New study reveals Andromeda’s dramatic history

A research team led by the University of Hertfordshire has unveiled the captivating history of Andromeda, our closest neighboring galaxy. Employing cutting-edge modeling techniques, Professor Chiaki Kobayashi and an international group of astrophysicists have deciphered crucial insights into the galaxy’s past through a method known as galactic archaeology. This approach involves analyzing the chemical composition of stars and the evolution of their host galaxy to reconstruct its history.

The forthcoming publication in The Astrophysical Journal Letters and the availability of the study on the arXiv preprint server delve into the elemental abundances within Andromeda, with a particular focus on planetary nebulae—structures formed from the outer layers of dying low-mass stars—and red-giant branch stars.

The analysis uncovers a striking revelation: Andromeda’s formation was far more tumultuous and forceful than that of our Milky Way. Following an initial, intense phase of star formation that gave birth to the galaxy, a secondary layer of stars emerged between 2 billion and 4.5 billion years ago. This secondary burst of star formation was likely ignited by a “wet merger,” which involves the merging of two gas-rich galaxies and triggers a significant wave of star formation.

Previously, scientists had surmised that Andromeda experienced a merger event, based on the positions and motions of individual stars within the galaxy. Professor Kobayashi’s research offers fresh insights into the nature and consequences of such a merger by examining the chemical compositions of stars, shedding light on the genesis of stars and elements throughout Andromeda’s history.

Professor Kobayashi, an esteemed Astrophysics professor at the University of Hertfordshire’s Center for Astrophysics Research, expressed the significance of this approach, saying, “This is a remarkable example of how galactic archaeology can offer novel perspectives on the universe’s history. By scrutinizing the chemical makeup of stars of different ages in Andromeda, we can unravel its past and gain a deeper understanding of its origins.

“While Andromeda, in many respects, resembles our Milky Way—both being similarly-sized spiral disk galaxies—our latest research underscores that its history is marked by more intense and dramatic episodes, with prolific star formation and distinct eras of star birth.”

Professor Kobayashi’s theoretical model predicts two distinct chemical compositions in the stars of Andromeda’s two disk components. One component has an oxygen-to-iron ratio ten times greater, while the other exhibits a similar balance of oxygen and iron. This model has received validation through spectroscopic observations of planetary nebulae and red-giant stars conducted with the James Webb Space Telescope (JWST).

This study represents an ongoing exploration by Professor Kobayashi into the origin of elements in the universe. As she explains, “Oxygen is one of the alpha-elements, produced by massive stars. Others in this category include neon, magnesium, silicon, sulfur, argon, and calcium.

“Planetary nebulae have allowed us to measure oxygen and argon, but Andromeda’s distant location necessitates the use of JWST to measure other elements, including iron. In the coming years, the JWST and large ground-based telescopes will continue to scrutinize Andromeda, further strengthening the weight of these groundbreaking findings.”

Source: University of Hertfordshire

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