Space Archaeology Reveals History of Galaxy Beyond Milky Way

Astronomers have developed a novel method for reconstructing the evolution of distant galaxies, opening a new field of study within astronomy. The research, published Monday in Nature Astronomy, details a technique dubbed “chemical archaeology.” This approach allows scientists to analyze the composition of galaxies beyond our own to understand their formation and growth.

“It’s the first time we’ve used a chemical archaeology method with this level of detail outside of our own galaxy,” says Lisa Kewley, director of the Harvard-Smithsonian Center for Astrophysics. The ability to trace galactic histories through chemical signatures represents a significant advancement in our understanding of the universe.

The team focused their research on NGC 1365, a spiral galaxy located relatively close to the Milky Way. Its disk-like structure is oriented in a way that provides a clear view from Earth. Observations were conducted using the Irenee du Pont telescope at the Las Campanas Observatory in Chile’s Atacama Desert.

Researchers achieved sufficient resolution to isolate and study individual star-forming regions within NGC 1365. By analyzing the light emitted from these regions, they were able to determine the abundance of various elements, particularly oxygen.

Hot, young stars emit intense light that excites nearby gases. Each element in these gases produces bright, narrow lines of light when excited, with oxygen being a key indicator. Astronomers know that galactic centers typically contain more heavy elements, including oxygen, while outer regions have less.

The distribution of oxygen is influenced by factors such as where and when stars formed, supernova explosions, and the flow of gas into and out of the galaxy. By mapping these oxygen patterns in NGC 1365, the researchers compared their findings to simulations of galaxy evolution dating back to shortly after the Big Bang.

Analyzing simulations of approximately 20,000 galaxies, the team identified one that closely matched the observed properties of NGC 1365. This allowed them to deduce the galaxy’s history of mergers and growth. Their analysis suggests that the central region of NGC 1365 formed early on and accumulated a significant amount of oxygen.

Researchers believe that gas in the outer regions of the galaxy accumulated over the following 12 billion years through collisions with smaller dwarf galaxies. They also suggest that the gas in the galaxy’s outer spiral arms may have formed relatively recently, within the last few billion years.

“It’s been very exciting to see our simulations match the data from another galaxy so closely,” says Lars Hernquist, a Harvard researcher. “The astronomical processes we simulate on computers are allowing us to see the evolution of galaxies, like NGC 1365, over billions of years.”

Hernquist adds, “Our study shows that NGC 1365 began as a small galaxy and slowly grew into a giant spiral through multiple mergers with smaller dwarf galaxies.” This finding provides valuable insight into how large galaxies like our own Milky Way are formed.

By studying galaxies like NGC 1365, which shares similarities with the Milky Way, researchers aim to understand the origins of our own galaxy—whether it is typical or unusual—and how we came to have the oxygen we breathe today, Kewley concludes.