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Scientists May Get Best View Yet of a Black Hole in Action

wired.com

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Re: Scientists May Get Best View Yet of a Black Hole in Action

#11

Post by pdonis »

One small nitpick about a statement in the article; it says:

Though we think of them as cosmic vacuum cleaners, black holes are actually just like any other massive body, such as a star. This means other objects can safely orbit them, until they get within a particular distance and pass what’s known as the event horizon, after which there is no escaping being sucked in.

Technically, you can't "safely orbit" a black hole if you're any closer to it than three times the horizon radius. That is, there are no stable free-falling orbits, like orbits around a planet or star, closer than that. If you want to get closer than that to the event horizon without falling in, you will need to continuously fire your rockets to hold yourself at altitude against the hole's gravity.

Re: Scientists May Get Best View Yet of a Black Hole in Action

#12

Post by fargolime »

pdonis wrote: post #10
fargolime wrote: post #8

If only black holes weren't illogical! [1] Any decent software developer (i.e. highly logical thinker) who knows basic info about black holes can look at the picture there to quickly see that black holes are inconsistent with the core postulate of general relativity, the equivalence principle. They're a bug! (which Einstein spent a decade trying to find, or some other way that nature could prevent black holes he thou…

Here's another relevant discussion on HN that you conveniently forgot to link to, which does explain in detail the flaw in your argument (the discussion you did link to does too, but not in detail): https://news.ycombinator.com/item?id=5233894 Click on "parent" to see the post of yours that I was responding to.

You've linked to that before, but there's nothing there that refutes the blog (not my argument). If there's a flaw it should be a sentence or two of logic, not multiple paragraphs that summarize as "it's not that simple". The blog shows that inertial frames falling through a horizon are that simple (after all, the equivalence principle demands that), and Taylor and Wheeler agree there. Extraordinary evidence is not a requirement per the scientific method. "Extraordinary" is not a scientific concept.

Re: Scientists May Get Best View Yet of a Black Hole in Action

#14

Post by higherpurpose »

pdonis wrote: post #11

One small nitpick about a statement in the article; it says: Though we think of them as cosmic vacuum cleaners, black holes are actually just like any other massive body, such as a star. This means other objects can safely orbit them, until they get within a particular distance and pass what’s known as the event horizon, after which there is no escaping being sucked in. Technically, you can't "safely orbit" a black h…

Technically there may be no "safe distance" at all, depending on how much time you're talking about. The whole galaxy seems to be caught in the spiral of a super massive blackhole, and it's just a matter of time before everything falls into it, although most stars will probably die out before they do. So I guess you could consider that "safe", since the time it takes to fall into the blackhole is longer than the time the object itself exists. Whole galaxies are probably drawn to each other, too, like we are to Andromeda and Andromeda to us.

Re: Scientists May Get Best View Yet of a Black Hole in Action

#15

Post by Oculus »

sillysaurus3 wrote: post #3

A question for the physicists on HN: I've heard that black holes emit radiation. But if nothing can go faster than the speed of light, and a black hole's gravity is so strong that not even light can escape, then how can a black hole emit anything? Is there a kind of black hole which is so massive that not even that radiation can escape, or do all black holes emit some kind of radiation? (In fact, do they emit radiati…

Is there a kind of black hole which is so massive that not even that radiation can escape, or do all black holes emit some kind of radiation? (In fact, do they emit radiation proportional to their size?)

Also armchair physicist here - my understanding is that since information can never be destroyed, Blackholes must emit something.

http://en.wikipedia.org/wiki/Black_hole_information_paradox

Re: Scientists May Get Best View Yet of a Black Hole in Action

#17

Post by andrewflnr » 

  Astronomers know that as recently as a few hundred years
  ago, the Milky Way’s central supermassive black hole was
  producing much more radiation.
Wow, what a near miss. Would that have been visible at all? To think that if human technology had kicked off a couple centuries earlier we might have observed a black hole eating something already, that the answers to our questions about black holes could be common knowledge... wow.

Re: Scientists May Get Best View Yet of a Black Hole in Action

#19

Post by ChuckMcM »

shire wrote: post #18

this might sound like a stupid question but what happens when you get sucked up by a black hole? what's in the other side of it.

If you read Stephen Hawking's book "A Brief History of Time" you will see that a variant on this question is what started him on the path of reasoning about black holes in the first place.

The question does not currently have a definitive answer. Although current mathematical analysis has in falling matter being dismantled at the sub-atomic level as it undergoes the tidal stresses associated with gravity. Basically if you were standing at the event horizon the pull on your feet would be several billion times the pull on your head.

The confounding factor is that if you're falling into a black hole the acceleration can get your velocity to nearly light speed, and at that velocity your perception of time slows, to the point of nearly stopping. So while people watching you fall in might see a burst of xrays as your physical being converted into energy, "you" might perceive nothing at all, simply that time stopped (which is really not something you can perceive) followed by your non-existence (which depending on your theology either has you returning you energy to the entropy of the universe or a visit with your deity and/or anti-deity if there a judgement step.)

Most theories do not currently postulate a 'far side' of a black hole, mostly because "hole" is a metaphor rather than a physical description of the object. In theory its really just a point where the numbers go out of whack because the equations have a divide by zero error there. This too is what fascinates a lot of people, the universe sets up this problem where it gets to divide by zero. A bit of calculus, a bit of fudging with infinities of both the positive and negative variety, and your guess is as good as anyone else's at this point.

Fun to think about though.

Re: Scientists May Get Best View Yet of a Black Hole in Action

#20

Post by pdonis »

fargolime wrote: post #12
pdonis wrote: post #10

Earlier quoted context omitted.

Here's another relevant discussion on HN that you conveniently forgot to link to, which does explain in detail the flaw in your argument (the discussion you did link to does too, but not in detail): https://news.ycombinator.com/item?id=5233894 Click on "parent" to see the post of yours that I was responding to.

You've linked to that before, but there's nothing there that refutes the blog (not my argument). If there's a flaw it should be a sentence or two of logic, not multiple paragraphs that summarize as "it's not that simple". The blog shows that inertial frames falling through a horizon are that simple (after all, the equivalence principle demands that), and Taylor and Wheeler agree there. Extraordinary evidence is not a…

there's nothing there that refutes the blog

I understand that you don't agree that what I posted refutes the blog, but I'm not trying to convince you, and I'm not going to rehash the argument here. I'm just linking to that discussion for the record, so others reading this thread will understand that your claims and the blog's claims about black holes are not undisputed.

(not my argument).

You may not have written the blog post, but you are claiming it's correct, so it is "your" argument in the only sense that matters here. If you're not willing to own the argument when it's challenged, then you shouldn't be linking to it.

If there's a flaw it should be a sentence or two of logic, not multiple paragraphs that summarize as "it's not that simple"

That's not the summary of what I said. The summary of what I said is this: the blog post's claims about what the theory of relativity actually says are not correct. So the blog post is not refuting the actual theory of relativity; it's refuting a straw man version of the theory that the blog post's author has constructed in his own head.

Taylor and Wheeler agree there

Agree with what? That there can be an inertial frame that falls through the horizon? Yes, of course. But that does not mean Taylor and Wheeler agree with the blog post's claims about black holes. The fact that there can be an inertial frame that falls through the horizon does not mean the blog post's claims about the details of how such frames work are correct. I went into detail about what's wrong with them in the thread I linked to.

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