Discovery of a new type of star "flashing" - Le Nouvel Observateur

SUN. This discovery, published Wednesday, June 12, 2013 in the journal “Astronomy and Astrophysics”, based on regular measurements of more than 3000 stars in the the cluster NGC 3766, a period of seven years. It was conducted by a team of astronomers from Geneva with the Swiss Euler telescope, installed at the La Silla Observatory (Chile) belonging to the European Southern Observatory (ESO).

In this cluster, the team Nami Mowlavi discovered, for the first time, a group of 36 stars with “tiny variations in their luminosity, of the order of 0.1% of normal brilliance stars, “said ESO in a statement. The frequency of these variations is between two and twenty hours.

But there is a “catch”. according to theoretical laws that govern the physics of stars, those observed by Swiss astronomers were not supposed jogging

MYSTERY. “Indeed, according to our estimates, these stars have a size between 2.5 and 3 times the size of the Sun. However, according to our theoretical models, internal mechanisms for light variability are not present in stars with such a mass “says Fabio Barblan researcher in astronomy at the University of Geneva, Sciences et Avenir.

“In fact when they close to that size of the Sun, the stars may be variations in brightness due to convection currents on the surface,” says Kevin Belkacem, astronomer at the Observatoire de Paris.

And when their size is much greater than that of the Sun, the convection effect becomes negligible. However, the properties of stellar plasma are such that highly compressed gas then emit violent pressure waves which can then generate light variations.

“But between the two, it was thought until now that there was a range of stars in which it was not possible to observe such light pulses,” concludes Kevin Belkacem. This publication seems to contradict this theory. “Therefore, it will improve our knowledge of stellar interiors,” says the researcher.

Stars that challenge existing knowledge

The origin of their variation remains unknown, but astronomers have observed that some seem to be equipped with a rapid turnover. They run at speeds equivalent to more than half of “critical speed”, the threshold at which the stars become “unstable” and eject their material into space.

“Under these conditions, the rapid rotation will have a significant impact on their internal properties, but we are not yet able to model the variations in brightness,” said Nami Mowlavi.

coronal holes. However, other physical phenomena could be the source of such light variations. “One can imagine that these stars are provided by location spots, like coronal holes on the Sun, appear darker image,” imagine Fabio Barblan.

Such a spot on a rotating star could therefore explain such light variations. Alternatively, it could be binary star, ie of stars accompanied by another celestial body orbiting around him. Its periodic passage between the lens telescopes and the star could then explain the brightness variations of the latter, said the Swiss researchers.

But for now, the mystery remains unsolved …

Erwan Lecomte AFP, 6/13/13

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