Have you ever wiped down a shelf with a cloth and watched the dust particles float away in a beam of light? That dust—ordinary, everyday dust—is related to the dust that, 4.5 billion years ago, formed the Earth. Grain by grain, these tiny particles clumped together, stuck together, and compacted until they formed rocks, and then entire planets.
Our Sun, on the other hand, was fortunate enough to be alone. No neighbors to disrupt this delicate dance, no foreign gravity to scatter the dust before it could form a world. But in our galaxy, this solitude is an exception: most stars live in pairs, trios, or even quartets. In these turbulent systems, does dust have a chance to survive long enough to form planets?
This is precisely the question Nicolás Cuello has been tackling since his arrival at the University of Grenoble Alpes in December 2023. As head of the Stellar-MADE team, he combines hydrodynamic simulations, celestial mechanics, and observations from the ALMA radio telescope to unravel the secrets of planet formation in the most turbulent environments in the universe.
Studying how planets form around multiple stars also means looking at our own Solar System from a radically new perspective.
Protoplanetary disks are those immense, thick rings of gas and dust—several times the size of the Solar System—that surround young stars and within which planets gradually form. In a single-star system, this disk evolves in a relatively orderly fashion. But what happens when one or more companion stars disrupt this fragile balance?
The gravitational forces generated by stellar companions can warp, cut through, or fragment the disks. They alter the dynamics of dust grains, accelerating or halting their growth into planetesimals. They can even trigger violent accretion episodes comparable to the outbursts of light from so-called FU Orionis stars—sudden, temporary flashes revealing a sudden influx of material onto the star, radically altering the chemical composition of the disk’s earliest solids.
Far from being purely theoretical, Nicolás Cuello’s research is grounded in very real systems. The triple star system closest to the Sun—comprising the binary star Alpha Centauri and Proxima Centauri—was the subject of a dynamical model published in 2024. The team asked: How much material was once available in the disks around the two Alpha Centauri stars to form planets? This is a practical question, since planets have been confirmed around Proxima Centauri, and others have been proposed in Alpha Centauri, making this neighboring triple star system a fascinating natural laboratory. More recently, the discovery of Earth-like exoplanets in the TOI-2267 binary system opens up a new perspective: Earth-like planets can indeed form in multi-star environments.
The simulations developed by the Stellar-MADE team can now help guide future astronomical observations by identifying which systems are most likely to host planets—a key challenge for missions such as PLATO (ESA), the VLT telescopes, and the ALMA and SKA radio telescopes.
Beyond his publications and international conferences, Nicolás Cuello has made the dissemination of knowledge an integral part of his project. A scientific comic book about exoplanets, translated into four languages, helps share the mysteries of planetary diversity with the public. Presentations at local schools and exhibitions on solarigraphy—which allows people to observe the Sun’s path across the sky—are just some of the initiatives that anchor basic research in everyday life.
After all, understanding how planets form around other stars also gives us a better understanding of why our own Solar System took the form it did, and what it might become in the distant future.
These stellar interactions shape the final structure of planetary systems long before the first planet even exists.
Planetary formation in multiple-star systems remains one of the most open areas of research in contemporary astrophysics. While observations from the ALMA telescope have revolutionized our understanding of protoplanetary disks, many questions remain: How exactly do giant planets form in these perturbed environments? What planetary architectures are possible around triple or quadruple star systems? How can we better detect these exoplanets using next-generation instruments?
The Stellar-MADE team, which is fully operational and involved in major international collaborations (FAUST, exoALMA, PLACID, PLATO), is today one of the few to address these questions in such an integrated manner, combining modeling, observation, and celestial mechanics. As instruments continue to improve in resolution, this approach promises major discoveries in the years to come.
