Earth is only one planet orbiting one star

Earth is only one planet orbiting one star among roughly a hundred billion stars in our Milky Way Galaxy. The Milky Way is only one galaxy of billions in the universe. Looking beyond the solar system into galactic and intergalactic space, we must stretch our minds to nearly unimaginable distances to look backward in time to events that occurred billions of years before the Earth formed, and attempt to fathom energy sources powerful enough to create an entire Universe. In this presentation we will look at the basics of how stars come to be? We will take a look at how they were born? We will talk about and explain the largest star in the universe, the sun. We will understand, how stars maintain their sequence. We will also take a look at the life and death of a star. In conclusion, we will look at other stars in the Universe.

• The Big Bang Theory states that the universe began with a cataclysmic explosion that instantly created space and time.

The BIG BANG Theory • The Big Bang Theory is the dominant scientific theory about the origin of the universe. • According to the big bang, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter in all directions.

Edwin Hubble observed all galaxies are moving away from each other • Hubble reasoned that they must have started moving outward from a common center at the same time. • Hubble began the Big Bang Theory when he stated that in the beginning, the entire universe was compressed into a single infinitely dense point. The point exploded, and our universe was instantly created. Ø Matter, energy and space came into existence with this single event. Ø The Big Bang was the start of space and time.

• The big bang was initially suggested because it explains why distant galaxies are traveling away from us at great speeds. The theory also predicts the existence of cosmic background radiation (the glow left over from the explosion itself). • The Big Bang Theory received its strongest confirmation when this radiation was discovered in 1964 by Arno Penzias and Robert Wilson, who later won the Nobel Prize for this discovery.

The Birth of a Star • • • Over time, dense regions of the Universe draw matter inward by gravity to form huge clouds of hydrogen and helium, called nebulae. Within each cloud, matter further agglomerates into billions of smaller bodies. As the atoms in the nebula accelerate inward under the force of gravity, they collide rapidly with one another. The center of each cloud becomes very dense and hot; under this intense heat, electrons are stripped away from their atoms, leaving a plasma of positively charged nuclei and negatively charged electrons. If this cloud is large enough, the gravitational attraction will accelerate the nuclei until they collide, with enough energy to fuse. Once Fusion is started, the collapsing portion of the original nebula becomes a Star.

• Nobody has ever traveled to the sun, the current thought is nobody ever will. • Mass is 2 x 10^30 kg. Although this number seems huge, the sun is only a star with average mass. • Diameter is 1. 4 million kilometers (109 earth diameters) • Our Sun is a star that holds about 99. 9 percent of all the matter in the solar system. Its hot atmosphere expands supersonically outward, creating a flow of electrically charged ions called the solar wind that sweeps outward past all the planets at nearly one million miles per hour.

• After Einstein discovered theory of relativity scientists began to look at nuclear reactions. • From these studies we found that the sun is powered by hydrogen fusion. Our knowledge of the core is derived from calculations of hydrogen fusion reactions and gravitational forces. • Sun is more than 15 million K and has enough hydrogen to fuel the fusion reaction for another 5 billion years.

• Called the solar atmosphere because its cool and diffuse compared to the core, even though the sun is actually gaseous. • The temperature is 5, 700 K and fusion doesn’t occur at this temperature, therefore the core heats the photosphere and the light we see comes from the atmosphere of hydrogen and helium. •

• Chromosphere (turbulent, diffuse, gaseous) is above the photosphere and can been seen by the eye during a solar eclipse • Spicules (jets of gas) shoot up from the chromosphere and look like flames • They are about 700 km across and 7000 km high and last for 5 -15 minutes • Corona is above the chromosphere, more diffuse, and about 2, 000 K • Appears as a halo around the sun during a solar eclipse • One hypothesis about how the photosphere (5700 K) heats the corona is the twisting magnetic fields that accelerate the particles in the corona

• Made from granules caused by convection currents that carry energy to the surface • These dark spots are the cooler areas of descending gas, which may be small and last a few days, or they can be 150, 000 km and last for months • Sunspots are 1000 degrees cooler than surrounding area and put off half the amount of energy • Remember from SCI 190 that heat travels from hot to cold objects? The sunspots are heated from the surrounding area and then disappear

• Apparent Luminosity of a star is its luminosity as seen from Earth. It appears luminous either because its intrinsically bright or because it’s close. • Absolute Luminosity is how bright a star would appear if it were a fixed distance away. • We use the standard distance of 32. 6 light years to calculate luminosities. • We use a scale in which the absolute luminosity of a star is divided by the absolute luminosity of the sun. • Therefore bright objects have a luminosity of over 1 and faint objects are less than one. • The color of a star is a measure of its temperature.

• Main Sequence stars are mainly hydrogen and helium and are fueled by hydrogen fusion • Major reason for difference in temperature and luminosity is that some are more massive than others • Gravity is stronger in more massive stars and the hydrogen nuclei are packed more tightly and move faster, thus the fusion is faster which makes the stars hotter and more luminous (upper left of H-R diagram)

• Between 1911 and 1913 the Hertzsprung- Russel Diagram (H-R diagram) was discovered, which plots luminosity (y) and temperature (x). • Observation: 90% of stars fall along a sinuous band from upper left (bright and hot) to lower right, called the main sequence. • Therefore, luminosity increases with temperature in main sequence stars. • To explain the stars that do not lie on the main sequence, we must consider the life and death of a star.

• The energy in a star the size of our Sun ins derived from Hydrogen fusion in the core. • When most of the hydrogen in the core is consumed, the star first contracts then expands as hydrogen fusion starts in the outer shell. • In the red giant phase, gravitational coalescence in the core and hydrogen fusion in the outer shell produce hundreds of times as much energy as was produced when the star was mature. • The star contracts again when helium fusion initiates in the core.

• As our Sun hydrogen nuclei fuse to form helium but the helium nuclei do not fuse to form heavier element. • For fusion to occur, two nuclei must collide so energetically that they over come their nuclear repulsion.

• the original nebula condenses • The star glows with the intense heat of the gravitational coalesces. • The star enters the main sequence when hydrogen fusion starts in the core. • After hydrogen fusion ends in the core, the star leaves the main sequence and passes through the red giant stage. • Finally, it explodes to produce a planetary nebula and then, • The remaining core glows as a white dwarf.

• If a star is larger than 1. 44 solar masses, a white dwarf does not form. • In this case, helium fusion ends, gravitational contraction produces enough heat to fuse carbon. Renewed fusion produces increasingly heavier elements. • When hydrogen or helium fuse, energy is released. In contrast, iron fusion absorbs the energy and cools a star. When this happens thermal pressure that forced the stellar gases outward diminishes , and the star collapses under the influence of gravity. • Due to this strange phenomena supernovas occur.

• Supernova- An exploding star that releases massive amounts of energy. • The star’s temperature reaches trillions of degrees and the star explodes. A supernova shines as brightly as hundreds of billions of normal stars and may even emit as much energy as an entire galaxy. • Observers from earth appears that a new brilliant star suddenly materialized in the sky, only to become dim and disappear to the naked eye within a few months. • Violent enough to send shock waves through the atmosphere of the star fragmenting atomic nuclei and shooting particles in all different directions.

• On February 24, 1987, an astronomer named Ian Shelton was carrying out research unrelated to Supernova’s. He walked and looked into the sky and saw a star with his naked eye. He looked up into the sky and saw a bright star where previously there was a dim one. • This was the first supernova explosion visible to the naked eye since 1604, five years before the invention of the telescope.

• Hydrogen and helium were the first elements to form when our Universe was 300, 000 years old. • All the stars in the universe were composed entirely of these two elements. • These old, first generation stars are called population II stars. • Within the cores hydrogen fused to helium changing the ratio of these two element in the Universe. • Elements heavier than iron formed during supernova explosions of massive population II stars. • When a star dies, it blasts gas and dust into space to form a new nebula. • The nebulae condenses once again into new, second generation stars called population I stars. Example: The sun • Stars begin life with primordial hydrogen and helium mixed with small concentration of heavy elements that we inherited from population II stars and from supernova explosions.

• Pistol Star- The largest star in the Universe • We discovered that the largest known star, in terms of mass and brightness, is the dramatically dubbed Pistol Star. • The Pistol Star is closer to the center of the Milky Way than we are, and isn't visible to the naked eye on account of galactic dust. It's about 100 times the size of our sun, and burns 10, 000 times as bright.