Astronomers are now Finding Planetary Disks Around the Smallest, Least Massive Stars

Astronomers have been watching planetary systems form around sun-like stars for decades. And now, new observations with the ALMA telescope reveal the same process playing out around the smallest, but most common, stars in galaxy.

The smallest stars in the universe, red dwarf stars, are known to have planetary systems, as shown by the famous examples of Proxima b and the TRAPPIST-1 system. But to date, astronomers have never seen one of these stars in the process of actually forming those planets.

But also to date, astronomers haven’t had ALMA, currently one of the most powerful telescopes in the world. ALMA (the Atacama Large Millimeter/submillimeter Array) is jointly operated by the European Southern Observatory (ESO), by the National Radio Astronomy Observatory (NRAO), and by the National Astronomical Observatory of Japan (NAOJ). The wavelengths of its observations are especially good at observing young planetary systems in the process of forming.

So that’s exactly what Nicolas Kurtovic, a PhD student at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, did, mapping and analyzing six protoplanetary disks around young very low-mass stars (VLMS), which are no bigger than 20% of the mass of the sun.

“Despite the tremendous progress in understanding planet formation during recent decades, we don’t know much on how the planets of the most common stars form,” Kurtovic said.

The observations showed the characteristic ring-like gaps in the disks around some of the young stars, which is a telltale sign of planet formation.

“This pilot study was a challenging task because the VLMS disks are small and possess relatively little material, resulting in feeble signals that are very hard to detect,” said Dr. Paola Pinilla. Pinilla leads a research group at MPIA titled “The Genesis of Planets” in which Kurtovic is a member.

These are crucial and very lucky observations, because the dust – an essential ingredient for seeding the formation of planets – tends to migrate inwards towards a young star, where it’s obliterated (and isn’t much use in building planets). For VLMS, this process can happen up to twice as fast as a sun-like star, shutting down planetary formation before it even starts.

However, these observations show that it’s still quite possible, leading to systems like Proxima b and TRAPPIST-1.

“We still do not know how common planets around red dwarf stars are”, Kurtovic conceded. “However, the longevity of red dwarf planetary systems is intriguing concerning habitability and hypothetical civilizations”, he added.