From: Damien Broderick (d.broderick@english.unimelb.edu.au)
Date: Thu Jan 04 2001 - 22:42:07 MST
Ah, those Matrioshka brains, they love to huddle in the dark.
http://www.newscientist.com/dailynews/news.jsp?id=ns9999296
1846 GMT, 4 January 2001
Invisible galaxies:
A trail of stars and gas reveals a dark matter galaxy, say astronomers
Stuart Clark
Astronomers have detected a bridge of matter extending from a galaxy,
apparently, towards nothing.
Neil Trentham, Ole Moller and Enrico Ramirez-Ruiz, at the Institute of
Astronomy, Cambridge, believe their finding means an invisible galaxy, made
entirely of dark matter, is lurking beside UGC 10214.
Astronomers believe that up to 90% of the Universe is made of non-luminous
material that betrays its presence only through the action of its
gravitational field. What this dark matter is remains a mystery.
The group's work, suggests that dark matter galaxies might eventually be
found to outnumber ordinary galaxies by a hundred to one.
Galactic collision
When galaxies collide it is common to see bridges of luminous material
being dragged from one to the other. Only in active galaxies are jets of
material seen emanating from individuals.
But despite UGC 10214's apparent isolation, Trentham believes visible trail
is a bridge: "It's too thick to be a jet from an active galaxy. Also, some
of the material is made up of stars and a jet would not push out stars."
Trentham has been working on formation theories for dark galaxies and
believes that they are celestial latecomers, incapable of making stars.
He told New Scientist: "Galaxies grow from perturbations in dark matter.
Normal galaxies began forming in the couple of billion years after the Big
Bang. As the haloes grow, they pull in gas to form stars.
"Now imagine five to 10 billion years after the Big Bang. The gas sitting
out between the galaxies has been heated by starlight and is travelling
fast. A late forming halo can no longer hold onto it because its speed is
so high. And without gas, the galaxy cannot form stars."
Possible candidates for dark matter include subatomic particles or failed
stars, called brown dwarfs. If it is the latter, Trentham believes it may
be possible to see these dark galaxies by their infrared glow.
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The research will be published in Monthly Notices of the Royal Astronomical
Society.
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