New research suggests that the carbon that serves as the building blocks of life "took the long way around" the galaxy before coming together to make up our bodies here on Earth.
The scientists behind this research discovered that carbon and other elements don't just sit placidly in galaxies after being forged by stars and dispersed by supernova explosions.
Instead, these elements hitch a ride on tremendous cosmic currents called "the circumgalactic medium" that leads them out of their galaxies into intergalactic space and then back in to serve as the building blocks of new stars, planets, moons, and even you.
"Think of the circumgalactic medium as a giant train station: It is constantly pushing material out and pulling it back in," team member and University of Washington doctoral candidate Samantha Garza said in a statement.
"The heavy elements that stars make get pushed out of their host galaxy and into the circumgalactic medium through their explosive supernova deaths, where they can eventually get pulled back in and continue the cycle of star and planet formation."
"Next stop: the Milky Way"
The existence of a circumgalactic medium was first suggested in research published in 2011.
Evidence for this intergalactic conveyor belt was delivered by the Hubble Space Telescope in the form of 500,000 light-year-wide halos of hot ionized oxygen surrounding star-forming galaxies.
This prior research suggested that this train line out of galaxies is powered by galactic outflows launching elements away at high speeds. This material is then dragged back into the galaxy by its gravitational influence.
This large, circulating cloud of material, including hot gases enriched in oxygen, was found to be absent from quiescent galaxies that had ceased star formation.
These new findings build on this initial research by suggesting that not only is the circumgalactic medium rich in oxygen, but it is also packed with carbon, arguably the most important element required for the development of life, albeit at lower temperatures.
It means that the materials that make up your body are intergalactic voyagers that have existed beyond the limits of the Milky Way.
"We can now confirm that the circumgalactic medium acts like a giant reservoir for both carbon and oxygen," Garza said. "And, at least in star-forming galaxies, we suggest that this material then falls back onto the galaxy to continue the recycling process."
Further studying the circumgalactic medium should help scientists better understand how the recycling of the material needed for new stellar bodies eventually subsides, halting star formation.
This could be an important factor in why some star formation dies down in galaxies, which, as stars continue to die, leads to a declining stellar population over cosmic timescales.
"The implications for galaxy evolution, and for the nature of the reservoir of carbon available to galaxies for forming new stars, are exciting," team member and University of Washington researcher Jessica Werk said. "The same carbon in our bodies most likely spent a significant amount of time outside of the galaxy."
The team's research was published Dec. 27 in The Astrophysical Journal Letters.
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