A team of astronomers led by the Center for Astrophysics | Harvard University and Smithsonian University has achieved the first success in using galactic archeology to uncover the past of galaxies beyond the Milky Way. This method examines the detailed chemical features of the Universe to reveal how galaxies form and evolve over time.
The study was published today. natural astronomyintroduces a new method to study how distant galaxies develop, establishing an emerging field known as “extragalactic archaeology.”
“This is the first time chemical archeology techniques have been used in such detail outside of our galaxy,” said lead author Lisa Curie, professor and director of the Center for Astrophysics at Harvard University. “We want to know how we got here. How did our own Milky Way form and how did we end up breathing the oxygen we breathe now?”
Mapping NGC 1365 using chemical clues
To conduct the study, the researchers used observations from a typhoon survey collected by the Irénée Dupont Telescope at the Las Campanas Observatory. They focused on NGC 1365, a nearby spiral galaxy whose wide disk faces Earth, providing a clear view. This allows scientists to zoom in and analyze individual regions where stars are actively forming.
Young, hot stars emit strong ultraviolet radiation, which activates nearby gas, Curie said. When this happens, elements such as oxygen produce a distinct, thin line of light that can be measured.
Astronomers already know that the centers of galaxies tend to be rich in heavy elements such as oxygen, while the outer regions tend to be poor in them. These patterns are formed by several processes, including when and where stars form and explode as supernovae, how gas moves in and out of galaxies, and their interactions with other galaxies in the past.
Tracing the evolution of galaxies over 12 billion years
By mapping how oxygen levels change across NGC 1365 and comparing those observations to advanced simulations from the Illustris project, the team reconstructed how the galaxy developed over 12 billion years. These simulations track the movement of gas, star formation, black hole activity, and chemical changes from just after the Big Bang to today.
The researchers examined about 20,000 simulated galaxies and identified one that closely matched NGC 1365. This comparison allowed us to piece together the galaxy’s probable growth and merging history.
Their findings indicate that the central region formed early and quickly became oxygen-rich. In contrast, the outer region formed gradually over billions of years through repeated mergers with smaller dwarf galaxies. The outer spiral arms likely formed more recently and were fueled by gas and stars brought in during these interactions.
“It’s very interesting to see that our simulations match data from another galaxy so well,” said Lars Hahnquist, Mallinckrodt Professor of Astrophysics at Harvard University and CfA astronomer. “This study shows that the astronomical processes we modeled on our computers form galaxies like NGC 1365 over billions of years.”
New tools for understanding galaxy formation
Overall, the results suggest that NGC 1365 started out as a relatively small galaxy and gradually grew into a massive spiral through multiple mergers with smaller neighboring galaxies.
Curie said the study highlights how chemical signatures in galactic gas can be used to uncover a galaxy’s past, establishing extragalactic archeology as a powerful new approach.
“This study shows very well how you can generate observations that are directly supported by theory,” she said. “I think it also affects how we work together as theorists and observers, because this project is 50 percent theory and 50 percent observation, and without one you’re missing the other. You need both to reach these conclusions.”
What does this mean for the Milky Way?
Studying galaxies like NGC 1365, which share similarities with the Milky Way, can help astronomers determine whether our galaxy’s history is typical or anomalous and better understand the different paths galaxies take as they evolve.
“Are all spiral galaxies formed in the same way?” Curie asked. “Are there differences in their formation? Where is the oxygen now distributed? Is our Milky Way galaxy different or unique in some way? These are the questions we want to answer.”
