  Here we report the detection of polarization variations due to nonradial
modes in the beta Cephei star beta Crucis. In so doing we confirm 40-year-old
predictions of pulsation-induced polarization variability and its utility in
asteroseismology for mode identification. In an approach suited to other beta
Cep stars, we combine polarimetry with space-based photometry and archival
spectroscopy to identify the dominant nonradial mode in polarimetry, f2, as l =
3, m = -3 (in the m-convention of Dziembowski) and determine the stellar axis
position angle as 25 (or 205) +/- 8 deg. The rotation axis inclination to the
line of sight was derived as approx. 46 deg. from combined polarimetry and
spectroscopy, facilitating identification of additional modes and allowing for
asteroseismic modelling. This reveals a star of 14.5 +/- 0.5 Solar masses and a
convective core containing approx. 28% of its mass -- making beta Crucis the
most massive star with an asteroseismic age.

Solar and Stellar Astrophysics;Instrumentation and Methods for Astrophysics