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rogerperkins
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I recently tried to calculate the mass of the black hole in the center of the milky way and it came out to 1.8x10e+53 kg, that can't be right, what's going on?
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rogerperkins said:I recently tried to calculate the mass of the black hole in the center of the milky way and it came out to 1.8x10e+53 kg, that can't be right, what's going on?
rogerperkins said:I ignored any effects from the mass in the rest of the galaxy, not sure if that's significant
morghen said:no calculations here, just logic:
Starting from the, considered true, fact that the black holes occupy space(like other compacted matter objects, stars, neutron stars):
black holes also have a range of mass, why? they express themselves via a volume(area) of space so that means that there is something holding contents of the black hole into a structure that occupies space. If it did not have a maximum mass it would simply be an infinetely small point being able to absorb everything, something like reverse big-bang.
i don't buy the "matter can't be compacted any further" statement...we have clear evidence that it was..
Where is the problem?If it did not have a maximum mass it would simply be an infinetely small point being able to absorb everything
It is not, at least not with the Schwarzschild radius. And it does not matter how it looks inside. The event horizon is just a result of GR in a region where GR is valid.If however the black hole is a solid globe of compressed matter that occupies space then there must be a critical mass point.
morghen said:So you're saying the observable diameter of the object has no corelation to its mass?
You're satisfied with "simply the distance from the center of the black hole to the event horizon" ?
Even if the event horizon is just a shell around a point with zero/one volume, what's behind the EH is probably not empty, but accelerating material that has passed the event horizon and it is heading towards the maximum gravity point...so there must be a flowing structure.
If however the black hole is a solid globe of compressed matter that occupies space then there must be a critical mass point.
hehe, this is a bit like saying: god went click and the light was on :PDrakkith said:Yes.
why not? what would you call it? or you think it just infalls without any rules/properties?Drakkith said:I would not call infalling material a "flowing structure".
why are you being sarcastic? how should i know? but if the black hole occupies any space at all there probably is a certain mass value after which there come changes within/out the black hole.Drakkith said:What is this critical mass point?
morghen said:hehe, this is a bit like saying: god went click and the light was on :P
why not? what would you call it? or you think it just infalls without any rules/properties?
why are you being sarcastic?
how should i know? but if the black hole occupies any space at all there probably is a certain mass value after which there come changes within/out the black hole.
Why would you believe the black hole is such a rigid and ultimate concept?
mfb said:Similar to all other objects, if you neglect relativistic effects. [itex]v=\sqrt{\frac{2GM}{r}}[/itex] where M is the mass inside for spherical mass distributions. For neutron stars, it might be useful to add some relativistic corrections, but the formula gives a good approximation.
no calculations here, just logic:
QUOTE]
As far as I can tell no a single statement you imagine is correct. I'm not saying there is no 'logic' in your thinking, in fact I can't make any sense of much of that post, but it seems you are extending classical analogies to relativistic black holes. That doesn't apply. It won't work.
Are you aware spacetime inside a black hole becomes very distorted...that is very, very curved. So you can't use classical measures of time and distance. Those are based on Eucledean space and a typical BH is described by Schwarzschild coordinates.
The volume of a BH is NOT the classical 4/3[pi]r3...nor is the surface area the classical 4[pi]r2 There is generally believed to be NO matter inside...although some may be infalling at a particular time. Did you know the curvature of a charged BH is different from that of one with no charge...because of the additional energy of an electromagnetic field.
Are you aware the absolute BH horizon begins to grow before matter reaches it? Are you aware that the 'radius' inside a BH is a time dimension, not a distance. That the singularity is a point in time not in space? Are you aware the relative horizon jumps discontinuously with changes in matter/energy? That a newborn BH exhibits violent, chaotic tidal oscillations of a BKL singularity...and these gradually disappear as the BH ages?
These are all things I don't think are available by any convenient logic; they flow from mathematical models of GR.
Here are a few descriptions I keep to remind me how strange BH actually are:
Kip Thorne says (Lecture in 1993 Warping Spacetime, at Stephan Hawking's 60th birthday celebration, Cambridge, England,)
The flow of time slows to a crawl near the horizon, and beneath the horizon time becomes so highly warped that it flows in a direction you would have thought was spacial: it flows downward towards the singularity. That downward flow, in fact, is why nothing can escape from a black hole. Everything is always drawn inexorably towards the future, and since the future inside a black hole is downward, away from the horizon, nothing can escape back upward, through the horizon.
Black Hole Complementarity
Leonard Susskind, THE BLACK HOLE WAR (his arguments with Stephen Hawking)(p238) Today a standard concept in black hole physics is a stretched horizon which is a layer of hot microscopic degrees of freedom about one Planck length thick and a Planck length above the event horizon.
(p258) From an outside observer’s point of view, an in falling particle gets blasted apart….ionized….at the stretched horizon…before the particle crosses the event horizon. At maybe 100,000 degrees it has a short wavelength and any detection attempt will ionize it or not detect it!
http://www.jimhaldenwang.com/black_hole.htm
{Inside the horizon:}
It is the coordinate with the minus sign that determines the meaning of “timelike. Notice how the minus sign has moved from the t coordinate to the r coordinate. This means that inside the event horizon, r is the timelike coordinate, not t. ... According to GR, inside a black hole, time is defined by the r coordinate, not the t coordinate.
In fact horizons are spheres of coordinate timelike singularities not ones of classical volume.
But in short, no there is no theoretical maximum size for a black hole, except for perhaps the sum of all the mass energy in the observable universe.
... in the heat death scenario, the energy density is so low that the system can be thought of as non-gravitational, such that a state in which energy is uniformly distributed is a thermal equilibrium state, i.e., the state of maximal entropy.
Naty1 said:no calculations here, just logic:
QUOTE]
As far as I can tell no a single statement you imagine is correct. I'm not saying there is no 'logic' in your thinking, in fact I can't make any sense of much of that post, but it seems you are extending classical analogies to relativistic black holes. That doesn't apply. It won't work.
Are you aware spacetime inside a black hole becomes very distorted...that is very, very curved. So you can't use classical measures of time and distance. Those are based on Eucledean space and a typical BH is described by Schwarzschild coordinates.
The volume of a BH is NOT the classical 4/3[pi]r3...nor is the surface area the classical 4[pi]r2 There is generally believed to be NO matter inside...although some may be infalling at a particular time. Did you know the curvature of a charged BH is different from that of one with no charge...because of the additional energy of an electromagnetic field.
Are you aware the absolute BH horizon begins to grow before matter reaches it? Are you aware that the 'radius' inside a BH is a time dimension, not a distance. That the singularity is a point in time not in space? Are you aware the relative horizon jumps discontinuously with changes in matter/energy? That a newborn BH exhibits violent, chaotic tidal oscillations of a BKL singularity...and these gradually disappear as the BH ages?
These are all things I don't think are available by any convenient logic; they flow from mathematical models of GR.
Here are a few descriptions I keep to remind me how strange BH actually are:
Kip Thorne says (Lecture in 1993 Warping Spacetime, at Stephan Hawking's 60th birthday celebration, Cambridge, England,)
Black Hole Complementarity
Leonard Susskind, THE BLACK HOLE WAR (his arguments with Stephen Hawking)
In fact horizons are spheres of coordinate timelike singularities not ones of classical volume.
Well I am not trying to model black holes I am just playing with ideas. You can humour me or not but I am just experimenting. I simply need a method of calculating a density and acceleration away from a point within that density.
hubble_bubble said:Can anyone tell me if the following statement from the above site is true.
"For a planet the mass of the Earth, this distance is only about a centimeter. So if the Earth were less than a centimeter in diameter, the escape velocity at the surface would be greater than the speed of light."
hubble_bubble said:I have found a page at superstringtheory.com that gives me what I need. Can anyone help in getting an understanding of this. I have no idea how I would translate this into code to produce data that can be graphed.
http://www.superstringtheory.com/blackh/blackh1a.html
Better still is there already a graphical representation.
Nabeshin said:What exactly do you want to graph?
This website seems a little silly; just looking at it, the author for some reason writes Newtonian gravity in arbitrary D dimensions, then just states the Einstein equations and the schwarzschild solution in D=4... OK. Nothing is flat out wrong, it's just strange (especially since nothing on this page has anything to do with superstring theory).
hubble_bubble said:I want to plot density of a mass against the calculated escape velocity. As stated above does a 1 cm Earth have an escape velocity that is greater than the speed of light? If so I would assume it has an event horizon. This would technically be equivalent to a black hole, but the mass is too small.
Chronos said:It appears you may be under the impression that matter density [pressure] effectively increaes rest mass, due to mass-energy equivalence. This is untrue. The effective mass of a black hole, or condensed matter object, is the same as its uncompressed progenitor mass.
mfb said:3 solar masses is the mass limit for the star in the calculations, the remaining black hole would have a lower mass (I think something like 2 solar masses?). However, no black holes of this size were detected yet, so this is a bit speculative.
hubble_bubble said:This postulation must be false.