Survey reveals secrets of planet birth around dozens of stars

planet forming discs
planet forming discs
A team of astronomers including UCL’s Professor Paola Pinilla have conducted one of the largest ever surveys of planet-forming discs, shedding new light on the fascinating and complex process of planet formation.

The research, published in three new papers in the journal Astronomy & Astrophysics, 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.

The stunning images of the discs were captured using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile.

Co-author Dr Paola Pinilla (Mullard Space Science Laboratory at UCL) said: " We are in an era of very powerful telescopes that can reveal many mysteries about planet formation. The images that we are getting are revealing so many substructures that we still do not understand. Unveiling these mysteries is and will be part of our theoretical research in our group on planet formation at MSSL at UCL. " 

Dr Christian Ginski of the University of Galway, Ireland, who was lead author on one of the papers, said: "This is really a shift in our field of study. We’ve gone from the intense study of individual star systems to this huge overview of entire star-forming regions."

To date more than 5,000 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 dustand 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. Dr Ginski said: "Some of these discs show huge spiral arms, presumably driven by the intricate ballet of orbiting planets."

Dr Antonio Garufi, of the Arcetri Astrophysical Observatory, Italian National Institute for Astrophysics (INAF), added: "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."

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.

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.

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 Spectro-Polarimetric High-contrast Exoplanet REsearch instrument ( SPHERE ) mounted on ESO’s VLT. SPHERE’s extreme adaptive optics system corrects for the turbulent effects of Earth’s atmosphere, yielding crisp images of the discs.

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 ) helped the team understand more about the amount of dust surrounding some of the stars.

The spectacular images provide researchers with a treasure trove of data to help unpick the mysteries of planet formation.

Per-Gunnar Valegård, a doctoral candidate at the University of Amsterdam, the Netherlands, who led the Orion study, said: "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."

    Mark Greaves

    m.greaves [at] ucl.ac.uk

    +44 (0)20 3108 9485
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