If you ever need to face the centre of our galaxy, just find the Sagittarius constellation. Sagittarius sits in an area of the sky that points to the heart of the Milky Way. And that beating heart is a supermassive black hole 4.6 million times the mass of the Sun. It’s called Sagittarius A* (Sgr A*) and it’s 26,000 light-years from Earth - close enough for us to see the hot gas that swirls around it. Sgr A* affects the orbits of nearby stars, which researchers can track to test things like Einstein’s general theory of relativity. A theory that’s still holding up after more than a century. 💪

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Sources:

1. Zimmermann KA. Sagittarius constellation: Facts about the archer. Space.com. Available at: space.com/21653-sagittarius-constellation.html (Last updated: May 2017; Accessed: Nov. 2021).

2. Boen B. Supermassive black hole Sagittarius A*. NASA. Available at: nasa.gov/mission_pages/chandra/multimedia/black-hole-SagittariusA.html (Last updated: Aug. 2017; Accessed: Nov. 2021).

3. Blome C, Lepo K, Perez Y. Black holes: Sagittarius A* - Identifying our galaxy’s supermassive black hole by tracking stars’ orbits. ViewSpace. Available at: viewspace.org/interactives/unveiling_invisible_universe/black_holes/sagittarius_a (Accessed: Nov. 2021).

4. Taylor Tillman N and Bartels M. Einstein’s theory of general relativity. Space.com. Available at: space.com/17661-theory-general-relativity.html (Last updated: Jun. 2021; Accessed: Nov. 2021).

✍️ Edit: The authors of a recent paper are challenging the idea that Sgr A* is a black hole. They’re proposing that it might be dark matter (‘darkinos’). We’ll have to wait and see.