All posts by fsyloslab

About fsyloslab

https://francescosyloslabini.info/

Sul ruolo della materia oscura nella fisica contemporanea

syloslabini

 

Alla fine del Settecento l’astronomo britannico William Herschel scoprì casualmente quello che si sarebbe rivelato essere il pianeta Urano. Osservando il suo moto di rivoluzione intorno al Sole si notarono delle anomalie rispetto alle previsioni della legge di gravitazione di Newton. Queste anomalie all’epoca rappresentavano un problema scientifico di primo piano, poiché nell’Ottocento l’astronomia era una scienza modello, che si proponeva di misurare con grande accuratezza le posizioni dei corpi celesti e di interpretare le osservazioni attraverso la teoria di Newton della forza di gravità.  Queste misure, come i relativi calcoli teorici, erano al tempo più precise e accurate di quelle di ogni altra disciplina scientifica.  Per interpretare le anomalie nella traiettoria di Urano, piuttosto che mettere in discussione la correttezza della legge di gravitazione di Newton, si ipotizzò che esse fossero dovute agli effetti gravitazionali di un ottavo pianeta che ancora non era stato osservato. Con questa ipotesi fu introdotta, per la prima volta, la «materia oscura» in astronomia ipotizzata per spiegare alcune differenze tra osservazioni e teoria attraverso i suoi effetti gravitazionali sulla posizione di un pianeta già osservato.

Continue reading Sul ruolo della materia oscura nella fisica contemporanea

Dynamics in the Galactic disk explaining radial and vertical velocities

Context: In our Paper I, by using statistical deconvolution methods, extended kinematics maps of Gaia-DR2 data have been produced in a range of heliocentric distances that are a factor of two to three larger than those analyzed previously by the Gaia Collaboration with the same data. It added the range of Galactocentric distances between 13 kpc and 20 kpc to the previous maps.
Aims: Here, we investigate the dynamical effects produced by different mechanisms that can explain the radial and vertical components of these extended kinematic maps, including a decomposition of bending and breathing of the vertical components. This paper as a whole tries to be a compendium of different dynamical mechanisms whose predictions can be compared to the kinematic maps.
Methods: Using analytical methods or simulations, we are able to predict the main dynamical factors and compare them to the predictions of the extended kinematic maps of Gaia-DR2.
Results: The gravitational influence of Galactic components that are different from the disk, such as the long bar or bulge, the spiral arms, or a tidal interaction with Sagittarius dwarf galaxy, may explain some features of the velocity maps, especially in the inner parts of the disk. However, they are not sufficient in explaining the most conspicuous gradients in the outer disk. Vertical motions might be dominated by external perturbations or mergers, although a minor component may be due to a warp whose amplitude evolves with time. Here, we show with two different methods, which analyze the dispersion of velocities, that the mass distribution of the disk is flared. Despite these partial explanations, the main observed features can only be explained in terms of out-of-equilibrium models, which are either due to external perturbers or to the fact that the disk has not had time to reach equilibrium since its formation.

Comments: 15 pages, 14 figures, accepted to be published in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2001.05455 [astro-ph.GA]
(or arXiv:2001.05455v1 [astro-ph.GA] for this version)

Commento sulle dimissioni del Ministro Fioramonti

logo_testata_roars

Le dimissioni di Fioramonti sono incentrate sull’entità del finanziamento: ma il nesso tra istruzione e sviluppo economico dovrebbe essere la questione cruciale, il rospo, da mettere al centro dell’agenda politica, che separa due visioni economiche e sociali completamente diverse e che invece continua ad essere assente.

Segue su Roars

Intervista su Radio Popolare (minuto 18:40)

Nobel In Physics: A Prize For Outstanding Discoveries Or A Socio-political Recognition?

By Francesco Sylos Labini and Martín López Corredoira .

This year the committee of the Nobel Prize in Physics has gifted the humanity with a poetic touch: “for contributions to our understanding of the evolution of the universe and Earth’s place in the cosmos”. The Nobel Prize in Physics 2019 was awarded for one half to

James Peebles “for theoretical discoveries in physical cosmology” and for the other half to Michel Mayor and Didier Queloz “for the discovery of an exoplanet orbiting a solar-type star”. We might discuss how much outstanding is the latter contribution to Physics, but at least we precisely know which discovery is awarded. On the other hand, we cannot say the same about the particular discovery of cosmology awarded and it does not seem to fulfill Alfred Nobel’s will, which was to endow “prizes to those who, during the preceding year, have conferred the greatest benefit to humankind”.

Continue here