Cataclysmic variable stars are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state.

What are cataclysmic variables in astronomy?

Cataclysmic variables (CVs) are binary star systems that have a white dwarf and a normal star companion. They are typically small – the entire binary system is usually the size of the Earth-Moon system – with an orbital period of 1 to 10 hours.

What is an example of a cataclysmic variable star?

Examples include T Pyxidis and RS Ophiuchi. Dwarf novae, or U Geminorum stars, are cataclysmic variables which are observed to brighten repeatedly, though by a smaller amount than classical novae. These are stellar mergers that become very red after outburst.