Your first supernova experience is likely to go something like this: You're innocently flying around, exploring a Space Biome for the first time, and you notice a jittery red flashing in the sky. Before you even begin to formulate a question about what's going on, there's a bright white light and bam, you're dead.
A supernova occurs only in a Space Biome, and appears as a few seconds of red flashing in the sky, followed almost immediately by a blinding flash of deadly white. Supernovas kill instantly, no matter how high your Survival and Stamina levels are and no matter what sorts of protective accessories you have. They occur every few minutes according to what seems to be a random pattern, and those few seconds of red flashing are your only warning. To be safe, figure anywhere from three to seven minutes since the last one, with a higher likelihood of it being around five minutes, and plan accordingly. In other words, don't assume you'll get the full five minutes after any given supernova.
The only way to survive a supernova is by getting yourself to the shielding that the background earth of an asteroid provides. Your bottom half (i.e., your avatar's "anchor block") must be in front of the background earth at the time of the white flash. As of December 2017, it appears there is one exception to this rule. Many asteroids have openings in them that contain no backdrop, where you can see stars behind you instead of the backdrop texture. These enclosed "windows" appear to be safe zones as well.
If you find yourself falling through space with no nearby asteroids, and the sky starts to flash red, you're done for. (Although if you have good reflexes, you might be able to slap a blue tele down before you fry, which will give you an easier way to get back to your spot once the supernova passes.)
As of December 2017, there is no world machine to "purify" a Space Biome of Supernovas. However, according to the Space Biome Launch Notes on the forum, one may be released at a later time. We say "at a later time" instead of the four-letter-word that begins with S because that word seems to jinx things.