25 chapter 25 beyond our solar system. the milky way galaxy 25.3 the universe a galaxy is a group...
TRANSCRIPT
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Chapter
2525Beyond Our Solar System
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The Milky Way Galaxy
25.3 The Universe
A galaxy is a group of stars, dust, and gases held together by gravity.
• The Milky Way is a large spiral galaxy whose disk is about 100,000 light-years wide and about 10,000 light-years thick at the center.
Size of the Milky Way
• Radio telescopes reveal that the Milky Way has at least three distinct spiral arms.
Structure of the Milky Way
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Structure of the Milky Way
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Types of Galaxies
25.3 The Universe
Spiral Galaxies• About 30% of all galaxies are spiral galaxies.
• They have large diameters of 20,000 to 125,000 light-years and contain both young and old stars.
• About 60% of galaxies are classified as elliptical galaxies.
Elliptical Galaxies
• They have the largest diameters of 200,000 light-years and contain old stars.
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Spiral Galaxies
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Elliptical Galaxy
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25.3 The Universe
• Irregular galaxies contain young stars.
In addition to shape and size, one of the major differences among different types of galaxies is the age of their stars.
Irregular Galaxies
• Only 10% of the known galaxies have irregular shapes and are classified as irregular galaxies.
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Irregular Galaxy
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The Expanding Universe
25.3 The Universe
• Hubble’s law states that the galaxies are retreating from the Milky Way at a speed that is proportional to their distance.
To help visualize the nature of the universe, imagine a loaf of raisin bread dough that has been set out to rise for a few hours. As the dough doubles in size, so does the distance between all the raisins. Those objects located father apart move away from each other more rapidly.
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Raisin Bread Dough Analogy
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The Big Bang
25.3 The Universe
The big bang theory states that at one time, the entire universe was confined to a dense, hot, supermassive ball. Then, about 13.7 billion years ago, a violent explosion occurred, hurling this material in all directions.
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El Universo
Tipos de galaxias
• Galaxias espirales
– Alrededor del 30% de todas las galaxias son galaxias espirales.
– Ellos tienen grandes diámetros de entre 20.000 y 125.000 años luz y contienen estrellas jovenes y viejas.
• elípticas Galaxias
– Alrededor del 60% de las galaxias se clasifican como las galaxias elípticas.
– Tienen los mayores diámetros de 200 mil años luz y contienen estrellas viejas.
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El Universo
• La Vía Láctea – Una galaxia es un grupo de estrellas, polvo y gases se mantienen unidos por la
gravedad.
• Tamaño de la Vía Láctea – La Vía Láctea es una gran galaxia espiral cuyo disco es de unos 100.000 años
luz de ancho y cerca de 10.000 años luz de espesor en el centro.
• Estructura de la Vía Láctea – Los radiotelescopios revelan que la Vía Láctea tiene al menos tres brazos
espirales distintas.
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El Universo
• Galaxias irregulares – Sólo el 10% de las galaxias conocidas tienen
formas irregulares y se clasifican como galaxias irregulares.
– Las galaxias irregulares contienen estrellas jóvenes.
– Además de la forma y tamaño, una de las principales diferencias entre los diferentes tipos de galaxias es la edad de sus estrellas.
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El Universo
El Universo en Expansión La ley de Hubble establece que las galaxias se están retirando de la
Vía Láctea a una velocidad que es proporcional a su distancia.
Para ayudar a visualizar la naturaleza del universo, imagina una barra de masa de pan con pasas que se ha expuesto a subir por unas horas. A medida que la masa doble su tamaño, también lo hace la distancia entre todas las pasas. Esos objetos situados aparte padre se alejan el uno del otro más rápidamente.
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El Universo
• El Big Bang
• La teoría del Big Bang dice que en un momento, todo el universo se limitaba a una bola densa, caliente supermasivo. Entonces, hace aproximadamente 13.7 millones de años, se produjo una violenta explosión, lanzando este material en todas las direcciones.
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25.3 The Universe
The Big Crunch?
• The future of the universe follows two possible paths:
1. The universe will expand forever.
2. The outward expansion will stop and gravitational contraction will follow.
• The view currently favored by most scientists is an expanding universe with no ending point.