Any astro-physicists around?

[cee-dee]

I've been thinking (OK, OK, I know that's a bad idea but....) we're told a Black Hole (in space) was formed by the collapse of a huge star? Before the collapse, the huge star could be seen? So, if the light from the huge star could have been seen OK then, how is it that after the collapse/explosion/super nova, nothing can be seen?

If the gravity of the Black Hole is such that nothing can escape, not even light, how come light could have been seen from the star before it's demise? Surely the gravity from the huge star should have been the same or more powerful when the star was still in existence as a star?

[right-then-petal]

Hmm That's Easy Light Takes Years Some TimesTo Reach Us

So If Planet  Blows Up We See The Light For Some Time

[cee-dee]

Yes Petal, we're seeing light from a very long time ago even though it's travelling at 186,000 miles per second, it's come from sooooooo far away that it's taken yonks to get here but the question is as I posed in the OP. 

The original star had very strong gravity but the light from it still "escaped" but after the collapse/explosion/super nova how come nothing is supposed to escape from the extreme gravity of the Black Hole? The Black Hole was "made/created from the remnants of the star so how come the Black Hole's gravity is so strong? Stronger than the gravity of the original star?

[tuckerbigdaddy5ngv]

It's got something to do with the star being compressed into a singularity ,don't ask me what that means,I have no idea 😀

[right-then-petal]

                                          

[*knight-rider*]

`If the gravity of the Black Hole is such that nothing can escape, not even light, how come light could have been seen from the star before it's demise?`

because gravity before a planets demise, is nowhere near as powerful as the gravity in a blackhole, hence the reason why light can`t escape it. Anything that enters a blackhole is compressed to almost an atomic level, that`s why on certain planets where the gravity varies from planet to planet, you`d survive fine on one, but would be crushed to nothing on another.

[cee-dee]

It's OK just saying that, but how come a Black Hole "made" from the original star has "more powerful gravity"?

After the explosion/super nova, surely there's less stuff at/in the Black Hole than when it was a star?

[cee-dee]

Anyway, when there's some sort of event/happening/process that the "scientists" can't explain clearly and logically, they "invent" something no-one, not even themselves understand!

[hill-walker]

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@cee-dee wrote:

After the explosion/super nova, surely there's less stuff at/in the Black Hole than when it was a star?

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Yes, but imagine the star being like an orange... it's just the "skin" that explodes outwards. The inner bit remains, and as the nuclear reaction that kept the star "inflated" has now ceased, gravity wins, and it starts to collapse inwards.

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@cee-dee wrote:

It's OK just saying that, but how come a Black Hole "made" from the original star has "more powerful gravity"?

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It doesn't have "more powerful" gravity as such, but, because it's now more compressed, it behaves differently. Imagine a light, fluffy cloud, drifting across the sky... then imagine taking the water vapour in it, and condensing it as a huge bucket of liquid water of the same mass. It could no longer float, gravity would take over, and it would plummet downwards.

[hill-walker]

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@cee-dee wrote:

Anyway, when there's some sort of event/happening/process that the "scientists" can't explain clearly and logically, they "invent" something no-one, not even themselves understand!

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Not quite "invent" 😉  They try to find logical reasons why/how things happen. Sometimes, you can categorically prove that something happens, without being able to explain or understand it. That's how theories arise, get tested, then get accepted or disproved.

[cee-dee]

I had to think a bit about your answer but we're not talking about clouds of water vapour above the Earth (or any other Planet). If a star with, let's say 30 Solar masses goes supernova and half of it is ejected leaving a mass (a black hole?) of 15 solar masses albeit condensed in to a much smaller "place", how come it has "more powerful" gravity than the original star? OK, so not even light can escape but is there any light there to escape?

[hill-walker]

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@cee-dee wrote:

If a star with, let's say 30 Solar masses goes supernova and half of it is ejected leaving a mass (a black hole?) of 15 solar masses albeit condensed in to a much smaller "place", how come it has "more powerful" gravity than the original star? 

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It doesn't. Prior to going bang, the star was kept inflated by the inner nuclear reaction; that's the only thing that stopped it collapsing. When the star runs out of fuel, and that reaction stops, gravity "wins" and the star collapses in on itself.

[cee-dee]

OK, so the reactions stopped it collapsing but that doesn't explain how light from the original star was able to "escape" (because we could see it) but after the collapse, nothing can be seen and from a distance, it appears that there is "nothing there" but we know (or think we know?) something is there because we are aware of a pull of gravity from that area.

[hill-walker]

Please bear in mind that I'm "not" an astro-physicist 😉

Let's use the earth as an example. On the surface, we experience gravity. If we were to climb Everest, though our mass would be the same, as we were further from earth's centre, gravity would have very slightly less effect, and we would weigh less. If we were to travel into space, far from the earth's centre, we effectively become weightless. So, looking at that in reverse, the closer you get to the centre of mass, the greater the effect gravity has.

It's a similar thing happening on a massive star. Whilst the star IS massive, gravity at the surface is relatively minor, and light can escape easily, so we can see it. As the star collapses, the surface gets smaller, and closer and closer to the massively compressed centre, and the effect of gravity becomes much more significant. Eventually, when it has collapsed to a small enough size, gravity is strong enough to stop anything overcoming it, even light.

[*knight-rider*]

Best thing to do is read up on them, rather than us trying to explain it in a way you understand and us to be honest 🙂

`https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html`

[cee-dee]

The whole idea of the thread was an attempt to provoke some interest and discussion but although people view, they don't post so thank you for taking the time and trouble to post.

[*knight-rider*]

`the thread was an attempt to provoke some interest and discussion but although people view, they don't post`

i think the problem with this stuff, is that not many people are interested in it, me, i love it and anything to do with the universe fascinates the hell out of me, especially the numbers 🙂 Problem is though, and i can`t speak for anyone else, i only know enough to be dangerous, an arm chair fan if you like, so i didn`t mean to be rude earlier by posting the link, it was just easier to do than `try` to explain blackholes myself, because as fascinated as i am with them, i still don`t understand them.

[cee-dee]

It's not just this thread and it's subject, it's most of the threads. Lotsas views but not many or no posts at all.

[hill-walker]

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@cee-dee wrote:

It's not just this thread and it's subject, it's most of the threads. Lotsas views but not many or no posts at all.

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No need to worry about lack of people participating on the forum - the Community Team have that all in hand; new badges for everyone, plus the new ranking system will persuade SO many more watchers to become posters, I'm sure, just as planned...

...unless it all vanishes into a black hole 😉

[cee-dee]

Hasn't it struck home yet with whoever's "in charge" that the last major "re-vamp" that some team or other foisted on "the community" was the event that drove away the majority of posters which were already massively depleted by other silly decisions?