Distant star makes music

By Dr David Whitehouse BBC News Online science editor

Astronomers have detected sound waves in the outer atmosphere of a star 130 light-years from Earth.

Synthesized, they come across as a lot of bass notes, say the researchers.

The detection technique the scientists used allows them to probe the outer layers of stars, to compare observational data with theoretical models to show how the stars should behave and develop.

The technique is the same one that has been used in the past decade to find more than 70 planets circling other stars.

Boom, boom

Three decades ago astronomers realised that the Sun vibrates like a giant musical instrument with well-defined notes or frequencies.

xi Hya oscillates with several periods of around three hours

The energy that excites these sound waves comes from the turbulent convective region just below the Sun's visible surface.

It was the observation of these solar sound waves - it is called helioseismology - that resulted in our vastly improved understanding of the Sun's interior.

It is possible to apply these techniques to other solar-type stars. Observations have shown that Alpha Centauri A - the nearest bright star to our Solar System - behaves very much like the Sun, and that some of the periods it displays are also quite similar to those in our star.

Now these vibrations have been picked up in other types of stars.

Big and red

An international group of astronomers has found that the giant star xi Hya behaves like a giant sub-ultra-bass instrument.

This star is located in the constellation Hydra. It has a radius about 10 times that of the Sun and its luminosity is about 60 times larger.

The astronomers observed xi Hya with the Swiss Euler telescope at the La Silla Observatory in Chile. They used the Coralie spectrograph, which is well known for numerous discoveries of exoplanets.

The new observations demonstrate that xi Hya oscillates with several periods of around three hours, and have speeds of up to two metres per second. This is somewhat smaller than expected, but the predictions are very uncertain as the conditions in xi Hya are so very different from those in the Sun.

xi Hya is considerably more massive than any other star in which solar-like oscillations have so far been detected. It is approaching the end of its life. It is about to expand its outer envelope to become a red giant star.