Three articles – available here, here, and here – published in the journal “Astronomy & Astrophysics” report different aspects of a large study of 86 protoplanetary disks located in three different regions of the Milky Way. Teams of researchers with several shared members used the SPHERE instrument mounted on ESO’s Very Large Telescope (VLT) in Chile as part of the GTO and DESTINYS observation programs. The findings offer a treasure trove of information about planetary formation in the cosmic neighborhood that could lead to advances in current models and aid follow-up studies.
The top image (ESO/C. Ginski, A. Garufi, P.-G. Valegård et al.) shows some of the systems observed and represented here not in scale to appear similar in size.
For years, astronomers have been studying very young stars and protostars surrounded by disks of materials in which they are finding planets in various stages of their formation. The SPHERE instrument was designed in particular to directly observe exoplanets but is also proving valuable in research into planetary formation. In this case, it allowed to observe disks also surrounding stars with half the mass of the Sun, usually too faint to be observed with other instruments.
The GTO and DESTINYS programs exploited the potential of SPHERE precisely to carry out a sort of census of protoplanetary disks in the cosmic neighborhood. The Taurus cloud and Chamaeleon I, part of the Chameleon cloud, are “only” 600 light-years from Earth while the Orion cloud, one of the regions of notable massive star formation, is about 1,600 light-years from Earth.
More data was obtained thanks to another instrument mounted on the VLT, X-shooter, to obtain estimates of the age and mass of the stars object of the study. The ALMA radio telescope, another amazing astronomical instrument that is often used to study protoplanetary disks, offered more information about the amount of dust surrounding some of the stars.
Christian Ginski of the University of Galway, Ireland, and lead author of one of the three new papers, stressed the shift that this large study of 86 forming systems brings compared to studies of individual systems. He also stressed the diversity found among the protoplanetary disks, which show notable differences in the gaps generated by the planets in their formation phase.
That’s echoed by Antonio Garufi of the Arcetri Astrophysical Observatory, Italian National Institute of Astrophysics, lead author of another article, who mentions rings and large cavities dug by planets in formation in some disks where others appear smooth and almost dormant amidst all that activity.
Having some sort of census of protoplanetary disks helps recognize patterns in those systems’ characteristics. For example, stars normally have at least one companion but at least in the Orion cloud, pairs and multiple groups of stars are less likely to have protoplanetary disks. The disks in that region also have an irregular appearance that suggests the presence of massive planets forming that can warp the disks or even cause them to become misaligned.
The three published articles represent only the beginning of the studies of the 86 planetary systems in their formation phase. Follow-up studies can exploit the information collected to examine one of them with the VLT instruments, with ALMA or other instruments, and in the future, with ESO’s ELT (Extremely Large Telescope), now under construction. As models of planetary formation improve, the secrets of those processes will gradually be revealed.
The bottom images show the protoplanetary disks in the Orion cloud (ESO/P.-G. Valegård et al.; IRAS), in the Taurus cloud (ESO/A.Garufi et al.; IRAS), and in Chamaeleon I ( ESO/C. Ginski et al.; ESA/Herschel).
