Celestia Forums

Hi all,

simulations of cold dark matter (CDM) models of the Universe predict
far more dark matter halos than are observed in association with
galaxies! For this reason, it has been hypothesized that there must
exist dark-matter halos, "galactic ghosts" so to speak, that
contain no stars whatsoever.


Exciting... and now an invisible
(dark-matter) galaxy has indeed been observed by radio astronomers.

Here is a "photo" of the "galactic ghost" VIRGOHI21



The type of galaxy (NGC 7479) that astronomers would have expected
to see within the above ellipse, based on the measurements taken:



Look here for more info and the original discovery paper

http://images.google.com/imgres?imgurl=http://www.astro.cf.ac.uk/groups/galaxies/fig1.gif&imgrefurl=http://www.astro.cf.ac.uk/groups/galaxies/latestnews.html&h=542&w=563&sz=10&tbnid=_AXNElyaUXcJ:&tbnh=126&tbnw=131&hl=en&start=1&prev=/images%3Fq%3Dvirgohi21%26hl%3Den%26lr%3D%26sa%3DN

VIRGOHI21, a huge cloud of neutral hydrogen with a mass 100 million
times heavier than our Sun, was first seen with the University of
Manchester's Lovell Telescope at Jodrell Bank, UK.


The graph shows the signal that was picked up by the telescope
showing the peak at the 21 cm Hydrogen-Line emitted by the
Hydrogen gas in the dark galaxy. The sighting was later confirmed with
the ARECIBO radio telescope in Puerto Rico.

The speed at which it spins indicates that there is more to VIRGOHI21
than hydrogen. The rotation velocity implies a mass 1000 times
greater than the amount of hydrogen, and at the distance of the Virgo
cluster this should be in the form of a galaxy shining at 12th
magnitude. However, when the team studied the area in question
using the Isaac Newton Telescope in La Palma, they found no visible
trace of an optical counterpart for VIRGOHI21 (see top image!).


Bye Fridger

That's just utterly bizarre. That there is absolutely no visible trace of ANYTHING there at all is really weird (and cool ).

So it's a big cloud of neutral hydrogen - no stars at all (so nothing illuminating it)? And presumably being neutral hydrogen there's no dust in it either to make it visible by obscuring objects behind it?

Evil Dr Ganymede wrote:That's just utterly bizarre. That
there is absolutely no visible trace of ANYTHING there at all
is really weird (and cool ).

So it's a big cloud of neutral hydrogen - no stars at all (so
nothing illuminating it)? And presumably being neutral
hydrogen there's no dust in it either to make it visible by
obscuring objects behind it?

It's actually MUCH more than a big cloud of neutral hydrogen!

A brief recap first:

You probably are aware of the standard method to infer about
the existence and size of dark-matter halos usually located
in the periphery of galaxies: you measure the galaxy's
rotation velocity and compare the result with what you expect
from its /luminous/ matter distribution. As is well known,
there is often a big mismatch and one has to require a large
amount of dark i.e. NON-VISIBLE matter to explain the
observed angular velocities! Fashionable dark matter
candidates are e.g. new particles from SUPERSYMMETRY
("neutralinos"), SUPERGRAVITY ("gravitinos") . But so far
noone really knows what the dark matter is made of!!! We
only know it's there.

Dark matter and dark energy are the biggest challenges in
cosmology at present.

Now as I wrote above, the presence of the neutral hydrogen
essentially allows to measure the rotational properties of the
invisible object. It turned out to spin so fast that we need a
factor 1000 of /dark matter/ to be present in that area
compared to the hydrogen.

Hum I wonder if this blows out my theory of what dark matter is.

My theory is that dark matter is not matter at all, but a deformation in space-time due to the lack of matter. The lack of matter actually works to repel matter away, not like anti gravity, but negative gravity. Its this push of negative gravity that is responsible for the speed discrepantly of matter other objects of matter.

My theory comes from my understanding of space-time, string theory, and the creation of the universe. I think that the easiest way to explain where negative gravity comes from, is to explain it so a child can understand it.

Imagine that the universe (devoid of matter) is a flat plain, the quantum foam would be another flat plain above the universe plain. One of the current theories says that our universe came into being when both plains touched, and caused the ?€?big bang.?€

If this were true, we would obviously see dark matter mostly there where there is no other matter. But quite on the contrary, we notice that the distribution of dark matter is rather similar to distribution of normal matter. The discovery of VIRGOHI21 is so interesting because it is the first occurence of such a great dark matter/normal matter relation.

Another thing to consider:
As you propably know, in the grand structure of cosmos - as known today - there are strands of galaxy clusters in HUGE patches of intergalactic vaccum (which is not completely empty, there is still ~1 H2 in 1 m??). If your theory would be right (intrinsic gravitative force inversely proportional to matter density), the gravitation from these patches would be so strong that no filaments could exist, the galaxies would be uniformly distributed.

I never said this, Dark matter is a lack of matter, it is a function of mass to space. What that function is, is unknown. Needless to say is you have two atom and separate them by some distance, gravity would stay that they should always attract, however my theory says that at some point the distance (emptiness) is so great that a repelling forces comes into play, and the atoms are being pushes away. Now if you had two groups of atoms. Each pair would be attracted to each other, but both groups given enough distance would repel each other.

Strangely enough with my theory, as time progresses the amount of?€?Dark Matter?€