An image of a dense, star-rich portion of our galaxy, the Milky Way, taken by the Hubble Space Telescope. (Credit: NASA/ESA/Hubble Heritage Team)
SEATTLE — The carbon atoms in your body have likely traveled much farther than you have, possibly hundreds of thousands of light-years into space and back. A new study reveals how galaxies, including our own Milky Way, operate vast recycling systems that send star-forged elements like carbon on epic journeys through space before they eventually become part of planets, and even living things.
Life as we know it depends entirely on elements created inside stars. Nearly all atoms heavier than helium — including the carbon in our DNA, the oxygen we breathe, and the iron in our blood — were forged in stellar furnaces and scattered across space when those stars died. But rather than drifting aimlessly through space, these life-essential elements appear to travel on massive conveyor belt-like currents extending far beyond their galaxies of origin.
Using the Hubble Space Telescope’s Cosmic Origins Spectrograph, lead author Samantha Garza’s international research team studied this galactic recycling system — known as the circumgalactic medium (CGM) — by examining how light from distant quasars was affected by the gas surrounding closer galaxies. They specifically tracked triply-ionized carbon, a form of carbon that has lost three electrons, serving as an important marker of the CGM’s composition and conditions.
“Think of the circumgalactic medium as a giant train station: It is constantly pushing material out and pulling it back in,” explains Garza, a University of Washington doctoral candidate, in a statement. “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 research, published in The Astrophysical Journal Letters, revealed a striking difference between active star-forming galaxies and their quieter counterparts. Among galaxies still actively forming stars, 72% showed significant amounts of carbon in their surrounding halos. In contrast, only 23% of passive galaxies — those that had largely stopped forming stars — displayed similar carbon signatures. In some cases, researchers detected carbon extending almost 400,000 light-years into space, four times the diameter of our own galaxy.
“The implications for galaxy evolution, and for the nature of the reservoir of carbon available to galaxies for forming new stars, are exciting,” says 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!”
This pattern mirrors a similar phenomenon previously discovered for another element, oxygen, suggesting that the relationship between a galaxy’s star formation activity and its recycling system is fundamental to galactic evolution. The presence or absence of these highly ionized elements provides crucial clues about how galaxies maintain their ability to form new stars — and eventually planets that could support life.
Understanding this cosmic recycling system could help explain why galaxies eventually cease forming stars. If the cycle of pushing material out and pulling it back in slows down or breaks down, a galaxy may lose its fuel source for creating new stars.
The team calculated that these galactic halos contain massive amounts of carbon — at least 3 million times the mass of our Sun. This substantial reservoir exists within a radius of about 120,000 light-years from each galaxy’s center, highlighting the vast scale of these galactic recycling systems and their potential role in seeding the universe with the building blocks of life.
Methodology
The researchers analyzed light from nine distant quasars passing through the gaseous halos of eleven star-forming galaxies using Hubble’s Cosmic Origins Spectrograph. By examining how this light was absorbed at specific wavelengths, they could determine the presence and amount of carbon in these galactic recycling systems. They combined these new observations with archival data to study a total of 46 galaxies.
Results
The study revealed a clear distinction between star-forming and passive galaxies’ recycling systems. Of the star-forming galaxies, 21 out of 29 showed significant carbon detection, while only 3 out of 13 passive galaxies showed similar detection. Statistical analysis confirmed this difference was significant with over 99% confidence.
Limitations
While substantial for this type of observation, the sample size of 46 galaxies was relatively small. Some absorption features were saturated, meaning the actual amount of carbon present could be higher than measured. The study focused on galaxies similar in size to the Milky Way, so the findings may not apply to much larger or smaller galaxies.
Discussion and Takeaways
The research reveals a fundamental recycling system operating at galactic scales, where elements created by stars journey far into space before returning to form new stars, planets, and potentially life itself. This process appears crucial for maintaining star formation, and its potential breakdown might explain why galaxies eventually stop forming stars. The study also demonstrates that the atoms in our own bodies are truly cosmic travelers, having likely spent significant time in this vast recycling system before becoming part of Earth.
Funding and Disclosures
The research was conducted using NASA/ESA’s Hubble Space Telescope through various programs, with observations obtained at the Space Telescope Science Institute. The study received funding from NASA and the National Science Foundation.
Publication Information
Published in The Astrophysical Journal Letters, Volume 978, Issue L12, January 2025. Authors include researchers from the University of Washington, National Research Council Herzberg Astronomy and Astrophysics, University of Colorado, North Carolina State University, and University of Victoria.
