The Voyager 1 space probe is currently about 11 billion miles from the sun. This is really, really far away: it's three or four times farther away from the sun than Pluto is. Astronomers have been expecting Voyager to to make the transition between our solar system and the rest of our galaxy, and it looks like that may have just happened.
From Voyager's distant perspective, the sun (our sun) looks like more or less any other bright star. The only way for the spacecraft to tell that it's still (technically) within our solar system is to measure the charged particles that our sun emits, the same solar wind that causes auroras and pushes solar sails. As Voyager travels outward, the force of this wind has been slowly decreasing, and recently it's slowed to a nearly unidentifiable trickle, signaling that Voyager is nearly beyond our sun's influence.
For the very first time, Voyager's instruments have also begun to detect gusts of charged particles blowing in the opposite direction, back towards our sun. Where are these particles coming from? Whatever's out there in the space between the stars. Interstellar space, they call it, and it's what makes up most of our galaxy. What's out there? We have no idea, we've never been there before, but we do know that it's something completely new.
Voyager 1 should have enough fuel and propellant to continue traveling outwards (and sending back data) until at least 2020, by which time it'll be about 12.5 billion miles from us. And even apart from all the valuable science that Voyager is performing, we should all be very proud (as a species) that we've managed to send a little piece of ourselves outside of the insignificant little corner of the universe that we call home.