[In an effort to clean off the gazillion astronomical pictures I’ve been collecting on my computer’s desktop, I’m posting one per day until they’re gone, and my PC heaves a sigh of relief.]
In 1901, an obscure star in the constellation of Perseus suddenly flared into brightness, becoming briefly one of the brightest stars in the sky. Called GK Persei (or Nova Persei 1901), it’s an odd beast. While some stars like this just fade away after such an event, even now, more than a century later, GK Persei still suffers through periodic explosions, emitting vast pulses of energy.
In 1902 it was found to have an expanding cloud of gas around it. Adam Block, of the Mt. Lemmon Observatory, put together a wonderful animation showing that nebula expanding over 17 years, from 1994 to 2011:
You can see why it’s called the Fireworks Nebula!
This type of system is called a cataclysmic variable star. It’s a binary: one of the stars is a white dwarf, an ultra-dense ball of matter that used to be the core of a normal star like the Sun. When that star reached the end of its life, it shed its outer layers, exposing its core to space.