[astroseminar at Sapienza] 24/11/2017 at 16:00: Francesco Sylos Labini

[Elia Battistelli]

Title: Transient spiral arms and galaxy rotation curves
Speaker:  Francesco Sylos Labini
Date: Friday, 24 November 2017
Time: 4:00pm
Location: Aula Conversi, Marconi Building, Dept. of Physics, Sapienza 
University

Abstract:
We describe how a simple class of out of equilibrium mass distributions 
evolve under their self-gravity to produce a quasi-planar spiral 
structure surrounding a virialized core, qualitatively resembling a 
spiral galaxy. The spiral structure is transient, but can survive tens 
of dynamical times, and further reproduces qualitatively noted features 
of spiral galaxies as the predominance of trailing two-armed spirals and 
large pitch angles. The mechanism leads generically to a characteristic 
transition from predominantly rotational motion, in a region outside the 
core, to radial ballistic motion in the outermost parts. Such radial 
motions are excluded in our Galaxy up to 15 kpc, but could be detected 
at larger scales in the future by GAIA. We explore the apparent motions 
seen by external observers of the velocity distributions of our toy 
galaxies, and find that it is difficult to distinguish them from those 
of a rotating disc with sub-dominant radial motions at levels typically 
inferred from observations. These simple models illustrate the 
possibility that the observed apparent motions of spiral galaxies might 
be explained by non-trivial non-stationary mass and velocity 
distributions without invoking a dark matter halo or modification of 
Newtonian gravity. In this scenario the observed phenomenological 
relation between the centripetal and gravitational acceleration of the 
visible baryonic mass could have a simple explanation.

web: https://agenda.infn.it/conferenceDisplay.py?confId=14596