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Thread: More black hole questions

  1. #1 More black hole questions 
    not ADM!N grmpysmrf's Avatar
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    So, I've heard that occasionally black holes, for some reason, switch "Off," meaning they don't feed anymore, until they switch back "on" for some reason. I understand the super massive black hole at the center of the milky way is switched "off" currently.

    In this "off" mode, the problem of getting there aside, would it be possible to go spelunk these holes? and (pun intended) get to the bottom of these mysteries? or just because they are switched off doesn't mean there is no longer body stretching amounts of gravity to ruin us?


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    Forum Professor Daecon's Avatar
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    How would "switching off/on" be physically possible?

    Would it not just be a case of not currently having large quantities of mass within the range of gravitational attraction until more matter happens to drift by?


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    not ADM!N grmpysmrf's Avatar
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    Quote Originally Posted by Daecon View Post
    How would "switching off/on" be physically possible?

    Would it not just be a case of not currently having large quantities of mass within the range of gravitational attraction until more matter happens to drift by?
    No, Switching "off" means just that. Matter that should be affected by the hole drifts harmlessly by. At least that's how I understood michio kaku (I think it was he who was talking about it, as well as a few others, on a particular episode (of the universe?) on the science channel) And then suddenly for no reason they kick back on and start sucking things up again

    I'm pretty sure they were also talking about the extreme danger these particular holes present because they are undetectable and when we get to the point that we can start travelling through space they could basically act like land mines in that we could fly right over one and not know it unless it switched on at that moment and we were sucked into it and trapped forever and even then those on board might not know it but everyone else in contact with the ship would.
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    Forum Masters Degree Implicate Order's Avatar
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    Quote Originally Posted by grmpysmrf View Post
    So, I've heard that occasionally black holes, for some reason, switch "Off," meaning they don't feed anymore, until they switch back "on" for some reason. I understand the super massive black hole at the center of the milky way is switched "off" currently.

    In this "off" mode, the problem of getting there aside, would it be possible to go spelunk these holes? and (pun intended) get to the bottom of these mysteries? or just because they are switched off doesn't mean there is no longer body stretching amounts of gravity to ruin us?
    When they say the black hole switches off, what they are meaning is that the black hole has consumed its surrounding accretion disc. This is when the system within which the gravitational effects of the black hole are dominant achieves an equilibrium and has consumed all stuff that has not consolidated into a stable orbit. Stars in the vicinity of a black hole at this equilibrium phase adopt stable orbits (just like planets around our sun) forever falling in orbit around the black hole. If something disturbs this equilibrium phase (such as an external gravitational source which enters the vicinity) the disruption to the field causes disequilibrium and the previous stable orbits may be compromised in addition to the gravitational stuff that was added to the system, leading to the creation of a further accretion disc which the black hole then commences absorbing. It is then said to 'switch on'. The gravitational field however is always felt and never switches off. It can however be altered by another massive gravitational body that enters the vicinity.

    PS As a space traveller, you could always look for the signature of a black hole, namely beware of dark regions that may represent event horizons :-))

    PPS I wouldn't fear a black hole. For example I would have the same fear of gravitational attraction in approaching any sun. You won't be able to readily observe or feel the radiation, but you will be able to measure the gravitational effects of the massive body. Sure once past the event horizon it's curtains as you can never escape but then again if you get to the surface of a sun, then that effectively is curtains anyway.....so it's curtains all round.....a bit like living in a shiek's tent so to speak.
    Last edited by Implicate Order; January 16th, 2014 at 02:34 AM.
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    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by grmpysmrf View Post
    No, Switching "off" means just that. Matter that should be affected by the hole drifts harmlessly by. At least that's how I understood michio kaku (I think it was he who was talking about it, as well as a few others, on a particular episode (of the universe?) on the science channel) And then suddenly for no reason they kick back on and start sucking things up again.
    Black holes definitely do not turn off in the sense of ceasing to have gravity. The only thing that happens is that they no longer have enough matter falling into them to create polar jets or other dramatic effects.

    I have never seen this Kaku person but, based on the ideas presented here by people who watch his programs, it sounds like you should treat most of what he says with great scepticism. I gather he is a scientist but he appears to be an appallingly bad science communicator. I don't know if he just explains things badly, grossly exaggerates or simply makes things up. Either way: Avoid!
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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    not ADM!N grmpysmrf's Avatar
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    Quote Originally Posted by Strange View Post
    I have never seen this Kaku person but, based on the ideas presented here by people who watch his programs, it sounds like you should treat most of what he says with great scepticism. I gather he is a scientist but he appears to be an appallingly bad science communicator. I don't know if he just explains things badly, grossly exaggerates or simply makes things up. Either way: Avoid!
    It probably has more to do with me (and others) not really understanding what he has said OR our inability to correctly recommunicate what he has said. Although, I guess there is the possibility that he has over simplified everything for the layperson like me, because there is no way I'm going to learn a lifetime of physics in a 1 hour program, so, while what he says may not be "technically/Mathematically" correct, it's close enough for the casual fan with a remote control in their hand. Either way, you gotta give him credit for generating interest.
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