Dark matter theories build strongly on curve fitting to get the picture right. MOND does not teach us anything about the underlying physics responsible for the described results. Our alternative with a different angle of approach which was born from establishing a new causal principle for gravity. The resulting discrete model of compressed quanta leads to the equivalent of a galaxy as a Rankine vortex with a central spinning black hole, with stars as co-rotating particles with a rotational velocity dropping inversely proportional to distance. As well as directly interpreting the redshift, not as a Doppler shift in side-faced observations of star rotation, but as an intrinsic property of space, thus only leading to an apparent rotational velocity proportional to distance. And when combined with a drop inversely proportional to distance, this leads to an apparent flat rotation curve. Within that context of a Rankine vortex, we interpreted the BTFR as a friction law in disguise.Hence a new prediction : The rotation speed of stars around black holes, beyond the quasi-solid body distance, will drop proportional to the distance, to be examined with face-on galaxy observations.