these objects not in pairs down to the mass of Jupiter in the Trapezium ClusterGromada Trapez. "Nobody's seen those before," says McCaughrean. But it was the discovery of 42 pairs of these objects, and one triple, that really set minds racingpobudzić wyobraźnię. "This was not something we were looking for at all," says Pearson.

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Many stars exist as pairs, or binariesukłady podwójne, a result of forming in proximity in relatively tight, dense nebulas of dust and gas like Orion. Jumbos are a different problem. If they were planets that once orbited stars but were ejected, it would be difficult to explain how they would end upskończyć in pairs. Two ejected planets passing each other would be unlikely to become gravitationally boundgrawitacyjnie związane as they flew through space. But their masses appear to be too low for them to have formed directly from the collapse of a cloud of gaszapadnięcie się chmury gazu, like a star. "These objects are way off the bottomdaleko od dna [of] where we think this works," says Christiansen, "which is partly why theorists are struggling."

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"It requires the orbits of the two planets to be relatively closely alignedstosunkowo blisko wyrównane," says Perna. But in such instances, pairs of Jumbos would be "an unavoidable consequencenieunikniona konsekwencja" of interactions between starsinterakcje między gwiazdami. Another ejectionwyrzucenie idea is that the pairs were already a planet-planet or planet-moon pair orbiting a young star together before they were ejected.

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Portegies Zwart favours a different explanation, where Jumbos form in the same way as stars, directly from the collapsezapadnięcie of a cloud of gas. Known as in-situna miejscu formation, this would require us to rethink how low the density of a gas cloud can be in order to trigger such a collapsewywołać takie zapadnięcie. But for Portegies Zwart, "I think in-situna miejscu formation is the only one in which I don't have theoretical problems," he says. "It is the most promising."

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One way to trigger the collapsewywołać zapadnięcie się of small clouds of gas into Jumbos might involve high-energy particlescząstki wysokoenergetyczne called cosmic rays. These pervadeprzenikać the Universe, emitted by explosive events such as supernovae or active black holes. Normally, if a cloud of galactic gasgaz galaktyczny – mostly hydrogen and helium – were too low density, it should have too much angular momentummoment pędu to collapse. The gas would simply be too dispersed and energetic to form objects as small as a Jumbo.

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Some aren't sure that Jumbos exist at all. Peter Plavchan, an astronomer at George Mason University in the US, says he thinks they could be stars masquerading asudające planets. He says the dusty nature of the Orion Nebula could disguise the light of the stars, making them appear redder, giving them a planet-like signaturesygnatura przypominająca planetę. "The more plausiblewiarygodne explanation is they're just two stars that are higher mass that appear to have the colours of planetary-mass objects," he says.

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McCaughrean says this could be the case for some of the Jumbos, but not all of them. "We've been careful in our analysis to rule outwykluczyć reddened low-mass background stars as potential contaminantszanieczyszczenia," he says. "The statistical chancesszanse statystyczne of all of the Jumbos being background sources [is low]."

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Pearson says that "even if just two or three of them are real, it means there's something missing from our entire understandingcoś brakuje w naszym pełnym zrozumieniu of how you make planets and stars".

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To find outdowiedzieć się for sure, we need further observationsdalsze obserwacje of the objects. McCaughrean and Pearson are on the casezajmować się sprawą – they have studied them more extensivelyobszernie with JWST this year, using the telescope to pick apartrozłożyć na części the light of the objects. They haven't yet released their latest findingsnajnowsze odkrycia, but when they do, they will be looking for signs of certain elements in the atmospheres of the Jumbos that could hint at their origin.

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Another option might be to study Jumbos with radio telescopes and track how fastśledzić jak szybko they are moving across the skyporuszające się po niebie. If the pairs are moving at the same speed away from a common star, that might support the ideawspierać pomysł they are ejectedwyrzucone planets. If not, it could hint at the in-situna miejscu model being correct.

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Rodriguez hopes to have more radio datadane radiowe on Jumbos from a US network of radio telescopes called the Very Long Baseline Array in the coming months, and another US network called the Very Long Array by the end of the year. "Then we will know if they are moving fast or breaking apartrozpadać się, which will favour an ejectionwyrzucenie mechanism," he says.

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An upcoming Nasa telescope called the Nancy Grace Roman Space Telescope, set to launchplanowany do wystrzelenia in 2027, could also study Jumbos. It will perform a survey of the Universebadanie Wszechświata to look for exoplanetsegzoplanety, but could also be used to look for objects inside the Orion Nebula, perhaps finding more Jumbos than even JWST can detect. "You could point outwskazać really faint objects down to about the mass of Saturn," says Melinda Soares-Furtado, an astrophysicistastrofizyk at the University of Wisconsin at Madison in the US.

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Studying other young nebulasmgławice for Jumbos could be useful too, confirming if these peculiarosobliwy pairs of objects are widespread across other regions of star formation. "Any young cluster would be interesting," says Portegies Zwart. There could even be some Jumbos drifting freely through spacedryfujące swobodnie przez przestrzeń awaiting discovery, and perhaps quite close to home. "There may be Jumbos near the Solar System but we have never spotted them because we didn't point atwskazać na them," he says.

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Regardless of what they turn outokazać się to be, Jumbos could help us "really understand these stellar nurseriesgwiezdne żłobki and what they have to teach us", says Soares-Furtado. For now the mystery continuestajemnica trwa.

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