Observations

>Phd Candidate - is enthusiastic, but a bit sloppy with the understanding of the physics.

They both tried to choose words suitable for the large audience. Choice of words in such settings doesn't reflect someone's understanding. Most popular descriptions of modern physics sound sloppy or even incorrect, because otherwise they get very technical.

>So, when a star dies, if the star is massive enough, there's a huge explosion, called a supernova, and the stuff that's left behind, that doesn't get blown away collapses into a tiny compact blob called a neutron star.
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That statement implies that:
- Supernova explosion may result in the whole stuff to get blown away completely

No, there is no such implication here. If there's always some stuff left, we can address it as the stuff that's left behind, the stuff that doesn't get blown away, two wordings of the same thing.

> - Neutron star forms after supernova explosion. [That is not true, because a neutral star forms before the explosion, not after].

Why exactly do you think so? When the outer layers of the original star are still there, can you really call the collapsing core a star?


>Another sloppy statement from this Phd Candidate:
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A black hole is sort of like a neutron star's big brother.
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But, actually, a black hole does not have to have a neutron star inside.

He doesn't say there's a neutron star inside, you're making things up again. It's a "big brother" in the sense of being more massive, creating stronger spacetime curvature and often being literally bigger. And "brother" because they are born in very similar processes.



>~~~The event horizon of the black hole forms, which is the shadow, the curve that's so strong that not even light can escape.~~~~~~~~~~
A curve of a black hole is "strong"? Really?

She's talking about spacetime curvature. Yes, black hole curves it stronger (at the "surface"), the very definition of its event horizon has to do with how spacetime is warped there to not let light outside.


>-----
it collapses to a black hole, and those are so dense that space-time breaks down.
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What does "space-time breaks down" even mean?

I can think of at least 3 things these words may mean. The swap of signs in the signature of the Schwarzschild metric between time and radius, so radius behaves like time and vice versa. The fact that for a static outside observer the region behind the horizon is excluded from our space, it's in the infinite future, no point on or below the horizon is there "now", no event there is simultaneous to any event of our history (in the simple model of a static black hole). There's also a third sense coming from certain quantum mechanical or string theory descriptions, where there's literally no spacetime at all under the horizon for old enough black holes.
Why do you call "crap" things you've never heard about?

>========
the star's gone, that black hole is empty.
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That means that Janna does not understand:
- That mass causes gravity.
- What "black hole" is.

No, it doesn't mean that. By Penrose–Hawking singularity theorems once the event horizon forms there's inevitably a singularity inside and all the matter quickly (by that matter's clocks) goes into that singularity and in some sense ceases to be in our spacetime, at least if we only follow the GR equations. All the volume under the horizon (singularity has zero volume) becomes empty space, so she's not incorrect, in pure GR sense. Gravity is not caused by just mass, in GR it's caused by energy and momentum, mass being a special case source of energy. Gravity itself also has gravity (see gravity self-interaction), so one may say the black hole is just the warping of spacetime having the same energy/mass as the matter that formed it. Of course these are more or less speculations based on following general relativity literally, but at least in this sense what she says makes perfect sense. If you don't see it, maybe you don't know what a black hole is? (we all don't know really, all we know is some indirect observations and our theories)