# Are black holes exists? (black hole formation) **URL:** \ **Category:** Factual Questions\ **Created:** [December 11, 2013, 11:42am UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063 "2013-12-11T11:42:05Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![mendi80](https://avatars.discourse-cdn.com/v4/letter/m/f1d935/32.png) [@mendi80](https://boards.straightdope.com/u/mendi80)\ **Post date:** [December 11, 2013, 11:42am UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/1 "2013-12-11T11:42:05Z")
We know that black hole (BH) cause the time flow around it to slow until zero in event horizon. So it looks like that a moment before the BH created, the time around it is slow down, so actually it will take it inf. time to come to be a real BH. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [December 11, 2013, 12:46pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/2 "2013-12-11T12:46:59Z")
That’s what it looks like from outside. But from the black hole’s point of view, time seems to be going ahead normally as the collapse continues. ---
**Author:** ![Revtim](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/revtim/32/1042_2.png) [@Revtim](https://boards.straightdope.com/u/Revtim)\ **Post date:** [December 11, 2013, 1:59pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/3 "2013-12-11T13:59:09Z")
SDMB alum ‘Bad Astronomer’ addressed this once: [http://blogs.discovermagazine.com/badastronomy/2007/06/19/news-do-black-holes-really-exist/#.UqhubdJZd8E](http://blogs.discovermagazine.com/badastronomy/2007/06/19/news-do-black-holes-really-exist/#.UqhubdJZd8E) > [@](#): > > This brings up a very interesting situation. If time takes forever to flow, then how does a black hole ever form? Imagine the core collapsing, and you’re looking at it from far away. You see it getting smaller, but the collapse also appears to be going more slowly because of the time dilation. Like Zeno’s paradox, you see the escape velocity approach the speed of light, but you’ll never see it actually get to the speed of light! Time would stretch out infinitely, and the collapse of the core would appear to you to stop. > > No black hole. > [@](#): > > However, have a care here: there is still a massive, dense, highly gravitational object there! So we still have what are essentially black holes in the cores of galaxies and forming when stars explode and all that, it’s just that, technically, well, they aren’t actually black holes. > [@](#): > > I will note that this is how I understand the situation, and I may have it wrong. This is very complicated stuff! This paper is by no means the last word on the subject — even the experts argue incessantly about it, and I’m no expert. Sounds like this is not a settled issue. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 11, 2013, 4:49pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/4 "2013-12-11T16:49:22Z")
Classically, it takes an infinite amount of time, as measured by any external observer, for a black hole to form. But black holes, like everything else in the Universe, are not classical objects. And while we can say precious little about the quantum mechanics of black holes, one thing that we can say is that the infinite time for formation, even from the outside reference frame, is wrong (though unfortunately this doesn’t help us narrow down the right answer very much). ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [December 11, 2013, 4:55pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/5 "2013-12-11T16:55:41Z")
Has your sig ever been more appropriate? ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [December 11, 2013, 5:03pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/6 "2013-12-11T17:03:37Z")
Additionally, there could plausibly be primordial black holes that do not originate as a collapsing star, possibly avoiding the “should take infinite time to form” problem in another way. ---
**Author:** ![bup](https://avatars.discourse-cdn.com/v4/letter/b/6bbea6/32.png) [@bup](https://boards.straightdope.com/u/bup)\ **Post date:** [December 11, 2013, 5:24pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/7 "2013-12-11T17:24:05Z")
> [@leahcim](#): > > Additionally, there could plausibly be primordial black holes that do not originate as a collapsing star, possibly avoiding the “should take infinite time to form” problem in another way. They theoretically could have formed during the Big Bang, right? ---
**Author:** ![Darth\_Panda](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@Darth\_Panda](https://boards.straightdope.com/u/Darth_Panda)\ **Post date:** [December 11, 2013, 5:38pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/8 "2013-12-11T17:38:39Z")
How is babby black hole formed? ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [December 11, 2013, 5:53pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/9 "2013-12-11T17:53:52Z")
All your black hole are belong to us! ---
**Author:** ![yanceylebeef](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yanceylebeef/32/12290_2.png) [@yanceylebeef](https://boards.straightdope.com/u/yanceylebeef)\ **Post date:** [December 11, 2013, 6:05pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/10 "2013-12-11T18:05:54Z")
So, stupid question…if one were to “fall” into a black hole, with all the stretching of time and whatnot, how long would it take from the fallee’s perspective? ---
**Author:** ![Revtim](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/revtim/32/1042_2.png) [@Revtim](https://boards.straightdope.com/u/Revtim)\ **Post date:** [December 11, 2013, 6:18pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/11 "2013-12-11T18:18:55Z")
> [@Darth\_Panda](#): > > How is babby black hole formed? they need to do way instain massive star ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 11, 2013, 6:24pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/12 "2013-12-11T18:24:41Z")
> [@](#): > > So, stupid question…if one were to “fall” into a black hole, with all the stretching of time and whatnot, how long would it take from the fallee’s perspective? It depends on the size of the black hole, but very short. Roughly the size of the black hole divided by the speed of light. ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [December 11, 2013, 7:24pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/13 "2013-12-11T19:24:15Z")
> [@Malacandra](#): > > All your black hole are belong to us! Glad I RTFT first, I was thinking the same thing–respectable merits of the question aside. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [December 11, 2013, 7:35pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/14 "2013-12-11T19:35:44Z")
I burning your black hole! ---
**Author:** ![Jonathan\_Chance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jonathan_chance/32/701_2.png) [@Jonathan\_Chance](https://boards.straightdope.com/u/Jonathan_Chance)\ **Post date:** [December 11, 2013, 8:41pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/15 "2013-12-11T20:41:23Z")
> [@Chronos](#): > > It depends on the size of the black hole, but very short. Roughly the size of the black hole divided by the speed of light. Wait. It doesn’t stretch out to an endless point? Or are you saying that - even though it took something less than infinite time - it wouldn’t appear that way to the subject? ---
**Author:** ![mendi80](https://avatars.discourse-cdn.com/v4/letter/m/f1d935/32.png) [@mendi80](https://boards.straightdope.com/u/mendi80)\ **Post date:** [December 11, 2013, 9:31pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/16 "2013-12-11T21:31:45Z")
> [@yanceylebeef](#): > > So, stupid question…if one were to “fall” into a black hole, with all the stretching of time and whatnot, how long would it take from the fallee’s perspective? The time flow of universe outside the falling astronout will accelerate. so the universe will come to its end before he will get to event horizon. So this is still coherent to say that no black hole exists. Or maybe we can say that the black hole exists only in the end of time. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 11, 2013, 9:44pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/17 "2013-12-11T21:44:31Z")
In the reference frame of an outside observer, it takes a long time, though our theories are insufficiently developed to say just how long. In the reference frame of an infalling observer, it takes a short time. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [December 11, 2013, 10:02pm UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/18 "2013-12-11T22:02:33Z")
> [@Revtim](#): > > SDMB alum ‘Bad Astronomer’ addressed this once: > [http://blogs.discovermagazine.com/badastronomy/2007/06/19/news-do-black-holes-really-exist/#.UqhubdJZd8E](http://blogs.discovermagazine.com/badastronomy/2007/06/19/news-do-black-holes-really-exist/#.UqhubdJZd8E) > > Sounds like this is not a settled issue. The paper which the bad astronomer bases that on leaves me unsatisfied as it seems to be asking the wrong questions. A black hole is defined by its absolute horizon (i.e. its event horizon), but the question they’re asking is not whether an absolute horizon forms and the set-up they use doesn’t even seem to be capable of answering that question. In particular you need to know what is going on inside the collapsing star to answer that question, but the choice of modelling the star as a Nambu-Gotu domain wall is totally inadequate to tell you what happens on the inside. Of course Krauss knows more about physics than me. Honestly it seems to me that the answer to this question depends on what simplifications are made. ---
**Author:** ![Jamicat](https://avatars.discourse-cdn.com/v4/letter/j/c67d28/32.png) [@Jamicat](https://boards.straightdope.com/u/Jamicat)\ **Post date:** [December 12, 2013, 3:31am UTC](https://boards.straightdope.com/t/are-black-holes-exists-black-hole-formation/676063/19 "2013-12-12T03:31:24Z")
The impulse…I…Could not frighth back! :mad: