Anomalous microwave emission from spinning nanodiamonds around stars
  Several interstellar environments produce 'anomalous microwave emission',
with brightness-peaks at tens-of-gigahertz frequencies. The emission's origins
are uncertain - rapidly-spinning nano-particles could emit electric-dipole
radiation, but polycyclic aromatic hydrocarbons proposed as the carrier are now
found not to correlate with Galactic signals. The difficulty is to identify
co-spatial sources over long lines of sight. Here we identify anomalous
microwave emission in three proto-planetary discs. These are the only known
systems that host hydrogenated nano-diamonds, in contrast to very common
detection of polycyclic aromatic hydrocarbons. Spectroscopy locates the
nano-diamonds close to the host-stars, at physically-constrained temperatures.
Developing disc models, we reproduce the emission with diamonds 0.75-1.1
nanometres in radius, holding less than or equal to 1-2 per cent of the carbon
budget. The microwave-emission:stellar-luminosity ratios are approximately
constant, allowing nano-diamonds to be ubiquitous but emitting below detection
thresholds in many star-systems. This can unify the findings with similar-sized
diamonds found within solar system meteorites. As nano-diamond spectral
absorption is seen in interstellar sightlines, these particles are also a
candidate for generating galaxy-scale anomalous microwave emission.
