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Most images of black holes are illustrations. Here’s what our telescopes capture

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Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#31

Post by PeterisP »

ars wrote: post #10
pdonis wrote: post #6

Earlier quoted context omitted.

> all those photos of super massive objects could be neutron stars Not if they are more massive than 2.7 times the mass of the Sun. That's the maximum mass for a neutron star (more precisely, it's the upper limit of the range of possible maximum masses, assuming the stiffest possible equation of state). Most of the objects referred to in the article are more massive than that, in some cases much more (the black hole…

> No amount of pressure can prevent a black hole from forming And yet suns with far more mass than is needed to make a black hole exist. Because simple heat pressure keeps the black hole from forming. Remember that the black hole doesn't just suddenly appear - to have enormous gravity the density must go up. If you prevent that from ever happening you can stop the black hole from ever starting in the first place. You…

"If you prevent that from ever happening" is the key part here. There's no magic that can prevent that - there are a number of factors (e.g. heat pressure, rotation, neutron degeneracy pressure, etc), all of which we can estimate, and which generally increase as the star shrinks/collapses.

An active main-sequence star can be very large without collapsing, as the nuclear reaction inside sustains its size. But for a neutron star the limit is much lower - under a certain mass limit, the stable size is still sufficiently large, but above a certain mass a neutron star can not be larger than the expected event horizon, there's nothing sufficient to prevent the collapse from happening, and it will collapse to a black hole.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#32

Post by 4ad »

oevi wrote: post #24

Black holes are an excellent example for so called "cognitive metaphors". Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the b…

No, black holes are topological holes. It's a mathematical abstraction, not merely a cognitive metaphor.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#33

Post by zrb05293 »

oevi wrote: post #24

Black holes are an excellent example for so called "cognitive metaphors". Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the b…

So for example is it more accurate to say that things fall...on to...rather than in to a black hole? That’s fascinating!

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#34

Post by 4ad »

ars wrote: post #16
podiki wrote: post #12

Earlier quoted context omitted.

Regarding your last point: that depends on your reference frame. From the outside it does appear to take "forever" to get into a black hole, but if you were the one falling in...it happens much quicker, certainly not taking an infinite amount of time.

That's true. But it's things from the outside that are falling in, and that make a black hole. Since they take an infinite amount of time to fall in, the black hole never forms in the first place. (I'm less sure about this paragraph, but I believe that) An object falling in also never sees a black hole, since the other things falling in are dilated relative to him, so there's still not enough mass to make a black hol…

You keep repeating this misconception even though you have been repeatedly been corrected over and over again. What you don't seem to realize is that the choice of coordinates in GR is arbitrary and local. There are types of coordinates that are singular at the event horizon, and there are others which are not. This has nothing to do with infalling vs. the exterior observer. You seem to think that time is somehow fixed for the exterior observer, but that couldn't be further from the truth.

This is really, really trivial and really basic GR. I don't really know what to suggest apart from MTW[1], except maybe this basic course from http://theoreticalminimum.com/courses/general-relativity/201.... If you understand what Penrose diagram are, and how to compute them, the answer is immediately obvious.

[1] https://en.wikipedia.org/wiki/Gravitation_(book)

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#35

Post by colechristensen »

zrb05293 wrote: post #33
oevi wrote: post #24

Black holes are an excellent example for so called "cognitive metaphors". Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the b…

So for example is it more accurate to say that things fall...on to...rather than in to a black hole? That’s fascinating!

Eh, that's taking it too far as the parent does.

"Hole" and "in" are pretty good metaphors for what a black hole is. It's hard to have any particularly accurate metaphors for what a black hole is because time dilation, the speed of light, curved space, etc. just aren't a part of life for any humans.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#36

Post by mrleiter »

oevi wrote: post #24

Black holes are an excellent example for so called "cognitive metaphors". Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the b…

Very true.

Although not specifically in this context, Ludwig Wittgenstein said:"The limits of my language mean the limits of my world."

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#38

Post by blackrock »

oevi wrote: post #24

Black holes are an excellent example for so called "cognitive metaphors". Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the b…

I would prefer if black holes were called "Dark Stars".

Because that really is what they are. A weird star that is so massive, its gravitational field distorted the fabric of its local space, that not even light can escape it.

It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. But its gravitational field is so intense, that even light cannot escape it. So, from the outside, the black hole appears dark. Hence, a dark star.

Perhaps if you are inside the Event Horizon of the black hole, then you can still see the light from the fusion of the star. But if you are outside of the Event Horizon, then you will only see the star as pitch black, since light can't even escape it.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#39

Post by JumpCrisscross »

blackrock wrote: post #38
oevi wrote: post #24

Black holes are an excellent example for so called "cognitive metaphors". Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the b…

I would prefer if black holes were called "Dark Stars". Because that really is what they are. A weird star that is so massive, its gravitational field distorted the fabric of its local space, that not even light can escape it. It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. But its gravitational field is so intense, that even light cannot…

> then you will only see the star as pitch black, since light can't even escape it

Would it be black? Right above the event horizon is flaming relativistic matter.

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