The dynamics of S-stars and G-sources orbiting a supermassive compact object made of fermionic dark matter

TL;DR

This study compares fermionic dark matter models and black hole models to explain the orbits of stars around Sgr A*, finding that current data slightly favors low-core fermionic DM configurations but cannot conclusively distinguish between models.

Contribution

It introduces a statistical framework using MCMC and Bayes factors to compare fermionic dark matter configurations with black hole models based on stellar orbital data.

Findings

Low-core fermionic DM models are slightly favored for S2 data.

No conclusive preference between models for G-objects.

Differences in orbital predictions are less than 1%, requiring more precise data.

Abstract

Surrounding Sgr A*, a cluster of young and massive stars coexist with a population of dust-enshrouded objects, whose astrometric data can be used to scrutinize the nature of Sgr A*. An alternative to the black hole (BH) scenario has been recently proposed in terms of a supermassive compact object composed of self-gravitating fermionic dark matter (DM). Such horizon-less configurations can reproduce the relativistic effects measured for S2 orbit, while being part of a single continuous configuration whose extended halo reproduces the latest GAIA-DR3 rotation curve. In this work, we statistically compare different fermionic DM configurations aimed to fit the astrometric data of S2, and five G-sources, and compare with the BH potential when appropriate. We sample the parameter spaces via Markov Chain Monte Carlo statistics and perform a quantitative comparison estimating Bayes factors for models that share the same likelihood function. We extend previous results of the S2 and G2 orbital fits for 56 keV fermions (low core-compactness) and show the results for 300 keV fermions (high core-compactness). For the selected S2 dataset, the former model is slightly favoured over the latter. However, more precise S2 datasets, as obtained by the GRAVITY instrument, remain to be analysed in light of the fermionic models. For the G-objects, no conclusive preference emerges between models. For all stellar objects tested, the BH and fermionic models predict orbital parameters that differ by less than 1%. More accurate data, particularly from stars closer to Sgr A*, is necessary to statistically distinguish between the models considered.