THERE’S A SUPERMASSIVE BLACK HOLE AT THE CENTRE OF THE MILKY WAY

At the centre of the Milky Way, the stars move in strange circles. They hurtle towards a bright radio source, turn in a tight hairpin and then race away again. Tracing the lines of their orbits reveals that they all overlap at a single point, known as Sagittarius A*.

The region is shrouded in a thick cloud of dust and gas, making it difficult to see, but in order to account for these highly elliptical orbits, astronomers have calculated that Sagittarius A* must contain around 4 million solar masses, compressed into a volume with a radius of about 25 million kilometres (15.5 million miles).