Task: Sentence Expansion
Input (English): Observations of the star S2 in orbit around Sagittarius A * were used to show the presence of the Milky Way 's central supermassive black hole .
Output (English): Observations of a number of stars orbiting around Sagittarius A * , most notably the star S2 , have been used to provide evidence for the presence of , and produce data about , the Milky Way 's hypothesized central supermassive black hole , and have led some scientists to conclude that Sagittarius A * is beyond any reasonable doubt the site of that black hole .