Paper of the month:  The Radial Acceleration Relation in Rotationally Supported Galaxies

November 28, 2016 by tiinatimonen

There are also other indications for the presence of this new type of non-baryonic matter, maybe the most famous is the Bullet Cluster, two colliding clusters of galaxies with an evidence of a split between visible matter and dark matter. However, it should be noted that there are alternative theories, which try to justify the observations, like the ones that modify the laws of gravity. The earliest was Milgrom's Modied Newtonian Dynamics (MOND) in 1983, which modies Newton's law. Although these theories fail in describing observations such as the Bullet Cluster mentioned above, they seem to be still fascinating for many scientists.

In this paper the authors study the radial acceleration relation in Rotationally Supported Galaxies. To do this, the authors use the Spitzer Photometry and Accurate Rotation Curves (SPARC) database which includes 175 disk galaxies. The key point is that, given the observed distribution of stars and gas, baryonic mass models can be constructed and the acceleration due to the baryonic components can be determined.

The authors find that the observed centripetal acceleration correlates strongly with that predicted by the baryons for all galaxies of all types (see Fig. 1).

This relation allows to deduce the distribution of dark matter entirely in terms of baryons, hence the baryon and the dark matter mass are strongly coupled.

One possible explanation of this relation could come from new dynamical laws as proposed by MOND models but up to now there is no entirely satisfactory interpretation of the empricial function found by the authors.

Figure 1: The centripetal acceleration observed in rotation curves is plotted against that predicted for the observed distribution of baryons. Nearly 2700 individual data points for 153 SPARC galaxies are shown in grayscale.