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Author Topic: How is a black hole distinguished from a massive non-luminous object?  (Read 11344 times)

Offline Soul Surfer

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Re: black hole questions
« Reply #25 on: 16/04/2012 09:08:41 »
I agree imatfaal We are always talking about what an outside observer would see and not what the object at a distance would experience.  This I believe is the biggest problem because most people do not believe that what they see as an outside observer is very different from what the traveller that they are observing would experience.  The traveller always thinks things are perfectly normal locally with the exception of local temperatures and gravity gradients of course.  Distant objects of course are distorted for them though.
 

Offline simplified

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Re: black hole questions
« Reply #26 on: 16/04/2012 17:16:51 »
Slowed time of star reduces brightness of the star relatively of our time. :P
 

Offline imatfaal

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Re: black hole questions
« Reply #27 on: 16/04/2012 18:20:08 »
I agree imatfaal We are always talking about what an outside observer would see and not what the object at a distance would experience.  This I believe is the biggest problem because most people do not believe that what they see as an outside observer is very different from what the traveller that they are observing would experience.  The traveller always thinks things are perfectly normal locally with the exception of local temperatures and gravity gradients of course.  Distant objects of course are distorted for them though.

QFT - Exactly.

"This I believe is the biggest problem because most people do not believe that what they see as an outside observer is very different from what the traveller that they are observing would experience."   I might have to steal that paragraph :-)
 

Offline syhprum

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Re: black hole questions
« Reply #28 on: 14/05/2012 06:24:43 »
"Not correct the smallest black holes observed have a mass of 5-10 solar masses"
Hoisted by my own petard, astronomers can be forgiven for using their own special units such as Solar masses for out of this world things but I wince when they go on about Ergs or Angstroms when there are proper well understood S.I units.

 

Offline imatfaal

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Re: black hole questions
« Reply #29 on: 14/05/2012 10:28:58 »
syhprum - Soulsurfer, or JP could confirm but I believe that once you get into physics properly systems of units and measurement become a very movable feast, with different sub-disciplines using different units and setting different constants equal to one, ignoring others etc.  As long as you are consistent - you should be safe, the danger lies when you start mixing n matching



from here http://blogs.scienceforums.net/swansont/archives/11498
« Last Edit: 14/05/2012 10:30:43 by imatfaal »
 

Offline yor_on

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Re: black hole questions
« Reply #30 on: 16/05/2012 02:20:57 »
I'm pretty sure they must exist, and that they must be really, really, weird phenomena considering that they can frame drag the space around them at the (almost) speed of light according to some ideas. That as they seem to spin that fast. there should be all kinds of weird phenomena due to that spin.

Both math and observations agree here.
 

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Offline acsinuk

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I think that the super massive black holes at the centre of each galaxy are 3D electromagnetic, and this central magnetic force field holds all the stars in that galaxy in positions so that they can spin together without interfering with each others orbits. If you cant see it then it has no mass; right; but magnetism has no mass either!
CliveS
 

Offline Robro

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When a "Black Hole" evaporates, do the enormous polar jets of gamma rays, plasma and particles also vanish? Is it possible to have a "Black Hole" without the gamma ray jets? Hmmm.
 

Online evan_au

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If they can get it to work, the LIGO gravity wave observatory should be able to detect black holes and other supermassive compact objects as they enter a death-spiral around each other, radiating away huge amounts of energy as gravitational waves.
By looking at the final orbits of the objects, they should be able to identify some objects which are definitely too compact and too massive to be anything but a black hole. Beyond a certain density, the "escape velocity" will exceed the speed of light, and it will become a black hole, no matter what it is made of...
It's a question of how much they can improve the sensitivity of the instrument, and what is the probability of a massive-enough event occurring close enough to our part of the galaxy...
 

Offline thebrain13

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Robro, I think the black hole would lose its gamma ray jets when it lost its magnetic field. moving charged particles can bend in a magnetic field, so if its strong enough the only places where it can escape are directly on the north and south sides. If the black hole loses its mass, it probably loses its magnetic field and thus its ability to bend as well.

And Yor On, my original thinking (and it's only a hunch) is that something is going to stop gravity from growing stronger and stronger indefinitely. What I think probably happens is that gravity weakens gravity. That is gravity doesn't grow linearly with each additional piece of mass but it gets weakened as the amount of mass in an area grows. eventually the strength of gravity will reach a maximum that peaks under the escape velocity of light allowing us to avoid all of this "going back in time/wormholes/whatever" type nonsense and conclude that black holes are just really dense objects with a ton of mass.

 

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