Scientists Reveal Malin 1’s Surprising Cannibalism of Dwarf Galaxies

A research team from the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune has uncovered that Malin 1, the largest known low-surface-brightness galaxy, is actively consuming dwarf galaxies. This significant discovery sheds light on the galaxy’s growth and challenges existing theories of galaxy formation.

The study, which utilized the Ultraviolet Imaging Telescope (UVIT) on the Indian satellite AstroSat, revealed unexpected activity in Malin 1’s central region. The team identified several young, star-forming clumps, contradicting the prevailing understanding that this area had ceased star formation. Lead author Manish Kataria, a PhD student under Prof Kanak Saha, emphasized the importance of understanding how giant, low-surface-brightness galaxies like Malin 1 evolve.

Kataria stated, “Understanding how giant, low-surface-brightness (GLSB) galaxies like Malin 1 grow is crucial, as their enormous, faint structures challenge existing galaxy formation theories.” This insight into Malin 1’s development could reshape scientific knowledge about galaxy evolution.

Insights from Spectroscopic Observations

In their investigation, the researchers conducted integral-field spectroscopic observations using the Multi-Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT) in Chile. They found that the C1 clump within Malin 1 is moving approximately 150 km/s faster than surrounding materials, indicating a high level of turbulence. This finding was unexpected given the otherwise stable appearance of the area.

The research team noted, “Moreover, the C1 clump appears only in certain velocity channel maps—strongly suggesting it has an external origin, likely a dwarf galaxy being cannibalised.” This revelation highlights the dynamic interactions occurring within Malin 1, challenging previous assumptions about its inactivity.

The study also revealed that beneath the C1 clump lies an ancient stellar population over 6 billion years old, exhibiting solar-like metallicity but low alpha-element abundance. Following an extended quiescent phase, a surge of star formation occurred in the last 200 million years, resulting in the formation of young, UV-bright stars.

Implications of Rapid Enrichment

The emergence of this young stellar population indicates rapid enrichment from core-collapse supernovae, a phenomenon consistent across other clumps in Malin 1. The chemical signatures and high velocities of the clumps suggest that the C1 clump is a remnant of a dwarf galaxy on a polar orbit. This trajectory likely facilitated the delivery of pristine gas from the early universe, essential for star formation.

Prof Saha, who supervised the project, recalled his initial observations of the UV clumps in Malin 1 several years ago. He speculated on their external origins, which has now been confirmed through the comprehensive analysis provided by Kataria and his team. “Thanks to the integral-field data from MUSE and the careful analysis by Manish, this idea was confirmed: Malin 1 is silently cannibalising smaller dwarf galaxies, a process that is transforming its central region,” said Prof Saha.

The findings from this study are set to be published in the Astrophysical Journal Letters in December 2025, adding to the growing body of knowledge surrounding galaxy formation and evolution. As researchers continue to explore the complexities of Malin 1, this study marks a significant step forward in understanding the intricate processes that govern our universe.