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New evidence for a Dark Galaxy

FOR RELEASE: Thursday January 12, 2006 9:20 AM EST

New evidence that VIRGOHI 21, a mysterious cloud of hydrogen in the Virgo
Cluster 50 million light-years from the Earth, is a Dark Galaxy was
presented today at the American Astronomical Society meeting in Washington,
D. C. by an international team led by astronomers from the National Science
Foundation's Arecibo Observatory and from Cardiff University in the United
Kingdom.

The new observations, made with the Westerbork Synthesis Radio Telescope in
the Netherlands, show that the hydrogen gas in VIRGOHI 21 appears to be
rotating, implying a dark galaxy with over ten billion times the mass of
the Sun. Only one percent of this mass has been detected as neutral
hydrogen - the rest appears to be dark matter.

But this is not all that the new data reveal. The results may also solve a
long-standing puzzle about another nearby galaxy. NGC 4254 is lopsided,
with one spiral arm much larger than the rest. This is usually caused by
the influence of a companion galaxy, but none could be found until now -
the team thinks VIRGOHI 21 is the culprit. Dr. Robert Minchin of Arecibo
Observatory says; "The Dark Galaxy theory explains both the observations of
VIRGOHI 21 and the mystery of NGC 4254."

The team have looked at many other possible explanations, but have found
that only the Dark Galaxy theory can explain all of the observations. As
Professor Mike Disney of Cardiff University puts it, "The new observations
make it even harder to escape the conclusion that VIRGOHI 21 is a Dark
Galaxy."

The team hope that this will be the first of many such finds. "We're going
to be searching for more Dark Galaxies with the new ALFA instrument at
Arecibo Observatory," explains Dr. Jon Davies of Cardiff University. "We
hope to find many more over the next few years - this is a very exciting
time!"


NOTES FOR EDITORS:

1. The following images will available on the web in a variety of sizes
up to 6 inches at 300 dpi at http://www.naic.edu/~rminchin/press as
soon as the embargo expires on Thursday January 12, 2006 9:20 AM EST

CAPTION: Dark Galaxy VIRGOHI 21 has no starlight but radio waves from
neutral hydrogen betray its existence. The contours superimposed on
this optical image indicate how much gas was detected. This material
was presented to the American Astronomical Society meeting in
Washington, D. C. on January 12, 2006.
CREDIT: Arecibo Observatory / Cardiff University / Isaac Newton
Telescope / Westerbork Synthesis Radio Telescope.

CAPTION: Neutral hydrogen gas streams between NGC 4254 (top left) and
the Dark Galaxy VIRGOH1 21 (center right) in this image made from
radio telescope observations at a wavelength of 21 centimeters. This
interaction could explain the mystery of NGC 4254's peculiar lopsided
shape. To the bottom left, a ring of gas can be seen around the
galaxy NGC 4262. This material was presented to the American
Astronomical Society meeting in Washington, D. C. on January 12, 2006.

CREDIT: Arecibo Observatory / Cardiff University / Westerbork
Synthesis Radio Telescope.

2. Arecibo Observatory is part of the National Astronomy and Ionosphere
Center, which is operated by Cornell University under a cooperative
agreement with the National Science Foundation

3. The research was partly funded by PPARC - the Particle Physics and
Astronomy Research Council. PPARC is the UK's strategic science
investment agency. It funds research, education and public
understanding in four broad areas of science - particle physics,
astronomy, cosmology and space science. PPARC is government funded
and provides research grants and studentships to scientists in British
universities, gives researchers access to world-class facilities and
funds the UK membership of international bodies such as the European
Organisation for Nuclear Research, CERN, the European Space Agency and
the European Southern Observatory. It also contributes money for the
UK telescopes overseas on La Palma, Hawaii, Australia and in Chile,
the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh
and the MERLIN/VLBI National Facility.

4. The Westerbork Synthesis Radio Telescope is operated by ASTRON
(Netherlands Foundation for Research in Astronomy) with support from
the Netherlands Foundation for Scientific Research (NWO).

5. The scientific paper "High resolution HI imaging of VIRGOHI 21 - a
dark galaxy in the Virgo Cluster" was presented on 12th January 2006
at the 207th meeting of the American Astronomical Society held in
Washington, D. C. Authors are Robert Minchin (Arecibo Observatory),
Jon Davies, Mike Disney (Cardiff University), Andy Marble, Chris Impey
(Steward Observatory), Peter Boyce, Diego Garcia, Marco Grossi
(Cardiff University), Chris Jordan (Jodrell Bank Observatory), Hugh
Lang, Sarah Roberts (Cardiff University), Sabina Sabatini
(Osservatorio Astronomico di Roma), and Wim van Driel (Observatoire de
Paris)

6. For an interview or further technical comment please contact:

Dr. Robert Minchin - Arecibo Observatory
Tel: ++1-787-878-2612 ext. 283 (contact through AAS during the
meeting)
E-mail: rminchin@naic.edu

Dr. Jon Davies - Cardiff University
Tel: ++44-(0)29-20-875255
E-mail: jonathan.davies@astro.cf.ac.uk