RRI study may redefine how the mass of the halo around galaxies is measured

A new research study from Raman Research Institute (RRI) has revealed that contributions from matter in the intergalactic medium (IGM) may be affecting measurements of the diffuse envelope surrounding a galaxy. According to the Department of Science and Technology, the study has far-reaching implications, given that the envelope holds power to make or break galaxies and measuring the mass is crucial for tracing how galaxies form. A galaxy evokes images of dust and stars sparkling within beautiful spirals. But beyond the galaxy’s outskirts lurks a diffuse, ghostly halo spreading out as far as 10 to 20 times the size of the galaxy. “Most of the galaxy’s mass lies beyond the stars in this halo, composed of the mysterious dark matter- the invisible glue keeping the universe together- and gas. The gaseous component of the halo is called the circumgalactic medium or CGM. The region outside the CGM, constitutes the IGM,” the department said. Mapping the distribution of gas in CGM is essential because the CGM connects the galaxy to the cosmic web- the filamentary scaffolding pervading the universe. In doing so, the CGM plays a critical role in galaxy evolution by controlling the inflow of gas into the galaxy and outflow from it. By measuring the amount of highly ionized oxygen- oxygen with five of its electrons stripped off- contained in the CGM, astronomers estimate the mass of the CGM. This new research from RRI uses models to suggest that a lot of the gas attributed to the CGM could be coming from the IGM. Published - December 25, 2025 09:31 pm IST

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