Category Archives: Highlights on physics papers

The giant arch of galaxies

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The discovery of a massive, nearly symmetric arc of galaxies spanning 300 Mpc has been announced. The size is definitely incompatible with the standard model of cosmology, but

  1. The size of the structure is an important initial piece of information, but it’s not clear how it was measured. It seems difficult to have been measured by determining the two-point correlation function as it would require very extensive volume samples.
  2. The key data to understand compatibility with current models concerns the amplitude of the structure, and measuring the amplitude requires the two-point correlation function (i.e., the conditional density)
  3. According to the standard model, the matter distribution on those scales should be super-homogeneous, resembling an ordered lattice (see figure below). Thus, there should be no structures, as explained in this paper (this is a paper that has never been fully understood in cosmology literature but has been absorbed into condensed matter physics literature).
  4. From our measurements, using the Zipf Mandelbrot law, we deduced a few years ago that larger structures are yet to be observed, so a structure of this magnitude was expected (but the amplitude needs to be measured).
  5. To properly measure the correlation function on those scales, we need to await data from the Euclid satellite, which will arrive in a couple of years.

Il grande arco di galassie

Highlights on physics papers,

E’ stata annunciata la scoperta di un gigantesco arco di galassie quasi simmetrico, che si estende per 300 Mpc . La dimensione è sicuramente incompatibile con il modello standard della cosmologia ma

1) la dimensione della struttura è una prima importante info ma non è chiaro come è stata misurata e mi sembra difficile che sia stata misurata dalla determinazione della funzione di correlazione a due punti come dovrebbe perché per farlo ci vogliono campioni molto estesi in volume

2) Il dato chiave per capire la compatibilità con i modelli attuali riguarda l’ampiezza della struttura e per misurare l’ampiezza ci vuole la funzione di correlazione a due punti

3) Secondo il modello standard a distribuzione della materia a quelle scale dovrebbe essere super-omogenea dunque una specie di reticolo ordinato come nella figura qui sotto e perciò niente strutture come spiegato in questo articolo (questo è un articolo che non è mai stato capito nella letteratura della cosmologia ma invece è stato assorbito nella letteratura della fisica della materia)

4) Dalle nostre misure, utilizzando la legge di Zipf Mandelbrot abbiamo dedotto qualche anno fa che le strutture più grandi devono ancora essere osservate e dunque una struttura così grande noi nel nostro piccolo ce l’aspettavamo (ma bisogna misurare l’ampiezza)

5) Per misurare in maniera corretta la funzione di correlazione su quelle scale dobbiamo aspettare dati del satellite Euclid che arriveranno tra un paio d’anni.

Dark matter disk model

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Title: The Tully-Fisher relation and the Bosma effect

Journal: Monthly Notices of the Royal Astronomical Society, Volume 527, Issue 2, January 2024, Pages 2697–2717, https://doi.org/10.1093/mnras/stad3278

Authors: Francesco Sylos Labini, Giordano De Marzo, Matteo Straccamore, and Sébastien Comerón

In this paper, Sylos Labini and collaborators introduce the dark matter disk model, which provides a new interpretation of the dynamics of disk galaxies. The motivation behind this model stems from the observed inconsistency between the observed flat rotation curves of spiral galaxies and the expected Keplerian decline based on the luminous matter in the galactic disk. Traditionally, this discrepancy has led to the conclusion that massive spherical dark halos dominate the gravitational dynamics of spiral galaxies.

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Il modello “dark matter disk”

Highlights on physics papers

Titolo: The Tully-Fisher relation and the Bosma effect

Journal: Monthly Notices of the Royal Astronomical Society, Volume 527, Issue 2, January 2024, Pages 2697–2717, https://doi.org/10.1093/mnras/stad3278

Autori: Francesco Sylos Labini, Giordano De Marzo, Matteo Straccamore, and Sébastien Comerón

In questo articolo, Sylos Labini e collaboratori introducono il modello del disco di materia oscura, che fornisce una nuova interpretazione della dinamica delle galassie a disco. La motivazione dietro questo modello deriva dall’incoerenza osservata tra le curve di rotazione piatte osservate nelle galassie a spirale e la diminuzione kepleriana attesa basata sulla distribuzione della materia luminosa nel disco galattico. Tradizionalmente, questa discrepanza ha portato alla conclusione che massicci alone sferici di materia oscura dominino la dinamica gravitazionale delle galassie a spirale.

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The Tully-Fisher relation and the Bosma effect

Highlights on physics papers, , , , ,

Francesco Sylos Labini, Giordano De Marzo, Matteo Straccamore, Sébastien Comerón

Monthly Notices of the Royal Astronomical Society, Volume 527, Issue 2, January 2024, Pages 2697–2717, https://doi.org/10.1093/mnras/stad3278

(https://arxiv.org/abs/2310.15673)

We show that the rotation curves of 16 nearby disc galaxies in the THINGS sample and the Milky Way can be described by the NFW halo model and by the Bosma effect at approximately the same level of accuracy. The latter effect suggests that the behavior of the rotation curve at large radii is determined by the rescaled gas component and thus that dark matter and gas distributions are tightly correlated. By focusing on galaxies with exponential decay in their gas surface density, we can normalize their rotation curves to match the exponential thin disc model at large enough radii. This normalization assumes that the galaxy mass is estimated consistently within this model, assuming a thin disc structure. We show that this rescaling allows us to derive a new version of the Tully-Fisher (TF) relation, the Bosma TF relation that nicely fit the data. In the framework of this model, the connection between the Bosma Tully-Fisher (TF) relation and the baryonic TF relation can be established by considering an additional empirical relation between the baryonic mass and the total mass of the disc, as measured in the data.

Our results on Scientific American

Highlights on physics papers,

Slow-moving stars at the Milky Way’s outskirts suggest our galaxy may be far lighter than previously believed, with profound implications for dark matter

…

The Gaia satellite, which was launched in 2013, offers the best-yet test of this simple notion via the spacecraft’s extraordinarily precise measurements of the three-dimensional positions and motions of stars in the Milky Way. But this testing has been a gradual process because the precision of Gaia’s reckoning improves in lockstep with how long it observes its stellar sample. Using Gaia, theoretical physicist Francesco Sylos Labini of the Enrico Fermi Study and Research Center in Italy and his associates saw subtle hints of a decline in the Milky Way’s stellar speeds a few years ago. Those hints became much more obvious in Gaia’s most recent data release, from 2022, which pegs stellar motions with twice the precision of a previous offering from 2018. Such improvements allow astronomers to plot the paths of stars with greater accuracy and out to much farther distances than before.

Read the complete article on Scientific American

Mapping the velocity fields of external galaxies

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Spiral galaxies exhibit a disc-shaped structure with relatively small thickness compared to their radial extent. Typically, these systems maintain a stable configuration, particularly in their innermost regions, where stars and gas follow nearly circular orbits around the galactic center under the influence of the gravitational field generated by the overall matter distribution of the galaxy. However, it is well-established that both in our own galaxy and in external galaxies, the motions of stars and other emitters are not solely confined to circular paths. Instead, they can exhibit additional components, such as radial or vertical motion. These non-circular motions arise due to various factors, including distortions in the mass distribution at large scales (e.g., the presence of spiral arms that represent local over-densities), deformations of the disc shape, or interactions with satellite galaxies. Such non-circular motions are prevalent and leave distinctive imprints on the velocity maps of galaxies.

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