Re: Dark matter hides, physicists seek (Forwarded)


"Andrew Yee" <ayee@xxxxxxxxxxxxxxxxxxxxxx> schreef in bericht
news:Pine.LNX.4.30.0701041809270.6635-100000@xxxxxxxxxxxxxxxxxxxxxxxxx

Dark matter hides, physicists seek
By Clara Moskowitz

Scientists don't know what dark matter is, but they know it's all over the
universe. Everything humans observe in the heavens -- galaxies, stars,
planets and the rest -- makes up only 4 percent of the universe,
scientists say. The remaining 96 percent is composed of dark matter and
its even more mysterious sibling, dark energy. Scientists recently found
direct evidence that dark matter exists by studying a distant galaxy
cluster and observing different types of motion in luminous versus dark
matter. Still, no one knows what dark matter is made of.


"Dark matter permeates everything," Cabrera says. "It just never collapsed
the way atoms did."

Since dark matter never formed stars and other familiar heavenly objects,
for a long time scientists never knew it was there. The earliest
indication of its existence came in the 1930s when Fritz Zwicky, a
Swiss-American astronomer, observed clusters of galaxies. He added up the
masses of galaxies and noticed that there was not enough mass to account
for the gravity that must exist to hold the clusters together. Something
else must provide the missing mass, he deduced.

Later in the 1970s, Vera Rubin, an American astronomer, measured the
speeds of stars in the Milky Way and other nearby galaxies. As she looked
farther out toward the edges of these galaxies, she found that the stars
do not rotate more slowly as scientists expected. "That didn't make any
sense," Cabrera says. "The only way you could understand it is if there
was a lot more mass there than what you saw in the starlight."

That is correct.
If you compare the rotation curve of our planets around the Sun
with the stars around the centre of our galaxy
then in the first case the speed almost decreases lineair with distance
(1/r)
while in the second case first there is an increase with distance
and after a certain distance the speed is constant and the rotation
curve becomes flat.
To explain the first is easy because the planets behave like point masses.
To explain the second requires that the 3D shape of the galaxy
including all the stars and planets have to be taken into account.
Such an explanation starts by taking all the visible stars into account.
Current observations reveal (Hubble) that galaxies are much larger
and consists of much more visible stars (made of ordinary matter)
than original thought of.
The result is that if you compare a simulated rotation curve of
a galaxy in the past (less stars) with the one now (more
stars) they become flatter and longer.
In short the difference with observation becomes less
and what is important less missing mass has to be included
to completely match observation. (of rotation curve)
In short less and less dark matter is required.

My prediction is that in the future no dark matter is required
to explain the rotations curves of our galaxy and all galaxies.

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



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Relevant Pages

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