There’s a new “nova” in the sky. Not a supernova, just a nova. But, what is a nova?
A classical nova happens in a special kind of tightly-orbiting binary star system: one where a relatively normal star pours a stream of hydrogen onto the surface of a companion white dwarf. When the layer of fresh hydrogen on the white dwarf’s surface grows thick and dense enough, the bottom of the layer explodes in a runaway hydrogen-fusion reaction — a hydrogen bomb in the shape of a thin shell roughly the size of Earth. The underlying white dwarf remains intact, and as new hydrogen builds up, the process may repeat in a few years to tens of thousands of years.
via Bright Nova in Delphinus – Observing Blog – SkyandTelescope.com. More technical data on this here, showing how it has peaked and is fading in magnitude again.