Publications

A nova is a cataclysmic event on the surface of a white dwarf in a binary system that increases the overall brightness by several ordersof magnitude. Although binary systems with a white dwarf are expected to be overabundant in globular clusters (GCs) comparedto the Galaxy, only two novae from Galactic globular clusters have been observed. We present the discovery of an emission nebulain the Galactic globular cluster M 22 (NGC 6656) in observations made with the integral-field spectrograph MUSE. We extract thespectrum of the nebula and use the radial velocity determined from the emission lines to confirm that the nebula is part of NGC 6656.Emission-line ratios are used to determine the electron temperature and density. It is estimated to have a mass of 1 to 17×10−5M.This mass and the emission-line ratios indicate that the nebula is a nova remnant. Its position coincides with the reported location of a‘guest star’, an ancient Chinese term for transients, observed in May 48 BCE. With this discovery, this nova may be one of the oldestconfirmed extrasolar events recorded in human history.