The Bright Beginnings of Planet Formation

With unprecedented detail, a team of astronomers led by MPE have imaged the youngest disks around new-born stars. These glowing, chaotic systems are hotter and heavier than expected, hinting that planets may start forming much earlier than previously thought.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), an international team including scientists from the Max Planck Institute for Extraterrestrial Physics (MPE) has captured the most detailed view so far of the youngest disks around newborn stars — the cradles where planets begin to form.

These Class 0/I protostellar disks, observed at 1.3 mm and 3 mm with a resolution of just 7.5 au, belong to 16 very young systems in star-forming regions such as Taurus, Ophiuchus, and Corona Australis. Most are still deeply embedded in their natal clouds, and thus actively growing by accreting mass from their surroundings.

The disks vary widely in size—from just a few astronomical units up to 100 au—but most are optically thick at millimetre wavelengths, indicating very dense, massive structures. Their dust masses range from roughly 30 to 900 Earth masses, suggesting that several may be marginally unstable under their own gravity. The disks are also much brighter and hotter than older systems, implying additional heating from accretion beyond stellar irradiation.

“These baby disks bridge the gap between the collapsing cloud and the later planet-forming stages,” says Paola Caselli, Director at the Center for Astrochemistry a MPE and one of the main authors of the study. “They provide the missing link for understanding how stars and planets emerge together.”

Early signs of planet formation

Some of the disks encircle binary stars, forming circumbinary disks about 100 au wide. In one such system, the team found evidence that dust grains are already growing, marking the first steps toward planets that could one day orbit two suns—like Tatooine in Star Wars.

Overall, the study shows that young disks are ten times brighter than more evolved ones, mainly because they remain optically thick and massive. Their dense inner regions may already host hidden planet formation that current observations cannot yet reveal.

“Our results show that self-gravity and accretion heating play a major role in shaping the earliest disks,” adds Hauyu Baobab Liu from the Department of Physics at the National Sun Yat-sen University Taiwan. “They influence both the available mass for planet formation and the chemistry that leads to complex molecules.”

Future observations with ALMA and VLA as well as upcoming facilities such as SKAO and ngVLA will help to to peer deeper into these obscured systems, helping to uncover how planets begin to form in the most extreme environments.