A faint and mysterious stream of microwaves emanating from star systems far out in the Milky Way could be caused by tiny diamonds, new research has suggested.

For decades scientists have been able to measure this ‘glow’ of microwave light, dubbed the anomalous microwave emission (AME), coming from a number of regions in the night sky, but have yet to identify its exact source.

In a new study led by researchers at Cardiff University and published today in the journal Nature Astronomy, an international team has shown that it is likely the microwaves are coming from tiny crystals of carbon, otherwise known as nanodiamonds, inside of dust and gas that surrounds newly formed stars.

This collection of dust and gas, known as a protoplanetary disk, is where planets begin to form and contains a whole host of organic molecules. The extremely hot and energized conditions within these disks are ideal for nanodiamonds to form.

Indeed, the nanodiamonds within protoplanetary disks, which are hundreds of thousands of times smaller than a grain of sand, are often found in meteorites on Earth.

“We knew that some type of particle was responsible for the microwave light, but its precise source has been a puzzle since it was first detected nearly 20 years ago,” said lead author of the study Dr Jane Greaves from Cardiff University’s School of Physics and Astronomy.