Link between dark matter and baryonic matter

In sci.astro message , Tue, 25 Oct 2016
18:30:03, Steve Willner posted:

In article ,
dlzc writes:
Individually, no. But in groups, with a center of momentum frame,
[photons] do have rest mass.

So the sum of a bunch of zeroes is non-zero? That's new physics.

I have no idea what "with a center of momentum frame" is supposed to
mean.

Standard physics says photons have momentum and energy but zero rest
mass. Photons react to gravity and (in principle, but I don't think
it has been measured) create gravity, but neither of those properties
requires rest mass.

Wikipedia page "Kugelblitz (astrophysics)" strongly implies that John A
Wheeler considered photon energy to create gravity.


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Am Mittwoch, 28. September 2016 16:55:10 UTC+2 schrieb dlzc:
Dear wor...:

If we are into opinions here...


But the oscillations in the rotation curves can not be overlooked, fully established: https://arxiv.org/abs/1604.01216
Please refer Figure 12.

In addition to the halo, the scientists had added two rings of dark matter as part of the DM model...

Why not equal two rings of normal matter? The rings of rock and ice are nevertheless common and ordinary cosmic formation.

In article ,
writes:
But the oscillations in the rotation curves can not be overlooked,
fully established: https://arxiv.org/abs/1604.01216
Please refer Figure 12.

Now published in MNRAS (Huang et al. 2016)
http://mnras.oxfordjournals.org/content/463/3/2623.full

In addition to the halo, the scientists had added two rings of dark
matter as part of the DM model... Why not equal two rings of
normal matter? The rings of rock and ice are nevertheless common
and ordinary cosmic formation.

I'm not sure, but the dark-matter rings seem to date back to
a 2003 paper
http://www.sciencedirect.com/science...70269303008633

The Huang et al. paper assumes cylindrical symmetry, and there's a
brief mention that non-axisymmetric structure could change the
conclusions. According to Table 4, the sum of the ring masses is
just over half the bulge+disk mass, so it's not obvious to me that
the rings have to be dark matter. However, this is based on just a
quick scan. I'm no expert on this subject, and a good answer would
take some work.

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Am Montag, 7. November 2016 23:41:41 UTC+1 schrieb Steve Willner:
In article ,
writes:

In addition to the halo, the scientists had added two rings of dark
matter as part of the DM model... Why not equal two rings of
normal matter? The rings of rock and ice are nevertheless common
and ordinary cosmic formation.

I'm not sure, but the dark-matter rings seem to date back to
a 2003 paper
http://www.sciencedirect.com/science...70269303008633


Thanks for this link.

Quotes:"In the past, rises (or bumps) in galactic rotation curves have been interpreted as due to the presence of spiral arms [17]. Spiral arms may in fact cause some of the rises in rotation curves."

[17] C. Yuan, Astrophys. J. 158 (1969) 871; W.B. Burton, W.W. Shane, in: W. Becker, G.I. Kontopoulos (Eds.), Proceedings of the 38th IAU Symposium the Spiral Structure of our Galaxy, Reidel, Dordrecht, p. 397; W.W. Shane, Astron. Astrophys. 16 (1972) 118.

Yupi!!

In article ,
dlzc writes:
Second Edition, Section 8.4, Sample Problem 8-2.

I'm looking at _Spacetime Physics_ by Taylor & Wheeler, Second
Edition, copyright 1992, problem 8-5. (Problem 8-2 is a simple
numerical calculation of E = mc^2.)

Quote: "A system consisting entirely of zero-mass photons can
itself have nonzero mass!"

I don't see that exact quote but perhaps am just missing it. There
are other words that amount to pretty much the same thought.

Some observations:
1. the only thing we are arguing about is terminology. Everyone
(well, everyone who actually understands the subject) agrees on what
the equations say and the results of calculations.

2. photons carry energy and momentum. Photon energy contributes to
gravitational attraction, i.e., bends spacetime, and photon momentum
must be included for conservation of momentum.

3. T&W use "mass" inconsistently. Sometimes they mean "relativistic
mass," E/c^2, and sometimes "rest mass." Modern terminology uses
"mass" to mean rest mass only. The term "energy" is used when older
texts would have used "relativistic mass."

4. at no place do I see T&W claiming a collection of photons somehow
acquires rest mass. Indeed, all their arguments (which are correct
so far as I can tell) are as valid for a single photon as for any
other amount of radiation.

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Help keep our newsgroup healthy; please don't feed the trolls.
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On Friday, 25 November 2016 23:37:50 UTC+1, Steve Willner wrote:

3. T&W use "mass" inconsistently. Sometimes they mean "relativistic
mass," E/c^2, and sometimes "rest mass." Modern terminology uses
"mass" to mean rest mass only. The term "energy" is used when older
texts would have used "relativistic mass."

4. at no place do I see T&W claiming a collection of photons somehow
acquires rest mass. Indeed, all their arguments (which are correct
so far as I can tell) are as valid for a single photon as for any
other amount of radiation.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

Just some thoughts.
IMO we should only use the word mass and not the word rest-mass.
My understanding is that objects exists and mass does not exist.
Mass is a purely a calculated value based on a model or theory.
The theory can be used Newton's law which starts with observations.
With the use of these observations (over a certain period) and with
the model the parameter mass can be calculated.
The use a different model and the same observations will result
in different mass values for the same objects.

Photons, using the same reasoning also have a mass.
The equation is m = E/c^2. The issue is what E ?
E is the amount of energy "released" when in some chemical reaction
a photon is released. This is in accordance with the law: Conservation
of energy. It is that "simple"

Gravitons using the same reasoning also have a mass.
The value is very low.

Nicolaas Vroom

Dear Nicolaas Vroom:

On Saturday, November 26, 2016 at 5:29:36 AM UTC-7, Nicolaas Vroom wrote:
On Friday, 25 November 2016 23:37:50 UTC+1, Steve Willner wrote:

3. T&W use "mass" inconsistently. Sometimes they
mean "relativistic mass," E/c^2, and sometimes "rest
mass." Modern terminology uses "mass" to mean rest
mass only. The term "energy" is used when older
texts would have used "relativistic mass."

4. at no place do I see T&W claiming a collection of
photons somehow acquires rest mass. Indeed, all
their arguments (which are correct so far as I can
tell) are as valid for a single photon as for any
other amount of radiation.

IMO we should only use the word mass and not the
word rest-mass.

It was not Mr./Dr. Wilner's contention it was rest mass. But the mass at rest in the center of momentum frame, should be considered rest mass.

A collection of two "photons", exact same energy, one directed "left", and one directed "right". The center-of-momentum frame is at rest with respect to you. The system's frame has zero net momentum, and non-zero energy. Therefore, it has rest mass... until the two photons propagate out past your distance from their "origin center". At which time, their gravitational component becomes undifferentiable by you from background.

http://www.phy.duke.edu/~lee/P53/sys.pdf

My understanding is that objects exists and mass
does not exist.

"Object" is a macroscopic definition, in that it confines properties to a location. Mass is likewise a property assigned by the system Universe, a "coordinate" in some sense.

Mass is a purely a calculated value based on a
model or theory. The theory can be used Newton's
law which starts with observations. With the use
of these observations (over a certain period) and
with the model the parameter mass can be
calculated.

Which may or may not be why we cannot narrow G down to more than 6 sig figs (and unstable), but can get sqrt( G * M_sun ) to 11 sig figs and stable.

The use a different model and the same observations
will result in different mass values for the same
objects.

Eotvos. We've tried that, and failed to find any variation.

Photons, using the same reasoning also have a mass.
The equation is m = E/c^2. The issue is what E ?
E is the amount of energy "released" when in some
chemical reaction a photon is released. This is in
accordance with the law: Conservation of energy. It
is that "simple"

(The mass of one proton) + (the mass of one electron) - (the mass of one H1 neutral atom) the (13.6 eV/c^2 photon) known to be emitted... by a tiny bit, perhaps the recoil of the formed atom.

Gravitons using the same reasoning also have a
mass. The value is very low.

No, string theory makes a prediction for that, and it is "unbelievably" high. At no point have they found any hint of a graviton, at any energy level tried.

Not even sure they've found the same "Higg's boson" fingerprint when running at higher energy levels.

David A. Smith

Dear Steve Willner:

On Friday, November 25, 2016 at 3:37:50 PM UTC-7, Steve Willner wrote:
In article ,
dlzc writes:
Second Edition, Section 8.4, Sample Problem 8-2.

I'm looking at _Spacetime Physics_ by Taylor &
Wheeler, Second Edition, copyright 1992, problem
8-5. (Problem 8-2 is a simple numerical
calculation of E = mc^2.)

No. Body of the chapter, worked example for section 8.4, labeled SAMPLE PROBLEM 8-2, which in my paperback copy is page 232.

David A. Smith

In article ,
dlzc writes:
Body of the chapter, worked example for section 8.4, labeled
SAMPLE PROBLEM 8-2, which in my paperback copy is page 232.

OK, got it now. I was looking on pp 254ff, which has a more detailed
explanation. I have the hardbound edition (from the library), but
p 832 seems to be the same. Key text:
A photon has no rest energy--that is, no mass of its own. However,
a photon can contribute energy and momentum to a system of objects.
Hence the presence of one or more photons in a system can increase
the mass of that system. Mo A system consisting entirely of
zero-mass photons can itself have non-zero mass!

I'll stand by my comments in my previous message. The issue is
terminology, not physics, and the text above is using "mass" in two
distinct ways. Nowadays, most physicists would not do that.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

Dear Steve Wilner:

On Monday, November 28, 2016 at 3:04:14 PM UTC-7, Steve Willner wrote:
....
I'll stand by my comments in my previous message. The
issue is terminology, not physics, and the text above
is using "mass" in two distinct ways. Nowadays, most
physicists would not do that.

OK.

Note that we were discussing "photon gas" trapped within a given radius from galactic center, and as a first blush it would be say 10,000 years (for a radius of 10,000 light years) of stellar output *assuming 1 part in 10^14, normal annual for our Sun), or about 1 part in 10^8 of the luminous mass. Far too low to be straining at anyway.

I think they are discussing only one mass, namely:
mass = rest mass = inertial mass = gravitational mass =/= relativistic mass, and I respect your belief to think they mean something else. I think you are wrong, but you have every right to it.

We can let this drop.

David A. Smith