This is a bit of comet dust trapped in aerogel. Capturing the stardust in this way reveals something new and fascinating about what's inside of comets — but it also looks really cool.
The thing about bits of comet is that they are going very, very fast. To get them to stop going fast takes a lot of deceleration. That deceleration has to occur over long distances, or it has to involve a lot of pressure, and therefore heat. Because both heat and pressure will transform the particles of dust, catching them and studying them posed a problem.
Enter aerogel and the Stardust mission. The Stardust mission sent a space craft up with aerogel, a sort of sponge made of silicon. This was no ordinary sponge. It's 99.8 percent empty space, and it conducts heat so poorly that there are plenty of shots of a blowtorch being taken to the bottom of a slab of aerogel while flowers or matches sit undisturbed on top of it. Aerogel also looks cool, with a slightly hazy blue color. In short, a particle of high-velocity dust could sink far into a block of aerogel without heating up or flattening out. And when it did, it would just leave a pretty, conical trail in a bright blue medium.
The triumph of the Stardust mission wasn't just aesthetic. Scientists found ice and the unreconstructed materials of the early Milky Way. This was expected. They also found rocks that had been made at incredibly high temperatures. Somehow material that saw the inside of some heated situations early on in galactic history ended up in the freezing cold comets. The exact mechanism for this is still unknown. For now, it's just good to know that comets are the result of both fire and ice.