Carbon, the essential building block of life, has a remarkable origin story.
Nearly all elements beyond hydrogen and helium, including carbon, oxygen, and iron, are created in stars.
When these stars die in explosive supernovae, they release these elements into space, fueling the formation of planets, moons, and even life itself.
But recent research has revealed that carbon doesn’t just float aimlessly in space—it embarks on a galactic journey that involves being pushed out of and pulled back into its home galaxy.
A team of scientists from the U.S. and Canada has confirmed that carbon and other elements take a complex path through the galaxy, traveling on massive currents known as the circumgalactic medium (CGM).
These currents act like a giant cosmic conveyor belt, circulating materials between galaxies and intergalactic space. This discovery was published on December 27 in The Astrophysical Journal Letters.
“The circumgalactic medium is like a massive train station, constantly sending materials out and pulling them back in,” explained Samantha Garza, a University of Washington researcher and the study’s lead author.
“The carbon in our bodies likely spent a significant amount of time outside the galaxy before returning and becoming part of the planets and life forms we see today.”
The CGM surrounds galaxies like a giant halo, extending hundreds of thousands of light-years into space.
It contains hot gases enriched with oxygen, as well as cooler materials like carbon.
These materials are pushed into the CGM by the explosive deaths of stars and later drawn back into the galaxy by gravity, fueling the formation of new stars and planets.
In this study, scientists used the Hubble Space Telescope’s Cosmic Origins Spectrograph to examine light from nine distant quasars—extremely bright cosmic objects—passing through the CGM of 11 galaxies.
By analyzing how the light was absorbed, they confirmed that large amounts of carbon exist in the CGM, with some carbon extending as far as 400,000 light-years into intergalactic space.
This research sheds light on how galaxies sustain star formation over time. “If the cycle of pushing material out and pulling it back in continues, galaxies can keep forming stars,” said Garza. However, when this process slows or stops, galaxies may transition into “stellar deserts,” where little or no star formation occurs.
Future studies will explore other elements in the CGM and investigate differences between galaxies that are still forming stars and those that have largely stopped. Understanding this cosmic recycling process could reveal not just the life cycle of galaxies but also the fate of our own Milky Way.
