The terminology used in the documentary "How the Universe Works" might have caused some confusion. The term "Sagittarius A star" refers to the object at the center of our Milky Way galaxy, but it is not actually a star. It is, in fact, a supermassive black hole called Sagittarius A* (pronounced "Sagittarius A-star").
Here's some clarification:
Supermassive Black Hole: Sagittarius A* (Sgr A*) is a supermassive black hole located at the center of the Milky Way galaxy. Supermassive black holes are characterized by their enormous mass, typically ranging from hundreds of thousands to billions of times the mass of our Sun. They are believed to exist at the centers of most galaxies, including the Milky Way.
"Sagittarius A*": The name "Sagittarius A*" is derived from its location in the Sagittarius constellation, where it appears as a bright radio source. The asterisk (*) is used to distinguish it from the surrounding stars and indicate its nature as a black hole.
Not a Star: Although the term "Sagittarius A star" is occasionally used, it is technically incorrect. A black hole is not a star, but rather an object formed from the collapse of a massive star's core. It lacks the structure and properties of a star, such as nuclear fusion or a solid surface.
To summarize, Sagittarius A* is a supermassive black hole situated at the center of our galaxy, the Milky Way. It is not a star but was given the name "Sagittarius A*" due to its location in the Sagittarius constellation. The confusion may arise from the documentary's use of the term "star" in conjunction with Sagittarius A*, but it is important to understand that it refers to a black hole, not an actual star.