The universe beyond
A great deal is known about the universe beyond our solar system. This knowledge hinges on the fact that stars, and even gases in the "empty" space between stars radiate energy in all directions into space. The key to understanding the universe is to collect this radiation and unravel the secrets it holds.
Star Birth
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The image on the left is a nebula. These are dark cool clouds full of interstellar matter and are the birthplace of stars. Nebulae are made up of dust and gases. In the Milky way, nebulae consist of 92% hydrogen, 7% helium, and less than 1% of the remaining heavier elements. Some nebulae become dense enough to begin to contract. A shock wave from an explosion of a nearby star may trigger this contraction. Once the process begins, gravity squeezes particles in the nebula pulling every particle toward the center. As the nebula shrinks, gravitational energy is converted into heat energy.
Protostar StageThe initial contraction takes a millions or so. Over time, the temperature of the gaseous body slowly rises until its hot enough to radiate energy from its surface. This is a protostar and is not hot enough to engage in nuclear fusion. Gravitational contraction continues, first slowly and then more rapidly.The collapse causes the core of the protostar to heat much more intensely than the outside. When the core reaches 10 million K, the pressure is so great that nuclear fusion of hydrogen begins and a star is born. At some point, the outward pressure balances the inward pressure and the star becomes a stable main sequence star.
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Main Sequence StageFrom this point in the evolution of a main sequence star until its death, the internal gas pressure struggles to offset the force of gravity. The hydrogen fusion continues for a few billion years and provides the outward pressure to support the star from collapsing. Stars age at different rates; massive stars radiate so much energy that they deplete their hydrogen fuel in only a few million years. The less massive ones remain stable for hundreds of billions of years. Once the hydrogen in the stars core is depleted, it evolves rapidly and dies. The less massive stars can delay this death by fusing heavier elements and becoming giants.
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Red Giant StageThis stage occurs because the zone of hydrogen fusion continually moves outward, leaving behind a helium core. All the hydrogen in the core is eventually consumed . While hydrogen fusion progresses in the outer shell, no fusion is taking place in the core. Without energy, the core no longer has enough pressure to support itself against the inward force of gravity and the core begins to contract. As it contracts, the core grows hotter and increase the hydrogen fusion in the stars outer shell . The result is a giant body hundreds to thousands of times larger that the main sequence star phase.
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Star Death
Stars expand as they grow old. As their core runs out of hydrogen and then helium, the core contacts and the outer layers expand, cool, and become less bright. This is a red giant or a red super giant (depending on the initial mass of the star). It will eventually collapse and explode. A star's life span and eventual fate are determined by the original mass of the star. A star will become either a black dwarf, neutron star, or black hole, depending on how massive it was. Sun-like stars will go from red giants to a planetary nebula to a white dwarf and then a black dwarf. Huge stars go from red super giants to a supernova a neutron Star. Giant Stars which have masses over 3 times the mass of the Sun go from red super giants to supernova to black holes.
Galaxies
A galaxy is a massive, gravitationally bound system consisting of stars, stellar remnants an interstellar medium of gas and dust, and, dark matter, an important but poorly understood component. The word galaxy is derived from the Greek galaxias, literally "milky", a reference to the Milky Way. Examples of galaxies range from dwarfs with as few as ten million stars to giants with a hundred trillion stars, each orbiting their galaxy's own center of mass. Galaxies contain varying numbers of star systems, star clusters and types of interstellar clouds. In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays. Super massive black holes reside at the center of all galaxies. They are thought to be the primary driver of active galactic nuclei found at the core of some galaxies. There are probably more than 170 billion (1.7 × 1011) galaxies in the observable universe.
The Milky Way Galaxy
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The Milky Way is the galaxy that contains our Solar System.This name derives from its appearance as a dim "milky" glowing band arching across the night sky, in which the naked eye cannot distinguish individual stars. The Milky Way appears like a band because it is a disk-shaped structure being viewed from inside. The fact that this faint band of light is made up of stars was proven in 1610 when Galileo Galilei used his telescope to resolve it into individual stars. In the 1920s, observations by astronomer Edwin Hubble showed that the Milky Way is just one of many galaxies. The Milky Way is a barred spiral galaxy 100,000–120,000 light-years in diameter containing 200–400 billion stars. It may contain at least as many planets. The Solar System is located within the disk, around two thirds of the way out from the Galactic Center, on the inner edge of a spiral-shaped concentration of gas and dust called the Orion Arm.
The Universe
Ever Expanding UniverseThe Doppler effect reveals to us that when a source is moving away, its light appears redder than it actually is because wavelengths appear lengthened. Those that are moving closer shift toward blue or shorter wavelengths. In this way, we can tell if a star is moving toward or away from earth. Edwin Hubble using his telescope concluded that more distant galaxies have red shifts and these red shifts indicate that the universe is expanding.
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Big BangThe Big Bang theory states that at one time, the entire universe was confined to a dense, hot super massive ball. About 13.7 billion years ago, a violent explosion occurred, sending this ball in all directions. This marked the beginning of the universe, where all matter and space were created at that instant..
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