HD50230 is the charming name of a young massive star at the heart of a publication which has just appeared in the journal Nature (1). If this star finds itself with the spotlights trained on it, it is because it is the first to reveal the movements which animate its core. It is for much more than the challenge itself that astrophysicists attempt to pierce the secrets of the stars’ depths, which are nonetheless inaccessible directly: the physico-chemical processes at work in the stars’ interiors influence their development and, on a greater scale, the chemical history of the galaxies, including our own Milky Way.

If the interior of a star cannot be observed directly, it can nonetheless be studied in an indirect way, through asteroseismology or stellar seismology. Its principle is the same as that used to study the depths of our planet on the basis of earthquakes.

A star resembles a heart which beats to rhythms which essentially depend on what it has within its innards. Its surface is permanently animated by a vibratory movement, the study of which is an open door onto its internal structure. From an observational point of view, a star’s vibrations are expressed by periodic variations in its brightness. Nonetheless, the amplitude of this variability of a star’s brightness is so very tiny that it is necessary to measure a star’s luminosity with a part per million precision to hope to ‘see’ its surface tremble. This precision can only be achieved by collecting a maximum of light originating from the star to be studied and thus to increase the duration of continuous observation…an objective which it is difficult to carry off with a telescope nailed to the ground and subject to the rhythm of the day-night cycle and to the vagaries of the weather, but it is conceivable with a space telescope…

(1) Degroote P., Aerts C., Baglin A ., Miglio A., Briquet M., Noels A., Niemczura E., Montalban J., Bloemen S., Oreiro R., Vučković M., Smolders K., Auvergne M., Baudin F., Catala C., Michel E., Deviations from a uniform period spacing of gravity modes in a massive star, Nature 464 (11 mars 2010), pp. 259-261.