Astronomers think that the little green smear at the bottom right of this picture may be the core of an exploded star that was blown out into space 15,000 years ago. It's very very big, it's moving very very fast, and it's coming right for us! Just kidding, we're safe. For now.
Exploding stars can cause lots of different cool things to happen. They can blow themselves into dust. They can form black holes. They can leave behind pulsars. And sometimes, they can act like the largest artillery pieces in the known universe, firing huge stellar remnants across space at unbelievable speeds.
In order for a star to launch itself, it first has to explode. And it has to be a particular kind of explosion: one that's not quite centered in the middle of the star. Stars aren't totally homogeneous, so sometimes the actual focal point of a supernova is off-center, creating an asymmetrical blast that kicks off a bunch of ex-star stuff in one particular direction. The core of the star still collapses into a neutron star or a black hole, but all the energy from the sideways supernova gives it a whack as it does so, sending it speeding away at (in this particular example) about six million miles per hour, which is fast enough to fly from where I'm sitting right now (in Washington DC) to Ulaanbataar (the capital of Mongolia) in about five seconds.
Here's a close-up of what the stellar remnant looks like now, 15,000 years after launch (click to see it larger):
Astronomers aren't positive that this is what we're looking at, but they're pretty sure. The green glow surrounding the presumed neutron star is called a "pulsar wind," and it's being blown backwards into a tail as the star speeds through gasses floating out in space. In the wider field picture up top, the purple represents X-rays being given off by energized gas leftover from the supernova.