# Black Hole.... Not so Black

Discussion in 'Astronomy, Exobiology, & Cosmology' started by RajeshTrivedi, Oct 1, 2014.

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Apologies, as I somehow missed your post among the rest of my notifications.
Actually, an Interesting point you have raised.
What you say appears logical with regard to stellar mass and SMBH.
All I can add is that once matter/energy reaches that quantum stage, it is highly degenerate anyway, and we still only have the one GR theory applying to all.
What I may do, is a "tashja"who is our expert professional opinion getter,

and E-Mail a few of my own and one in particular that did frequent another forum I was on.

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7. ### KilljoyKlownWhateverValued Senior Member

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I have great admiration for the GR theory, but don't think it is the end all. Highly degenerate is an apt description that many still take to mean singularity and I just don't believe in them anymore than I believe in God. I think the degenerate process continues as the mass increases. We get to observe some of that process on this side of the EH (white dwarfs & neutron stars). Just because the mass contracts below the EH I don't believe it should be viewed as fully compressed no matter how massive it gets. Since we can't know what the mass on the other side of an EH is like, a newly formed solar BH mass could be just a single millimeter below the EH and we'd never know it.

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Agreed, GR is not the be all or end all, still its the best we have got.
And using it, and the associated Schwarzchild radius, once that is reached, further collapse is compulsory.

Agreed again, I don't believe too many physicists do accept the classical BH point Singularity.
Since GR gives up the ghost, so to speak, at the quantum/Planck level, this is where I see the Singularity beginning, and according to some definitions of singularity, in that they do begin when all accepted models break down.

Here in your finality, you seem to be invoking a "Michell/Newtonian Dark Star.....or some may call it a Frozen Star.

9. ### KilljoyKlownWhateverValued Senior Member

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I hadn't heard about this before, but I have wondered if there are any more original thoughts or ideas that haven't been thought of before. I don't really have a firm belief about the possible forms matter might have on the other side of the EH, but I do like to keep an open mind about it. If current theories are not being challenged all the time we would never make any advancements would we.

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wiki
http://en.wikipedia.org/wiki/John_Michell
John Michell (25 December 1724 – 29 April 1793) was anEnglish clergyman and natural philosopher who provided pioneering insights in a wide range of scientific fields, including astronomy, geology, optics, and gravitation. Considered "one of the greatest unsung scientists of all time",[1] he was the first person known to propose the existence of black holes in publication, the first to suggest that earthquakes travel in waves, the first to explain how to manufacture artificial magnets, and the first to apply statistics to the study of the cosmos, recognizing that double stars were a product of mutual gravitation. He also invented an apparatus to measure the mass of the Earth. He has been called both the father of seismology and the father of magnetometry.

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11. ### rcscwcRegistered Senior Member

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Surely, mass cannot vanish into a poof. Mass is energy and Laws of Thermodynamics do hold.

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The point is that the BH is mainly just critically curved spacetime.
The mass is in a degenerate state at the Singularity.
The following explains it far better than I can.
http://curious.astro.cornell.edu/question.php?number=219
extract:
There is a rough analogy between a black hole and an atom. In both cases, the mass is concentrated in a tiny region at the center, but the "size" of the object is much bigger. You can use the Schwarzschild radius to calculate the "density" of the black hole - i.e., the mass divided by the volume enclosed within the Schwarzschild radius. This is roughly equal to (1.8x1016 g/cm3) x (Msun / M)2, where M is defined as above. From the point of view of an outside observer, this might as well be the actual black hole density, since the distribution of matter within the Schwarzschild radius has no effect on the outside.

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Starting from Newton's gravitational theory, we give a general introduction into the spherically symmetric solution of Einstein's vacuum field equation, the Schwarzschild(–Droste) solution, and into one specific stationary axially symmetric solution, the Kerr solution. The Schwarzschild solution is unique and its metric can be interpreted as the exterior gravitational field of a spherically symmetric mass. The Kerr solution is only unique if the multipole moments of its mass and its angular momentum take on prescribed values. Its metric can be interpreted as the exterior gravitational field of a suitably rotating mass distribution. Both solutions describe objects exhibiting an event horizon, a frontier of no return. The corresponding notion of a black hole is explained to some extent. Eventually, we present some generalizations of the Kerr solution.

extract:
Its metric can be interpreted as the exterior gravitational field of a suitably rotating mass distribution.

14. ### SchmelzerValued Senior Member

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First, the argument if "gravity gravitates" is void. What is considered to be the "source", which "gravitates", is quite arbitrary - as arbitrary as the decision what to write on the left side or the right side of the equations. Write it this way:

$g^{ab}\partial_a \partial_b g^{mn} + T_g^{mn}(g^{ab}, g^{ab}_{,k}) + T_m^{mn}(...) = 0$

and you can, as well, consider the non-linear expression containing only first derivatives as a source term too - don't forget that the energy-momentum tensor depends on the metric too, so, adding this term means only a little bit more dependence on the metric.

It is definitely not "excuse" - the Sun radiates as gravitational waves something in the order of a few kilowatts. So, there was never a justified expectation that one can observe gravitational waves from known sources.

But what about unknown sources? What about gravitational waves created new the Big Bang? They would travel almost undistorted through the universe, and they could be much more powerful than what the known sources give.

Of course, the question how much is justified to spend for fundamental science is a subtle one. But spending a few billions on gravitational radiation detection is clearly better for humankind than to spend the same money for some more tanks and nuclear rockets. And, once it is accepted to spend some billions for fundamental physics at all, then the part of these billions spend on gravity waves is unproblematic. Because it is quite clear that, after some time, one will be able to observe gravitational waves from known sources, and this will be a great increase in the observational power of astronomers. And don't forget that negative results are also important scientific results: They can falsify some theories, say, about the Big Bang, which would lead to extremely powerful sources of gravitational waves which we would observe already today.

15. ### Q-reeusValued Senior Member

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According to standard GR, LHS and RHS of EFE's equates uniquely as curvature = SET (stress-energy tensor) - RHS exclusive of 'gravitational energy-momentum density' as possible source term):
https://en.wikipedia.org/wiki/Einstein_field_equations
https://en.wikipedia.org/wiki/Einstein_field_equations#Vacuum_field_equations (explicitly, Ricci curvature tensor is zero if SET is zero.)
http://en.wikipedia.org/wiki/Stress–energy_tensor (defined first para).

Sure one can mathematically swap terms around, but then what is being equated? It's no longer curvature = non-gravitational source density. Not in any full sense. Given the Ricci tensor is zero whenever SET is zero, any vacuum 'gravitational field' is guaranteed thereby to be source free i.e. cannot be a source of it's own gravity.
That must be so regardless of determination in an inertial or accelerated frame, hence independent of any 'g' field felt in a given frame. Hence independent of any computed 'local gravitational field energy density'. In good analogy to an EM wave having frame-dependent energy density but zero charge density in any frame.
Only by means of subterfuge is this artfully and seemingly overcome.

Such is the actual situation in GR, though not as practiced by many. In say Yilmaz gravity, the claim is made gravity does indeed self-gravitate in a fully self-consistent way. Certainly the Yilmaz exponential metric equivalent to Schwarzschild metric in GR, does have the property of a non-zero vacuum Ricci curvature as required for such claim.
You are I presume referring to so-called HFGW's owing to thermal collisions mainly in the core region. Interestingly, it was shortly after posting links to just such worked calculations, in a thread elsewhere, I came to reverse my opinion from arguing in favor of such GW's (not just HFGW's), to arguing against. Once seen, it's laughably obvious the so-called quadrupole mode TT-gauge GW's with '+' and 'x' polarizations, are an impossibility. I have yet to figure if any other mode is allowable (GR says no) but won't elaborate here.
You are surely aware, after all the initial fanfare, BICEP 2 is dead and buried - 'bitten the dust' as some like to pun. A great personal relief for me, and obvious bitter disappointment to many others. Hope lives on that BICEP 3 (or maybe 4 or 5 or...) will recover some scraps or hints of primordial GW's, but even then, others have worked out alternate possible non-GW sources for 'B' modes. It might be very hard to tease one possibility from another. So far, no need. AS for LIGO, VIRGO etc., well hopes are kept alive. If there are eventually any detections such 'direct' routes, I will bet any money you like it would not be of the quadrupole mode TT-gauge variety. Binary pulsar results must have another explanation.