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

105 points · 61 comments · jandrewrogers

jahnu · 1789828933 · 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://en.wikipedia.org/wiki/VY_Canis_Majoris" rel="nofollow">https://en.wikipedia.org/wiki/VY_Canis_Majoris
<a href="https://nineplanets.org/vy-canis-majoris/" rel="nofollow">https://nineplanets.org/vy-canis-majoris/
1. margalabargala · 1789836996 · focus · HN ↗
  > therefore an average density of 5.33 to 8.38 mg/m3
  That'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 · 1789837360 · 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.
    throwaway89864 · 1789838565 · focus · HN ↗
    Astra says this claim is misleading. Sun's average energy output per cubic meter is three orders of magnitude smaller than that of a compost heap. The fusion core is comparable though.
    Retric · 1789842065 · focus · HN ↗
    The energy density of specific compost heaps varies by several orders of magnitude it’s not a single number. Volume, moisture content, internal temperature, external temperature, materials being composted, etc all play a significant role.
    mordechai9000 · 1789848618 · focus · HN ↗
    Stellar fusion could also be a factor in a sufficiently large compost heap.

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