Can stars exist outside a galaxy?

Thanks to Matt Bothwell for the answer!

James - Galaxies are systems of stars, gas and dust orbiting around a centre of mass. In the case of large galaxies, like our own Milky Way, more than a hundred billion stars circle the supermassive black hole at its centre, but can stars exist outside of this orbit? Here's Matt Bothwell, public astronomer at the University of Cambridge.

Matt - This is a great question. The very short answer is yes. The interesting bit is how they get out there. All stars form inside galaxies. You need a dent cloud of molecular gas to form a star, and these dense clouds only exist inside galaxies. As a side note, when astronomers talk about a dense cloud of gas, this isn't what most people would think of as dense. A dense cloud of gas in space has far fewer atoms per cubic metre than the best vacuum on earth. So while stars always form inside galaxies, sometimes they are unlucky enough to be thrown out. Now, there's a concept in physics known as escape velocity. Basically the speed you need to travel in order to escape the gravitational pull of an object. Earth's escape velocity is around 40,000 kilometres per hour. So if you want to escape Earth's gravity, this is how fast you have to launch yourself. You need to go really, really fast to escape a galaxy. The Milky Way's gravitational pull is a lot bigger than Earth's, and so you need to travel at around 2 million kilometres per hour. We do, in fact, see rogue stars in intergalactic space, and so the big question is what could possibly fling them out at this absurd speed? We think there are two things that could do it. Firstly, when two galaxies collide, the gravitational forces of the collision could fling millions of stars out into intergalactic space. And secondly, super massive black holes can slingshot things at very ridiculous speeds and throw things out of a galaxy. In 2012, a team of astronomers noticed around 700 stars beyond the edge of the Milky Way, heading off into the intergalactic darkness. All of these stars showed signs of originating in the very heart of the Milky Way in the super massive black hole's back garden. In other words, before they were thrown out. It's not all doom and gloom though for these stars. Any planet orbiting one of these rogue stars ejected would have one of the most spectacular views in the universe standing on one of these planets, you'd be able to look up and see an entire galaxy covering the sky. I think that would be worth the journey.