Astronomers have discovered the cosmic equivalent of an overbearing parent dropping by uninvited to a teenagers’ party to make sure they all have enough water. An aging star has been detected for the first time passing through a young star-forming region, delivering elements that could have been crucial for life on Earth to form.
The discovery was initially made in the third data release of Gaia, a satellite that maps the positions of billions of stars and other objects across our galaxy. This long-term view of the sky makes it great for spotting interlopers – stars that are just whizzing through an area but weren’t born there themselves.
Most previously identified interlopers have been fairly young stars, but now astronomers have seen a surprisingly old one moving through a star-forming region where it doesn’t belong. This kind of intergenerational interaction wasn’t thought to ever happen, the team says.
The aging interloper is what’s known as an Asymptotic Giant Branch (AGB) star, which are red giants in their twilight years that have run out of hydrogen fuel and started burning helium instead. And it turns out this visit could have delivered elements that change the course of evolution on stars and planets forming in the region.
AGB stars produce huge amounts of radioactive isotopes like aluminum-26 and iron-60. It’s thought that these isotopes played an important role in making Earth habitable, driving the early heating of the planet’s interior and indirectly contributing to plate tectonics. Without them, Earth might have stayed a lifeless rock.
But how those isotopes got here has remained a mystery. Previous ideas have included a supernova going off very nearby while the Sun was forming, but that raises questions of how the developing solar system survived. The discovery of AGB stars swinging past and sprinkling their elements could explain it more neatly, with the team's models showing the solar system could have captured them from a passing AGB star in high enough amounts to feed the early Earth and other planets.
“Until now, researchers have been skeptical that these old, evolved stars could ever meet young stars that are forming planets, so this discovery reveals much more about the dynamics, relationships and journeys of stars,” said Dr. Richard Parker, lead author of the study. “By showing that AGB stars can meet young planetary systems, we have shown that other sources of aluminum-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.”
To get a better idea of how often this scenario might play out, future work will start off by searching for other examples of aging stars visiting youngsters.
The research was published in the Astrophysical Journal Letters.
Source: University of Sheffield
