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Stellar acoustics sound like sunspots

  • CoRoT space telescope sees pressure waves in stars
  • Technique can be used to see “starspots” similar to sunspots
  • Gives clues to stellar magnetism, which can affect planets

In a bid to unlock longstanding mysteries of the Sun, including the influence on Earth of its 11-year cycle, an international team of scientists has successfully studied a distant star.

By monitoring the star’s “sound waves”, the team has revealed a magnetic cycle similar to the Sun’s solar cycle.

The study, conducted by scientists at the National Centre for Atmospheric Research (NCAR) and colleagues in France and Spain, is being published this week as a “Brevia” in the journal Science.

The scientists used a space telescope called CoRoT to study a star known as HD49933, located 100 light-years away. The team examined the star’s acoustic fluctuations, using a technique called “stellar seismology.”

Stars are big, rumbling cauldrons of super-hot gas. Those rumbles—like earthquakes—are actually pressure or “sound” waves, and they can be picked up as tiny Doppler shifts in the stars’ light spectrums.

Careful study of those sound waves can reveal details about activity on the surface of stars. In the case of HD49933, the scientists detected the signature of “starspots,” areas of intense magnetic activity on the surface that are similar to sunspots.

While magnetic cycles have previously been observed in other stars, this is the first time such a cycle has been discovered using the stellar seismology technique.

“Essentially, the star is ringing like a bell,” says NCAR scientist Travis Metcalfe, a co-author of the new study. “As it moves through its starspot cycle, the tone and volume of the ringing changes in a very specific pattern, moving to higher tones with lower volume at the peak of its magnetic cycle.”

“We’ve discovered a magnetic activity cycle in this star, similar to what we see with the Sun,” says co-author and NCAR scientist Savita Mathur. “This technique of listening to the stars will allow us to examine potentially hundreds of stars.”

Artist's impression of the CoRoT space mission

Artist's impression of the CoRoT space mission studying a distant star (not to scale).

Implications for life on distant planets

The team hopes to assess the potential for other stars in our galaxy to host planets, including some perhaps capable of sustaining life.

“Understanding the activity of stars harbouring planets is necessary because magnetic conditions on the star’s surface could influence the habitable zone, where life could develop,” says CEA-Saclay scientist Rafael Garcia, the study’s lead author.

The habitable zone is the orbital distance from a star where temperatures are neither too hot nor too cold for life as we know it to survive.

Studying many stars with stellar seismology could help scientists better understand how magnetic activity cycles can differ from star to star, as well as the processes behind such cycles.

The work could especially shed light on the magnetic processes that go on within the Sun, furthering our understanding of its influence on Earth’s climate. It may also lead to better predictions of the solar cycle and resulting geomagnetic storms that can cause major disruption to power grids and communication networks.

The scientists examined 187 days of data captured by the international Convection Rotation and Planetary Transits (CoRoT) space mission.

Launched on December 27, 2006, CoRoT was developed and is operated by the French National Centre for Space Studies (CNES) with contributions from Austria, Belgium, Brazil, Germany, Spain, and the European Space Agency. CoRoT is equipped with a telescope and a CCD camera sensitive to tiny variations in the light intensity from stars.

The study authors found that HD49933 is much bigger and hotter than the Sun, and its magnetic cycle is much shorter. Whereas past surveys of stars have found cycles similar to the 11-year cycle of the Sun, this star has a cycle of less than a year.

Adapted from information issued by NCAR / UCAR / Institute of Astrophysics of the Canaries.

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