[HN Gopher] Orion's mysterious free-floating planets
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       Orion's mysterious free-floating planets
        
       Author : belter
       Score  : 22 points
       Date   : 2024-05-31 12:52 UTC (1 days ago)
        
 (HTM) web link (www.bbc.com)
 (TXT) w3m dump (www.bbc.com)
        
       | largbae wrote:
       | The article spends a lot of time painting it as mystery before
       | this seemingly obvious paragraph: "Portegies Zwart favours a
       | different explanation, where Jumbos form in the same way as
       | stars, directly from the collapse of a cloud of gas. Known as in-
       | situ formation, this would require us to rethink how low the
       | density of a gas cloud can be in order to trigger such a
       | collapse. But for Portegies Zwart, "I think in-situ formation is
       | the only one in which I don't have theoretical problems," he
       | says. "It is the most promising."
       | 
       | Why would a nebula not produce _every_ possible size of object
       | over its billions of years?
       | 
       | Maybe this is how stars actually form, gas accretes into chunks
       | of icy matter similar to what happens in Saturn's rings. Then
       | those small objects gravitationally meet and sometimes coalesce
       | into moons, then small planets, big planets, brown dwarves etc.
       | finally when enough stuff has coalesced, the gravity is strong
       | enough to cause fusion and boom you have a star.
        
         | powerbroker wrote:
         | This seems the most straightforward of explanations. I know
         | that a planet tends to loose its heat (and visibility in
         | infrared) quickly after formation -- and might be hard to spot
         | as a rogue planet.
         | 
         | But, the Zwart explanation seems to suggest that the pairs are
         | still potentially drawing stuff in, and might not be the final
         | form that the planet-pairs will take once they exist (or
         | consume) the nebulae. Nothing seems to be stopping these pairs
         | from evolving into stars themselves (aren't binaries far more
         | common than solitary suns, like our own?).
        
         | jessriedel wrote:
         | (Purposely terrible writing, but par for the course in popular
         | science.)
         | 
         | More specifically: although it's certainly plausible there's a
         | threshold in nebular dynamics for solid object formation
         | because clouds of less total mass fail to congeal, I see no
         | reason a prior why this mass threshold would coincide with the
         | mass necessary to start fusion (i.e., the lightest brown
         | dwarfs). And since we have seen brown dwarfs just above the
         | threshold, but those below it would have been invisible to use
         | before the past ~decade, it seems completely natural to find
         | free-floating planets just below the threshold now that we have
         | acquired the technology to see them.
        
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