Ellen Phiddian
Cosmos science journalist
The carbon on the Earth – and therefore, in us – probably spent some time outside the Milky Way galaxy before forming our planet, according to a new study.
The study, published in The Astrophysical Journal Letters, finds that after being made inside stars, carbon atoms spend some time circling the galaxy in giant currents.
“The same carbon in our bodies most likely spent a significant amount of time outside of the galaxy!” says co-author Jessica Werk, an astronomer at the University of Washington, USA.
The researchers were using the Hubble Space Telescope to study the circumgalactic medium: a huge cloud of gas that envelops each galaxy.
“Think of the circumgalactic medium as a giant train station: It is constantly pushing material out and pulling it back in,” says co-author Samantha Garza, a doctoral student at the University of Washington.
“The heavy elements that stars make get pushed out of their host galaxy and into the circumgalactic medium through their explosive supernovae deaths, where they can eventually get pulled back in and continue the cycle of star and planet formation.”
Researchers already knew that the circumgalactic medium could host oxygen atoms. This study, which examined the media around 11 star-forming galaxies, found evidence of carbon as well.
“We can now confirm that the circumgalactic medium acts like a giant reservoir for both carbon and oxygen,” says Garza.
“And, at least in star-forming galaxies, we suggest that this material then falls back onto the galaxy to continue the recycling process.”
The team says their findings could help to understand more about how galaxies form – and stop forming – stars.
“The implications for galaxy evolution, and for the nature of the reservoir of carbon available to galaxies for forming new stars, are exciting,” says Werk.
They think it’s possible that a slowing down of the currents in the circumgalactic medium could be the cause of “stellar deserts”, when galaxies stop forming new stars.
“If you can keep the cycle going — pushing material out and pulling it back in — then theoretically you have enough fuel to keep star formation going,” says Garza.
