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Chapter 11 Summary, www.cengage.com/resource_uploads/static_resources/0495015784/11457/chapter11.html.

How Stars Form - STARBASE, www.ph.surrey.ac.uk/astrophysics/files/how_stars_form.html.

“T Tauri Stars | COSMOS.” Centre for Astrophysics and Supercomputing, astronomy.swin.edu.au/cosmos/T/T Tauri Stars.

“Bok Globules.” Www.cfa.harvard.edu/, 21 Oct. 2013, www.cfa.harvard.edu/news/su201023.

“Herbig-Haro Object | COSMOS.” Centre for Astrophysics and Supercomputing, astronomy.swin.edu.au/cosmos/H/Herbig-Haro Object.

Darling, David. “Bipolar outflow.” The Worlds of David Darling, www.daviddarling.info/encyclopedia/B/bipolar_flow.html.

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If a star falls in the main sequence, it will follow the mass-luminosity relationship where the larger the mass, the brighter the star will be. This isn't true for super giants and dwarfs. High mass stars have short lives and burn through fuel much quicker. When they die, they go supernova. Low-mass stars have long lives and eventually become white dwarfs. Stars considered to be massive can leave behind a black hole when they die.

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Many stars make their energy using the proton-proton cycle, which is the same cycle the Sun uses to make its energy. Stars can also use the CNO cycle to make energy, but this cycle requires the star to be at a higher temperature than the proton-proton cycle requires. Stars that are more massive than 1.1 solar masses have the ability to use the CNO cycle to make their energy, while stars that are less massive than that can only use the proton-proton cycle. https://www.cengage.com/resource_uploads/static_resources/0495015784/11457/chapter11.html

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Observations of protostars have shown us that molecules fall to the central object of the star and some material is shot out. This creates jets that plow into the surrounding molecular clouds creating Herbig-Haro objects. They are bright knots of emission that can contain up to 20 earth masses worth of material.
http://astronomy.swin.edu.au/cosmos/H/Herbig-Haro+Object

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The law of hydrostatic equilibrium says that the weight pressing down upon a layer of gas within a star must be balanced by the pressure within the gas. This shows that inner stars have to be hotter because that way they'll be able to support more weight. Upper-main-sequence stars for example, must be hotter inside for they are massive stars. This allows them to use the CNO cycle. https://www.cengage.com/resource_uploads/static_resources/0495015784/11457/chapter11.html

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Bok Globules are very cold and dense clouds of gas and dust. They are nearly opaque and block out light even when surrounded by stars. They're relatively small and almost always contain multiple young stars. Since they appear much closer to earth than other larger cloud complexes like the nebulae Orion, they're frequently used to study early star formation.
https://www.cfa.harvard.edu/news/su201023

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The stream of matter in two opposing directions from a central object, usually a star, is called bipolar flow. Bipolar outflows represent significant periods of mass loss within in a star's lifetime. These periods tend to occur during the protostar and pre-main-sequence phase. It happens again during the red giant phase, just before the production of a planetary nebula. http://www.daviddarling.info/encyclopedia/B/bipolar_flow.html

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T-Tauri stars are variable stars which show both periodic and random fluctuations in their brightness. They are only less than 10 million years old and are low to intermediate mass stars. They have central temperatures too low for nuclear fusion to have started. http://astronomy.swin.edu.au/cosmos/T/T+Tauri+Stars

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The gravitational collapse of gas and dust within interstellar molecular clouds, which have mass many times greater than the mass of a single star, is what causes the birth of a star. Spiral patter is the key to star formation. Massive stars are formed by interstellar clouds encountering spiral arms, causing the clouds to be compressed, which triggers star formation. Once that pattern starts, it continues in a cycle. http://www.ph.surrey.ac.uk/astrophysics/files/how_stars_form.html

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The Reflection Nebula is a star that appears to be blue and illuminates a nearby cloud of gas and Interstellar dust. The Interstellar dust grains in the Reflection Nebula have a diameter of 0.01mm to 100mm.

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Astronomers have discovered the Interstellar Medium because it was easily visible in the Orion Nebula. They have concluded that the space between the stars is filled with low-density gas dust which is the Interstellar Medium. You can see evidence that the dust within a cloud is made of very small particles when the dusty clouds reflect the light of slightly cooler stars. The Interstellar Medium is not uniformly distributed throughout space.