Right at the center of this image, there's a dim orange dot. Somewhere around that dot, one of the stars in a binary system once went supernova, creating the vast red gaseous remnant you see all around it.
The problem is that no one can find the other star in that binary system, the one that should have been left over when the star went supernova. And that's bad news, because this is a Type Ia supernova, a particular type of cosmic explosion that happens when a white dwarf explodes. Because white dwarfs always have just about the same mass when they explode in these supernovas, they always have the same luminosity, which makes Type Ia supernovas incredibly useful in calculating the distances of faraway galaxies. Indeed, it was measurements of just these supernovas that helped reveal the existence of dark energy.