Re: Einstein's 1939 paper challenging the existence of black holes

On May 7, 12:40 am, "Juan R." González-Álvarez
<juanREM...@xxxxxxxxxxxxxxxxxxxx> wrote:
Eric Gisse wrote on Wed, 06 May 2009 21:23:34 +0000:

(...)

S. Doeleman, et. al "Event horizon-scale structure in the
supermassive black hole candidate at the galactic center", Nature
455, 4 Sept. 2008, p 78.

Precisely this is my point. First you would notice their use of "black
hole candidate" in their title, just as I propose. Now take a look to
the abstract

http://www.nature.com/nature/journal/v455/n7209/abs/nature07245.html

(...)

Perhaps we could start calling it the unicorn candidate.  Sure that's
nonsense but like you say, we don't really _know_ now do we?

Give me a citation of an author equating the scientific and rigorous term
"black hole candidate" with your ridiculous term "unicorn candidate" or I
will conclude that again you do not understand the difference between
rigorous scientific research and sci-fi movies or between scientific
knowledge and your own misconceptions.

You missed the point.

The object known as the "black hole" has specific predictions, all of
which are satisfied by current observation in the instance of Sgr A*.

But since you seem to think there is still a fair amount of
uncertainty (that you can't quantify), we might as well call it the
unicorn candidate because it doesn't matter what is found you just
won't be satisfied.


The cores of most galaxies *are thought* to harbour supermassive black
holes

...as supported by observation...

says "are thought" not "are observed".

I'm gonna go with my original thought of "as supported by
observation".

How many documented examples of galaxies with supermassive dark
objects pushing past a million solar masses would you like? I can
think of one in which the spin has been reasonably well measured, and
several others in ApJ that are simply taken for granted.

Just do me a favor and tell me where the goal post is so it can't be
moved when it is reached.


[...] Sgr A* [...] is the closest example of this phenomenon, with an
*estimated black hole mass* that is 4,000,000 times that of the Sun

"estimated" like the Earth-Sun distance is "estimated" to be 93 million
miles.

An *estimated black hole mass* of 4 millions (was 3.7 before and 2.6
earlier...) has not the same status than Earth-Sun distance.

Oh, so because the mass changed because of improved observations it is
just an _estimation_ ?

a) Look at the error bars. For the last few years, the values have
been pretty consistent within margin - around 4 million solar masses.
b) The older value of 2.6 million solar masses used a value for the
Earth-Sgr A* distance that had larger uncertainties than its' current
value, and it was also based on the orbit of exactly *one* star - S2.
http://www.mpe.mpg.de/ir/GC/res_s2orbit.php?lang=en

Regardless, this is all nitpicking. You are trying to wedge in
uncertainty that does not exist by pointing to what appear to be
conflicting results without an understanding of the state of the art
OR how it has progressed in the last decade.


I know nobody doubting about the existence of the distance, but Sgr A*
continues being considerd a bright and very compact astronomical radio
source *supposed* to be the location of a supermassive black hole.

We are all open to alternatives that pass the laugh test.


Ghez, et. al : "Stellar orbits around the galactic center black hole",
ApJ 2-05 ; 744-757

Actually it is ApJ 620. Usually I'm pretty good with proper
transcription. That's why I write in pencil!


I would prefer a more rigorous "around the pressumed galactic center black
hole".

Well I guess reading the title and immediately dismissing it _is_ an
alternative to reading the abstract or even, god forbid, the entire
article itself.

If you have a problem with Ghez's methodology, I'd be glad to hear it.
Otherwise, don't dismiss an article just because it doesn't play to
your prejudices.


There is many possibilities and alternatives we cannot rule out.

We most certainly can make a damn good guess, by a very loose usage of
GR as well!

Buchdhal's theorem states that for a spherically symmetric
distribution of mass with reasonable energy conditions, under
hydrostatic equilibrium, the _MAXIMUM_ amount of mass M you can stuff
inside a given radius R is bounded by 4Rc^2 / 9 G. The orbital
kinematics put a naive upper bound on the size of the object to be
about 45AU - 500 Schwarzschild radii. Doeleman's work moves the bound
to less than a half dozen radii.

There's no way, not with GR.


http://arxiv.org/abs/0902.0346

  "In summary, what our calculation suggests is that it might be possible
  to have a black hole without having a black hole."

Only if you buy the assumption that vacuum polarization is relevant
during collapse. That's one of many major assumptions that are pretty
flimsy.


Black hole mimickers: regular versus singular behavior 2008: Phys. Rev.
D78, 024040. José P. S. Lemos, Oleg B. Zaslavskii

I don't have access to recent Phys. Rev. D issues, but since you
dismissed Ghez's work out of hand I don't suppose you'll make a fuss.


How to tell a gravastar from a black hole 2007: Class. Quant. Grav. 24,
4191-4206. Cecilia B. M. H. Chirenti, Luciano Rezzolla

   "Gravastars have been recently proposed as potential alternatives to
   explain the astrophysical phenomenology traditionally associated to
   black holes, raising the question of whether the two objects can be
   distinguished at all."

Etc.

Have you actually _read_ about the object? It is not anything this
side of "acceptable" as an alternative.

Given that you won't (or can't) read Ghez's paper in ApJ, and clicking
on the "Full Text" button regarding Doeleman's work was too hard (or
you don't have access), I'll presume that Class. Quan. Grav. is
outside your reach. So here's an open access description of the
Gravastar - tell me if you think it passes the laugh test.

http://www.fc.up.pt/pessoas/luis.beca/phisky/PhiSky%20Wiltshire.pdf


[...] This is less than the *expected* apparent size of the event
horizon of the *presumed* black hole [...]

So?

So I propose to continue using precise terms as "presumed black hole" and
similar ones.

Can I expect such equally precise terminology for your personal
preferences regarding field theories of gravitation versus metric
theories?


"It is an open question whether or not the Sgr A* source is centred on
the black hole. Indeed, several models predict an offset between Sgr A*
and the black hole position."

That's what the article says. Comment?


Even though I equate Sgr A* with the associated black hole, there's
plenty of reason to doubt that the radio emission source Sgr A* is not
at the exact same position as the black hole.

Do you doubt this?


Read the last 2 paragraphs, as opposed to selective quoting of the
abstract.

Contrary you can believe, from your own misreadings, the authors are not
contradicting their own abstract.

Do you have a specific argument you would like to make?


(...)

Moreover a comprensehive reading of his work shows they did not prove
existence of black holes.

...and a comprehensive reading of other works do not "prove" the
existence of neutron stars, extrasolar planets, or prions.

Mostly because science doesn't prove.

Remind above was my reply to your unfounded claim:

  Some "rigorous" people will never be satisfied no matter how heavy the
  burden of proof is.

It has the virtue of being true.


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