Saturday, August 30, 2014

Sonograms of Young Stars

An optical image of the region NGC 2264 containing a cluster of young stars. Astronomers have measured pulsations in the light of some of these stars and used them to infer the physical processes underway before they mature and begin to burn hydrogen fuel.Credit: ESO 

The evolution of a star depends crucially on its initial birth mass and composition, and developments in its early lifetime. These initial properties determine, for example, the production of the chemical elements forged later on in the star's nuclear furnace, and its early angular momentum affects the subsequent distribution of its internal energy. Astronomers are therefore working to understand the physical processes underway in the very earliest stages of a star’s life after a dense clump of interstellar matter has contracted, warmed, and begun the stellar gestation processes.

In the early stages of a star's life, its central temperature and density are not yet high enough to initiate significant nuclear burning; its energy comes from the release of gravitational energy, and it circulates via gas motions. As the internal temperatures rise and the hot gas becomes more transparent, this internal energy begins to redistribute itself through radiation as well through gas motions. Then, as these and related processes compete for primacy, the star starts to vibrate slightly, an effect which can be observed as periodic variations in the star's surface through the luminosity and temperature. In some young stars it is possible to use "asteroseismology" – the measurement of these acoustic patterns - to explore the star’s structure and evolution.

CfA astronomer Dimitar Sasslov has joined with a team of other investigators to study the surface vibrations in thirty-four young stars. Their ages are constrained by their emission spectra or by their being members of stellar clusters whose ages are known to be less than about ten million years, either signaling likely periodic vibrations in the young stars. The team finds a clear relation between seismic observables and evolutionary status, and in particular they are able to infer the internal stellar processes underway and the star’s corresponding evolutionary development. By analogy to a sonogram, this technique of asteroseismology is able to probe the unborn, and offers a new probe of the earliest stages of a star's life.

"Echography of Young Stars Reveals Their Evolution," K. Zwintz, L. Fossati, T. Ryabchikova, D. Guenther, C. Aerts, T. G. Barnes, N., Themes, D. Lorenz, C. Cameron, R. Kuschnig, S. Pollack-Drs, E. Moravveji, A. Baglin, J., M. Matthews, A. F. J. Moffat1, E. Poretti, M. Rainer, S. M. Rucinski, D. Sasselov, W. W. Weiss, Science, 345, 550, 2014.