A researcher from Sejong University has applied a new theory of gravity, proposed by physicist Erik Verlinde, to predict the central surface density of dark matter in galaxies. This study, published in Physics of the Dark Universe on September 20, suggests that Verlinde’s "emergent gravity" theory can explain certain observed properties of galaxies without requiring the existence of dark matter. The research adds to ongoing efforts to understand whether dark matter is a real substance or if modifications to gravity itself could explain the universe's behavior. Since the 1970s, astronomers have observed that stars in the outer parts of galaxies move much faster than expected based on Newtonian gravity and the visible matter alone. This discrepancy has been interpreted as evidence for dark matter—an invisible form of matter that exerts gravitational pull but does not emit light. However, some scientists have explored alternative explanations by modifying the laws of gravity instead of assuming the presence of dark matter. In 1983, Mordehai Milgrom proposed a modified gravity theory called MOND (Modified Newtonian Dynamics), suggesting that gravity behaves differently at very low accelerations. More recently, Verlinde’s "emergent gravity" theory, introduced in 2016, aims to explain gravitational effects on galactic scales without dark matter. Astronomical observations have revealed a surprising pattern: the "central surface density" of dark matter—defined as the product of the central dark matter density and the size of the central region—remains nearly constant across galaxies, even when their brightness varies by a factor of 400,000. This value typically falls between 90 and 220 M⊙/pc², where M⊙ represents the mass of the Sun and pc² is square parsecs, a unit of area used in astronomy. In the new study, Youngsub Yoon used Verlinde’s theory to calculate what this central surface density would be if dark matter were real. His result, 170 M⊙/pc², closely matches the observed value. Yoon’s study builds on a relation he proposed in 2024 to address a technical challenge in Verlinde’s theory. Unlike Newtonian gravity, which allows the gravitational effects of multiple masses to be simply added, Verlinde’s theory does not support this "superposition principle." Yoon’s proposed relation helped overcome this issue, enabling him to calculate the dark matter density in a way that aligns with observations. He noted that this consistency with real-world data supports the idea that a gravity theory without dark matter can explain galaxy dynamics. Yoon also mentioned that other recent studies, such as those by Professor Kyu-Hyun Chae on binary stars, have also found deviations from Newtonian gravity in weak gravitational fields. He hopes that combining these findings will help test new gravity theories and advance our understanding of the universe.