Formation of the Universe



Formation of the Universe

|Formation of the Universe: |

|Astronomers theorize that the universe was first formed 10 to 15 billion years ago. At that time, all of the matter in the |

|universe was melded together into an incredibly dense ball that was no more than a millimeter or so in diameter. The ball then |

|exploded in what is known as the big bang. |

|Big Bang Theory |Theory stating that the universe formed in an instant, enormous explosion |

Formation of Stars:

Stars begin as a portion of a nebula.

|Nebula |A large cloud of gas and dust spread out in an immense volume |

Stars form in the following stages:

1. In the densest portion of the nebula, gravity exerts force on nearby particles of gas and dust.

2. This area of the nebula becomes denser as the particles of gas and dust are pulled closer and closer together. At this point, the contracting cloud of gas and dust is a protostar.

3. At some point, the contracting cloud of gas and dust becomes so dense and hot that nuclear fusion commences. At this point, the cloud of gas and dust is a star.

Energy Production in Stars:

A star's energy comes from nuclear fusion.

|Nuclear fusion |Process by which two or more nuclei with small masses join together, or fuse, to form a larger, more massive |

| |nucleus, along with the production of energy. |

     Nuclear fusion occurs only under conditions of extremely high pressure and temperature. As fusion occurs, energy produced in the star's core moved outward towards the sun's exterior. Around a star's core is a radiative zone, which is a region of very tightly packed gas where energy is transferred mainly in the form of electromagnetic radiation.

Facts about The Sun:

[pic]

Size:

The diameter of the sun is approximately 1.4 million kilometers. The sun accounts for 99.8 percent of our solar system's mass.

Temperature:

The core of the sun is about 15 million degrees Celsius. This high temperature allows fusion to take place. The sun's corona is cooler-it is only around 2 million degrees Celsius.

Energy:

Like any other star, the sun's energy is produced from nuclear fusion.

The Milky Way:

The sun is one of billions and billions of stars in our galaxy, which is known as the Milky Way. The Milky Way is around 100,000 light years from end to end.

Gravity in the Solar System

|The force exerted on smaller objects by larger objects, pulling the smaller objectsinward toward them, is called gravity. |

When looking at how our solar system behaves, gravity is the force responsible for many of the things we see. A few of the effects of gravity are listed below.

1. The gravitational force causes the planets to orbit the sun. If it weren't for gravity, the planets would simply fly off into space.

2. A star is born when gravity causes gas and dust from a nebula to become so dense and hot that nuclear fusion starts.

3. Many planets are formed by a process called accretion, where chunks of material are drawn to bigger chunks of material by gravity and are slammed together until enough material has been gathered to produce a planet.

Star Life Cycle

The universe is made up of billions of galaxies which are each made up of billions of stars, which are constantly dying and being born. Just like anything else, stars have a life cycle and can only exist for a certain amount of time before burning out.

|All stars go through certain phases in their life cycle. First, a protostar is formed within a large cloud of gas and dust, called|

|a nebula. Then, the star enters a stage called main sequence which takes up the majority of its life cycle. After a star has |

|finished main sequence, it enters its giant or super giant stage. This is the last stage of life for a star before its death. |

1. Protostar - Within a nebulae, which is a huge cloud of dust and gas, gravitational forces cause the dust and gas to collapse and become more dense. This marks the beginning of a protostar. As gravity pulls in more gas and dust from the surrounding nebulae, the ball of material continues to collapse and become more and more dense, causing the material within the protostar to become more and more active, resulting in an outward force as the material fights collapse. This is a critical point in the life cycle of a star. At this point, it is determined whether or not the protostar will actually become a star. If the force of the material pushing out equals the force of gravity making the material collapse, then fusion will take place and a star is born. If this does not happen, then the protostar will never become a star and will end its life as a brown dwarf. Once fusion occurs and the protostar becomes a star, the star has entered main sequence.

2. Main Sequence - A star spends the majority of its life fusing hydrogen into helium. It is this fusion that keeps the star from collapsing under its own gravity and causes the star to shine and send out heat into space. As the star sends out energy, gravity continues to collapse the core of the star making it hotter. Once the star runs out of hydrogen fuel, it will begin fusing helium atoms, becoming hotter, and then only the largest stars will fuse carbon atoms after it runs out of helium atoms, once again becoming even hotter. However, the fusing of hydrogen atoms takes up the majority of a star's life by far. As the star gets older and begins to run out of fuel, the outer layers of the star will start to expand as the star loses its fight with gravity. This is when the star enters its red giant or super red giant stage, depending on how big the star is initially.

3. Giant or Super Giant - Once a star runs out of hydrogen fuel, the core begins to quickly contract and the star is forced to begin fusing helium into carbon to fight gravity. While this is happening, the outer layers of the star begin to expand quickly and the star takes on a much darker red color. This phase is called "red giant" in small and medium sized stars and "super red giant" in larger stars. Once the star completely runs out of fuel, it is forced to give into gravity and the star dies.

4. Death - Once a star runs out of fuel and is forced to give into gravity, the remaining material is collapsed inward by gravity very quickly. In small and medium sized stars, death is relatively quiet. The star contracts as far as gravity can force it to and it becomes a white dwarf. After it cools, which takes billions of years, a white dwarf becomes a black dwarf. In larger stars, when fuel runs out and the material contracts a huge explosion occurs. Depending on the size of the star, this explosion is called a nova or supernova. These explosions are so large that they outshine their entire galaxy. Most of these large stars become neutron stars, which are made of incredibly dense material and continue to give off radiation. The largest stars will end their life by becoming a black hole. This happens when gravity is so strong that the material continues to collapse until it reaches a point. Black holes are so dense and have such a strong gravitational pull that not even light can escape them.

It is important to know that the length of a stars life cycle varies from star to star. Actually, the larger a star is, the shorter its life cycle will be. Even though larger stars have more fuel to start with, they are forced to burn fuel so much faster than smaller stars because of the stronger gravitational forces that they run out of their fuel much quicker and have much shorter life cycles than smaller stars.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download