February 26, 2024

It’s the cosmic equivalent of an overbearing parent uninviting to a teenage party to make sure they all have enough water, astronomers have found. For the first time, an aging star has been found passing through a young star-forming region, providing elements crucial for the formation of life on Earth.

The discovery was first made in the third data release from the Gaia satellite, which maps the positions of billions of stars and other objects in the Milky Way. This long-term view of the sky is perfect for spotting interlopers—stars that simply whiz past a region without themselves being born there.

Most of the intruders previously found were fairly young stars, but now astronomers have discovered a surprisingly old star passing through a star-forming region where it doesn’t belong. Such intergenerational interactions were previously thought not to occur, the team said.

The aging interloper is a so-called asymptotic giant branch (AGB) star, which is an aging red giant that has exhausted its hydrogen fuel and started burning helium. As it turns out, the visit may have brought elements that altered the evolution of the stars and planets that formed in the region.

AGB stars produce large amounts of radioactive isotopes such as aluminum-26 and iron-60. These isotopes are thought to have played an important role in making Earth habitable, driving early warming of the planet’s interior, and indirectly promoting plate tectonics. Without them, Earth might still be a lifeless rock.

But how these isotopes got here remains a mystery. Previous ideas included a supernova exploding nearby as the sun was forming, but this raised questions about how the developing solar system survived. The discovery that AGB stars wobble and scatter their elements explains this phenomenon more succinctly, and the team’s models suggest that the solar system may have captured enough elements from a passing AGB star to feed early Earth and other planets.

Dr Richard Parker, lead author of the study, said: “Until now, researchers have wondered whether these ancient, evolving stars would encounter young stars that are forming planets, so this discovery reveals more about the dynamics, relationships and journeys of the stars.” “By showing that AGB stars can meet young planetary systems, we have shown that other sources of aluminum-26 and iron-60, such as winds from supermassive stars and supernovae, may not be needed to explain the origin of these chemical elements in the solar system.”

To better understand how often this happens, future work will start by looking for other examples of older stars visiting younger ones.

The study was published in Astrophysical Journal Letters.

source: University of Sheffield