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Black Holes or Black Hole Stars? Astronomers Spar over 'Little Red Dots'

105 points · 61 comments · jandrewrogers

  1. jahnu · · focus · HN ↗
    One thing worth noting is our popular notion of what a star seems to be is quite different from what astronomers have.

    One example, Canis Majoris has a radius of about 1420 solar radii. But its mass is roughly 17±8 times the mass of the Sun and therefore an average density of 5.33 to 8.38 mg/m3. “It is over 100.000 times less dense than Earth’s atmosphere at sea level.”

    <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;VY_Canis_Majoris" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;VY_Canis_Majoris

    <a href="https:&#x2F;&#x2F;nineplanets.org&#x2F;vy-canis-majoris&#x2F;" rel="nofollow">https:&#x2F;&#x2F;nineplanets.org&#x2F;vy-canis-majoris&#x2F;

    1. margalabargala · · focus · HN ↗
      &gt; therefore an average density of 5.33 to 8.38 mg&#x2F;m3

      That&#x27;s nuts. How on earth does fusion happen at that density? Is there a denser core that actually fuses, and the outer fluffy bits just glow from the inner heat?

      1. adrianN · · focus · HN ↗
        Averages are quite misleading. The core is obviously a lot denser. Our sun has an average energy output per cubic meter that is comparable to a compost heap.
        1. margalabargala · · focus · HN ↗
          Sure, but now I&#x27;m left wondering what the size of the body doing fusion is. If most of the star is glorified glowing atmosphere, I want to know the mass and radius of the fusing bits.
          1. peri-cl · · focus · HN ↗
            There&#x27;s dedicated Wikipedia articles responsive to this,

            <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Solar_core" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Solar_core

          2. idiotsecant · · focus · HN ↗
            Depends on the class of the star. Our sun? About 1&#x2F;4 radius and in is fusion reaction. But it gets weird in other stars. In red giants the fusion zone is a very small shell around a dead core. Maybe something like earths orbit in radius, but very very thin.
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