Sagittarius A* is a compact astronomical radio source at the center of the milky way that was discovered by Karl Jansky, in 1931. The radio source was latter named as Sagittarius A.
Nicolaus Copernicus discovered the Solar System between the year 1473- 1543. He asserted that the Sun is the center of the universe, and planets oscillate around it in perfect circles.
Gravitational Waves were discovered by Albert Einstein in the 1916. His theory of general relativity states that gravity results from how mass warps the fabric of space and time.