字幕表 動画を再生する 英語字幕をプリント It might be odd to get your head around, but galaxies can and do collide. But far from an wild party of death, galaxies collisions yield hotbeds for new star formation, leading astronomers to suspect that this not-so-violent event is actually a driving factor behind galactic evolution. The big question here is how can galaxies collide and not just destroy everything? It helps to think about what a galaxy really is. Every galaxy is made up of some 100 billion stars with planets orbiting their host stars, but those stars are really far apart. Take the Milky Way for example. We're about here on the edge of a spiral arm called Orion Spur. It looks crowded in our little neighborhood, but our nearest neighbor Alpha Centuri A, is actually 4.3 light years away. So galaxies might full of stars, but those stars are really far apart, meaning the likelihood of two hitting is pretty low. But that doesn't mean nothing happens, because there is stuff in those vast distances. The “space” between stars is actually full of gas and dust. Within these regions are dense pockets of interstellar material, called molecular clouds, that collapse under their own mass and gravity, forming protostars and eventually new stars. When galaxies collide, it's this material — the interstellar gas and dust — that interacts gravitationally with some neat results. In a collision, one galaxy can rip material from another, disrupting star formation and adding more material to its own molecular clouds. A direct collision between these gases can also result in shockwaves reverberating through both galaxies, triggering new regions of star formation where there wasn't any before. Aside from generating new pockets of star formation, both close passes and full-on collisions cause gravitational interactions begetting interesting changes, causing spiral arms, tidal tails, and even rings. Two spiral galaxies could merge and form an elliptical galaxy with more active star formation than either had before. But it's not like this happens overnight… not that there's a “night” where galaxies are concerned. This process can take millions of years. Which is a good thing because our own Milky Way is on a crash course with the Andromeda galaxy, but we've got a good 4 billion years… That should be enough time to live my best life. If you want more cosmic science in your feed be sure to subscribe to Seeker. And if you want to know what happens when galaxies die, Trace has more on that right here. You know what'd be awesome? If after the Andromeda collision our sky lit up with tons of newly forming stars!