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Soundgarden was apparently prophetic with their hit song "Black Hole Sun."
May Chris Cornell rest in peace. He should have seen this.
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.”
https://en.wikipedia.org/wiki/VY_Canis_Majoris
https://nineplanets.org/vy-canis-majoris/
My layman definition of what a star is is "it's somewhere in the sky and it gives off light". The word "density" wouldn't even come to my mind
Yes and no. It’s fluffy on the outside, but at the core it’s likely denser than our sun.
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.
Why doesn’t the stuff just falls in towards the center? It just floats there??
Radiation pressure! There is so much heat (= photons) radiating outwards, that it counteracts the gravitational pull.
Wow I knew that stars have that radiation pressure but had no idea it caused mass to get so crazy far away from the ignited area of the star!
These giant stars burn so very very bright. And correspondingly only live a few tens of millions years at most.
What’s particularly interesting to me is that for stars the size of our sun, regular old gas pressure dominates. The sun’s atmosphere is held up essentially just from the temperature (and therefore high kinetic energy) of the plasma.
Only once you get to 10+ solar masses does radiation (light) pressure begin to become significant, and at 50+ solar masses is when it dominates and the atmosphere is held up by the momentum of light.
I always wonder when do they stop considering the outer layers part of the star and not relatively dense solar wind soup. Nobody says Earth has 7000km radius, even tho there's traces of exosphere past 500km.
The outer boundary is the point where a photon has a ~50% chance of escaping without encountering another particle.
Do you have a source? I'd love to read more. :)
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?
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.
Sure, but now I'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.
There's dedicated Wikipedia articles responsive to this,
https://en.wikipedia.org/wiki/Solar_core
Depends on the class of the star. Our sun? About 1/4 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.
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.
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.
Of course it's misleading, thats the point GP was trying to make. Averages belie truth in large, diverse systems with extremes
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.
These objects (black hole stars) seem to be far larger than that,
https://en.wikipedia.org/wiki/Quasi-star#Formation_and_prope... (Caption: "Size comparison of a hypothetical quasi-star to some of the largest known stars")
Is there an experiment that could resolve this? Literally resolve these objects better, or otherwise distinguish between these hypotheses?
Is there anything behind these objects they could lens?
Any decent human being would have called these Black Hole Suns.
I just twisted my mouth sides upwards with my fingers to form a smile in agreement.
Sadly, those won't come.
Dr. Becky take: https://www.youtube.com/watch?v=KuTVjuXu7uE
PBS Space Time: https://www.youtube.com/watch?v=FMdrD_jcYgE
love those channels
They are great but you forgot Anton! He definitely belongs with them in my opinion, he is a wonderful person after all :)
Link: https://youtu.be/gUobqtANMfE?si=NVG26d6Aoc2XNEWg
Anton is definitely wonderful! He explains everything very well with no drama and BS. High information density and yet very clear!