More on dark matter aliens :-) [Fwd: [>Htech] Completely dark galaxies]

From: Brian Atkins (
Date: Fri Jan 12 2001 - 23:16:16 MST

Perhaps they have formed a spherical armada and are closing in on our galaxy.

-------- Original Message --------
Subject: [>Htech] Completely dark galaxies
Date: Fri, 12 Jan 2001 15:14:10 -0500
From: Larry Klaes <>
CC:,, "Also" <>

Subject: Completely dark galaxies (Forwarded)
Date: Thu, 04 Jan 2001 11:57:16 -0500
From: Andrew Yee <>
Organization: Jet Propulsion Laboratory - Pasadena CA


Date: 4 January 2001 For immediate release

Ref. PN 01/01


Dr Jacqueline Mitton
RAS Press Officer
Office & home phone: Cambridge ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892
RAS web:

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Dr Neil Trentham
Institute of Astronomy, University of Cambridge
Phone: (+44) (0)1223 366095
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The universe could be harbouring numerous galaxies that have no stars at
all and are made entirely of dark matter. Astronomers may ultimately
discover that completely dark galaxies outnumber the familiar kind populated
by shining stars and gas, perhaps by as many as 100 to 1. This intriguing
prediction is made by Drs Neil Trentham, Ole Moller and Enrico
Ramirez-Ruiz of the University of Cambridge in a paper to be published
in the Monthly Notices of the Royal Astronomical Society.

There is already a considerable amount of evidence that bright galaxies
contain large amounts of dark matter, often ten times more than the mass
of all their stars put together. There must be extra mass that we do not
see to account for the observed movements of the stars under the influence of
the gravity of the whole galaxy. In some galaxies we see so few stars they
are incapable of holding themselves together as a galaxy. They would have
long since scattered through space without the gravity of unseen matter to
keep them together.

"Observationally, a picture is emerging that there is a lot of dark
matter in the universe and that most galaxies possess a great deal of it,"
says Neil Trentham. "On the theory side, the cold dark matter theory predicts
that there are many low-mass galaxies for every massive one, but we
don't see many of them around. That could simply be because very few stars --
perhaps none at all -- have formed in them. So the question is, 'How do
we look for these completely dark galaxies?' "

It's a difficult challenge, and the best technique will depend on the
nature of the dark matter, which is still unknown. Trentham and colleagues
some suggestions. If the dark matter is composed entirely of fundamental
particles, dark galaxies may act as gravitational lenses, distorting the
appearance of distant galaxies that happen to lie behind them. If the
dark matter includes some brown dwarfs their infrared radiation may be
detectable. The same will be true if the galaxies contain any dead
stars, such as white dwarfs or black holes. If they are nearby, it might be
possible to detect these stellar remnants acting as gravitational lenses
on the light of individual stars in other galaxies beyond them. Several
lensing events in a small area of sky would suggest the presence of a dark

The researchers have identified one place where a dark galaxy may exist,
using yet another phenomenon that hints at the presence of an invisible
object. They noticed that a galaxy called UGC 10214 has a stream of
material flowing out of it, as if it is interacting with another galaxy.
But in this case, the stream of material is apparently flowing towards


1. An image of UGC 10214 may be found at

2. Neil Trentham and Enrico Ramirez-Ruiz are at the Institute of
   University of Cambridge. Ole Moller was at the Cavendish Laboratory,
   University of Cambridge when this work was done and is now at the
   University of Groningen in The Netherlands.

3. The paper on this work was accepted by the Monthly Notices of the
Royal Astronomical Society in October 2000 but the publication date has
not yet been scheduled.

Andrew Yee

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