Measuring galaxy sizes is essential for understanding how they were formed and evolved across time. However, traditional methods based on l ight concentration or isophotal densities often lack a clear physical meaning. A recent study from Trujillo+20 explores a more physically motivated definition: the radius R 1, where the stellar surface density falls to 1 solar masses per parsec square —roughly the threshold for gas to form stars in galaxies like the Milky Way. In this work, Arjona-Gálvez+25 uses over 1,000 galaxies from several state-of-the-art cosmological simulations (AURIGA, HESTIA

The Universe is not distributed uniformly. Galaxies are arranged in a gigantic cosmic web made of voids, filaments, and galaxy clusters. These filaments act as enormous “cosmic highways” through which matter and galaxies flow toward the densest regions of the Universe. Understanding how these structures influence galaxy evolution is one of the major goals of modern astrophysics. In this work, we analyzed hundreds of thousands of galaxies from the Sloan Digital Sky Survey (SDSS) to study how galaxy density changes around cosmic filaments in the nearby Universe. Our main goal was to determine

Only a handful of observations truly constrain the nature of dark matter, which is why dozens of different physical models are still viable. Several of the most popular alternatives predict that dark matter halos slowly “thermalize” over time, gradually changing shape and expanding until they form a central region of nearly constant density -- a core. This transformation would not occur if the dark matter particles were completely collision-less, as assumed in the standard model. Therefore, the presence or absence of such a core provides a powerful way to distinguish between the standard