Final answer:
Most galaxies, including the Milky Way, have a supermassive black hole at their center. This has been confirmed through the study of star orbits near the galactic center, showing they orbit a mass of about 4 million solar masses. The presence of an extensive dark matter halo around the galaxy has also been inferred from these observations.
Step-by-step explanation:
At the center of most galaxies, including our own Milky Way, is a supermassive black hole. Over the course of many years, observations have been conducted using various methods including near-infrared telescopic imaging and radio wave data. The UCLA Galactic Group, utilizing data from the W. M. Keck telescopes among others, determined the orbits of stars near our galaxy's center. Their rapid motions and orbits suggest they are influenced by a massive gravitational presence, leading scientists to conclude the existence of a supermassive black hole with a mass of approximately 4 million solar masses. Additionally, the total mass of our Galaxy has been estimated to be at least 2 × 10¹² solar masses, with a significant portion of this mass attributed to dark matter that extends about 200,000 light-years from the galactic center.