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mimizorro Wrote: ------------------------------------------------------- > Astronomers have spotted a "dwarf" galaxy some 10 > billion light-years away which may be made mostly > of the mysterious material called dark matter. > > The dwarf was found using a technique called > gravitational lensing. It is only the second dark > dwarf ever seen, and it is by far the most > distant. > > The fact that so few dwarf galaxies are seen in > our own cosmic neighbourhood has remained a > conundrum in astronomy. > > The study in Nature could explain it: they may be > overwhelmingly dark matter. > > > http://news.bbcimg.co.uk/media/images/57965000/jpg > /_57965220_57965219.jpg > > The light bent by a dark-matter-dominated galaxy > can form what is known as an "Einstein ring" > > > Dwarf galaxies often occur in the periphery of > larger galaxies, where they are known as > satellites - the Milky Way may have many as well. > > "According to the theory of galaxy formation, > you'd expect thousands of these satellites," > explained lead author of the study Simona Vegetti > of the Massachusetts Institute of Technology. > > "But if you look at the Milky Way we only find 30, > so it's important to understand how many > satellites are really there, and important to look > at other galaxies other than the Milky Way," she > told BBC News. > > That will help determine if our cosmic > neighbourhood of galaxies - the Local Group - is > unusual, or if the theory of galaxy formation is > incomplete. > > Massive question > Dark matter is so named because it does not > interact with light - it cannot be seen directly, > as the stars and dust of the cosmos can. > > However, it does have mass - making up 85% of the > mass in the Universe - and the effects of that > mass can be spotted. > > Gravitational lensing is a technique in which an > object that lies between Earth and a distant light > source can actually act as a "lens"; the object's > mass bends the distant galaxy's light, magnifying > and distorting it. > > By using computer models of how that magnification > and distortion should work, the mass of the > lensing galaxy - and where that mass is > distributed - can be determined. > > Gravity acting across vast distances does not seem > to explain what astronomers see > Galaxies, for example, should fly apart; some > other mass must be there holding them together > Astrophysicists have thus postulated "dark matter" > - invisible to us but clearly acting on galactic > scales > At the greatest distances, the Universe's > expansion is accelerating > Thus we have also "dark energy" which acts to > drive the expansion, in opposition to gravity > The current theory holds that 73% of the Universe > is dark energy, 23% is dark matter, and just 4% > the kind of matter we know well > The technique was recently used to develop the > widest view of dark matter distribution in the > Universe ever produced. > > Dr Vegetti and colleagues in the US and the > Netherlands have now used the Keck telescope in > Hawaii to study the lensing caused by a distant > elliptical galaxy called JVAS B1938+666. > > They found a discrepancy in comparing with the > image that their detailed computer model suggested > should come from the system. > > Something with a mass about 200,000,000 times that > of our Sun is in the periphery of the image they > see. > > Yet that source of mass is not visible in the > image of the galaxy itself. > > "It's very hard to tell at the moment because the > telescopes are just not powerful enough to see > such dim galaxies so far away," Dr Vegetti said. > > "But is most likely dominated by dark matter, or > maybe there are a few stars hiding here and > there." > > The team must continue the hunt for such > satellites to get to the bottom of the dark > mystery. > > "We were kind of lucky that the first one we > looked at also had a satellite," Dr Vegetti said. > > "If we find other galaxies or satellites, it will > tell us whether we need to change the properties > of dark matter; if we don't find enough, then dark > matter must be different from what we think." > > BBC news > 18 January 2012 Last updated at 19:34 GMT