An eerie echo coming from the Milky Way's supermassive black hole has been detected. It was emitted about 200 years ago when the dark abyss stirred from a state of dormancy, say scientists.
The sound marks a very intense period of activity as gas and dust were gobbled up. Particles drifted into the event horizon - a point of no return where not even light can escape.
When a black hole feeds on this infalling material, bursts of bright X-ray light bounce and echo. It can be turned into sound waves. Corresponding author Dr Frederic Marin, of Strasbourg University in France, said: "It reveals the past awakening of this gigantic object - which is four million times more massive than the Sun."
