Stars, dust, you and me, all the things that we see — only make up about 4 percent of the entire universe, rest is what we call as "Dark Matter".
What is Dark Matter ?
Scientist believe, that the gravity of visible matter is not strong enough to form galaxies and complex structures. Stars are most likely to scatter all over the place and not form galaxies. So we know there is something else inside or around them, something that does not emit or reflects light, something dark and there is lot of it and scientists can estimate based on its gravitational effects on surrounding matter.
Meet the New Discovery - Dragonfly 44, The massive galaxy consists almost entirely of dark matter. Its 300 million light-years away, 100000 light-years wide and is located in the nearby constellation named "Coma". Dragonfly 44 is an incredibly large, about the size of the Milky Way, but its diffuse and dim galaxy with far fewer stars, only 0.1%. The Milky Way has more than a hundred times then that. So What's holding those few stars in place?
Star velocities are an indication of the galaxy’s mass ... The faster the stars move, the more mass its galaxy will have. The stars in Dragonfly 44 were observed to be moving much faster than what was expected for a galaxy of its brightness. Galaxies rotate at such speeds, they’d rip themselves apart if the only thing trying to hold them together was their own gravitational force. Something else has to be holding them. Physicists think the answer is a whole lot of dark matter.
Scientists used the world's most powerful telescopes, the Gemini North telescope at the Gemini Observatory and the Keck II telescope at the W.M. Keck Observatory, to monitor it and observations says that the galaxy is made of 99.9% dark matter. Wow..
While the galaxies believed to be made up almost entirely of dark matter have been discovered before, but they are usually quite small, one such is named VIRGOHI21 and is about 50 million light-years away, it appears to contain no visible stars, has 99.9 percent dark matter and is about 10th the size of Milky Way. Dragonfly 44 discovery is special because finding a galaxy with like of the Milky Way, that is almost dominated by dark matter was unexpected. Hence scientists feel, the discovery of Dragonfly 44 challenges existing notions on the formation of galaxies.
Despite years of searching, we have no idea what dark matter actually is, but this invisible matter seems crucial to the stability of the Universe.