A standard candle slowly burns down

A standard candle slowly burns down. Cepheid stars are remarkable beacons. Each pulses with a regular frequency related to its intrinsic brightness. An astronomer can therefore determine the distance to a Cepheid by comparing its observed and intrinsic luminosities. Cepheids, in turn, calibrate other classes of luminosity-signaling standard candles that can be viewed from farther away. Iterating the process yields a cosmic distance ladder that enables distance estimation across the cosmos. Astronomers had long thought the behavior of Cepheids was unchanging, but Pauline Barmby of the University of Western Ontario and colleagues now report that of 29 Cepheids that the team studied, about one-fourth are losing mass. As they do so, they shroud themselves with dust that could introduce errors in distance estimations. The figure, from an earlier, related study, shows an IR image obtained with the Spitzer Space Telescope of one such star, Delta Cephei. The red region...