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One of the biggest mysteries in astrophysics concerns “Dark Matter”. Evidence shows it is the dominant form of mass in the Universe. However, we know little about its composition because it emits little or no light, hence we call it “Dark”. Instead, we infer its presence in galaxies from their dynamics – more mass is required than observed. Following the discovery in the 1970s of the problem of missing mass in galaxies, the “Cold Dark Matter” theory was developed and gives our best understanding of the nature of Dark Matter. An alternative to requiring Dark Matter is that maybe the the force of gravity does not have a simple 1/r2 Newtonian fall off with radius. This has led to the MOdified Newtonian Dynamics (MOND) prescription for the gravitational force law. Recently McGaugh et al (2016) showed that MOND predicts a very tight relationship between the observed gravitational acceleration in galaxies and that expected from their normal matter (the mass discrepancy acceleration relationship or MDAR, see figure below), which they claimed could not be easily accounted for in standard models of galaxy formation and evolution which include Dark Matter. In this project we will test a scenario, the “stable disk model” for galaxy evolution that fits in well with the Cold Dark Matter theory and may account for MDAR.



Dr Aaron Ludlow

ARC Future Fellow

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