Do scientists think black holes have singularities

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wolram

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Do scientists think black holes have singularities and event horizons or
think they are as described, why think they are nothing more than a dark
massive body?
 
they were predicted mathematically
 

wolram

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yourdadonapogostick said:
they were predicted mathematically
And there is not a chance the prediction was wrong?
 
seeing as black holes have been observed, i doubt it is wrong.
 

wolram

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yourdadonapogostick said:
seeing as black holes have been observed, i doubt it is wrong.
Do you have a reference?
 

Phobos

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wolram said:
why think they are nothing more than a dark
massive body?
We would need to identify some mechanism that can counteract the collapse of all that matter/mass/gravitational force. Under Relativity, there is none...hence the singularity.

But I think one application of string theory has an alternate model that does not include a singularity (check out topics on information retrieval from a black hole).

IIRC, a few years ago there were also discussions about a "gravastar" model of the black hole which did not include singularities (some kind of exotic space instead).

But the current model has the best support so far.
 

Pengwuino

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How did they mathematically discover black holes? Is it explainable in a post or should i go find a book...
 
it is a prediction of GR. i don't specifically know how they did it, though.
 

pervect

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wolram said:
Do scientists think black holes have singularities and event horizons or
think they are as described, why think they are nothing more than a dark
massive body?
The theory of general relativity is what predicts that massive enough bodies will have event horizons and singularities. It is expected that quantum gravity will replace singularities with something else, but since the singularities are "hidden" behind the horizon, this doesn't make a great deal of difference - we are not expecting to be able to observe naked singularities.

As to why we believe GR is the right theory of gravity a short and very partial recap goes something like:

The observed magnitude of bending of light by the gravity of the sun and other objects (gravitational lensing).

The recession of the oribit of mercury

Radar time delay meausrements of venus (the Shapiro effect).

Observations of the rate of slowing of binary pulsars. This last result is one of the few results in the "strong field" regime, so it's especially important for black holes.

Soon, we will have results from gravity probe B, which will confirm (or deny) the frame-dragging predictions of GR (the Lense-Thirring effect).
 
soon? we still have a few years for GPB to give results
 

wolram

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It seems LIGO is quite negative.
 

amt

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I think black holes are obvious phenomenons. If you think 'escape velocity' then it seems much more realistic than simply stating 'black holes', as though it is some mysterious object. However the point of convergence or 'singularity' in a BH is quite speculative. They say that can lead to another Universe etc etc...
 

russ_watters

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Pengwuino said:
How did they mathematically discover black holes? Is it explainable in a post or should i go find a book...
Not discover, predict. Its kinda a two-part prediction:

-First, if you get enough force (pressure) due to gravity and, say, the collapse of a dying star, it was calculated that the pressure developed was greater than the structural integrity of a neutron, causing the neutron to collapse. I'm a little fuzzy on how this leads to a singularity, and I know there is still some debate over whether the result of the collapse is a singularity or just a lump of dense matter of an unknown form. Regardless, that leads to the second part:

-If there is enough mass in a small enough volume, the excape velocity of the object will be greater than C. With an escape velocity greater than C, not even light can escape. Hence: black hole.

Now, the usual question: if light can't escape, how can we find them? Well, further calculations revealed that matter falling into a black hole would accelerate, get hot, and start emitting electromagnetic energy (light) before it passed that point of no return (the event horizon). The calculated frequency of the em radiation was in the range of X-rays. So the first black holes were found by looking for stars with invisible binary companions, sucking matter from them and emitting x-rays as that matter disappears into oblivion.
 

pervect

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wolram said:
It seems LIGO is quite negative.
This has been discussed before - LIGO's results (non-results) are consistent with GR.
 

Pengwuino

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What does binary mean
 

russ_watters

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Pengwuino said:
What does binary mean
Binary star system - two stars orbiting each other.
 

Danger

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Initially, Subramanian Shandrashakar calculated that a star of 3.2 Solar masses would not be able to halt its own gravitational collapse at the neutron star stage. His predictions, however, were based upon a static black hole. Karl Schwartzchild later refined the formulae to work for rotating holes. Even further refinements dealt with electrically charged holes. Hawking then got into it with the 'evaporation' prediction. Newer theories are continuing to investigate and speculate. One initial prediction, in Schartzchild's time, was that if a hole had too much spin or charge, the event horizon would split at the equator and allow something to navigate through the hole without hitting the singularity. (Don't get excited about space-travel through one, though; the tidal forces would still rip the matter into subatomic particles.)
 

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