Nearly 400 years have passed since a supernova was last observed directly in the Milky Way (by Kepler, in 1604). Numerous Galactic supernovae are expected to have occurred since then, but only one (Cassiopeia A) may have been seen. The historical record of supernovae is therefore incomplete, as demonstrated by the spatial distribution of young supernova remnants. The discovery of γ-ray emission from the decay of ~(44)Ti nuclei associated with Cassiopeia A, the youngest known remnant, has revealed a new way to search for the remnants of other relatively recent supernovae (less than ～ 1,000 years old). Here we report the discovery of ~(44)Ti line emission from a previously unknown young supernova remnant, in the direction of the Vela remnant. We estimate a distance of ～200 parsecs and an age of ～680 years for the remnant, making it the closest young remnant to the Earth. Why it was not recorded historically remains unknown.
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