1. Observational evidence: The observation of stellar orbits and the dynamics of gas near the centre of the Milky Way strongly support the presence of a massive, compact object with gravitational influence. The observed motions of stars and gas can be accurately explained by the gravitational pull of a supermassive black hole.
2. Absence of alternative explanations: While dark matter is a hypothetical form of matter that interacts only through gravity, there is no known mechanism or particle candidate that could explain the presence of a massive dark matter halo instead of a black hole at the centre of the Milky Way.
3. Consistency with larger-scale observations: The existence of supermassive black holes at the centres of galaxies is now widely accepted and observed across the universe. The Milky Way's supermassive black hole, known as Sagittarius A*, falls within this paradigm, and its properties are consistent with those of other observed black holes.
4. Formation and evolution scenarios: The formation and evolution of supermassive black holes are supported by theoretical models and observations. It is believed that they grow from smaller seed black holes through mergers and accretion of matter. The massive dark matter halo hypothesis lacks a clear explanation for the formation and growth of such a massive object.
While the dark matter halo hypothesis cannot be entirely ruled out, it remains highly speculative and faces several challenges in explaining the observed phenomena at the centre of the Milky Way. The evidence and theoretical considerations currently favour the supermassive black hole scenario as the most likely explanation.
