Understanding the motion, shape, structure, density and quantity of galaxies in the universe is the largest scale scientific pursuit of mankind with many questions still remaining.
At the level of the galaxy itself, astronomers have found that stars revolve around the center of galaxies at a constant speed over a wide range of distances from a galaxy's center. This behavior was not expected, assuming a free Newtonian potential. This contradiction has led scientists to speculate on the existence of extra mass called Dark Matter or the need for extra parameters in for Modified Newtonian Dynamics.
Other astronomical models predict that small galaxies in the early Universe evolved into the massive galaxies of today by coalescing. Recent observations by the Hubble Space Telescope have found some of these early galaxies, existing only 100 years after the big bang. Scientists were surprised to see their density so low raising many questions about how the early galaxies must have formed. Three of the galaxies appear to be slightly disrupted – rather than being shaped like rounded blobs, they appear stretched into tadpole-like shapes. This is a sign that they may be interacting and merging with neighbouring galaxies to form larger, cohesive structures. Other observations using wide field telescopes looking back to a time when it was a fifth of its present age have revealed an enormous string of galaxies about 300 million light-years long. This new structure defies current models of how the Universe evolved, which can't explain how a string this big could have formed so early.
