MODELING MATTER DISTRIBUTION IN THE SOLAR NEIGHBORHOOD: A COMPARATIVE STUDY OF DARK MATTER AND MOND HYPOTHESES USING GAIA DR3 DATA

• Main Author: Ali Syaifudin, Muhammad
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/76472
• Institution: Institut Teknologi Bandung

The distribution of positions, velocities, and colors of stars around the Sun is compiled from various selected catalogs, namely Gaia DR3, RAVE6, APOGEE-2 (SDSS), GALAH3, and LAMOST7. Main sequence stars of spectral classes A, F, and G are initially used as tracers to obtain the vertical number density profile and the vertical velocity distribution profile. These profiles are then employed to determine the distribution of dark matter around the Sun using the Poisson equation and the Bahcall model. The tracers are divided into 15 categories based on their colors, with a total of approximately ? 50,000 stars. From the obtained data, three hypotheses describing the distribution of matter and the law of gravity in the Galaxy are tested. These hypotheses are examined by fitting the data using the MCMC (Markov Chain Monte Carlo) method with an implementation of the Affine Invariant written in the Rust programming language. The results from MCMC show that the density of dark matter around the Sun ranges from 0.83 × 10?2M? pc?3 to 6.81 × 10?2M? pc?3, depending on the tracer. Hypothesis testing is performed using the values of the Bayes factor and posterior predictive probability. From this analysis, the conclusion is drawn that a Galaxy model containing a dark matter halo is more likely compared to a model that does not consider dark matter. In the hypothesis that does not involve dark matter, the modified Newtonian dynamics (MOND) proposed by Milgrom is used as the gravitational law. The analysis yields that the acceleration parameter a0 in the MOND hypothesis is (1.18±0.13)× 10?10 m s?2, which is consistent with the previous studies using galactic rotation curves.