Novae are caused by runaway thermonuclear burning in the hydrogen-rich atmospheres of accreting white dwarfs, which leads to a rapid expansion of the atmosphere and the ejection of most of its mass. Theory predicts the existence of a ‘fireball’ phase following directly on from the runaway fusion, which should be observable as a short, bright and soft X-ray flash before the nova becomes visible in the optical wavelengths. Now, astronomers using...
