The colossal black hole at the centre of the Milky Way hasn’t always been so quiet.
Our galaxy’s supermassive black hole, called Sagittarius A* (Sgr A*), is relatively inactive now, but observations of the gas clouds around it hint that it may have released a powerful blast of X-rays about 205 years ago.
When a black hole puts out an X-ray flare, that radiation can bounce off any gas in the …