The XVII workshop on Statistical Mechanics and non Perturbative Field Theory

The XVII workshop on Statistical Mechanics and non Perturbative Field Theory will be held in Bari from 13 to 15 December, 2017. My Talk on “Transient Spiral Arms and Rotation Curves” will be on Dec. 14th at 15.10. Program here. 

 

SM&FT2017-HPC

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Riscatto e stop allo sfruttamento per scuole e università pubbliche

radio-popolare

Sfruttamento e riscatto. Le parole della protesta degli studenti e dei ricercatori. Contro l’alternanza scuola lavoro e per la liberazione delle istituzioni pubbliche della formazione. La settimana scorsa ci sono stati cortei in diverse città italiane, altri se ne annunciano per il prossimo 16 dicembre. Per quel giorno il ministero dell’istruzione ha convocato gli “Stati Generali dell’Alternanza”. Che idea della formazione c’è dietro la pratica dell’alternanza scuola-lavoro? E soprattutto quale idea di lavoro risulta da queste pratiche? Perchè in Italia si disinveste dalla ricerca e si lascia la crescita e lo sviluppo nelle mani degli incentivi fiscali, anziché degli investimenti? A Memos oggi ne abbiamo parlato con Giacomo Cossu (Rete della Conoscenza), Franscesco Sylos Labini (fisico, ricercatore e presidente di Roars) e Gianfranco Viesti (economista e curatore della ricerca sugli atenei italiani “L’Università in declino”). La trasmissione si è conclusa con Maria Silvia Fiengo, editrice (Lo Stampatello), che ha raccontato l’iniziativa “Mille libri in omaggio alle scuole”.

Link al PodCast

 

Transient spiral arms and galaxy rotation curves

telescopioSee the live streaming of this talk on Thursday November 30, 10:30 GMT (GMT+1 Summer time).

Abstract

We describe how a simple class of out of equilibrium, rotating and asymmetrical 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. As our models are highly idealized, a detailed comparison with observations is not appropriate, but generic features of the velocity distributions can be identified to be potential observational signatures of such a mechanism. Indeed, 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.

 

Instituto de Astrofísica de Canarias

Transient spiral arms and galaxy rotation curves

Diapositiva126by Francesco Sylos Labini (R)

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.

Transient spiral arms from far out of equilibrium gravitational evolution

sylos-movie-dynamic-frame

We describe how a simple class of out of equilibrium, rotating and asymmetrical 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. As our models are highly idealized, a detailed comparison with observations is not appropriate, but generic features of the velocity distributions can be identified to be potential observational signatures of such a mechanism. Indeed, 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.

Comments: 14 pages, 9 figures, The Astrophysical Journal in press. Two movies of the simulation is available at this link: this http URL
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:1711.01913 [astro-ph.GA]
(or arXiv:1711.01913v1 [astro-ph.GA] for this version)