Galaxy Rotation Problem: Dark Matter, Modified Gravity or just Baryons?

The deviation of a galaxy from exhibiting a Keplerian curve either indicates the presence of dark matter or the breakdown of Newtonian dynamics. Dark matter still remaining undetected raises a concern whether it exists or not and can the galaxy rotation problem be addressed by modifying the laws of gravity. However, considering the baryonic matter distribution to solve this discrepant behaviour would prove to be a turning point. In this Letter I present the theoretical study regarding the kinematics and dynamics of spiral galaxies by considering the distribution of baryonic matter only. The study of Ultra Diffuse Galaxies (UDGs) and Low Surface Brightness (LSB) galaxies which are considered to be dominated by dark matter has also been taken into account. The distribution of baryonic matter throughout a galaxy and its role in influencing both; the nature of galaxy’s rotation curve as well as the nature of variation of gravitational acceleration throughout a galaxy has been discussed. We will also compare a planetary system with a galaxy to find out why a planetary system exhibits a Keplerian curve whereas a galaxy deviates from it. The study provides explanation for a galaxy’s non-declining rotation curve without considering the presence of dark matter and also without modifying the laws of gravity.