Dr. Mengyuan Xiao 
Geneva observatory, Université de Genève

Unveiling the Origins of Ultra-Massive Galaxies in the Early Universe

Research Focus: 

The early Universe is more extreme than we thought. One of the most remarkable discoveries from the James Webb Space Telescope (JWST) is the unexpected abundance of ultra-massive galaxies – nearly Milky Way mass – already in place less than one billion years after the Big Bang. These galaxies form stars with striking efficiency, raising fundamental questions about the physical processes driving galaxy formation at cosmic dawn. Dr. Mengyuan Xiao has already published several papers reporting the discovery of these massive galaxies.

Dr. Mengyuan Xiao's research focuses on how these colossal systems could have formed so rapidly. At the core of her work lies the investigation into two key questions: How efficiently did these early galaxies form stars and how quickly did they quench? What role did dense cosmic environments play in accelerating their growth? To answer these, Dr. Xiao will combine observational data from the world's most advanced telescopes – including JWST, ALMA (Atacama Large Millimeter/submillimeter Array – the most powerful radio telescope on Earth), and NOEMA (Northern Extended Millimeter Array – a state-of-the-art radio interferometer) – to measure their gas content, star formation activity, and surrounding environment.

Her research will be one of the first systematic studies of early ultra-massive galaxies. It will provide crucial insights into how and when the first generation of massive galaxies assembled, potentially challenging current models and reshaping our understanding of the early Universe

Further Background: 

Mengyuan Xiao earned her B.Sc. in Science of Chinese Materia Medica, then her M.Sc. and Ph.D. in Astrophysics from Nanjing University, where her doctoral thesis received an "Excellent Doctoral Thesis" Award. She also completed a joint Ph.D. program at CEA Saclay, France, via a China Scholarship Council (CSC) Fellowship. In 2023, she became a Postdoctoral Researcher at the Geneva Observatory, University of Geneva.

Her scientific contributions include the 2023 MERAC funding and travel Awards by the Swiss Society for Astrophysics and Astronomy (SSAA), refereeing for Astronomy & Astrophysics, the Astrophysical Journal, act as a reviewer for the French National Research Agency (ANR) 2025, and numerous international conference talks. In 2024, she published a first-author Nature paper detailing the discovery of three massive galaxies.

Beyond research, she champions science communication and mentorship, engaging the public (e.g., explaining the James Webb Space Telescope to the public during the Geneva Observatory’s 250th anniversary open day) and co-organizing colloquia and journal club to foster scientific exchange.