What is a nebula? In essence, nebulae are concentrations of gas dominated by hydrogen, helium, and stardust. They are crucial structures in our universe, since within them stars are born from the condensation and aggregation of matter. Some nebulae are regions where new stars form, but there are also other nebulae that make up the remains of dead stars or that are ending their days.
With their fantastic appearance, which inevitably dazzles us, there are millions of them in our cosmos and, the name of this mass of celestial, diffuse and luminous cosmic matter, derives from its appearance as a nub.
How many types of nebula are there?
Nebulae, which come in different shapes and sizes, are divided into four fundamental types: reflection nebulae, emission nebulae, absorption nebulae, and planetary nebulae.
Reflection nebulae: These nebulae reflect the light of nearby stars that do not emit enough radiation for the nebula to be illuminated, thus these dust clouds reflect the light of a nearby star and appear bluer than the star because of the way in that starlight is scattered by the nebula’s dust particles. Example: The Pleiades Nebula or Seven Sisters.
Emission nebulae: These nebulae emit their own light as hydrogen atoms are excited by the powerful ultraviolet light from nearby stars; the hydrogen ionizes and generates the glow of the nebula. It is the most common type of nebula. They are visible, as we see, because they emit light thanks to the energy they receive from nearby stars. Example: The Omega or Horseshoe Nebula.
Absorption nebulae: Also called dark nebulae, they are characterized by not emitting light, hides the stars it contains, so they are not directly visible. It was the astronomer William Herschel , who discovered this type of nebula. Example: the Horsehead nebula.
Planetary nebulae: These nebulae shine because the light that comes from the associated star is absorbed by the atoms of the nebula; that is, they are envelopes of gas detached from dying stars that are expelling material into space. These outer layers of gas expand into space, forming a nebula that is usually shaped like a ring or bubble. Example: The Helix Nebula.
Thanks to today’s powerful telescopes and long exposures we can observe beautiful and colorful images that reveal the entire range of colors of the nebula, hydrogen in pink, blue, helium, nitrogen in red, blue-green in oxygen …
Let’s see a sample of the most spectacular nebulae in our cosmos.
