Nebulae
Jan. 27 - Written by Kevin Jie
Nebulae are giant interstellar structures of gas and dust formed from the outer layers of a dying star. These structures can span anywhere from tens to hundreds of lightyears across. A nebula can morph into various patterns and obtain different colors. Similarly to stars, nebulae are unique to one another. Distinguishable by looking at their respective shapes and luminosity. However, shape and color aren’t the only differentiating features. Every nebula has a varying lifetime. In the realm of astronomy on an interstellar scale, the “varying” factor can become a broad term.
It is often mentioned that just like stars in the stellar life cycle, nebulae too can take different paths, diverging lives with alternate endings. Although a fun idea, this isn’t always true. It’s a common misconception that nebulae can only either be stellar or planetary, but the requirements to become one of two are far too vague to be a category on its own. This is why in the astronomy world, nebulae are categorized based on a few more characteristics. Alongside planetary and stellar nebulae, there are also emission, dark, and reflection nebulae.
Emission nebulae are created from the intense radiation from nearby stars. The star floods the gasses in the nebula with so much UV radiation that a process called ionization occurs. This process releases large amounts of energy in the form of light, illuminating the nebula like a lightbulb. Ionization can create a large spectrum of light according to the element it interacts with, but the most common color that results from ionization is red, from hydrogen. This explains why most emission nebulae are red due to the abundance of hydrogen in the universe as a whole.
Sharpless 2-305
An example of an emission nebula.
Not everything in a nebula is subject to ionization. Particles such as ice and snow have highly reflective properties and can exist without evaporating due to the cold environment of space. Objects, like moons, asteroids, and carbon dust can also reflect light depending on the atmosphere or position relative to a star. Nebulae with a large quantity of these objects will glow in areas where the reflections are occurring. These nebulae are called reflection nebulae. Unlike the majority of emission nebulae that radiate red light, reflection nebulae are mainly blue as it’s the most efficient color for reflecting off of the gasses and dust in space.
Gas and dust within a nebula can alter what color it gives off and how bright it shines. However, not all nebulae contain the necessary qualities to illuminate. A dark nebula, also referred to as an absorption nebula, is a collection of interstellar gasses and particles that are so dense that they conceal visible light. Because of a dark nebula’s light obscuring qualities, they often appear as completely black blobs in the night sky. These interstellar shadows are formed from molecular hydrogen, ices, and other space-faring bodies that gather in large groups. These objects end up joining together in massive chains that move as one, creating a dense snake-like formation.
Barnard 59, 65, 66, and 67
Examples of dark nebulae.
The Helix Nebula
A planetary nebula with a white dwarf in the middle.
IC 2118
An example of a reflection nebula
Now is about the time to clear up some misunderstandings and unclear statements. Stellar and planetary nebulae are considered separate categories but with misleading names and unstated requirements. Believe it or not, planetary nebulae have nothing to do with planets. As stated by ESA Hubble, “...despite their name, they have nothing to do with planets.” The primary reason that planetary nebulae are called planetary nebulae is because of how much they look like planetary disks. As for stellar nebulae, the term ‘stellar nebula’ is given to those structures that have the requisite material to form stars.
Space would be a dark abyss, a void with no direction that reaches infinitely in all directions, if not for the stars that light the way. Born from nebulae, which just like everything else, follows its own perpetual cycle. Nebulae are the crowns of the galaxy and jewels of the cosmos.
Astron Original Document -
Nebulae
Jan. 27 - Written by Kevin Jie
Nebulae are giant interstellar structures of gas and dust formed from the outer layers of a dying star. These structures can span anywhere from tens to hundreds of lightyears across. A nebula can morph into various patterns and obtain different colors. Similarly to stars, nebulae are unique to one another. Distinguishable by looking at their respective shapes and luminosity. However, shape and color aren’t the only differentiating features. Every nebula has a varying lifetime. In the realm of astronomy on an interstellar scale, the “varying” factor can become a broad term.
It is often mentioned that just like stars in the stellar life cycle, nebulae too can take different paths, diverging lives with alternate endings. Although a fun idea, this isn’t always true. It’s a common misconception that nebulae can only either be stellar or planetary, but the requirements to become one of two are far too vague to be a category on its own. This is why in the astronomy world, nebulae are categorized based on a few more characteristics. Alongside planetary and stellar nebulae, there are also emission, dark, and reflection nebulae.
The Helix Nebula
A planetary nebula with a white dwarf in the middle.
Emission nebulae are created from the intense radiation from nearby stars. The star floods the gasses in the nebula with so much UV radiation that a process called ionization occurs. This process releases large amounts of energy in the form of light, illuminating the nebula like a lightbulb. Ionization can create a large spectrum of light according to the element it interacts with, but the most common color that results from ionization is red, from hydrogen. This explains why most emission nebulae are red due to the abundance of hydrogen in the universe as a whole.
Sharpless 2-305
An example of an emission nebula.
Not everything in a nebula is subject to ionization. Particles such as ice and snow have highly reflective properties and can exist without evaporating due to the cold environment of space. Objects, like moons, asteroids, and carbon dust can also reflect light depending on the atmosphere or position relative to a star. Nebulae with a large quantity of these objects will glow in areas where the reflections are occurring. These nebulae are called reflection nebulae. Unlike the majority of emission nebulae that radiate red light, reflection nebulae are mainly blue as it’s the most efficient color for reflecting off of the gasses and dust in space.
Gas and dust within a nebula can alter what color it gives off and how bright it shines. However, not all nebulae contain the necessary qualities to illuminate. A dark nebula, also referred to as an absorption nebula, is a collection of interstellar gasses and particles that are so dense that they conceal visible light. Because of a dark nebula’s light obscuring qualities, they often appear as completely black blobs in the night sky. These interstellar shadows are formed from molecular hydrogen, ices, and other space-faring bodies that gather in large groups. These objects end up joining together in massive chains that move as one, creating a dense snake-like formation.
IC 2118
An example of a reflection nebula
Now is about the time to clear up some misunderstandings and unclear statements. Stellar and planetary nebulae are considered separate categories but with misleading names and unstated requirements. Believe it or not, planetary nebulae have nothing to do with planets. As stated by ESA Hubble, “...despite their name, they have nothing to do with planets.” The primary reason that planetary nebulae are called planetary nebulae is because of how much they look like planetary disks. As for stellar nebulae, the term ‘stellar nebula’ is given to those structures that have the requisite material to form stars.
Space would be a dark abyss, a void with no direction that reaches infinitely in all directions, if not for the stars that light the way. Born from nebulae, which just like everything else, follows its own perpetual cycle. Nebulae are the crowns of the galaxy and jewels of the cosmos.
Astron Original Document:
Barnard 59, 65, 66, and 67
Examples of dark nebulae.