Re: Astronomers: 'Dark' galaxy discovered

From: josephus (dogbird_at_earthlink.net)
Date: 02/25/05 

Date: Fri, 25 Feb 2005 02:03:37 GMT

Harvest Dancer wrote:

> I found this fascinating.
>
> http://www.cnn.com/2005/TECH/space/02/24/dark.galaxy/index.html
>
> Astronomers: 'Dark' galaxy discovered
>
> (SPACE.com) -- Astronomers have discovered an invisible galaxy that
> could be the first of many that will help unravel one of the universe's
> greatest mysteries.
>
> The object appears to be made mostly of "dark matter," material of an
> unknown nature that can't be seen.
>
> Theorists have long said most of the universe is made of dark matter.
> Its presence is required to explain the extra gravitational force that
> is observed to hold regular galaxies together and that also binds large
> clusters of galaxies.
>
> Theorists also believe knots of dark matter were integral to the
> formation of the first stars and galaxies. In the early universe, dark
> matter condensed like water droplets on a spider web, the thinking
> goes. Regular matter -- mostly hydrogen gas -- was gravitationally
> attracted to a dark matter knot, and when the density became great
> enough, a star would form, marking the birth of a galaxy.
>
> The theory suggests that pockets of pure dark matter ought to remain
> sprinkled across the cosmos. In 2001, a team led by Neil Trentham of
> the University of Cambridge predicted the presence of entire dark
> galaxies.
>
> The newfound dark galaxy was detected with radio telescopes. Similar
> objects could be very common or very rare, said Robert Minchin of
> Cardiff University in the UK.
>
> "If they are the missing dark matter halos predicted by galaxy
> formation simulations but not found in optical surveys, then there
> could be more dark galaxies than ordinary ones," Minchin told
> SPACE.com.
>
> In a cluster of galaxies known as Virgo, some 50 million light-years
> away, Minchin and colleagues looked for radio-wavelength radiation
> coming from hydrogen gas. They found a well of it that contains a
> hundred million times the mass of the Sun. It is now named VIRGOHI21.
>
> The well of material rotates too quickly to be explained by the
> observed amount of gas. Something else must serve as gravitational
> glue.
>
> "From the speed it is spinning, we realized that VIRGOHI21 was a
> thousand times more massive than could be accounted for by the observed
> hydrogen atoms alone," Minchin said. "If it were an ordinary galaxy,
> then it should be quite bright and would be visible with a good amateur
> telescope."
>
> The ratio of dark matter to regular matter is at least 500-to-1, which
> is higher than I would expect in an ordinary galaxy," Minchin said.
> "However, it is very hard to know what to expect with such a unique
> object -- it may be that high ratios like this are necessary to keep
> the gas from collapsing to form stars."
>
> Long road to discovery
> Other potential dark galaxies have been found previously, but closer
> observations revealed stars in the mix. Intense visible-light
> observations reveal no stars in VIRGOHI21.
>
> The invisible galaxy is thought to lack stars because its density is
> not high enough to trigger star birth, the astronomers said.
>
> The discovery was made in 2000 with the University of Manchester's
> Lovell Telescope, and the astronomers have worked since then to verify
> the work. It was announced today.
>
> "The universe has all sorts of secrets still to reveal to us, but this
> shows that we are beginning to understand how to look at it in the
> right way," said astronomer Jon Davies of Cardiff University in the UK.
> It's a really exciting discovery." Additional radio observations were
> made with the Arecibo Observatory in Puerto Rico. Follow-up optical
> work was done with the Isaac Newton Telescope in La Palma. Astronomers
> from the UK, France, Italy and Australia contributed to the research.
> The project is now searching for other possible dark galaxies.
>
> Dark matter makes up about 23 percent of the universe's mass-energy
> budget. Normal matter, the stuff of stars, planets and people,
> contributes just 4 percent. The rest of the universe is driven by an
> even more mysterious thing called dark energy.
>

I note that you clearly separate the dark matter from the baryonic
matter... the galaxy is dark but not like dark matter. It has hydrogen.
                      josephus

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