Scientists from Pune’s IUCAA unearth Malin 1’s cannibalistic nature

A study by a team of scientists from the Inter-University Centre for Astronomy and Astrophysics, located in Pune, shows how Malin 1, the largest known low-surface-brightness galaxy, is quietly cannibalising dwarf galaxies.
Malin 1 has continued to puzzle astronomers since its discovery. In an official statement issued in Pune, IUCAA authorities said that while observing Malin 1 with the Ultraviolet Imaging Telescope (UVIT) onboard AstroSat, the team identified a number of young star-forming clumps in its central region.
Manish Kataria, the lead author of the paper, is a PhD student under the supervision of Prof Kanak Saha at the IUCAA.
“Understanding how giant, low-surface-brightness (GLSB) galaxies like Malin 1 grow is crucial, as their enormous, faint structures challenge existing galaxy formation theories,” Kataria said in the statement.
Since the central region otherwise resembles a quenched galaxy—meaning star formation has largely ceased, the presence of this bright UV clump was surprising and prompted the team to investigate further, the researchers said.
The study uncovers hidden evidence of subtle mergers, shedding light on the galaxy’s ongoing growth. The findings were published in the Astrophysical Journal Letters in December 2025.
According to the official statement, using integral-field spectroscopic observations from the Multi-Unit Spectroscopic Explorer (MUSE) instrument on the Very Large Telescope (VLT) in Chile, the researchers found that the C1 clump is moving roughly 150 km/s faster than the surrounding material and exhibits high turbulence.
“This is unexpected, given that the central region is otherwise quenched, settled, and appears undisturbed. Moreover, the C1 clump appears only in certain velocity channel maps—strongly suggesting it has an external origin, likely a dwarf galaxy being cannibalised,” researchers said in the statement.
Using a detailed stellar population modelling of the MUSE spectra, the team performed a kind of archaeology of the C1 clump and the rest. Beneath the C1 clump lies an old stellar population, more than 6 billion years old, with solar-like metallicity and low alpha-element abundance. After a long quiescent phase, a burst of star formation occurred in the last 200 million years, producing the UV-bright stars in the C1 clump along with extremely metal-poor young stars.
Rapid enrichment
This young population is highly alpha-enhanced, indicating rapid enrichment by core-collapse supernovae. The same pattern is observed in the other clumps. Together, the chemical signatures and high velocities strongly suggest that the C1 clump is the remnant of an infalling dwarf galaxy on a polar orbit. This orbit likely allowed pristine, early-universe–like gas, fuel for making such young stars, to be delivered to Malin 1. The dwarf galaxy was shredded into four parts or more, all sharing very similar ages and chemical properties.
Prof Saha, who supervised the project, recalls noticing the UV clumps several years ago while examining the UVIT data on Malin 1 and speculating that they might be of external origin. “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,” Prof Saha said.