The device has exceeded its specifications

The stars and astronomers had until then very superficial relationships. This situation, especially frustrating for the latter, will change. It is the promise of work published this week by the Paris Observatory and its partners, which earned top honors in the coverage of "Science." The authors have put for two years the new space telescope "Corot" to three stars. Under their attacks, HD49.933, HD181.420 and HD181.906 eventually reveal a portion of their below. For Annie Baglin, responsible scientific mission Corot (French project 70), the results are unexpected. "The device has exceeded its specifications." "We have now a tool to explore the Interior of stars", she welcomed.

So far, space or terrestrial telescopes had only the activity of the surface of stars. Should imagine in what state out light that crossed the diameter of these fireballs. In the Sun, the star the best known, photons need to squeeze in a matter so dense and hot that they put millions of years out. The journey to the land is for them a walk of Health concluded in eight minutes. The light from the depths of the star lost en route all information on its origins.

Kettle boiling

Astronomers have adopted the strategy of geologists. They were able to explore the bowels of the Earth using seismology: they listen to the waves of earthquakes which spread in the world and related surface a lot of information. The chance of astronomers is that earthquakes of star are permanent. The nuclear reactions that take place in their heart are removing huge bursts of energy dissipating upwards, as the kettle boiling water. Reached the surface, these kinds of gas bubbles emerge as very noisy scarring. Acoustic waves then play the role of the raindrops on the surface of a drum, or a bow on a violin. The stars vibrate as a musical instrument according to several harmonics. Each part of the spectrum describes a particular layer of the star as the waves penetrate more or less deeply according to their frequency. Astronomers can not listen to the music of the stars because the sound does not cross the outer void. However, the mechanical waves of the star affect its electromagnetic pulse, which comes to us.

It took years to make the sensor technology offers sufficient sensitivity to detect these slight variations in light. Stellar seismology was first tested on the Sun by the Soho space telescope. The sensitivity of the large "camera" Corot ("Les Echos" of December 27, 2006) had to make great progress to exploit the vibrations of 100 to 200 light-years of here three stars in the milky way. He came to measure very low vibration spreads, the order of the hundredth of a degree of temperature on a surface of 6500 degrees. Performance are as much to the system of signal processing filter parasitic light from Earth, Corot did orbiting to 900 kilometers.

The surprise of its users, the telescope was so sensitive that he was able to save the signature of the scarring that animate the surface of the three stars. "We thought that these signals coming from the scarring would create parasites to filter for good measure vibrations." "But we found that scarring data are exploitable", was in is still not Annie Baglin.

Rosetta Stone

Astronomers have chosen to focus their work on these three stars because they are the most similar to the Sun in the window of observation of Corot. They weigh between 1.2 and 1.4 times the solar mass and are a bit warmer. "Everything we know about the stars comes from our modeling", explains Eric Michel. Modeling of the Sun is the most successful because of its proximity. For researchers, the Sun is the Rosetta Stone for decrypt other stars. With the data of the new three stars, they first will be able to move their models. The first steps have confirmed this need: their oscillations are 25 lower than those provided for by the theory.

These three stars will also serve researchers to address more complex stars. "The Sun, it is the most boring star, causes the Annie Baglin mischievous. It is an old star who lost the memory of its initial phases. When there is interest as me in the formation of stars and the universe, we like the younger stars. "Youth is turbulent: it shines more, turns on itself with high rotation speeds. The technique of the photometry then loses pedals. These three slightly younger than the Sun stars push astronomers to their limits. The vibration of the three stars are 1.5 times stronger and their granulation has been 3 times finer.

For Eric Michel, the internal workings of these stars is more complex than that of the Sun. 300-400 Researchers working on the data will still take time to interpret their results, expected in early 2009. Corot, he will abandon the stars for a few months to concentrate on exoplanets, its second mission. "We have no competitor in seismology, but the search for exoplanets has become very competitive," smiles Annie Baglin.