Microwaves from far-out star systems could be tiny diamonds, researchers say

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, an international team has shown that it is likely the microwaves are coming from tiny crystals of carbon, otherwise known as nanodiamonds, inside 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 energised conditions within these disks are ideal for nanodiamonds to form.

The nanodiamonds within protoplanetary disks – that 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.

“In a Sherlock Holmes-like method of eliminating all other causes, we can confidently say the best and likely only candidate capable of producing this microwaves glow is the presence of nanodiamonds around these newly formed stars.”

The team used the Robert C. Byrd Green Bank Telescope in West Virginia and the Australia Telescope Compact Array to examine three young stars emitting AME light.

By studying the infrared light that was coming from the protoplanetary disks surrounding the stars, the team were able to match this with the unique signature that is naturally given off by nanodiamonds.

The team noted that the unique signal came from hydrogenated nanodiamonds, in which the crystalline carbon structure is surrounded by hydrogen-bearing molecules on its surface.

“This is a cool and unexpected resolution of the puzzle of anomalous microwaves radiation,” Dr Greaves said.

“It’s even more interesting that it was obtained by looking at protoplanetary disks, shedding light on the chemical features of early solar systems, including our own.”

– The study, Anomalous microwave emission from spinning nanodiamonds around stars, is published in the journal Nature Astronomy.