The aftermath of a nova explosion

Artist's view of a **nova explosion**, an astronomical transient event consisting of the sudden appearance of a bright *apparently new star* in the celestial sphere. After the sudden increase in brightness, a nova fades slowly in weeks or months. This phenomenon occurs in close binary systems including a white dwarf (WD), the stellar core of a dying star composed mainly of electron degenerate matter, and a main-sequence or giant star. Owing to the proximity of the two stars in the binary system, the WD attracts accreted matter to its surface. The matter gradually accumulates on the surface of the WD until it reaches a critical temperature that causes the ignition of rapid runaway fusion: a violent thermonuclear explosion occurs that expels stellar material into the circumstellar medium. The nova sweeps away the dense accreting material on the equatorial plane and the companion star, producing an hourglass-shaped shock that propagates through the circumstellar medium and a bow shock around the companion star.