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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. Sharlin · 1789830557 · focus · HN ↗
  The surface radius of a star is defined based on optical thickness. If you were there, the star would in fact look like a fairly well-defined opaque spheroid with the reported radius. The density of the photosphere plasma is near zero, but there’s a lot of it.
  1. brabel · 1789844059 · focus · HN ↗
    Why doesn’t the stuff just falls in towards the center? It just floats there??
    kulahan · 1789855107 · focus · HN ↗
    To add on to the other response, think of it like the star “leaking” into space. It’ll be defined as a pretty radically different size at some point in the future, even as it’s still undergoing fusion.

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