Bremsstrahlung is also the dominant emission mechanism for H II regions at radio wavelengths.
•
It is very similar to X-rays produced by bombarding metal targets with electrons in X-ray machines (as above) only it is produced by high speed electrons from beta radiation.
Because temperatures are increasing from several hundred to many thousand kelvin during collapse, the processes can be molecular recombination, collision-induced emission, molecular emission, excimers, atomic recombination, radiative attachments of ions, neutral and ion Bremsstrahlung, or emission from confined electrons in voids.
The suggestion at the time was the correlation was due to free-free or Bremsstrahlung emission from ionized gas caused by young hot stars which are formed in these dusty regions.