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,
emitting no star light, 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. Their results not
only indicate the presence of a dark galaxy but also explain the
long-standing mystery of its strangely stretched neighbour.
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."
Gas from NGC 4254 is being torn away by the dark galaxy, forming a
temporary link between the two and stretching the arm of the spiral
galaxy. As the VIRGOH1 21 moves on, the two will separate and NGC
4254's unusual arm will relax back to match its partner.
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:
Results published in 2005 first suggested that VIRGOH1 21 is a dark
matter galaxy. For more information see
http://www.pparc.ac.uk/Nw/dark_galaxy.asp
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
or in advance by email from Julia.maddock@pparc.ac.uk
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 (centre right) in this image made from radio
telescope observations at a wavelength of 21 centimetres. 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
Julia Maddock
PPARC Press Office
Tel +44 1793 442094
Email Julia.maddock@pparc.ac.uk
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Julia Maddock
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