Research Student

Mr Indranil Banik

School contact page

Mr Indranil Banik
School of Physics & Astronomy
University of St Andrews
North Haugh
St Andrews KY16 9SS
Scotland, UK

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Room 321
Phone 3142
e-mail ib45

Galaxies are observed to have rotation curves that can't be explained using the existing theory of gravity, which works like Newtonian gravity in the outskirts of galaxies. At least, this is true if one assumes the visible light is a good indicator of where the mass is. Thus, one possibility is that there is additional invisible mass, called dark matter. The other option is to modify the law of gravity, in which case it would need to behave as an inverse distance law rather than the usual inverse square law at very low accelerations. I believe this is much more reasonable, especially considering that the transition acceleration (1.2e-10 m/s^2) is close to that below which a classical gravitational field would have less energy density than the vacuum (dark) energy, suggesting a low-energy quantum correction common in other areas of physics. Thus, I work with Hongsheng Zhao on testing the hypothesis that gravity is indeed modified in this way. This is mostly achieved by investigating the Local Group of galaxies. For this work, I was one of three winners last year of the American Astronomical Society's Duncombe Prize for research by PhD students into dynamical astronomy - I showed that the dark matter + Newtonian gravity picture does not easily account for the observations. I also gave a talk for the AAS this year about the dynamics of Local Group galaxies (second link) where I went through how the observations contain some key features that are expected in modified gravity. Some of the main points are summarised in a press release (first link). I recently made further progress through a SUPA travel grant to visit P. J. E. Peebles in Princeton (USA) and a RAS summer student grant to hire David O'Ryan. This ongoing work suggests that the planes of satellites around the Milky Way and Andromeda could be a natural outcome of modified gravity because it implies a past close interaction between these galaxies, a process we simulated hundreds of times with different parameters.

Press release
Dynamics of Local Group Galaxies: The Case for Modified Gravity