Most images of black holes are illustrations. Here’s what our telescopes capture • Hacker News Board

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

#161

Post by qubex » Thu, Mar 01, 2018, 9:01 AM UTC

pdonis wrote: post #146

qubex wrote: post #69

Earlier quoted context omitted.

First and foremost: GR guarantees that an event horizon will form. Oddball exotic states of matter (quark stars, fuzz balls, whatever) might form in proper time within the event horizon, halting collapse before it reaches the singularity state of infinite compaction. (Since time freezes at the event horizon, these states would occur infinitely far in the future from the perspective of any external observer and might…

> Oddball exotic states of matter (quark stars, fuzz balls, whatever) might form in proper time within the event horizon, halting collapse before it reaches the singularity state of infinite compaction. No, this is not correct. Once an event horizon forms, everything inside the horizon will hit the singularity, because the singularity is not a place in space, it's a moment of time, which is in the future (and the not…

That is what GR predicts. However we know that GR is incomplete because it is incompatible with quantum field theory. I was trying to illustrate what can be relied upon to be true even if ultimately GR gets superseded by deeper theories: namely, we can rely on an event horizon forming at the schwartzchild radius whatever the ultimate fate of the in-falling matter may be (in an infinite future).

Furthermore, whereas you and I apparently know what a null surface is, I was trying to illustrate what infinite time dilation means without resorting to very specialist knowledge.

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

#162

Post by qubex » Thu, Mar 01, 2018, 9:05 AM UTC

IntronExon wrote: post #153

pdonis wrote: post #152

Earlier quoted context omitted.

> We don’t actually know if there’s a singularity within the event horizon. Not if we take quantum effects into account, no. I was describing what classical GR predicts. I agree that GR also predicts that it should break down in the regime close to the singularity. It's also worth noting that there is a school of thought among physicists that says that quantum effects are non-negligible even at the horizon of a black…

Agreed on all points, and the firewall is interesting, but I can’t see how it doesn’t somehow create a privileged frame of reference. It’s still very cool/terrifying, even in the already notoriously cool/terrifying realm of black holes.

The whole controversy about the firewall hypothesis is that I’d does create a privileged frame of reference, directly contradicting general relativity (that indirectly forms the basis for predicting the firewall’s existence).

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

#163

Post by coryfklein » Thu, Mar 01, 2018, 6:32 PM UTC

InclinedPlane wrote: post #159

Retra wrote: post #155

Earlier quoted context omitted.

Hawking radiation takes energy away from the inside of a black hole.

Certainly, but the radiation still comes from outside the event horizon.

Sounds like the confusion here comes from labeling matter outside the event horizon as "not the black hole". With this wording you can say that nothing escapes the black hole by forever shrinking the region of what constitutes the black hole.

In the end, matter/energy that was inside the black hole can eventually exist in a region that is no longer referred to as part of the black hole.

^ This being my non-physicist layman interpretation, I'm happy to be enlightened if I'm wrong.

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

#164

Post by pdonis » Fri, Mar 02, 2018, 3:01 AM UTC

qubex wrote: post #161

pdonis wrote: post #146

Earlier quoted context omitted.

> Oddball exotic states of matter (quark stars, fuzz balls, whatever) might form in proper time within the event horizon, halting collapse before it reaches the singularity state of infinite compaction. No, this is not correct. Once an event horizon forms, everything inside the horizon will hit the singularity, because the singularity is not a place in space, it's a moment of time, which is in the future (and the not…

That is what GR predicts. However we know that GR is incomplete because it is incompatible with quantum field theory. I was trying to illustrate what can be relied upon to be true even if ultimately GR gets superseded by deeper theories: namely, we can rely on an event horizon forming at the schwartzchild radius whatever the ultimate fate of the in-falling matter may be (in an infinite future). Furthermore, whereas y…

> we can rely on an event horizon forming at the schwartzchild radius whatever the ultimate fate of the in-falling matter may be (in an infinite future)

This is not necessarily true if the quantum "firewall" speculations end up panning out (I think they're unlikely, as I posted elsewhere in this thread, but it's an open area of debate).

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

#165

Post by podiki » Fri, Mar 02, 2018, 7:11 AM UTC

ars wrote: post #17

podiki wrote: post #14

Earlier quoted context omitted.

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.

There are indeed people who closely study the process of forming a black hole from collapsing matter, hoping to understand things like the singularity and event horizon. I have not ever heard of any good results that show that a black hole for some reason cannot be formed, but I'm sure people are investigating. This would be very surprising if found, and there doesn't seem to be any evidence against black holes actually forming. So the mainstream, and as far as we can tell, correct, view is that black holes can, do, and have formed.

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

#166

Post by podiki » Fri, Mar 02, 2018, 7:16 AM UTC

wallace_f wrote: post #115

podiki wrote: post #14

Earlier quoted context omitted.

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…

OP's claim is that black holes infinite amount of time to form, because matter would take an infinite amount of time to fall into it. Personally, as a layman on the subject of black holes, what I understand is that mass does take infinite amount of time to fall into an event horizon. But I don't know about the formation process of how/when that event horizon is formed. Perhaps you can help me, and him, understand why…

Put simply, matter certainly falls into a black hole in finite time. Black holes merge, as LIGO recently observed gravitational waves from, if that helps give some "direct" evidence.

Yes, studying the exact formation for a black hole is a subject under investigation. From what little I've heard in the past, there is nothing surprising happening, but I guess people are hoping that could lead to some understanding. Not sure what they do, numerical GR I suppose, maybe compare to alternative gravity theories to see if any differences are predicted.

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

#167

Post by podiki » Fri, Mar 02, 2018, 7:18 AM UTC

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…

Also, did we forget of LIGO's recent observations of black hole mergers, in perfect agreement with the GR calculations? Nothing else (known, or proposed) can match that.