Longstanding Cepheid Mass Mystery Finally Solved

An artist’s impression of the binary system OGLE-LMC-CEP0227, which contains a classical Cepheid variable star. By measuring this system, astronomers were able to settle a longstanding debate over the masses of these types of stars. Image credit: ESO/L. Calçada

Cepheid variable stars – a class of stars that vary in brightness over time – have long been used to help measure distances in our local region of the Universe. Since their discovery in 1784 by John Pigott, further refinements have been made about the relationship between the period of their variability and their luminosity, and Cepheids have been closely studied and monitored by professional and amateur astronomers.

But as predictable as their periodic pulsations have become, a key aspect of Cepheid variables has never been well-understood: their mass. Two different theories – stellar evolution and stellar pulsation – have given different answers as to the masses that these stars should be. What has long been needed to correct this error was a system of eclipsing binary stars that contained a Cepheid, so that the orbital calculations could yield the mass of the star to a high degree of accuracy. Such a system has finally been discovered, and the mass of the Cepheid it contains has been calculated to within 1%, effectively ending a discrepancy that has persisted since the 1960s.(…) Read the rest of Longstanding Cepheid Mass Mystery Finally Solved (423 words)

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