A、A satellite in the universe. B、A person in a fairy tale. C、A term in the star sign. D、A supermassive black hole. D新闻中提到。Sagitt

　　(3)Astronomers say they are on course to take the first-ever image of the edge of a black hole known as event horizon early next year. (4)The team will focus on a supermassive black hole called Sagittarius A-star (A* ) at the heart of the Milky Way. More details from Jonathan Web. "The event horizon is the round boundary of a black hole from which nothing including light can escape. But its cloud of gas and dust are sucked and squeezed into it ablaze with energy. It’s this swirling halo that would allow the Event Horizon Telescope to capture the shadow of the black hole itself for the very first time. Based on many simulations of this unexplored frontier, the team behind the telescope has chosen to use very short radio waves which should penetrate the surrounding chaos and review the black hole shadow. "
　　3. What is the news report mainly about?
　　4. What is Sagittarius A* ?