This is an image of M83 with Hydrogen alpha data added.

Hydrogen alpha is light emitted by a hydrogen atom when an electron that has been "excited" by an input of energy (in the form of a photon) releases that energy and drops back to a lower orbit. Its wavelength is within the range of wavelengths that the human eye sees as red.

In a galaxy, regions of active star formation are usually strong in Ha emission. In this image, the reddish clumps in the spiral arms tell us that stars are forming at a rapid rate. Newly formed hot young stars emit enormous UV radiation that serves to boost electrons in hydrogen gas in the spiral arms to higher energy levels, producing the Ha emissions shown here.

Hot young massive stars live fast and die young - hence the number of supernovae that have been observed in this galaxy. The shockwaves from such exploding stars also serve to initiate the formation of new stars and the cycle starts again.

The Ha data comprises just under 3 hours of exposures added to the LRGB image displayed earlier.

Taken with Planewave CDK 12.5 and SBIG STX16803