We now know where hypervelocity stars come from. Binary stars systems are very common and as a matter of fact, there is a good chance that our solar system started that way. Our Sun had a twin that was pushed away at some point in the remote past. So, once in a while, one of these binary systems comes too close to the central black hole of our galaxy, one of the stars (the unlucky one) goes beyond the event horizon of the BH and consequently it is captured by it, never to be seen ever again!! the other, on the other hand, gets released (kinda like in a hammer throw) and pushed away from the BH at a very high speed. So high in fact, that in a mere thirty million years, a short time at the scale of a solar system, the star moves beyond the borders of the galaxy and finds itself in the intergalactic void, literally in the middle of nowhere. Imagine a totally starless sky!! It's estimated that there are about ten to the eighteenth power such stars in the entire universe, one billion of billions!!!