Astro Fact of the Day
Matter likes company. About 95% of galaxies belong to groups (like our own galaxy, the Milky Way) or clusters. 5% or so go it alone in the void, though. The galactic loners seem to do alright, though. They seem to have more gas and more sustained stellar formation, probably because they don't experience gas stealing close encounters with other galaxies.
There are lonely stars outside galaxies too, and lots of planets outside of stellar systems. Mostly these latter two probably started out as insiders but got booted out by gravitational interactions.