The Milky Way galaxy is a typical spiral galaxy which consists of a black hole at its centre, a barred bulge and a disk which contains spiral arms. The complex structure of the Galaxy makes it extremely difficult and challenging to model its mass distribution, particularly for the Galactic disk which plays the most important role in the dynamics and evolution of the Galaxy. Conventionally an axisymmetric disk model with an exponential brightness distribution and a constant mass-to-light ratio is assumed for the Galactic disk. In order to generate a flat rotation curve, a dark halo also has to be included. Here, by using the recently released Gaia billion-star map, we propose a Galactic disk mass distribution model which is based on the star density distribution rather than the brightness and mass-to-light ratio. The model is characterized by two parameters, a bulge radius and a characteristic length. Using the mass distribution model and solving the Poisson equation for the Galaxy, we obtain a flat rotation curve which reproduces the key observed features with no need for a dark halo.

Enbang Li received his B.Sc, Maters and Ph.D degrees in 1984, 1987 and 1990 respectively from Tianjin University, Tianjin, China. He is currently working at School of Physics, the University of Wollongong, Australia. His research areas include astrophysics, optics and photonics, particularly photonic sensing for biomedical and engineering applications. So far he has authored and co-authored more than 250 technical publications (including papers published in Nature Photonics, Nature Communications) with more than 1,770 SCI citations and an H-index of 23. He also has 35 granted patents.