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Astronomy Origin and Fate of the Universe Hubble’s Law Hubble’s law basically says that the universe is expanding. That is to say that the space between galaxies is increasing; with greater distance is greater speed. Closer galaxies are moving apart slower than those galaxies farther away. HOW DO WE KNOW? Hubble’s Evidence = Spectra Spectra are the colors produced when the wavelengths of light are separated. The Doppler Effect The Doppler effect is a change of light or sound wavelengths as a source moves toward or away from the observer. Red shift = source is moving away so wavelengths stretch into longer wavelengths Blue shift = source is moving closer so wavelengths squeeze into shorter wavelenghts. BLUE TO YOU. Deep Space Phenomena Based on the observed rates of expansion it is believed that about 15-20 billion years ago all matter was concentrated into one “primeval atom”. This “atom” exploded and sent all matter and space expanding = BIG BANG What are Stars? • Star = a hot, glowing sphere of gas that produces energy by fusion (of hydrogen molecules). –Some stars produce more energy therefore they are hotter. How Do Stars Form? • Nebula = a cloud of dust and gas where stars are born. –Here gravity pulls particles together and nuclear fusion starts at 10,000,000 oC and a star is born. The Horse Head Nebula More Horse Head Nebula Shots Types of Stars Depending on the conditions within a nebula, different types of stars can form: Red Giants = big, “cool” stars White Dwarfs = “small”, hot stars How Are Stars Classified? • Stars are classified by: –Temperature –Color –Luminosity / Brightness Stars are Classified by Temperature and Color. • HOT BLUE COLD WHITE YELLOW ORANGE RED BROWN What is a Main Sequence Star? What is a Main Sequence Star? • The H-R diagram represents a pattern that was discovered that allows stars to be compared by brightness and color. • The majority of stars are found in a band stretching diagonally across the diagram called the “Main Sequence”. • Stars start out in the Main Sequence and as the core cools, they move onto the giant category. A few rare stars are bigger and brighter and become supergiants. Stars are Classified by Brightness • Actual brightness is how bright a star really is. • Actual brightness does not change, it is an absolute value. • Example: a 40 watt light bulb is actually converting 40 watts of energy into light. • Apparent brightness is how bright a star looks from earth. • Apparent brightness changes depending on distance from earth and viewing conditions (atmosphere). • Example: a 40 watt light bulb 10 feet away appears brighter than a 40 watt bulb 100 feet away. …And After Stars are Born? Life Cycle of a Star Neutron Stars A neutron star results when a white dwarf collapses and the pressure converts the electrons into atomic nuclei to produce neutrons. The outer portion of a neutron star may explode with incredible force producing a supernova. What is a Supernova? • Supernova is when the core of a star collapses and the outer portion explodes. This is the “death of a star”. • What remains when a star dies out depends on the mass of the star. – Material from the explosion may form a new star called a pulsar – a rapidly spinning neutron star. – The most massive stars collapse into black holes. What is a Black Hole? • Black Hole = the most dense thing known to exist in the universe. The gravity of a black hole is so great that even light can not escape the pull of a black hole. The massive density of Black Holes creates a gravitational force that pulls in anything that comes within reach: the reach of this force is called the event horizon. The fate of objects that enter a Black Hole is still uncertain. ?