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 Post subject: Dark Galaxy Puzzle
PostPosted: Mon Jun 25, 2007 9:02 pm 
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This article also has some interesting connotations on Dark Matter/Energy
There is an update available in the form of a newsletter from these guys...to whom credit and thanks is given for this piece...
How it a "hangs"together, nobody is sure at this point, but the lines are open and the calls are comming in....
We`ll have to await the developements as they happen...be sure to follow the links provided for a clearer picture of the situation..
bergle




'Dark galaxy' continues to puzzle astronomers [ul] [li]1519 20 June 2007 [li]NewScientist.com news service [li]Stuart Clark [/li][/ul][url "http//space.newscientist.com/article.ns?id=dn12100&print=true"][/url][url "http//space.newscientist.com/emailarticle.ns?id=dn12100"][/url][url "http//space.newscientist.com/feeds.ns;jsessionid=KMODCNIGODID"][/url][url "http//www.newscientist.com/contactsyndication.ns"][/url][url "http//space.newscientist.com/data/images/ns/cms/dn12100/dn12100-1_600.jpg"][img]http//space.newscientist.com/data/images/ns/cms/dn12100/dn12100-1_250.jpg[/img][/url] [url "http//space.newscientist.com/data/images/ns/cms/dn12100/dn12100-1_600.jpg"]Enlarge image[/url] Radio telescopes detect a large cloud of hydrogen gas (contour lines) where no stars can be found (Image R Minchin/Arecibo Observatory/Cardiff U/Isaac Newton Telescope/WSRT) Tools[url "http//www.digg.com/submit"][/url][url "http//space.newscientist.com/feeds.ns;jsessionid=KMODCNIGODID"][/url][url "http//space.newscientist.com/feeds.ns;jsessionid=KMODCNIGODID"][/url] [url "http//reddit.com/submit"][/url][url "http//www.newsvine.com/_tools/seed&save"][/url][url "http//www.citeulike.org/posturl?url='+encodeURIComponent(location.href)+'&title='+encodeURIComponent(document.title)+'"][/url]Related Articles [ul] [li][url "http//space.newscientist.com/article/dn11980"]Smallest galaxy hints at hidden population[/url] [li]04 June 2007 [li][url "http//space.newscientist.com/article/dn7056"]Astronomers claim first 'dark galaxy' find[/url] [li]23 February 2005 [li][url "http//space.newscientist.com/article/dn4272"]Astronomers find first 'dark galaxy'[/url] [li]20 October 2003 [li] [li]Web Links [/li] [li][url "http//www2.naic.edu/~rminchin/"]Robert Minchin, Arecibo Observatory[/url] [li][url "http//www.nottingham.ac.uk/~ppzmrm/"]Michael Merrifield, University of Nottingham[/url] [li][url "http//www.astron.nl/p/WSRT2.htm"]WSRT[/url] [/li][/ul]
[url "http//space.newscientist.com/data/images/ns/cms/dn12100/dn12100-2_600.jpg"][img]http//space.newscientist.com/data/images/ns/cms/dn12100/dn12100-2_250.jpg[/img][/url] [url "http//space.newscientist.com/data/images/ns/cms/dn12100/dn12100-2_600.jpg"]Enlarge image[/url] Neutral hydrogen gas streams between NGC 4254 (top left) and the dark galaxy VIRGOH121 (centre right) in this radio image. The new study suggests VIRGOHI21's gravity is responsible for NGC 4254’s lopsided shape; previously, it was thought to have been caused by an interaction with the galaxy NGC 4262 (bottom left) (Image R Minchin/Arecibo Observatory/Cardiff U/Isaac Newton Telescope/WSRT)
The Hubble Space Telescope has failed to reveal the expected number of stars in the mysterious, galaxy-sized cloud of hydrogen known as VIRGOHI21. The research bolsters the idea that the gas cloud is the only known example of a 'dark galaxy' that never kick-started star birth.
Galaxies are thought to coalesce from normal, or baryonic, matter that has collected in clouds of hypothetical dark matter. But surveys have turned up fewer galaxies than expected, suggesting that – for unknown reasons – some galaxies are stillborn, and simply fail to form stars.
The [url "http//space.newscientist.com/article/dn7056-astronomers-claim-first-dark-galaxy-find.html"]discovery of VIRGOHI21[/url] in 2005 seemed to provide the first evidence that dark galaxies existed. However, a number of researchers suggested that VIRGOHI21 was pulled out of the nearby galaxy NGC 4254 when another galaxy called NGC 4262 shot past it at 900 kilometres per second. Indeed, NGC 4254 has a single prominent arm of stars that curls round towards VIRGOHI21, suggesting some sort of link between the two.
But Robert Minchin of the Arecibo Observatory discounts such "hit-and-run" models. "If the hydrogen in VIRGOHI21 had been pulled out of a nearby galaxy, the same interaction should have pulled out stars as well," says Minchin.
He and colleagues used Hubble to observe a patch of sky 50,000 by 50,000 light years across, centred on the hydrogen cloud's position. They found just 119 red giant stars. That is the number found in a typical region of the same size in intergalactic space and three times fewer than expected if the cloud were a large piece of celestial wreckage. Heavyweight galaxy
Instead, Minchin believes NGC 4254's arm of stars was created by the gravity of VIRGOHI21 itself. He came to this conclusion after studying the object with the Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands, which detects emission from atoms of hydrogen. Watch an [url "http//www2.naic.edu/~rminchin/virgohi21.html"]animation showing VIRGOHI21 and its two galactic neighbours from a variety of perspectives[/url].
The new, relatively high-resolution WSRT measurements suggest that VIRGOHI21 is indeed a single object, ruling out previous suggestions that its rotation was an illusion caused by two passing gas clouds.
But they do confirm a mystery raised by previous studies. The object's normal matter weighs a few hundred million times the mass of the Sun. But its dark matter – inferred by studying the rotation speed of the cloud – appears to weigh at least 100 times as much.
That ratio is much higher than expected – in all other galaxies, dark matter outweighs normal matter by a factor of only 10. "Even if this is a dark galaxy, it is not what you expect to find. The number of baryons is too low," says Michael Merrifield of the University of Nottingham in the UK, who was not on Minchin's team.
Minchin acknowledges that this is a puzzle. A number of surveys at Arecibo and other radio observatories aim to find more examples of dark galaxies, which could shed light on how much dark matter they contain. So far, however, the surveys are finding little to match the characteristics of VIRGOHI21. [url "http//space.newscientist.com/article.ns?id=dn12100&print=true"][/url][url "http//space.newscientist.com/emailarticle.ns?id=dn12100"][/url][url "http//space.newscientist.com/feeds.ns;jsessionid=KMODCNIGODID"][/url][url "http//www.newscientist.com/contactsyndication.ns"][/url]
[url "http//space.newscientist.com/subscribe.ns;jsessionid=KMODCNIGODID?promcode=nsspaceartend"][/url]
"There is far more on heaven and earth than accounted for in your philosophy Horatio!"
Quote from Shakespeare`s Hamlet.....
bergle
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