Astronomy is, for the most part, the realm of spectacular images but NASA’s Chandra X-ray Observatory team has been titillating our hearing by turning the data observatories collect from cosmic objects into sonification. The latest to get this treatment is Sagittarius A*, the supermassive black hole at the center of the Milky Way.
Last week, the Event Horizon Collaboration announced the first direct image of the extraordinary object that sits at the heart of our galaxy. And now you can hear it.
Differences in volume track the changes in brightness in the material around the event horizon of Sagittarius A* (pronounced A-star, the star denoting a black hole). The event horizon is the "surface" of the black hole, the boundary of no return. Once something passes it, it can never escape the black hole, including light. Material closer to the black hole – which moves faster than that further out – is represented by higher frequencies.
The sonification is created to give a 3D stereo sound, so that you can hear it straight on and then it moves clockwise and from one ear to the next.
Sagittarius A* is located about 27,000 light-years away. It has a mass equivalent to about 4.1 million Suns. While massive, black holes are incredibly dense. The whole image would fit within the orbit of Mercury. Seeing something so (relatively) small so far away, required a telescope the size of Earth. We don't have one but we can use a clever physics trick to make many different ground-based telescopes around the world work together and act like one, which is what the Event Horizon Telescope collaboration is. Its precision is so high, that it would be equivalent to seeing a donut on the surface of the Moon.