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The dark matter model.
In our own galaxy we have an evident missing mass effect. Three or five times
more mass should be necessary to balance centrifugal force. Our sun, orbiting
at 230 km/s around the center of the galaxy, should have gone away, with his
planets, since millions of years. The situation is worse for clusters of galaxies,
that should "evaporate", for the individual proper velocoties of the galaxies
are higher than the escape velocity of the cluster.
You perhaps know that the circular orbitation velocity of a satellite, around
the Earth, is close to 9 km/s. The escape velocity is 11 km/s. We need to
give a space station a velocity higher than 11 lm/s if one wants it to escape
Earth's attraction and visit distant planets, like Jupiter or Saturn.
Suppose we would observe satellites orbiting around the Earth at 20 km/s.
We should conclue that the mass of the Earth has been underestimated. In the
30's, Fritz Zwick pointed out this for galaxies and clusters of galaxies,
from velocity measurement ( Doppler effect ) and mass evaluation ( photometry
) This problem is still embarrassing. How to manage it ?
The today's classical answer is called "dark matter". People think that a
large amount of hidden mass exists in galaxies and clusters. Their argument
is the following. Galaxies produce gravitational mirages : multiple images
of distant quasars. Clusters of galaxies bend space and produce other mirages
: multiple images of galaxies. The space telescope brought many, now. The
observed mass is too weak to explain such strong effects. So that the astronomers
consider this as a proof of the existence of invisible dark matter. Some say
that the gravitational lensing is a new way to "weight" galaxies and clusters.
Others have started to map the universe, basing their design on this gravitational
lensing effect.
There are mass concentrations in the planets especially in the Moon.We call
it "Mascons". When a satellite flies around the moon, we can record its path
very precisely, with a laser. This path is not perfectly circular. It is modified
by underground mass concentrations. Some suppose these mass concentration
correspond to ancient impact of heavy huge bodies. Doing that, we found the
mass mapping of the Moon on measurements of the geodesics around it.
Similarly we could say that gravitational lensing refers to geodesics (light's
path). Then the analysis of such geodesics may be a method to evaluate hidden
mascons in galaxies and clusters of galaxies. In our own works you will find
an alternative interpretation of such strong lensing effects.We think they
mainly could be due to negative lensing, cause by surrounding "ghost matter".
Returning to the classical interpretation through dark matter, what could
it be made of ? Astronomers think about MACHOs ( MAssive Compact Halo Objects
). Possibly : faint stars, too faint to be detected. Detection method : occultation.
Stars are very small objects.A galaxy, considered as a gas whose stars would
be "molecules" is a very rarefied gas. So that the chance that a star masks
another one is very weak. But there are many. The sky survey can be managed
by computers. They at last can analyze the light emission variation of a great
number of stars, automatically. Some are due to known binary systems. Methods
make it possible to discriminate between binary systems effect and distant
occultation by "dark stars", machos.
Results : disappointing.
Another candidate : exotic matter, like hypothetic massive neutrinos. Not
confirmed at the present day. The French astrophysicist Fran�ois Combe suggested
that large amounts of very cold hydrogen could exist, in the Universe. So
cold that it could not be detected. She used this invisible hydrogen to "explain"
the aspect of the rotation curve of galaxies ( large peripheric circular velocities
) and to produce (transient) spiral structures. Dark matter is invoked for
everything. Some use it to "explain" the VLS, the Very large structure of
the Universe. Many journals publish such works ( Astrophysical Journal, Astronomy
and Astrophysics, and so on...), apparently without any state of mind, as
a "natural approach". Like black holes, dark matter does exist, in the pages
of journals, Ithink. In this cosmic hypermarket you can choose hot or cold
dark matter, dwarf or giant black holes, as you like.
Strange epoch. Before the italian Torricelli's discovery (1640) : the discovery
of atmospheric pressure, people believed that mercury climbed in barometers
because its horror of the void.
Nature hates void.....
Before Torricelli, people measured the level of void's hate.
(100)
**- But... Idon't see anything : It's all black !
- Normal. It's dark matter's map.**
For publishing managers and referees, some speculations are arbitrarily permissible,
some others, no.
