The first image of a planet being born


For the first time we can see, in a corner of the sky, a planet that is being born. It collects, collects matter, gas and dust, thickens in a small spiral that orbits around its young mother star. It is one of the primordial phases that shape a new world. This planetary embryo does not yet have a name but its star does: AB Aurigae is located about 520 light years from us.

In the cradle of new planets

The planets are born from the concentration of matter inside a “protoplanetary disk” that surrounds the young stars. For some time, astronomers have noticed great movement around AB Aurigae (in the constellation of Auriga, also visible from our hemisphere). They keep an eye on it because it is just a few million years old and for this reason it is surrounded by a dense cloud of gas and dust. It is also quite close (not visible to the naked eye, but binoculars are enough): an opportunity to ‘spy’ on what is happening around there.The same thing happened four billion years ago near our sun that had just turned on: “We have to observe very young systems to capture the moment when the planets really form,” he explains Anthony Boccaletti of the Observatoire de Paris, first signature of the study published on Astronomy & Astrophysics. A few years ago, an instrument of the European southern observatory (Eso), Alma, made it possible to visualize for the first time the two large arms that wrap the star with their spiral.

The cloud of gas and dust around AB Aurigae. On the right the zoom in the internal part where is the zone in which a new planet is being born. The blue disk indicates the size of the orbit of Neptune, compared with the new planetary system (Credits: ESO / Boccaletti et al.)

With the Sphere instrument of the Very large telescope (Vlt) also by the Eso, this time it was possible to zoom in between the swirls of that chaos and discovered an anomalous area. A small ‘lump’, a ball of matter that has all the air of being a concentration that is growing, under the pressure of its own gravity. It is a new world, a new “place” in the universe that takes shape. Sphere, which specializes in hunting and photographing extrasolar planets, has captured the faint glow (especially compared to the emissions of the star) that comes from the inside of that cloud, in the infrared wavelengths.

Waves of gas

The international team led by Boccaletti described what he saw. A “disturbance” inside that disk of gas that extends well beyond 150 Ua (an astronomical unit is equal to the average distance of the Earth from the Sun). The effect is that of a wave, which triggers the birth of the planets. That bright dot, where matter is concentrated, is one of those areas, the scientists write, where the ‘waters’ stirred and gave birth to two smaller spiral arms: “It is foreseen by some theoretical models of planetary formation – He says Anne Dutrey, of the Laboratoire d’Astrophysique de Bordeaux, co-author of the study – one that wraps itself inward and the other that expands outward and that meet in the area of ​​the planet. And they allow gas and dust to aggregate on the planet that is forming and make it grow. “

Although it seems very close to the star, in this photograph, that ‘ball of matter’ is at the same distance from its star that Neptune (the most distant planet in our solar system) has compared to the Sun: 30 astronomical units: 4.5 billions of kilometers. But we are still in the inner part of the disk, where the matter is denser and more likely to aggregate.

The black disk in the center is the place that the star occupies, obscured as with a parasol to be able to distinguish the weakest details of emissions from the surrounding areas. Thus was born what scientists consider the first image of a planet to be born. Sphere’s eye is not new to this type of discovery. In 2018 he took the first snapshot of a newly formed planet around the star Pds 70, we can define him as a newborn baby, in comparison to which what orbits around AB Aurigae is an embryo.

And who knows how many are still growing around there. When ready, the Elt, the Extremely large telescope, which will be the largest in the world, will collect the testimony of Alma and Sphere to discover ever sharper details. Peering also much closer to the star, to find new clues and findings on how new worlds are born and how, a few billion years ago, ours too was born and raised.

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Mario Calabresi
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