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Nebulae
Nebulae
The Carina Nebula (Diffuse Emission)
Stars begin as clouds of gas and dust collecting in space, usually remnants of recently dead or dying stars. These clouds are called nebulae. The four main classifications of nebulae are dark, diffuse reflection, diffuse emission, and planetary nebulae. Over tens of millions of years, the dust and gas that make up these vast clouds condenses into a core that will power a star— and potentially our future society.
Dark Nebulae
Dark Nebulae
Lynds Dark Nebula 183
A dark nebula is defined by its characteristic shadowy appearance. Higher than average proportions of interstellar dust (any non-gaseous materials found in space) prevent light from passing through these nebulae. Although they contain regions of concentrated mass that may lead to the formation of stars, dark nebulae possess very little thermal energy, with an average temperature of 7 to 15 Kelvin. This incredibly low molecular kinetic energy will be key in a dark nebula's transition to becoming a star.
Diffuse Reflection Nebulae
Diffuse Reflection Nebulae
Witch Head Nebula
Despite their compositional similarities with dark nebulae, diffuse reflection nebulae appear very differently because of their close proximity to stars. Reflection nebulae exist in a region far enough away from neighboring stars to avoid the ionization (the process of gaining or losing an electron) of its hydrogen, yet close enough so that they are able to reflect the stars' light. Reflection nebulae are often distinguished by their blue hue resulting from the interaction of the stars' light with the space dust.
Diffuse Emission Nebulae
Diffuse Emission Nebulae
Emission Nebula IC 417
The second form of diffuse nebula differentiates itself by emitting its own light. This occurs because emission nebulae exist closer to their diffusing stars than reflection nebulae. This closer proximity causes the neutral (containing equal quantities of protons and electrons) hydrogen atoms in the nebula to be broken into protons and electrons by the stars' intense UV radiation. As these protons and neutrons are bound back into their original low-energy hydrogen atom, they emit photons (packets of light energy) at a wavelength of 656.3nm, giving the light a red color.
Planetary Nebulae
Planetary Nebulae
The Ring Nebula
The last category of nebula, the planetary nebula, is what directly results from the death of a star up to eight times the size of the sun. After swelling up to become a Red Giant, the star releases a shell of gas leaving behind a dying White Dwarf star. Planetary nebulae are the only category that do not lead directly into the formation of stars, however, they still represent a critical phase in the cycle of solar life.
Protostar Formation
Protostar Formation
Artist's Rendition of Protostar Formation
As a nebula ages, gravity pulls the cloud's mass together towards a central point. As more mass collects, the temperature of the once cold matter begins to rise as pressure builds in accordance with Gay-Lussac's Law, which states that pressure and temperature of a gas are directly related. An increase in temperature means that the molecules inside the core are moving more rapidly, so collisions between particles will occur more often and more energetically. Protostars occur at this intermediate phase between a nebula and a star, in which the core's mass and temperature are still rising. They possess a concentrated, high-mass core as a star does, however, this core is not yet massive enough to foster the fusion reactions necessary to consider the celestial body a star.
Planet Formation
Planet Formation
The Formation of our Solar System
As the core's gravitational pull increases with its gaining mass, the nebula begins to collapse entirely. When it does, excess matter forms a protostellar disk that spins around the protostar. The gas and dust in the disk will be the building blocks for any planets that may surround the future star.
The Birth of a Star
The Birth of a Star
In order to become a star, the core must reach a temperature of approximately 10 million Kelvin so that nuclear fusion can take place. Fusion is the process of combining two or more smaller nuclei together to create a more massive nuclei and release a great amount of energy. The most common type of fusion occurring in stars follows the Proton-Proton (p-p) chain diagram. In step 1, two protons collide, but every so often, one of the protons is ripped apart by nuclear forces into a neutron which bonds to the other proton, forming deuterium. In step 2, another proton collides with the deuterium, forming helium-3. When the helium-3 from step to combines with another helium-3 from another p-p chain, they form helium-4 and release two protons individually. Each step of this process creates an immense amount of energy, and together, they combine with countless more reactions occurring simultaneously in the core to power the star. Once fusion has occurred, the protostar has finally transitioned to becoming a full-fledged star and can continue to burn through its hydrogen supply for billions of years, depending on the star's mass. Fusion reactions are often considered the "holy grail" of energy generation because they produce a continuous flow of easily usable thermal and light energy for long periods of time (in the case of stars). Most remarkably, the fuel source, hydrogen, is nearly limitless in its availability, as it is the most abundant element in the universe.
"I enjoyed this stellar explanation of stars' origins and am eager to learn what will happen next in the lives of these great gaseous giants!"
Worry not Mr. LaQuatra! Continue to the Life of Stars for information on the second chapter of every star's life.
Works Cited
Information:
Brill, Richard. “How Is a Star Born?” Scientific American, Springer Nature, www.scientificamerican.com/article/how-is-a-star-born/.
“Emission Nebula.” Cosmos, Swinburne University of Technology, astronomy.swin.edu.au/cosmos/E/Emission Nebula.
Hosch, William L. “Proton-Proton Cycle.” Encyclopedia Britannica, Encyclopedia Britannica, 25 Jan. 2018, www.britannica.com/science/proton-proton-cycle.
Mathis, John S. “Reflection Nebula.” Encyclopedia Britannica, Brill, Richard. “How Is a Star Born?” Scientific American, Springer Nature, Www.scientificamerican.com/Article/How-Is-a-Star-Born/., www.britannica.com/science/reflection-nebula.
“Protostar.” Las Cumbres Observatory, Las Cumbres Observatory, 2018, lco.global/spacebook/protostar/.
Taylor, David. “A Star Is Born.” The Life and Death of Stars, Northwestern University, June 2012, faculty.wcas.northwestern.edu/~infocom/The Website/birth.html.
“Types of Nebulae.” Astronoo, Astronoo, 1 June 2013, www.astronoo.com/en/articles/type-of-nebulae.html.
Images:
Top Banner: https://www.spacetelescope.org/images/heic0910e/
The Carina Nebula: https://en.wikipedia.org/wiki/Nebula#/media/File:Carina_Nebula_by_ESO.jpg
Lynds Dark Nebula 183: https://apod.nasa.gov/apod/ap171021.html
Witch Head Nebula: https://www.nasa.gov/multimedia/imagegallery/image_feature_1209.html
Emission Nebula IC 417: https://www.noao.edu/image_gallery/html/im1166.html
The Ring Nebula: https://en.wikipedia.org/wiki/Ring_Nebula
Artist's Rendition of Protostar Formation: http://www.sci-news.com/astronomy/protostars-powerful-whirlwinds-04456.html
A Star is Born video: https://www.youtube.com/watch?v=mkktE_fs4NA
The Formation of our Solar System: https://phys.org/news/2015-03-clues-dawn-solar.html
The P-P Chain: http://faculty.wcas.northwestern.edu/~infocom/The%20Website/birth.html
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