Using multi-epoch observations from the Atacama Large Millimeter/submillimeter Array (ALMA), researchers from the Shanghai Astronomical Observatory of the Chinese Academy of Sciences have conducted the first statistical search for millimeter continuum variability in massive protoclusters, identifying five variable sources among 383 condensations in 22 massive star-forming regions and establishing the first statistical constraints on such variability.

Published recently in The Astrophysical Journal, the findings highlight the unique capability of high-resolution interferometric observations for studying protostellar variability and open new opportunities for time-domain studies of massive star formation.

Variability at millimeter and submillimeter wavelengths is thought to trace changes in the mass accretion process of young stars. However, systematic searches have so far been largely confined to nearby low‑mass star‑forming regions, with evidence in high‑mass protostars remaining scarce.

To bridge this gap, the team analyzed multi‑epoch observations from the ALMA‑QUARKS and MaMMOtH surveys, spanning timescales from a few hours to over two years. Through meticulous image alignment and flux calibration, they achieved high‑precision measurements of continuum emission and performed a statistical analysis of millimeter variability in massive protoclusters.

According to the researchers, the most striking case emerged from the massive star‑forming region I13111–6228. When comparing ALMA observations from 2023 and 2024, they detected a strong brightening signal in the difference image. Further analysis revealed that the source is associated with a hypercompact H II region. In just about one year, its 1.3 mm continuum peak intensity increased by approximately 68%, well beyond the expected observational uncertainties.

This study extends millimeter variability research beyond nearby low‑mass star‑forming regions and into the domain of massive protoclusters, showcasing the unique capability of high‑resolution interferometric observations for probing variability in complex star‑forming environments. Future surveys with larger samples and longer temporal baselines will help reveal how often such variability occurs and what physical mechanisms drive it, the researchers said.

This research was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, and several international collaborative research programs.