Category Archives: Events

La formazione e l’innovazione

Conferenza  “La formazione e l’innovazione”, 19 aprile alle ore 20,45  a Treviglio (Bg) presso l’Istituto Oberdan in viale M. Merisio 14.

 

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Rischio e previsione. Cosa può dirci la scienza sulla crisi.

trPer l’astrofisico Sylos Labini economisti e politici avrebbero bisogno di adottare una mentalità scientifica perché la scienza può aiutare a capire la crisi economica e può fornire soluzioni originali. Ogni giorno ci viene ripetuto che esistono delle leggi di mercato, la domanda e l’offerta, che condizionanole nostre vite. Queste norme appaiono come ‘naturali’ quanto la legge di gravità, e gli economisti, utilizzando equazioni e modelli matematici, sono percepiti come gli scienziati destinati a comprenderle e a interpretarle. Ma veramente possiamo fidarci delle previsioni dell’economia come di quelle della fisica? Ancora di più: l’economia è davvero una scienza? A questa prospettiva Sylos Labini contrappone le intuizioni offerte dalla fisica moderna prendendo in considerazione i recenti sviluppi sullo studio dei sistemi caotici e complessi.

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Il flagello del neoliberismo

Presentazione del libro di Andrea Ventura “Il flagello del neoliberismo. Alla ricerca di una nuova socialità” che si terrà nell’ambito della manifestazione “Libri Come” all’Auditorium Parco della Musica, venerdì 16 marzo alle 20. Insieme  all’autore e a me interverranno Andrea Filippi,  segretario nazionale Fp Cgil Medici,  Donatella Coccoli, giornalista di Left.

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.