As a former planetarium director and a current professor of astronomy, I have shown slides of the 'eagle nebula' and other similar gas complexes such as the 'horse-head nebula' in Orion. These two regions are favourites since they show more than one type of nebula. These regions are called dark, reflection, and emission nebulae. Dark nebulae are made mostly of dust.
Emission nebulae are fluorescent regions of gas glowing in the presence of embedded stars.
Reflection nebulae are cold un-ionized gas. When dark nebulae collide with emission nebulae, features like those noted in the HST image result. The dust pushes its way through the hot gas. Gas along the front edge of the collision compresses and glows hotter. This results in the whitish appearing areas at the edges of the dark 'fingers' of dust.