GRAVITY observes young star feeding from its surrounding disk

A team of astronomers have observed for the first time the columns of matter that build newborn stars. This detailed look inside the young stellar system, using the GRAVITY instrument built at the Max Planck Institute for Extraterrestrial Physics (MPE) and operated at the ESO Very Large Telescopes, revealed that the material is guided by magnetic fields and comes from the disks surrounding these stars, the same disks that eventually give rise to planets. In fact, our Solar System would have gone through this process 5 billion years ago when it formed.

Astronomers believe that young stars acquire matter via their magnetic fields and that this material falls towards the surface at supersonic velocities. The findings, published today in the journal Nature, help astronomers to better understand how stars like our Sun form, and how the disks surrounding these stellar youngsters give rise to planets similar to the Earth.

The team, led by Rebeca Garcia Lopez working at University College Dublin and the Dublin Institute for Advanced Studies in Ireland, looked at one of the closest young stars to us, in the constellation of Hydra, the water snake. The star is a stellar toddler with an age of ‘only’ a few million years. “This star is special because it is located very close to the Earth at only about 200 light years away and the disk of material surrounding the star is directly facing us,” says Rebeca Lopez. “This makes it the ideal candidate to probe how matter from a planet forming disk is channelled on to the stellar surface.”  

Surprisingly, this process has never been directly observed before, despite the fact that it occurs on scales equivalent to a few solar radii. While that may seem like a large distance, the problem is that the nearest young star is so far away that it requires some of the biggest telescopes in the world, and very sophisticated instrumentation, to observe it. The GRAVITY instrument combines the light of four 8-metre ESO telescopes into a super-telescope, with a resolution equivalent to that of a telescope 130 metres in diameter. “With this instrument, one could pick out individual cars on the moon - or the details of the protoplanetary disk surrounding the young star,” says MPE scientist Frank Eisenhauer, who led the development of the GRAVITY instrument.

Such a protoplanetary disk - the birthplace of planets - forms when matter is still being acquired by the young star. Earth-like planets are believed to form in the inner regions of these disks where enormous amounts of energy are released by the accretion process. The astronomers imaged the emission coming from hot gas, and found that its size and velocity matched what theoretical models predicted.

“This is the first time, that observations confirm detailed theories of how a young star accretes material from the disk,” points out Paola Caselli from MPE. “This gives us important clues on how columns of material from the disk are guided by magnetic fields onto the surface of young stars. Moreover, resolving the accretion region will allow us to shed light onto the important mechanisms of irradiation and consequent chemical processing of disk material on its way toward the formation of terrestrial-like planets.”

This research was conducted by an international team led by Irish astronomers with collaborators from France, Portugal, Germany and the European Southern Observatory (ESO), which Ireland recently joined. The GRAVITY collaboration is named after the instrument developed in a collaboration by the Max Planck Institute for Extraterrestrial Physics, LESIA of Paris Observatory / CNRS / Sorbonne Université / Univ. Paris Diderot and IPAG of Université Grenoble Alpes / CNRS, the Max Planck Institute for Astronomy, the University of Cologne, the CENTRA - Centro de Astrofisica e Gravitação, and the European Southern Observatory.