Many different types of molecules have been detected on the tiny dust grains in dark nebulae. Small dark nebulae are called Bok globules. ☁ DARK NEBULAEĪ dark nebula (DN), also called an absorption nebula, is an interstellar dust cloud dense enough to obscure the visible wavelengths of light from objects behind it, such as background stars and emission or reflection nebulae. PPNs form before the planetary nebula phase, where the gas is ionized to form an emission nebula. This gas reflects the light of the red giant. Protoplanetary nebulaeĪ protoplanetary nebula (PPN) is a type of reflection nebula that consists of gas ejected from red giant stars late in their life. The energy from the nearby stars is insufficient to ionize the gas in the cloud to create an emission nebula, but is enough to to make the dust visible. ⚟ REFLECTION NEBULAEĪ reflection nebula (RN) is a cloud of interstellar gas and dust that reflects the light of nearby stars. HH objects are commonly found in star-forming (HII) regions. Herbig-Haro objectsĪ Herbig-Haro (HH) object is a type of emission nebula formed when narrow jets of partially ionized gas ejected by newborn stars collide with nearby clouds of gas and dust at high speed. These newborn stars then ionize and light up gas and dust around them. HII regionsĪn HII region is a type of emission nebula consisting of an area within a giant hydrogen gas cloud that has collapsed under gravity to create a star-forming region. Planetary nebulae generate many of the heavier elements in the periodic table as a result of the high temperatures from the expulsion. Planetary nebulaeĪ planetary nebula (PN) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives before they become a white dwarf. Planetary nebulae, HII regions, and Herbig-Haro objects are different types of emission nebulae. The most common source of ionization are high-energy photons emitted from a nearby hot star. An emission nebula (EN) is an ionized gas cloud that emits light of various wavelengths.
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