ESA's Gaia satellite spots 'retired stars' passing through young star-forming area

Observation of AGB using Gaia observatory

The interaction between the evolved and young stars took place in a region where scientists believe stars, like our Sun, form. These interloping stars did not form in this particular area, but they were observed traveling across it. 

The ESA's Gaia satellite observatory, which was launched with the purpose of locating billions of stars in our home galaxy, detected this unexpected finding.

“Gaia is revolutionizing our ideas about how stars form, and then subsequently move in the Galaxy. This discovery of an old, evolved star in close proximity to young planet-forming stars is a wonderful example of the power of serendipity in scientific research,” said Christina Schoettler, who found the retired AGB stars in the Gaia data. 

Chemical elements produced by the AGB 

Previous scientific studies have found that these old stars generate high amounts of radioactively unstable chemical elements, including aluminium-26 and iron-60. 

It could be possible that such types of stars delivered these chemical elements to the young solar system while the planets, including Earth, were still forming. And may have had a big role in the early internal heating of our planet's core. Additionally, as per the study, aluminium-26 and iron-60 may have aided plate tectonics on our planet. 

“By showing that AGB stars can meet young planetary systems, we have shown that other sources of Aluminium-26 and Iron-60, such as the winds and supernovae of very massive stars, may not be required to explain the origin of these chemical elements in our Solar System,” explained Parker.  

Following this study, the team plans to look for further interactions between retired stars and nascent star-forming areas to see if this is a typical occurrence. 

The results have been reported in The Astrophysical Journal Letters. 

Study abstract:

Short-lived radioisotopes, in particular 26Al and 60Fe, are thought to contribute to the internal heating of the Earth, but are significantly more abundant in the solar system compared to the interstellar medium. The presence of their decay products in the oldest solar system objects argues for their inclusion in the Sun's protoplanetary disk almost immediately after the star formation event that formed the Sun. Various scenarios have been proposed for their delivery to the solar system, usually involving one or more core-collapse supernovae of massive stars. An alternative scenario involves the young Sun encountering an evolved asymptotic giant branch (AGB) star. AGBs were previously discounted as a viable enrichment scenario for the solar system due to the presumed low probability of an encounter between an old, evolved star and a young pre-main-sequence star. We report the discovery in Gaia data of an interloping AGB star in the star-forming region NGC2264, demonstrating that old, evolved stars can encounter young forming planetary systems. We use simulations to calculate the yields of 26Al and 60Fe from AGBs and their contribution to the long-term geophysical heating of a planet, and find that these are comfortably within the range previously calculated for the solar system.