What's the name of the black hole region that creates the gravitational force holding the Milky Way together?

Sagittarius A*

Explanation:

Holding the Milky Way together requires a massive object that can exert strong gravity over objects that are tens of thousands of light years away. This strong gravity is provided by a supermassive black hole near the center of the galactic bulge; the region occupied by this black hole is called Sagittarius A * (pronounced "A star").