The Carina Nebula is 8.500 lightyears away in the constellation Carina. It was discovered by Nicolas-Louis de Lacaille in 1752 from his observatory in the Cape of Good Hope. It is one of the most active star forming regions in our galaxy with over 60.000 young stars and a total mass of over 1 Million M☉ (the solar mass). 
High energy ultraviolet photons from the young stars strip the surrounding hydrogen atoms of their electron. When these free electrons recombine with protons they cascade down the energy levels. As electrons fall from the third to the second lowest energy level, they emit a photon with a wavelength of 656 nanometer, the hydrogen alpha band, visible as deep-red light.
Hydrogen alpha.
The cluster Bochum 11 with the typical red glow of the ionised hydrogen gas.
The hypergiant Eta Carinae, one of the most massive stars in the Milky Way,  and the Keyhole nebula. 
The central region is divided into the Northern Cloud around the cluster Trumpler 14 and the Southern Cloud around the cluster Trumpler 16. This cluster with the hypergiant star Eta Carinae and over 40 O-type stars is the core of the Carina Nebula Complex. 
The image shows 64 O-type stars, 3 Wolf-Rayet stars and the hypergiant Eta Carinae.