Mass/Density

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Mass/Density

Postby timur555 » Fri Aug 06, 2010 2:06 am

Does a black hole/singularity have an infinite mass/density?....
was thinking that if so , then only one black hole with an infinitely dense singularity(infinite mass) would alone account for all dark matter/energy by itself by nature of this infinite density/mass , never mind all the other black holes that exist supermassive or not..the dark matter/energy that is being speculated upon seems to have a finite figure/quantity even if it is 90 odd percent more than we know about , but if there are things out there of an infinite mass/density then surely only one of these would easily account for all dark matter/energy ..and the rest..infinitely...am sure (hope)someone else must have thought about this and probably i'm not understanding something ..perhaps someone could explain...
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RE: Mass/Density

Postby brianb » Fri Aug 06, 2010 9:20 am

Finite mass, infinite density ... Unless you believe in string theory in which case there is [i]no singularity[/i] as a black hole contracts to a single string i.e. the final dimension is of the order of 10^-35 metres. But don't forget that the local distortion of space/time caused by the large mass makes definition of terms like "size" somewhat difficult.

It makes more sense - from the point of view of an outside observer - to consider the mass of a black hole as being uniformly distributed within its event horizon.
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RE: Mass/Density

Postby sftonkin » Fri Aug 06, 2010 1:30 pm

First off, I think we need to acknowledge that Dark Matter is functionally indistinguishable from the proposed planet Vulcan: both are masses that were invented to try to force-fit observations to what were presumed to be universal laws of physics.

There is a very big problem with trying to ascribe black holes to the effects that led to dark matter being invented. The gravitational effects of black holes will show relativistic deviations from Newtonian (inverse-square law) gravity. The rotation curves of galaxies, that dark matter was invoked to explain, have almost an opposite requirement of gravity, i.e. that the mass distribution of dark matter has to be such that, if the rotation was due to only the observed mass of galaxies, gravity would have to have an inverse (as opposed to inverse square) relationship to mass in weak gravitational fields. (See Milgrom's MOND hypothesis.)
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RE: Mass/Density

Postby brianb » Fri Aug 06, 2010 11:30 pm

[quote]There is a very big problem with trying to ascribe black holes to the effects that led to dark matter being invented.[/quote]
It does sound very improbable, but not physically impossible. If there was a large population of stellar mass black holes distributed in the galactic halo, this could provide the missing mass. The real problems are that the black holes would have to get made i.e. there would need to be a population of primeval stars of which the massive ones have gone supernova - so where are the lighter stars & why do we not see heavy element dust clouds ejected by the SNe? We need a different method of producing a population of stellar mass black holes in the halo, that seems to be at least as great an issue as postulating that the dark matter is in some other form. Plus a large population of black holes in the galactic halo would case lensing events.

Deviations from the inverse square law of gravitation ... well I personally think that such a model can only cause more issues than it solves. Supersymmetry theory, and weakly interactive massive particles, seems to solve the issue much more tidily. Experimental evidence is lacking but hopefully something may be learned by continued operation at full power of the Large Hadron Collider.


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RE: Mass/Density

Postby sftonkin » Sat Aug 07, 2010 12:33 pm


[quote]ORIGINAL: brianb

Deviations from the inverse square law of gravitation ... well I personally think that such a model can only cause more issues than it solves. Supersymmetry theory, and weakly interactive massive particles, seems to solve the issue much more tidily.[/quote]

Indeed so. There is neither observational evidence nor theoretical basis for MOND.
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