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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. lrasinen · 1789837901 · focus · HN ↗
  Average density for non-uniform objects is pretty useless, since the cubic volume scaling makes a mess of things.
  As an example, I pulled the stats for an electric locomotive. 19x3x4.4 meters, mass 90 metric tonnes. That's an average density of about 1/3rd of water.
  1. Rygian · 1789849267 · focus · HN ↗
    So a locomotive floats. Interesting.
    TeMPOraL · 1789890285 · focus · HN ↗
    Locomotive itself? Probably not. If you turned its abstract bounding box into real box - thin, negligible mass, enough strength not to break up - and evacuated the air inside, then yes, the box with locomotive in it should float.

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