Groundbreaking Insights Into Planetary Genesis

This research brings together observations of more than 80 young stars that might have planets forming around them in spectacular discs. This small selection from the survey shows 10 discs from the three regions of our galaxy observed in the papers. Credit: ESO/C. Ginski, A. Garufi, P.-G. Valegård et al.

Astronomers have unveiled new details of planet formation by observing over 80 young stars with ESO’s Very Large Telescope, highlighting the diversity and complexity of planet-forming discs in our galaxy.

In a series of studies, a team of astronomers has shed new light on the fascinating and complex process of planet formation. The stunning images, captured using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile, represent one of the largest-ever surveys of planet-forming discs. The research brings together observations of more than 80 young stars that might have planets forming around them, providing astronomers with a wealth of data and unique insights into how planets arise in different regions of our galaxy.

“This is really a shift in our field of study,” says Christian Ginski, a lecturer at the University of Galway, Ireland, and lead author of one of three new papers published on March 5 in Astronomy & Astrophysics. “We’ve gone from the intense study of individual star systems to this huge overview of entire star-forming regions.”

The Diversity of Cosmic Nurseries

To date, more than 5000 planets have been discovered orbiting stars other than the Sun, often within systems markedly different from our own Solar System. To understand where and how this diversity arises, astronomers must observe the dust- and gas-rich discs that envelop young stars — the very cradles of planet formation. These are best found in huge gas clouds where the stars themselves are forming.

Much like mature planetary systems, the new images showcase the extraordinary diversity of planet-forming discs. “Some of these discs show huge spiral arms, presumably driven by the intricate ballet of orbiting planets,” says Ginski. “Others show rings and large cavities carved out by forming planets, while yet others seem smooth and almost dormant among all this bustle of activity,” adds Antonio Garufi, an astronomer at the Arcetri Astrophysical Observatory, Italian National Institute for Astrophysics (INAF), and lead author of one of the papers.

Planet-forming discs around young stars and their location within the gas-rich cloud of Orion, roughly 1600 light-years from Earth. The mesmerizing images of the discs were captured using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument mounted on ESO’s Very Large Telescope (VLT). In total, the team observed 23 stars in the Orion region, detecting planet-forming discs around 10 of them. The uneven appearance of some of the discs in this region might suggest that massive planets are embedded within them, since these could cause the discs to warp and become misaligned. The background image shows an infrared view of Orion captured by the Infrared Astronomical Satellite. Credit: ESO/P.-G. Valegård et al.; IRAS

Insights From Vast Star-Forming Regions

The team studied a total of 86 stars across three different star-forming regions of our galaxy: Taurus and Chamaeleon I, both around 600 light-years from Earth, and Orion, a gas-rich cloud about 1600 light-years from us that is known to be the birthplace of several stars more massive than the Sun. The observations were gathered by a large international team, comprising scientists from more than 10 countries.

Planet-forming discs around young stars and their location within the gas-rich cloud of Taurus, roughly 600 light-years from Earth. The stunning images of the discs were captured using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument mounted on ESO’s Very Large Telescope (VLT). In total, the team observed 43 stars in the Taurus region, all of which are pictured here (though planet-forming discs were only detected in 39 of these targets). The background image shows an infrared view of Taurus captured by the Infrared Astronomical Satellite. Credit: ESO/A.Garufi et al.; IRAS

The team was able to glean several key insights from the dataset. For example, in Orion they found that stars in groups of two or more were less likely to have large planet-forming discs. This is a significant result given that, unlike our Sun, most stars in our galaxy have companions. As well as this, the uneven appearance of the discs in this region suggests the possibility of massive planets embedded within them, which could be causing the discs to warp and become misaligned.

Planet-forming discs around young stars and their location within the gas-rich cloud of Chamaeleon I, roughly 600 light-years from Earth. The stunning images of the discs were captured using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument mounted on ESO’s Very Large Telescope (VLT). In total, the team observed 20 stars in the Chamaeleon I region, detecting discs around 13. The background image shows an infrared view of Chamaeleon I captured by the Herschel Space Observatory. Credit: ESO/C. Ginski et al.; ESA/Herschel

While planet-forming discs can extend for distances hundreds of times greater than the distance between Earth and the Sun, their location several hundreds of light-years from us makes them appear as tiny pinpricks in the night sky. To observe the discs, the team employed the sophisticated Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE) mounted on ESO’s VLT. SPHERE’s state-of-the-art extreme adaptive optics system corrects for the turbulent effects of Earth’s atmosphere, yielding crisp images of the discs. This meant the team were able to image discs around stars with masses as low as half the mass of the Sun, which are typically too faint for most other instruments available today. Additional data for the survey were obtained using the VLT’s X-shooter instrument, which allowed astronomers to determine how young and how massive the stars are. The Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, on the other hand, helped the team understand more about the amount of dust surrounding some of the stars.

This composite image shows the MWC 758 planet-forming disc, located about 500 light-years away in the Taurus region, as seen with two different facilities.
The yellow color represents infrared observations obtained with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s Very Large Telescope (VLT). The blue regions on the other hand correspond to observations performed with the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner.
These facilities allow astronomers to map how dust is distributed around this and other stars in different but complementary ways. SPHERE captures light from the host star that has been scattered by the dust around it, whereas ALMA registers radiation directly emitted by the dust itself. These observations combined help astronomers understand how planets may form in the dusty discs surrounding young stars.
Credit: ESO/A. Garufi et al.; R. Dong et al.; ALMA (ESO/NAOJ/NRAO)

As technology advances, the team hopes to delve even deeper into the heart of planet-forming systems. The large 39-meter mirror of ESO’s forthcoming Extremely Large Telescope (ELT), for example, will enable the team to study the innermost regions around young stars, where rocky planets like our own might be forming.

For now, these spectacular images provide researchers with a treasure trove of data to help unpick the mysteries of planet formation. “It is almost poetic that the processes that mark the start of the journey towards forming planets and ultimately life in our own Solar System should be so beautiful,” concludes Per-Gunnar Valegård, a doctoral student at the University of Amsterdam, the Netherlands, who led the Orion study. Valegård, who is also a part-time teacher at the International School Hilversum in the Netherlands, hopes the images will inspire his pupils to become scientists in the future.

References
This research was presented in three papers that were recently published in Astronomy & Astrophysics. The data presented were gathered as part of the SPHERE consortium guaranteed time program, as well as the DESTINYS (Disk Evolution Study Through Imaging of Nearby Young Stars) ESO Large Programme.

1. “The SPHERE view of the Chamaeleon I star-forming region. The full census of planet-forming disks with GTO and DESTINYS programs” by C. Ginski, A. Garufi, M. Benisty, R. Tazaki, C. Dominik, A. Ribas, N. Engler, T. Birnstiel, G. Chauvin, G. Columba, S. Facchini, A. Goncharov, J. Hagelberg, T. Henning, M. Hogerheijde, R.G. van Holstein, J. Huang, T. Muto, P. Pinilla, K. Kanagawa, S. Kim, N. Kurtovic, M. Langlois, C. Manara, J. Milli, M. Momose, R. Orihara, N. Pawellek, C. Pinte, C. Rab, T.O.B. Schmidt, F. Snik, Z. Wahhaj, J. Williams and A. Zurlo, 5 March 2024, Astronomy & Astrophysics.
   DOI: 10.1051/0004-6361/202244005

The team is composed of C. Ginski (University of Galway, Ireland; Leiden Observatory, Leiden University, the Netherlands [Leiden]; Anton Pannekoek Institute for Astronomy, University of Amsterdam, the Netherlands [API]), R. Tazaki (API), M. Benisty (Univ. Grenoble Alpes, CNRS, IPAG, France [Grenoble]), A. Garufi (INAF, Osservatorio Astrofisico di Arcetri, Italy), C. Dominik (API), Á. Ribas (European Southern Observatory, Chile [ESO Chile]), N. Engler (ETH Zurich, Institute for Particle Physics and Astrophysics, Switzerland), J. Hagelberg (Geneva Observatory, University of Geneva, Switzerland), R. G. van Holstein (ESO Chile), T. Muto (Division of Liberal Arts, Kogakuin University, Japan), P. Pinilla (Max-Planck-Institut für Astronomie, Germany [MPIA]; Mullard Space Science Laboratory, University College London, UK), K. Kanagawa (Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Japan), S. Kim (Department of Astronomy, Tsinghua University, China), N. Kurtovic (MPIA), M. Langlois (Centre de Recherche Astrophysique de Lyon, CNRS, UCBL, France), J. Milli (Grenoble), M. Momose (College of Science, Ibaraki University, Japan [Ibaraki]), R. Orihara (Ibaraki), N. Pawellek (Department of Astrophysics, University of Vienna, Austria), T. O. B. Schmidt (Hamburger Sternwarte, Germany), F. Snik (Leiden), and Z. Wahhaj (ESO Chile).

2. “The SPHERE view of the Taurus star-forming region. The full census of planet-forming disks with GTO and DESTINYS programs” by A. Garufi, C. Ginski, R. G. van Holstein, M. Benisty, C. F. Manara, S. Pérez, P. Pinilla, Á. Ribas, P. Weber, J. Williams, L. Cieza, C. Dominik, S. Facchini, J. Huang, A. Zurlo, J. Bae, J. Hagelberg, Th. Henning, M. R. Hogerheijde, M. Janson, F. Ménard, S. Messina, M. R. Meyer, C. Pinte, S. P. Quanz, E. Rigliaco, V. Roccatagliata, H. M. Schmid, J. Szulágyi , R. van Boekel, Z. Wahhaj, J. Antichi, A. Baruffolo and T. Moulin, 5 March 2024, Astronomy & Astrophysics.
   DOI: 10.1051/0004-6361/202347586

The team is composed of A. Garufi (INAF, Osservatorio Astrofisico di Arcetri, Italy [INAF Arcetri]), C. Ginski (University of Galway, Ireland), R. G. van Holstein (European Southern Observatory, Chile [ESO Chile]), M. Benisty (Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, France; Univ. Grenoble Alpes, CNRS, IPAG, France [Grenoble]), C. F. Manara (European Southern Observatory, Germany), S. Pérez (Millennium Nucleus on Young Exoplanets and their Moons [YEMS]; Departamento de Física, Universidad de Santiago de Chile, Chile [Santiago]), P. Pinilla (Mullard Space Science Laboratory, University College London, UK), A. Ribas (Institute of Astronomy, University of Cambridge, UK), P. Weber (YEMS, Santiago), J. Williams (Institute for Astronomy, University of Hawai‘i, USA), L. Cieza (Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Chile [Diego Portales]; YEMS), C. Dominik (Anton Pannekoek Institute for Astronomy, University of Amsterdam, the Netherlands [API]), S. Facchini (Dipartimento di Fisica, Università degli Studi di Milano, Italy), J. Huang (Department of Astronomy, Columbia University, USA), A. Zurlo (Diego Portales; YEMS), J. Bae (Department of Astronomy, University of Florida, USA), J. Hagelberg (Observatoire de Genève, Université de Genève, Switzerland), Th. Henning (Max Planck Institute for Astronomy, Germany [MPIA]), M. R. Hogerheijde (Leiden Observatory, Leiden University, the Netherlands; API), M. Janson (Department of Astronomy, Stockholm University, Sweden), F. Ménard (Grenoble), S. Messina (INAF – Osservatorio Astrofisico di Catania, Italy), M. R. Meyer (Department of Astronomy, The University of Michigan, USA), C. Pinte (School of Physics and Astronomy, Monash University, Australia; Grenoble), S. Quanz (ETH Zürich, Department of Physics, Switzerland [Zürich]), E. Rigliaco (Osservatorio Astronomico di Padova, Italy [Padova]), V. Roccatagliata (INAF Arcetri), H. M. Schmid (Zürich), J. Szulágyi (Zürich), R. van Boekel (MPIA), Z. Wahhaj (ESO Chile), J. Antichi (INAF Arcetri), A. Baruffolo (Padova), and T. Moulin (Grenoble).

3. “Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): The SPHERE view of the Orion star-forming region” by P.-G. Valegard, C. Ginski, A. Derkink, A. Garufi, C. Dominik, A. Ribas, J.P. Williams, M. Benisty, T. Birnstiel, S. Facchini, G. Columba, M. Hogerheijde, G. R. van Holstein, J. Huang, M. Kenworthy, C.F. Manara, P. Pinilla, Ch. Rab, R. Sulaiman and A. Zurlo, 5 March 2024, Astronomy & Astrophysics.
   DOI: 10.1051/0004-6361/202347452

The team is composed of P.-G. Valegård (Anton Pannekoek Institute for Astronomy, University of Amsterdam, the Netherlands [API]), C. Ginski (University of Galway, Ireland), A. Derkink (API), A. Garufi (INAF, Osservatorio Astrofisico di Arcetri, Italy), C. Dominik (API), Á. Ribas (Institute of Astronomy, University of Cambridge, UK), J. P. Williams (Institute for Astronomy, University of Hawai‘i, USA), M. Benisty (University of Grenoble Alps, CNRS, IPAG, France), T. Birnstiel (University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Germany [LMU]; Exzellenzcluster ORIGINS, Germany), S. Facchini (Dipartimento di Fisica, Università degli Studi di Milano, Italy), G. Columba (Department of Physics and Astronomy “Galileo Galilei” – University of Padova, Italy; INAF – Osservatorio Astronomico di Padova, Italy), M. Hogerheijde (API; Leiden Observatory, Leiden University, the Netherlands [Leiden]), R. G. van Holstein (European Southern Observatory, Chile), J. Huang (Department of Astronomy, Columbia University, USA), M. Kenworthy (Leiden), C. F. Manara (European Southern Observatory, Germany), P. Pinilla (Mullard Space Science Laboratory, University College London, UK), Ch. Rab (LMU; Max-Planck-Institut für extraterrestrische Physik, Germany), R. Sulaiman (Department of Physics, American University of Beirut, Lebanon), A. Zurlo (Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Chile; Escuela de Ingeniería Industrial, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Chile; Millennium Nucleus on Young Exoplanets and their Moons).