Birth of Stars Since my entire thesis for this paper is about how a star is born, I guess the first thing I should start out with is by telling you exactly what a star is. Stars are self-luminous gaseous spheres. They shine by generating their own energy and radiating it off into space. The stars’ fuel for energy generation is the stuff they are made of — hydrogen, helium, carbon, etc. — which they burn by converting these elements into heavier elements. Nuclear fusion occurs, which is when the nuclei of atoms fuse into nuclei of heavier atoms. The energy given off by a star through nuclear burning heats its interior to many millions and, even in some cases to Pleiades Star Cluster hundreds of millions to billions of degrees Fahrenheit. It causes heat to flow from the interior toward the surface, where it is released out into space and makes the star shine. Because stars are only so big, they will eventually use up their nuclear fuel and run out of energy. (University of Oregon, Unknown) The first step in making new stars is to compress a cloud in order to strengthen gravity’s effect so that the cloud material can contract and break-up into smaller units that eventually collapse to form stars. The clouds in the inter-stellar space are called Inter-stellar Medium, which are mainly made up Rho Ophiuchi of hydrogen and helium. The cloud itself is very cold, somewhere around a hundred degrees Kelvin, which is far below -150C. All particles in the cloud attract each other by gravitational force. According to calculations of scientists, a cloud having the mass comparable to the mass of our Sun will be able to hold itself together due to the gravity pushing against it. As traveling compression waves move past a cool molecular cloud, it compresses the cloud, driving the particles closer together. If the compressed cloud has no way to stop the contraction, it’ll continue to collapse and raise the gas pressure sufficiently to resist further contraction. Supernova 1994D Another possible explanation for the contraction that is occurring at this time is due to shockwaves from surround supernovas. (Kippenhahn, 1994) At this point the contracted interstellar clouds are called Bok globules. Globules are usually a few light years in size and they are made up of hydrogen and dust. “At some point, however, a significant amount of energy goes into dissociating molecular hydrogen to form atomic hydrogen; later more energy is needed to ionize all chemical species.” Basically after this the cloud doesn’t have a whole lot of energy left and it starts to contract even more. During this time around the particles that make up the cloud have been getting even hotter and have been giving off more visible light and less infrared Dark Bok Globules in IC 2944 radiation. Because it is cooler dust in the surrounding stellar nebula out of which the star is forming, it absorbs photons, heats up, and gives off energy as infrared radiation. As the star cools it also starts to spin much more rapidly. So, the stellar nebula hides the baby star until most of the surrounding gas and dust in the nebula is either attracted to it or blown away by it.(Goldberg, 1982) Eagle Nebula—formed by forming stars During the next step of star formation the spin, pressure, and temperature inside the interstellar cloud continue to increase. Due to these increases the Bok Globules will split into the protoplanetary disk and the central core. The protoplanetary disk has the potential to actually change form and become planets. On the other hand, the central core will go on to become one of those loveable pin pricks of light in the sky that we call stars. (Strobel, Unknown) During the next step of stellar birth, the core continues to increase in temperature and whenthe forming star has stabilized itself, then it has become a protostar. The temperature of a protostar’s surface is about 4000 K, and energy in its deep interior is transported to the surface entirely by convection. Eventually, temperature and luminosity Artistic Depiction of Protostar rise to the highest level that they can reach on the H-R diagram and the protostar becomes a pre-main sequence star. At this point its radius is about the same as the Earth’s distance from our Sun. Gravity eventually raises the temperature in a protostar’s core to 1 million K and past, which is hot enough to even melt some of the lighter metals on the periodic table. Eventually when the core reaches a temperature of a few million degrees or more, the burning of Hydrogen begins. When that happens, it ignites for the first time and shines as an adult star. The ignition blows off the remaining rocks and dust that, before this point in time, covered the protostar from our spying eyes. After a certain amount of time, the core reaches a critical point where it begins to resist the force of gravity and its compression slows. Astronomers define the zero-age main sequence as the point when a protostar stops contracting, becomes stable, and they get all their luminosity by burning hydrogen. To give you an idea of how long it takes for a star to go from the stage of being a protostar to the point where hydrogen burning begins and the star becomes stable, it took our Sun about 30 million years to bridge that gap. Stars that are larger than our Sun’s mass bridge this gap quite quickly, while for the smaller stars, the protostar period is much longer than that for the Sun. (Hansen, 1994) Our star has now formed and it has finally reached it’s adult stage of life. The adult star is not very interesting at all. It contains mostly hydrogen and it will burn for much longer than you or I could even possibly begin to imagine. The hydrogen inside the star is converted into helium by the means of nuclear fusion. Stars that start their lives with masses less than about eight solar masses stop their nuclear burning trip with helium burning at the core. Stars that start their lives with masses greater than about Model of Star’s internal process eight solar masses continue their nuclear burning and go on to produce such products as neon, magnesium, silicon, and sulfur. Eventually, silicon and sulfur ignite in the star’s core to form iron and nickel. (Hansen, 1994) Various info about star at mature stage In conclusion, before I wrote this paper I would have to say that even though every night when I happen to glance upwards I see a whole bunch of stars, I never even had the slightest idea of where they came from until now. Stars come from these cosmic nurseries that scientists and astronomers refer to as nebulas in one of the oddest ways imaginable. I learned quite a bit about where stars come from and I hope to continue to learn even more about stars in the not so distant future. M-29 Butterfly Nebula


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