The constellation Sagittarius is characterized as a Centaur drawing back a bow to shoot an arrow. The center of the Milky Way galaxy is an astronomical radio-frequency source in Sagittarius called Sagittarius A*, which is frequently shortened to Sgr A*. This shortened version is pronounced “saj – a – star”. Sgr A-Star is thought to be the location of a supermassive black hole. This is also our strongest source of Hawking radiation.
To understand the significance of all this as it relates to Robot Dawn, you will have to wait until its publication.