1 A New Galaxy & Mysterious Dark Matter Washington: Astronomers have discovered a "dwarf" galaxy some 10 billion light-years away which they believe is consisting mainly of mysterious "dark matter". The dwarf galaxy, only the second ever to be discovered, is incredibly distant and extremely small. It orbits as a satellite of a larger galaxy. Though telescopes can't spot the dwarf galaxy, scientists detected its presence through the tiny distortions its gravity causes to light that passes it by. It weighs about 190 million times the mass of the sun , a seemingly hefty sum, although typical galaxies pack in the mass of tens of billions of suns, SPACE.com reported. Scientists think dark matter, which may be made of some exotic particle that doesn't reflect light, makes up about 98 per cent of all matter in the universe. Yet it has never been detected directly. Discovering dark objects like this tiny, distant galaxy could help researchers understand better what dark matter is and how it affects regular matter around it, they said. The finding, detailed in the journal Nature, suggest that the fact so few dwarf galaxies can be seen in our own cosmic neighborhood may be explained by them being mainly composed of dark matter. "This is the lowest mass galaxy that we've seen at this distance by far," said study co-author Matthew Auger of the University of California, Santa Barbara. Even farther away is another galaxy whose light passes by the dark dwarf and its host on its way to Earth. As this light travels through space, it is bent by the gravity of the intervening galaxy and its satellite, causing a distorted and curved picture called an "Einstein ring". This process is called gravitational lensing. Though most of this warping is caused by the larger gravitational tug of the host galaxy, researchers used a computer model to detect a slight excess of warping caused by the tiny addition of the dwarf 2 satellite's gravity. The astronomers also took help of high-resolution images taken by the Keck Observatory in Hawaii, using a system called adaptive optics to compensate for atmospheric blurring. "The image quality in the data we used here is somewhat better than the quality you can get from the Hubble Space Telescope," Auger said. Dwarf galaxies aren't a rarity in the cosmos; even our Milky Way has them. In fact, the newfound galaxy is about the same size as our own galaxy's Sagittarius dwarf satellite. The discovery could help astronomers find similar objects and confirm or reject theories about the structure of the cosmos. Theory predicts that galaxies should be surrounded by halos of smaller, satellite blobs of mass, said University of California, Davis, physics professor Chris Fassnacht, who aided in the satellite’s discovery. But they had not previously detected the predicted satellites of more distant galaxies. Because most of the mass of galaxies is made up, not of stars, but of “dark matter,” which does not absorb or emit light, these distant objects may be very faint or even completely dark. The team looked for faint or dark satellites of distant galaxies using a method called gravitational lensing. Using the Keck II telescope at the W.M. Keck Observatory on Mauna Kea, Hawaii, with “adaptive optics,” they found two galaxies aligned with each other, as viewed from Earth. The nearer object’s gravitational field deflects the light from the more distant object as the light passes through or near the other object’s gravitational field, creating a distorted image as if passed through a lens. By analysing these distorted images, the researchers could determine if there were any satellite galaxies clustered around the “lens” galaxy. Adaptive optics make constant, tiny adjustments to the telescope mirror to compensate for the effects of the Earth’s atmosphere. As a result, the Keck telescopes can achieve higher resolution than the 3 Hubble Space Telescope. The technique can now be applied to many more galaxies, Fassnacht said. “As we collect more objects, we can do more precise tests of our simulations and make predictions about the structure of the universe,” he said. First author Simona Vegetti, a postdoctoral researcher at the Massachusetts Institute of Technology, said: “Now we have one dark satellite, but suppose that we don’t find enough of them — then we will have to change the properties of dark matter. "For the first time we're getting information about something with a mass that's comparable to some of the smaller Milky Way satellites but outside of the local universe," said co-author David Lagattuta of the University of California. "Add in the fact that it's something like six or seven billion light years away, it's really true that we've never been able to see something like this before!" The Milky Way's satellites are also little understood, as they are hard to observe, and theory predicts many more of them than have been discovered. Scientists hope that finding more dwarf galaxies around distant hosts may help shed light on the problem. The finding was described in a paper published online in the journal Nature.