Illustration star forming disk
​Artist’s impression of the streams of hot gas that build up stars. Matter from the surrounding protoplanetary disk, the birthplace of planets, is channeled onto the stellar surface by magnetic fields shocking the surface at supersonic velocity.​​​
​​Dr. Mark A. Garlick​

New insights into the birth of Sun-like stars

Astronomers have for the first time observed a crucial part of the process that our Sun went through when it was no more than a baby. A very young so called protostar was observed gathering material from the disk of matter that surrounds it – the same disk in which planets later will form.  
– This is the first direct observation of a process that our Solar System would have gone through when it formed 5 billion years ago, says Rubén Fedriani, astronomer at Chalmers and member of the Irish-led research team. The study was published in Nature, August 26.
Astronomers believe that young stars acquire matter via their magnetic fields and that this material falls towards the star’s surface at supersonic velocities. The new observational findings, published August 26 in 
Nature (A measure of the size of the magnetospheric accretion region in TW Hydrae in Nature), help astronomers to better understand how stars like our Sun form, and how the disks surrounding these stellar embryos can give rise to planets similar to the Earth. 

The team, led by Rebeca García López 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 “only” one million years old (an age equivalent to that of a human embryo). 

– This star is special because it is located very close to the Earth at only 160 light years away and the disk of material surrounding the star is directly facing us. This makes it the ideal candidate to probe how matter from a planet forming disk is channeled on to the stellar surface, says Rebeca García López. 
García López and her colleagues discovered emissions coming from hot gas and found that the size and velocity of the gas matched what theoretical models had predicted.

– After eliminating all other scenarios, such as the hot gas could originate from matter expelled from the disk or stellar surface (that is from a  wind) there was only one remaining possibility to explain our observations: that the hot gas emission must come from the accretion flows of matter! concludes Alessio Caratti o Garatti, a study co-author from the Dublin Institute for Advanced Studies in Ireland. 

The disk surrounding a young star is known as a protoplanetary disk. Such disks are the birthplace of planets, which can form 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 accreting process. 

– Therefore, understanding how these processes occur is crucial to our understanding of the formation of planets and even the Earth, says Tom Ray from the Dublin Institute for Advanced Studies.

– What we want to do now is to see how the material left over from the star formation process is transformed into planets, says team member, Rubén Fedriani from Chalmers University of Technology in Sweden. Rubén Fedriani’s contribution to the research helped explain some of the physical parameters, the fundamental one being the size of the gas-emitting region. 

More information about the research team 

This research was conducted by an international team led by Irish astronomers with collaborators from France, Portugal, Germany and the European Southern Observatory (ESO). The team is part of the GRAVITY collaboration, named after the instrument they helped develop, which 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). 

This work was in part supported by the European Research Council and Science Foundation Ireland. 

Published: Fri 28 Aug 2020.