GETTING TO THE HEART OF THE (DARK) MATTER

We've mapped it, but the exact nature of dark matter remains elusive. And for most astronomers that's okay

- DR KATIE MACK

In early August, astronomers announced that they had created a map of dark matter from the early Universe. Dark matter is the mysterious, invisible stuff that astronomers say underlies all structure in the cosmos.

Articles reporting the achievement described the innovative observational technique of searching for tiny distortions of patterns in the cosmic microwave background radiation, the backlight of the Universe that originates from the Big Bang. These distortions appear because mass bends space, even if that mass belongs to an invisible kind of matter.

Tellingly, these reports did not delve into the mystery of what dark matter is, or question whether it even exists. For most astronomers, most of the time, dark matter's fundamental nature is entirely beside the point. Despite having never directly detected it, scientists have good reason to believe that dark matter is real.

The first story that everyone tells is that galaxies seem to be rotating at impossible speeds. The stars at the outer edges of spiral galaxies are orbiting around the centre so quickly that if something wasn't providing extra gravity to hold them in, they would have already escaped into intergalactic space, like children flung off a merry-go-round that's spinning too fast.