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Riccardo Della Monica

Publications and source records attributed to Riccardo Della Monica.

25 records · Page 2Linked to original sources
arXiv2023

The Galactic Center as a laboratory for theories of gravity and dark matter

The Galactic Center of the Milky Way, thanks to its proximity, allows to perform astronomical observations that investigate physical phenomena at the edge of astrophysics and fundamental physics. As such, it offers a unique laboratory to probe gravity, where one can not only test the basic predictions of General Relativity, but is also able to falsify theories that, over time, have been proposed to modify or extend General Relativity; to test different paradigms of dark matter; and to place constraints on putative models that have been formulated as alternatives to the standard black hole paradigm in General Relativity. In this review we provide a general overview of the history of observations of the Galactic Center, emphasizing the importance, in particular on the smallest-observable scales, that they had in opening a new avenue to improve our understanding of the underlying theory of gravity in the surrounding of a supermassive compact object.

astro-ph.GA↗
arXiv2023

Narrowing the allowed mass range of ultralight bosons with the S2 star

It is well known that N-body simulations of ultralight bosons show the formation of a solitonic dark matter core in the innermost part of the halo. The scale length of such a soliton depends on the inverse of the mass of the boson. On the other hand, the orbital motion of stars in the Galactic Center depends on the distribution of matter whether be it baryonic or dark, providing an excellent probe for the gravitational field of the region. In this Letter we propose the S-stars in the Galactic Center as a new observational tool, complementary to other astrophysical systems, to narrow down the range of allowed values for an ultralight dark matter candidate boson mass. We built mock catalogs mirroring the forthcoming astrometric and spectroscopic observations of S2, and we used a MCMC analysis to predict the accuracy down to which the mass of an ultralight boson may be bounded, and we showed that, once complementary constraints are considered, this analysis will help to restrict the allowed range of the boson mass. Our analysis forecasts the bound on the mass of an ultralight boson to be $< 10^{-19}$ eV at the 95% of confidence level.

gr-qc↗
arXiv2022

Testing Horndeski gravity with S2 star orbit

We have explored a completely new and alternative way to restrict the parameter space of Horndeski theory of gravity. Using its Newtonian limit, it is possible to test the theory at a regime where, given its complexity and the small magnitude of the expected effects, it is poorly probed. At Newtonian level, it gives rise to a generalized Yukawa-like Newtonian potential which we have tested using S2 star orbit data. Our model adds five parameters to the General Relativity model, and the analysis constrains two of them with unprecedented precision to these energy scales, while only gives an exclusion region for the remaining parameters. We have shown the potential of weak-field tests to constrain Horndeski gravity opening, as a matter of fact, a new avenue that deserves to be further, and deeply, explored near in the future.

gr-qc↗
arXiv2022

Constraining MOdified Gravity with the S2 Star

We have used publicly available kinematic data for the S2 star to constrain the parameter space of MOdified Gravity. Integrating geodesics and using a Markov Chain Monte Carlo algorithm we have provided with the first constraint on the scales of the Galactic Centre for the parameter $α$ of the theory, which represents the fractional increment of the gravitational constant $G$ with respect to its Newtonian value. Namely, $α\lesssim 0.662$ at 99.7% confidence level (where $α= 0$ reduces the theory to General Relativity).

gr-qc↗
arXiv2022

Unveiling the nature of SgrA* with the geodesic motion of S-stars

Despite the huge improvements guaranteed by future GRAVITY observations of the S0-2 star, these will not be able to unveil the fundamental nature, whether black hole or wormhole, of the central supermassive object. Nevertheless, observing stars orbiting closer to the central gravitational source could allow to distinguish between the black hole and wormhole nature of this object at more than 5$σ$. Firstly, we have used publicly available astrometric and spectroscopic measurements of the S0-2 star to constrain the metric around the supermassive object without finding any evidence either favouring or ruling out the wormhole nature. Secondly, we have designed a mock catalogue of future observations of the S0-2 star mirroring the accuracy and precision of GRAVITY. Afterwards, we firstly tested our methodology showing that our procedure recovers the input model, and subsequently we demonstrated that the constraining power of such a dataset is not enough to distinguish between black hole and wormhole. Finally, we built some toy models representing stars orbiting much closer the central object than S0-2. We used these toy models to investigate which are the ideal orbital features and observational strategies to achieve our aim of unveiling the fundamental nature of the central supermassive object, demonstrating that a star with a period of the order of $\sim 5$ years and a pericentre distance of $\sim 5$ AU could identify the nature of the central object at almost 5$σ$ accuracy.

astro-ph.GA↗
arXiv2021

Orbital precession of the S2 star in Scalar-Tensor-Vector-Gravity

We have obtained the first constraint of the parameter space of Scalar-Tensor-Vector-Gravity using the motion of the S2-star around the supermassive black hole at the centre of the Milky Way, and we did not find any serious tension with General Relativity. We used the Schwarzschild-like metric of Scalar-Tensor-Vector-Gravity to predict the orbital motion of S2-star, and to compare it with the publicly available astrometric data, which include 145 measurements of the positions, 44 measurements of the radial velocities of S2-star along its orbit, and the recent measurement of the orbital precession. We employed a Monte Carlo Markov Chain algorithm to explore the parameter space, and constrained the only one additional parameter of Scalar-Tensor-Vector-Gravity to $α\lesssim 0.410$ at 99,7$\%$ confidence level, where $α=0$ reduces this modified theory of gravity to General Relativity.

gr-qc↗