  Recent multi-wavelength ALMA observations of the protoplanetary disk orbiting
around Elias 2-27 revealed a two armed spiral structure. The observed
morphology together with the young age of the star and the disk-to-star mass
ratio estimated from dust continuum emission make this system a perfect
laboratory to investigate the role of self-gravity in the early phases of star
formation. This is particularly interesting if we consider that gravitational
instabilities could be a fundamental first step for the formation of
planetesimals and planets. In this Letter, we model the rotation curve obtained
by CO data of Elias 2-27 with a theoretical rotation curve including both the
disk self-gravity and the star contribution to the gravitational potential. We
compare this model with a purely Keplerian one and with a simple power-law
function. We find that (especially for the $^{13}$CO isotopologue) the rotation
curve is better described by considering not only the star, but also the disk
self-gravity. We are thus able to obtain for the first time a dynamical
estimate of the disk mass of $0.08\pm0.04\,M_{\odot}$ and the star mass of
$0.46\pm0.03\,M_{\odot}$ (in the more general case), the latter being
comparable with previous estimates. From these values, we derive that the disk
is 17$\%$ of the star mass, meaning that it could be prone to gravitational
instabilities. This result would strongly support the hypothesis that the two
spiral arms are generated by gravitational instabilities.
