How did the universe originate and evolve to produce the galaxies, stars, and planets we see today?
How did we get here? In order to understand how the Universe has changed from its initial simple state following the Big Bang (only cooling elementary particles like protons and electrons) into the magnificent Universe we see as we look at the night sky, we must understand how stars, galaxies and planets are formed. There are many questions associated with the creation and evolution of the major constituents of the cosmos. A basic question astronomers must address is, how did the Universe create its first stars and galaxies? Once these entities were created, how did they influence subsequent galaxy, star and planet formation? This is an important question, because these later objects are made of elements that can only have been created by the first generation of stars. It is still unknown whether the Universe created black holes with the first generation of stars or whether these exotic objects were created by the first generation of stars. Because black holes represent the most extreme physical conditions of spacetime and generate some of the most energetic phenomena following the Big Bang, they are the ultimate physical laboratories for testing theories of the Universe. We now know that our Universe has a "foamy" structure. The galaxies and clusters of galaxies that make up the visible Universe are concentrated in a complex scaffold that surrounds a network of enormous cosmic voids. However, in addition to the "normal" matter that makes up the visible parts of the Universe, scientists have discovered that there are vast amounts of unseen matter. This so-called, "dark matter" makes up roughly 27% of the matter-energy content of the Universe, while the visible pieces account for only about 5% of the total. Clearly, if we hope to understand the structure of the Universe and the processes by which it formed and evolves, we must first understand the distribution of this important but unseen dark matter and the ways in which it interacts with and influences normal matter. Though astronomers have been studying stars for thousands of years, it is only in the past 35 or so years that they have been able to employ instruments that detect light across the entire electromagnetic spectrum–from radio waves to gamma rays–to peer into the dusty clouds where stars are born in our own Galaxy. If we are to comprehend how the Universe makes stars–and planets that orbit them today–we must continue these studies with ever more powerful telescopes.
HE LIFE CYCLE OF A STAR
Outlined below are the many steps involved in a stars evolution, from its formation in a nebula, to its death as a white dwarf or neutron star. NEBULA
A nebula is a cloud of gas (hydrogen) and dust in space. Nebulae are the birthplaces of stars. There are different types of nebula. An Emission Nebula e.g. such as Orion nebula, glows brightly because the gas in it is energised by the stars that have already formed within it. In a Reflection Nebula, starlight reflects on the grains of dust in a nebula. The nebula surrounding the Pleiades Cluster is typical of a reflection nebula. Dark Nebula also exist. These are dense clouds of molecular hydrogen which partially or completely absorb the light from stars behind them e.g. the Horsehead Nebula in Orion. Planetary Nebula are the outer layers of a star that are lost when the star changes from a red giant to a white dwarf. STAR
A star is a luminous globe of gas producing its own heat and light by nuclear reactions (nuclear fusion). They are born from nebulae and consist mostly of hydrogen and helium gas. Surface temperatures range from 2000�C to above 30,000�C, and the corresponding colours from red to blue-white. The brightest stars have masses 100 times that of the Sun and emit as much light as millions of Suns. They live for less than a million years before exploding as supernovae. The faintest stars are the red dwarfs,...
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