The Galactic Centre

The centre of our Milky Way galaxy is located roughly 27 000 light-years away from the Earth in the direction of the constellation of Sagittarius (the Archer). The interstellar dust that fills the Milky Way blocks our direct view of the Milky Way's central region in visible light. However, observations in infrared light of this 900 light-year-wide region have revealed a crowded place housing many thousands of stars.

Also lurking at the heart of the Milky Way is a supermassive black hole known as Sagittarius A* (pronounced "Sagittarius A star"). This brilliant and very compact astronomical radio source has an estimated mass of about 4 million solar masses confined inside a sphere with a diameter of 44 million km — only about 60 solar radii. A recent study involving 16 years of observations that monitored the motions of 28 stars orbiting this massive object has indicated that at least 95% of the mass sensed by the stars within the galactic core must be contained within this supermassive black hole. Flares have also been detected at the position of the black hole, which is thought to be rotating very rapidly.

Harlow Shapley was the first scientist to calculate the Galactic Centre coordinates in 1918 while studying the distribution of the globular clusters. The location of the Galactic Centre in the Southern Hemisphere’s sky is one of the reasons for the presence of ESO telescopes in Chile.