Re: Dark matter hides, physicists seek (Forwarded)


"Nicolaas Vroom" <nicolaas.vroom@xxxxxxxxxx> schreef in bericht
news:Thuvh.316448$HS2.6325285@xxxxxxxxxxxxxxxxxxxxxxxx

As part of ongoing interest in galaxy simulation I have also
written 3 programs in excel to do the same.
The three documents to describe each is available at:
1 http://users.pandora.be/nicvroom/circ11.xls.htm
2 http://users.pandora.be/nicvroom/grotc.xls.htm
3 http://users.pandora.be/nicvroom/grotcexp.xls.htm
(At those url's you can retrieve the excel programs in zip format)

In the book Galactic Dynamics by James Binney and
Scott Tremaine at page 23 we can read:
"It is a remarkable fact that the circular speed curves still remain
flat even at radii well beyond the outer edge of the visible galaxy,
thus implying the presence of invisible or dark mass
in the outer parts of the galaxy (see $10.1.6)"
What this quote implies that dark matter is the sole and only
explanation beyond a certain distance.
This may be true in principle, the problem is that stil more
visible matter is discovered at larger distances, making this
assumption a less strict requirement.
At solar scale the same can be said about the kuiper belt
objects which make our solar system larger and larger with
at galaxy type scales invisible objects.

The simultions in the above mentioned programs are
based on a disc with a fixed height of 1 unit and a variable
disc density which decreases as a function of distance.
In the case of a bulge size of 10 units the density of the bulge
is 0.24 and the starting value of the disc density 0.87
in order to get a flat rotation curve.
This may be strange. However you get the same results if
you take the disc height as 3 units. The starting disc density
value is than 0.29, making the crossing between bulge and disc
more fluent.

However this also raises a new issue: what is the average
height as a function of distance.

In Astronomy of November 1992 at page 45 in the article
"The grand Illusion. What we see in the night sky is a widly
misleading representation of the universe" by Ken Croswell
He makes the point that "often" the brightest objects have
the smallest mass and the dimmest objects have the heighest
mass, which implies how difficult it is to estimate mass
as a function of luminosity.

For me it is difficult to understand why the scientific community
assumes dark matter in a sperical distribution as a tool to explain
galaxy rotation curves and not visible/baryonic matter in the disc.
In my opinion the first step should be to explain a galaxy rotation
curve by only assuming baryonic matter in the bulge and the disc
The second step should be define the stars that make up this
mass based on a distribution as explained at page 48 of the above
mentioned document.
Step three should be to calculate the luminosity of this galaxy
assuming that many stars are hided by other stars in the foreground.
The fourth step should be to compare this luminosity which
what is observed.

My question is how large is this discrepancy ?
My guess: not much

A different question to answer is:
Why is darkmatter (if required) not all situated in the disc.

Nicolaas Vroom
http://users.pandora.be/nicvroom/


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