Deciphering a star’s spiral shell

In the constellation Sculptor some 1000 light-years away, the aging red giant R Sculptoris is expelling large amounts of its mass through a strong stellar wind supplemented by periodic thermal pulses. The pulses, short-lived phases of explosive helium burning in a thin region just outside the star’s carbon–oxygen core, envelop the star in a spherical shell of gas and dust.

In one of the first published results from the Atacama Large Millimeter/submillimeter Array, Matthias Maercker (European Southern Observatory and the University of Bonn) and colleagues report that previously observed clumps in the shell around R Sculptoris belie a surprising interior spiral structure, shown here. Some 40 arcseconds across, the spiral indicates the presence of an unseen orbiting companion star with a period of 350 years. The detailed structure of the spiral enables the determination of several important properties of both the binary system and the thermal pulse, with implications for understanding and modeling late stellar evolution and, possibly, the future fate of our sun. (M. Maercker et al., Nature 490, 232, 2012; image courtesy of ALMA (ESO/NAOJ/NRAO)/M. Maercker et al.)

To submit candidate images for Back Scatter, visit http://contact.physicstoday.org .