Imagine the sight in the early hours of the morning. During the night, a thin layer of snow has Imagine the scene in the early morning: overnight, a thin layer of snow has settled on the ground, illuminated by a radiant sun. It's the perfect opportunity to build a snowman with the kids (or grandchildren...). You quickly wake them up, serve them breakfast, and dress them warmly. But by the time you're ready, the warmth of our star has done its work, and there will be no chubby snowman in sight. At best, you can form a few small snowballs. This scenario adapted to an astronomical context, is what an international team described on Thursday, February 29th, in Science: they observed that the radiation from very bright stars causes the gas contained in a protoplanetary disk to evaporate, preventing the formation of giant planets similar to our Jupiter and Saturn.

The scene being observed by these astrophysicists is unfolding in the Orion Nebula, the closest of all stellar nurseries, less than 1,300 light-years away. Dubbed a nursery because of its role in the birth of stars and planets, the Orion nebula is, as Olivier Berné, a CNRS research scientist in astronomy based in Toulouse and lead author of the Science study, explained, "at most a few million years old. That's one-thousandth of the age of the Solar System, which is over 4.5 billion years, and we can truly say that we're witnessing the infancy of these stars."

This is the moment when planets form in the disks of gas and dust that surround newborn suns. Using the most powerful instrument currently at their disposal, the James Webb Space Telescope (JWST), researchers focused on the protoplanetary disk named d203-506. It is home to a dwarf star, invisible because it is hidden by the material of the disk. However, this hidden star is not at peace in its nebulous corner, for just a few light-years away lies the Trapezium cluster, a group of stars, some of them very large and bright. "The most massive," explained Berné, "is a hundred thousand times brighter than the Sun."

For d203-506, this dazzling neighborhood is not without consequences, as it emits highly energetic ultraviolet (UV) and X-ray radiation. Thanks to the JWST instruments, astrophysicists have been able to determine the extent to which the surface of the disc is heated by this light. The temperature is estimated at a thousand degrees Celsius. As the IRAP researcher points out, "temperature is a measure of particle agitation. When they get too agitated, they can acquire a speed that allows them to escape the gravitational field." In other words, the protoplanetary disk loses its gas.

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