A task force manifesto has been published that aims to study how the star formation environment influences the evolution of protoplanetary discs and planetary formation around young stars.
Protoplanetary discs are structures of gas and dust that orbit newly formed stars (called either pre-main sequence stars or protostars) during the very early stages of their evolution. In fact, they generally disperse in less than 10 million years.
Despite their relatively short lifespan, protoplanetary discs are of enormous importance. From the star's point of view, for example, they convey both the accretion of gas from the surrounding environment onto the star itself and the ejection of large amounts of gas in the form of strong winds and rapid, highly collimated jets. Furthermore, as their name suggests, discs are the place where planetary systems can form around young stars.

The evolution of discs, their physical and chemical properties, and their dispersion times can also be influenced by the surrounding environment. This occurs through three phenomena, technically called feedback processes.
In dense stellar environments, typical of star-forming regions in their early evolutionary stages, gravitational interaction between nearby stars can have a strong impact on the morphology, structure, and physical properties of discs. These interactions, called “close encounters”, can induce intense transient accretion phenomena, disperse part of the disc's mass or facilitate the aggregation of solids into planetary embryos.
Another important process is induced by massive stars that may be present in the star-forming region, as these stars radiate enormous amounts of ultraviolet radiation. If a protoplanetary disc is irradiated by UV radiation emitted by nearby massive stars (even up to a few light-years away), part of this radiation is absorbed by the gas and dust in the disc. This triggers a series of processes that alter its thermal structure and chemical properties and, in the most extreme cases, can lead to the rapid dispersion of the disc itself. This phenomenon is known as photoevaporation. A similar process can also be triggered by an intense flow of high-energy particles, such as cosmic rays.

As mentioned, the disc conveys the accretion of gas onto the central star. This accretion process typically ends in less than 3-5 million years. In some cases, however, more evolved systems are observed in which the disc recaptures uncontaminated material from the surrounding environment, triggering a late accretion phenomenon. It is believed that this material may have a significant impact on the planetary formation process within the disc.

The study of environmental effects on the evolution and dispersion of protoplanetary discs is therefore of fundamental importance for understanding, for example, which environments and epochs are most favourable for the formation of planetary systems. To this end, an international team of about 50 astronomers has formed a task force to analyse these effects from every angle: through new high-resolution spatial and spectral observations of individual protoplanetary discs close to us, studies of populations of protoplanetary discs in rich star-forming regions at great distances, and the development of chemical-physical models.

A veritable manifesto of this task force was recently presented in the article ‘The past, present and future of observations of externally irradiated disks,’ published in The Open Journal of Astrophysics. The article illustrates the state of the art of studies on environmental effects in the evolution of protoplanetary disks and strategies for future observations with latest-generation instruments, such as ALMA and the James Webb Space Telescope. Among the participants in the task force is astronomer M. G. Guarcello of INAF – Palermo Astronomical Observatory.

The attached figure (click here to view it in full) shows two images of protoplanetary discs. On the left, the object YSO 294-606 in the Orion Nebula, observed with JWST/NIRCam, which shows no signs of environmental effects. In the panel on the right, however, is the object YSO 244-440 observed with VLT/MUSE. The latter is immersed in a nebula produced by gas “evaporated” from the disc due to the photoevaporation process induced by nearby massive stars.