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The Life Cycle of the Sun and of Vega
Transcript of The Life Cycle of the Sun and of Vega
Very large stars (red giants) are often called Super Giants. These stars have diameters up to 1000 times that of the Sun and have luminosities often 1,000,000 times greater than the Sun. Protostar This phase of the star's life describes the period of time in which the star is gaining energy and stability. This is when the forces of gravity and of the powerful core push against eachother and battle for the upper hand, only to reach a state of equilibrium in the main phase of the star's life. These are cooler and fainter stars, approximately one tenth the mass and diameter of the Sun. They burn very slowly and have estimated lifetimes of 100 billion years. This is when the fuel in the core of the star begins to run out and the star shrinks in terms of size, energy release, and brightness. This is very small, hot star, the last stage in the life cycle of a star like the Sun. White dwarfs have a mass similar to that of the Sun, but only 1% of the Sun's diameter; approximately the diameter of the Earth. The surface temperature of a white dwarf is 8000C or more, but being smaller than the Sun their overall luminosity's are 1% of the Sun or less.
White dwarfs are the shrunken remains of normal stars, whose nuclear energy supplies have been used up. White dwarf consist of degenerate matter with a very high density due to gravitational effects, i.e. one spoonful has a mass of several tons. White dwarfs cool and fade over several billion years. Sun This is the explosive death of a star, and often results in the star obtaining the brightness of 100 million suns for a short time. The amounts of energy thrown in every direction is nearly unfathomable. These stars are composed mainly of neutrons and are produced when a supernova explodes, forcing the protons and electrons to combine to produce a neutron star. Neutron stars are very dense. Typical stars having a mass of three times the Sun but a diameter of only 20 km. If its mass is any greater, its gravity will be so strong that it will shrink further to become a black hole. Pulsars are believed to be neutron stars that are spinning very rapidly. Black holes are believed to form from massive stars at the end of their life times. The gravitational pull in a black hole is so great that nothing can escape from it, not even light. The density of matter in a black hole cannot be measured. Black holes distort the space around them, and can often suck neighbouring matter into them including stars. This is where the sun is right now. It was formed about 4,500,000,000 (four and a half billion) years ago and we expect it to carry on pretty much as it is now for a few billion years yet. The Sun’s diameter is about 870,000 miles wide. The Sun is 109 times wider than Earth, and is 333,000 times heavier. That means if you put the Sun on a scale, you would need 333,000 objects that weigh as much as the Earth on the other side to make it balance. OR... Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus. It is a relatively close star at only 25 light-years from Earth, and, together with Arcturus and Sirius, one of the most luminous stars in the Sun's neighborhood.
Vega has been extensively studied by astronomers, leading it to be termed "Arguably the next most important star in the sky after the Sun.” Vega was the northern pole star around 12,000 BC and will be so again around AD 13,727 when the declination will be +86°14' Vega was the first star other than the Sun to be photographed and the first to have its spectrumrecorded. It was one of the first stars whose distance was estimated through parallax measurements. Vega has served as the baseline for calibrating the photometric brightness scale, and was one of the stars used to define the mean values for the UBV photometric system.
Vega is only about a tenth of the age of the Sun, but since it is 2.1 times as massive its expected lifetime is also one tenth of that of the Sun; both stars are at present approaching the midpoint of their life expectancies. Vega has an unusually low abundance of the elements with a higher atomic number than that of helium. Vega is also a suspected variable star that may vary slightly in magnitude in a periodic manner. It is rotating rapidly with a velocity of 274 km/s at the equator. This is causing the equator to bulge outward because of centrifugal effects, and, as a result, there is a variation of temperature across the star's photosphere that reaches a maximum at the poles. From Earth, Vega is being observed from the direction of one of these poles.
Based on an observed excess emission of infrared radiation, Vega appears to have a circumstellar disk of dust. This dust is likely to be the result of collisions between objects in an orbiting debris disk, which is analogous to the Kuiper belt in the Solar System. Stars that display an infrared excess because of dust emission are termed Vega-like stars. Irregularities in Vega's disk also suggest the presence of at least one planet, likely to be about the size of Jupiter, in orbit around Vega.