[HN Gopher] Cesium detected in the atmosphere of a hot white dwarf
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       Cesium detected in the atmosphere of a hot white dwarf
        
       Author : wglb
       Score  : 55 points
       Date   : 2022-11-15 02:53 UTC (1 days ago)
        
 (HTM) web link (phys.org)
 (TXT) w3m dump (phys.org)
        
       | freeqaz wrote:
       | What is the significance of this finding? I see something about
       | "Radiative levitation" which means nothing to me. Is the idea to
       | prove that fusion is still happening in these stars somehow?
        
         | [deleted]
        
         | Ygg2 wrote:
         | Look at wikipedia
         | https://en.m.wikipedia.org/wiki/Radiative_levitation
         | 
         | Essentially. Big ions capture photons better.
        
         | Nevermark wrote:
         | > The mechanism is that heavier elements have large photon
         | absorption cross-sections when partially ionized (see opacity),
         | so efficiently absorb photons from the radiation coming from
         | the core of the star, and some of the energy of the photons
         | gets converted to outward momentum, effectively 'kicking' the
         | heavy atom towards the photosphere. [0]
         | 
         | I.e. radiation pushes heavier elements to the surface,
         | increasing their visibility to us much higher than their
         | fraction of stellar mass
         | 
         | [0] https://en.wikipedia.org/wiki/Radiative_levitation
        
           | throw1234651234 wrote:
           | I read that and still don't see the significance. Admittedly,
           | I am very far from the topic.
        
             | vikingerik wrote:
             | The significance is that these elements detected in a star
             | don't mean they exist throughout the star, but only in the
             | outer layers. So we don't need to somehow adjust theories
             | of stellar evolution to explain how all that cesium got
             | produced somewhere and this star got full of it. There's
             | only a small amount of cesium, which fits within existing
             | theories (produced from past supernovas), it's just
             | unusually visible.
        
         | AtlasBarfed wrote:
         | I am not a physicist or astronomer, but I would think
         | detectable levels of trans-iron isotopes would call into
         | question some of the assumptions about heavy element production
         | in stars. IIRC anything heavier than iron is not an exothermic
         | nuclear reaction.
         | 
         | I speculate the astronomers are trying to figure out how
         | detectable amounts of a very heavy element are in the outer
         | layers of the star where the emission lines can be detected.
         | Later stage stars are layered by the elements produced in
         | fusion.
         | 
         | I thought that dwarfs resulted from stars lacking the
         | gravitational pressure to create fusion in the core to reach
         | those elements. So how did they get there at all?
         | 
         | And if it's detectable in the halo of the star, that means
         | there is enough in the lower levels (since late-stage stars are
         | basically layers of each atomic number where they are fused)
         | that some of it migrates to somewhere where the lines show up
         | in the star's light emissions?
         | 
         | Maybe it's just stuff left over from a previous star's
         | supernova when the star formed? I can't see that resulting in
         | enough that it would appear.
         | 
         | Anyway, those are my amateurish questions.
        
           | vikingerik wrote:
           | It _is_ stuff left over from a previous star 's supernova.
           | That's the only way anything heavier than iron and nickel
           | gets produced. It is a small amount, but it's more visible
           | than its raw proportion, because it gets suspended in the
           | stellar atmosphere, because the large atoms get hit by a lot
           | of radiation pressure.
           | 
           | The point of this is that we _don 't_ need to rethink heavy
           | element production (or at least not by much), because known
           | processes suffice.
        
         | martinclayton wrote:
         | It's the first time this particular element has been observed
         | in this context. Other trans-iron elements have been seen in
         | the atmospheres of hot white dwarfs before, so not that
         | surprising.
        
       | es7 wrote:
       | Is it aliens?
        
         | Ygg2 wrote:
         | It's (almost) never aliens.
        
         | avian wrote:
         | It's aliens and they are failing do de-cesify their economy.
        
           | moffkalast wrote:
           | Just a regular ol' alien nuclear waste landfill star, nothing
           | to see here.
           | 
           |  _Subscribe for more fun anthropomorphic projections you can
           | tell yourself_
        
         | ksaxena wrote:
         | With the barrage of Astronomy articles that have been hitting
         | HN front page of late, perhaps we should start asking, "Is it
         | Aliens yet?"
        
         | hashtag-til wrote:
         | Underrated comment
        
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