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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

#11

Post by ars »

IntronExon wrote: post #9
ars wrote: post #4

Keep in mind as well that no observation has yet distinguished between a neutron star and a black hole. i.e. all those photos of super massive objects could be neutron stars, and we would not be able to tell the difference. They are assumed to be black holes because of the mass, but if there is something in the law of physics that prevents black holes from forming we would not know. We do not have a theory on quark d…

I think you’re confusing the lack of knowledge of whether or not singularities really form, with whether or not black holes form. There are very clearly black holes, but of course we can have no way of knowing if they contain singularities. Quark stars could exist, it not with the masses observed in Sag A*. Quark degeneracy pressure isn’t going to support the mass of millions, or even billions of suns. It might be th…

What's a black hole without a singularity? A neutron star? Is there a distinction you are making? To me a black hole and a singularity are the same thing. Are you using a different definition?

> Quark degeneracy pressure isn’t going to support the mass of millions, or even billions of suns.

Why not? If the star is very large the density (and thus gravity) never get high enough.

For example, if you consider the milky way as a single object, then that's an object resisting the mass of billions of suns.

The mass is irrelevant, what matters is the density.

> As for time dilation... no. In no way could that magically overcome collapse.

It can keep mass from ever reaching the surface of the black hole (singularity). At least as far as we are concerned. It takes mass an infinite time to actually get to the surface, so the black hole can never grow.

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

#12

Post by podiki »

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…

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.

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

#13

Post by podiki »

ars wrote: post #11
IntronExon wrote: post #9

Earlier quoted context omitted.

I think you’re confusing the lack of knowledge of whether or not singularities really form, with whether or not black holes form. There are very clearly black holes, but of course we can have no way of knowing if they contain singularities. Quark stars could exist, it not with the masses observed in Sag A*. Quark degeneracy pressure isn’t going to support the mass of millions, or even billions of suns. It might be th…

What's a black hole without a singularity? A neutron star? Is there a distinction you are making? To me a black hole and a singularity are the same thing. Are you using a different definition? > Quark degeneracy pressure isn’t going to support the mass of millions, or even billions of suns. Why not? If the star is very large the density (and thus gravity) never get high enough. For example, if you consider the milky…

A better definition is a black hole is something with an event horizon.

(for your last comment, see my previous response)

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

#14

Post by podiki »

ars wrote: post #4

Keep in mind as well that no observation has yet distinguished between a neutron star and a black hole. i.e. all those photos of super massive objects could be neutron stars, and we would not be able to tell the difference. They are assumed to be black holes because of the mass, but if there is something in the law of physics that prevents black holes from forming we would not know. We do not have a theory on quark d…

I'll take your comment in good faith, but there are very good reasons to believe black holes exist and that, for instance, the center of our galaxy contains a very massive black hole and not a neutron star. This is basic general relativity, which only has (physical and theoretical) evidence in support of it. While quantum gravity is still very much uncertain, that would (most likely) only have to do with understanding the possible singularity inside black hole. Otherwise, defining a black hole as "a thing with an event horizon" is purely a general relativity prediction, consistent with all of the other predictions and observations.

(Disclaimer: theoretical physicist)

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

#15

Post by podiki »

booleandilemma wrote: post #5

If nothing can escape black holes how is it they “spew” things?

They also (are believed to, based on famous calculations by Hawking) radiate like a black body with a temperature related to their mass. And this leads to them losing mass over time, eventually evaporating. (Leaving what is a subject of much debate.)

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

#16

Post by ars »

podiki wrote: post #12
ars wrote: post #10

Earlier quoted context omitted.

> 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…

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 hole, even for the object falling in.

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

#17

Post by ars »

podiki wrote: post #14
ars wrote: post #4

Keep in mind as well that no observation has yet distinguished between a neutron star and a black hole. i.e. all those photos of super massive objects could be neutron stars, and we would not be able to tell the difference. They are assumed to be black holes because of the mass, but if there is something in the law of physics that prevents black holes from forming we would not know. We do not have a theory on quark d…

I'll take your comment in good faith, but there are very good reasons to believe black holes exist and that, for instance, the center of our galaxy contains a very massive black hole and not a neutron star. This is basic general relativity, which only has (physical and theoretical) evidence in support of it. While quantum gravity is still very much uncertain, that would (most likely) only have to do with understandin…

You skipped a step. Yes, the general relativity prediction of a black hole is solid once it exists. But you have to construct that black hole in the first place. And it's that part that's on shaky ground.

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

#18

Post by KnightOfWords »

ars wrote: post #4

Keep in mind as well that no observation has yet distinguished between a neutron star and a black hole. i.e. all those photos of super massive objects could be neutron stars, and we would not be able to tell the difference. They are assumed to be black holes because of the mass, but if there is something in the law of physics that prevents black holes from forming we would not know. We do not have a theory on quark d…

I'm afraid that's not really accurate. The most massive neutron star observed is just under 2 solar masses, which is difficult to explain if event horizons do not exist. Quark and strange stars are hypothetical objects intermediate in mass between neutron stars and black holes, not suggested replacements for the latter.

It is true we don't fully understand neutron stars and we certainly don't understand what happens inside the event horizon.

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

#19

Post by saagarjha »

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…

> 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.

See this excellent answer on Physics StackExchange: https://physics.stackexchange.com/questions/5031/can-black-h.... In a nutshell (if I'm interpreting this correctly), yes, to an outside observer you never observe the black hole form since it would take an infinite amount of time for light signals from the newly formed black hole to reach you. However, to any observers that fell into the black hole (and so were in the same frame of reference), the black hole would form in finite time.

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

#20

Post by saagarjha »

ars wrote: post #11
IntronExon wrote: post #9

Earlier quoted context omitted.

I think you’re confusing the lack of knowledge of whether or not singularities really form, with whether or not black holes form. There are very clearly black holes, but of course we can have no way of knowing if they contain singularities. Quark stars could exist, it not with the masses observed in Sag A*. Quark degeneracy pressure isn’t going to support the mass of millions, or even billions of suns. It might be th…

What's a black hole without a singularity? A neutron star? Is there a distinction you are making? To me a black hole and a singularity are the same thing. Are you using a different definition? > Quark degeneracy pressure isn’t going to support the mass of millions, or even billions of suns. Why not? If the star is very large the density (and thus gravity) never get high enough. For example, if you consider the milky…

> For example, if you consider the milky way as a single object, then that's an object resisting the mass of billions of suns. The mass is irrelevant, what matters is the density.

Uh, no. What's keeping the Milky Way from collapsing is the fact that it's rotating, not its density. Any cloud of matter that is initially non-rotating will eventually collapse due to gravity, no matter what its initial density was.

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