Galaxies are vast systems of planets, stars, gas, dust and dark matter bound together by gravity. Scientists estimate that there are around 170 billion galaxies in the observable universe, ranging in size from tens of millions of stars to one hundred trillion stars. The shape and composition of a galaxy is influenced by interactions with neighboring galaxies and dramatic galactic collisions that often take place. Our own galaxy, the Milky Way, is set to eventually collide with our neighbor Andromeda.
Using powerful supercomputers, scientists are able to virtually turn back time and simulate the formation and growth of galaxies from shortly after the Big Bang. Scientists believe that galaxies probably begin life as spinning clouds of stars and dust traveling through space. As whirling clouds cross paths, they become intertwined and spiral into larger systems. Successive collisions can send material hurtling towards the edge of the forming galaxy, producing star filled spiral arms.
Thanks to a new simulation by NASA’s Goddard Space Flight Center, we can watch 13.7 billion years of galactic evolution unfold in just 46 seconds.
—[Learn more here](http://svs.gsfc.nasa.gov/vis/a010000/a011500/a011534/index.html)