Astronomers say they've learned how to listen to the "heartbeat" of fledgling stars within stellar nurseries to gauge how old they are and learn more about how stars are born then change with age.

In the stellar nurseries -- giant clouds of cosmic gas -- stars form as parts of the cloud condense by gravitational attraction, growing increasingly hotter until they start fusing hydrogen, the same process that drives our own sun.

That's a sign their stellar "childhood" is over and they are considered "adult" stars.

Until then it's hard to tell the age of a star in its gas 'womb,' but now astronomers report a new technique involving observations of the acoustic vibrations of a star using ultrasound to help find out if it is an infant, a toddler or an adolescent.

For their study the researchers looked at the vibrations, caused by internal radiation pressure, of 34 stars aged 10 million years or younger.

They chose stars with masses between one to four times that of our sun.

"Our data shows that the youngest stars vibrate slower while the stars nearer to adulthood vibrate faster," says lead researcher Konstanze Zwintz of the University of Leuven in Belgium.

"We now have a model that more precisely measure the age of young stars," she says. "And we are now also able to subdivide young stars according to their various life phases."

The stars in the study showed periods of vibrations -- a 'heartbeat' -- ranging from 15 minutes to five hours.

A star is considered born when it becomes visible in optical wavelengths, but determining its age has always been a challenge facing astronomers.

Theoretical physicists have suggested young stars might vibrate at different rates than older stars, but the study led by Zwintz has provided the first concrete evidence of that fact based on actual observations of stars, in this case in a nebula known as the Christmas Tree Cluster.

Data for the study was gathered using Canadian and European satellites and ground-based telescopes including the European Southern Observatory facility in Chile.

In addition to determining a star's age, the acoustic vibration technique can yield clues to its future "life style," Zwintz says, such as whether it will live fast and die young or lead a more sedate life.

"A star's mass has a major impact on its development: stars with a smaller mass evolve slower," she says. "Heavy stars grow faster and age more quickly."