Carbon atoms in our bodies travelled galaxies before returning on cosmic 'conveyor belt'

Carbon is essential to life on Earth. Elements like carbon and oxygen make up around 84% of our bodies. But these elements only exist because stars, like huge furnaces, spawned them into existence during their deaths.

The atoms that make up our bodies might have been made in the stars, but according to new research, they likely took an incredible journey before becoming part of us.

A new study, published in Astrophysical Journal Letters, has confirmed that carbon and other star-formed atoms take an circuitous journey. Instead of drifting randomly through space after being created by dying stars, carbon travels through huge currents before being recycled.

These currents, called the circumgalactic medium, work like giant conveyer belts, pushing material out of galaxies and pulling it back in to be recycled.

The findings suggest that the carbon in our bodies has already been part of stars, planets, moons, and even life forms before becoming part of us.

"Think of the circumgalactic medium as a giant train station: It is constantly pushing material out and pulling it back in," said lead author Samantha Garza, a University of Washington doctoral candidate.

"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."

"The implications for galaxy evolution, and for the nature of the reservoir of carbon available to galaxies for forming new stars, are exciting," said co-author Jessica Werk, UW professor and chair of the Department of Astronomy.

"The same carbon in our bodies most likely spent a significant amount of time outside of the galaxy!"

The research was conducted using the Cosmic Origins Spectrograph on the Hubble Space Telescope.

The spectrograph measured how light from nine distant quasars (ultra-bright sources of light in the cosmos) is affected by the circumgalactic medium of 11 star-forming galaxies. Put simply, researchers measured how light changes as it passes through gas and dust surrounding the galaxies.

The Hubble readings found that the light was being absorbed by a vast amount of carbon in the circumgalactic medium. It even found carbon extending almost 400,000 light years into intergalactic space—that’s four times the diameter of our own galaxy!

"We can now confirm that the circumgalactic medium acts like a giant reservoir for both carbon and oxygen," said Garza. "And, at least in star-forming galaxies, we suggest that this material then falls back onto the galaxy to continue the recycling process."

More research is needed to fully understand how other elements circulate the system and how this process differs between galaxies.

"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," said Garza.

Understanding this could tell us not just when galaxies transition into stellar deserts devoid of young stars, but why.