NASA/ESA/Hubble Heritage Team
Carbon, oxygen and iron only exist on Earth because they were forged in stellar furnaces and later flung into the cosmos when their stars died. In an ultimate act of galactic recycling, planets like Earth are formed by incorporating these star-built atoms into their makeup, be it the iron in Earth’s core, the oxygen in its atmosphere or the carbon in the bodies of Earthlings.
A team of scientists based in the U.S. and Canada recently confirmed that carbon and other star-formed atoms don’t just drift idly through space until they are dragooned for new uses. For galaxies like ours, which are still actively forming new stars, these atoms take a circuitous journey. They circle their galaxy of origin on giant currents that extend into intergalactic space. These currents — known as the circumgalactic medium — resemble giant conveyer belts that push material out and draw it back into the galactic interior, where gravity and other forces can assemble these raw materials into planets, moons, asteroids, comets and even new stars.
The circumgalactic medium is like a giant train station, constantly pushing material out and pulling it back in. 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 carbon in our bodies most likely spent a significant amount of time outside of the galaxy.
In 2011, a team of scientists for the first time confirmed the long-held theory that star-forming galaxies like ours are surrounded by a circumgalactic medium — and that this large, circulating cloud of material includes hot gases enriched in oxygen. Researchers have since determined that the circumgalactic medium of star-forming galaxies also circulates lower-temperature material like carbon.