The Star Formation Rate (SFR) is defined as the rate at which stars are forming in a galaxy and it is usually measured in solar masses per year.

Maths Equations

$$x = {-b \pm \sqrt{b^2-4ac} \over 2a}$$

The surface temperature Teff of stars increases with mass. Massive stars are therefore very bright and release a lot of photons with the capability of ionising hydrogen, the most abundant atom in the ISM. However, massive stars are relatively short lived compared to low mass stars, which means that the number os massive stars is more or less proportional to the instantaneous star formation rate. Their high luminosities make them also easy to find and their ionising