Comparison between an observed galaxy (right) and a simulated galaxy (left) showing similarities in mass and size.
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A new study published in Astronomy & Astrophysics unveils a powerful way to determine the size of dark matter haloes—the massive, invisible structures that host galaxies—by simply measuring how large galaxies appear in deep astronomical images.
Researchers Ignacio Trujillo and Claudio Dalla Vecchia, from the Instituto de Astrofísica de Canarias (IAC) and the Universidad de La Laguna (ULL), demonstrate that galaxy size can serve as a precise proxy for halo size, offering measurements up to six times more accurate than previous methods.
Using the cutting-edge EAGLE cosmological simulations, the team showed that a physically motivated definition of galaxy size, based on where star formation naturally ceases, correlates extremely tightly with halo size. This breakthrough opens a new path for mapping dark matter in the universe.
“We are entering a new era of deep astronomical observations, where the faintest edges of galaxies become visible,” said Ignacio Trujillo. “These observations are powerful tools, allowing us to probe the properties of the dark matter haloes that shape galaxies, with unprecedented accuracy.”
“Numerical simulations have reached the point where they can robustly predict how galaxy sizes relate to their haloes,” added Claudio Dalla Vecchia. “This predictive power gives us confidence that we can use observational data to infer the invisible dark matter structures with remarkable precision.”
The findings suggest that by analyzing deep imaging surveys, astronomers will be able to chart the distribution and properties of dark matter haloes across cosmic time more accurately than ever before.
Article: and "An accurate measure of the size of dark matter haloes using the size of galaxies", A&A, 704, A312 (2025). DOI: https://doi.org/10.1051/0004-6361/202556635
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