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

jahnu•about 2 hours ago

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/

margalabargala•2 minutes ago

> 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?

Sharlin•about 2 hours ago

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.

FranOntanaya•about 2 hours ago

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.

antognini•39 minutes ago

The outer boundary is the point where a photon has a ~50% chance of escaping without encountering another particle.

usrnm•about 2 hours ago

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

dpriddle•about 2 hours ago

Yes and no. It’s fluffy on the outside, but at the core it’s likely denser than our sun.

benji-york•38 minutes ago

Any decent human being would have called these Black Hole Suns.

JumpCrisscross•39 minutes ago

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?

ck2•38 minutes ago

Dr. Becky take: https://www.youtube.com/watch?v=KuTVjuXu7uE

PBS Space Time: https://www.youtube.com/watch?v=FMdrD_jcYgE

love those channels

debo_•about 3 hours ago

Soundgarden was apparently prophetic with their hit song "Black Hole Sun."

TimeBearingDown•about 2 hours ago

May Chris Cornell rest in peace. He should have seen this.

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

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