2 What is the Big Bang Theory? The Big Bang Model the most widely accepted theory for the start of our universeIt hypothesizes that the universe began 12 to 14 billion years agoAt that time, the entire Universe was inside a bubble that was thousands of times smaller than a pinhead. It was hotter and denser than anything we can imagine
3 Continued…Then it suddenly exploded – the Universe that we know was born!Time, space and matter all began with the Big Bang. In a fraction of a second, the Universe grew from smaller than a single atom to bigger than a galaxy and it kept on growing at a fantastic rateIt is still expanding todayAfter the big bang, the universe expanded quickly (and continues to expand) and then cooled down enough for atoms to form.Gravity pulled the atoms together into gas clouds that eventually became stars, which comprise young galaxies
4 How Do We Know the Universe is Expanding? Remember this!!?!The Doppler Effect! It isn’t going away…
5 How Does The Doppler Effect relate to the Universe Expanding? Stars and galaxies are not getting bigger; rather, the space between all objects is expanding with timeThe expansion of the universe was discovered in 1929, by American astronomer Edwin HubbleWhen Edwin Hubble, the astronomer for whom the Hubble Space Telescope is named, measured the spectrum of distant stars and galaxies, he observed extra amounts of red light (red shifting).
6 What is the red shift?Red shift occurs when a light-emitting body moves away from us. Light waves traveling in front of a body bunch up as it travels; light waves at the trailing end stretch out. The stretched-out light waves are said to be red shifting. Hubble concluded that the red shift means the stars and galaxies are actually moving away, which led him to develop the theory of an expanding universe.
7 Expansion of the Universe Proven by the Doppler shiftStarlight moving towards Earth is bluishStarlight moving away from Earth is reddishAll galaxies outside the our galaxy indicate a red shift – therefore they are moving away from us
8 galaxiesA galaxy is a group of billions of individual stars, star systems, star clusters, dust and gas (hydrogen and helium) bound together by gravityThere are billions of galaxies in the universe, and they are classified by size and shapeEarth is in the Milky Way galaxyThere are about 200 billion stars in the Milky Way100,000 light years wide!
9 Different Types of Galaxies There are 3 types of galaxies: elliptical, spiral, and irregularEllipticalMost common type of galaxyShaped like large, 3-D ellipse (looks like a football)Spiral (like the Milky Way) – have spiral arms that wind out, youngest stars at the center of the spiralNormal – arms start close to centerBarred – arms extend from a large barIrregular – many different shapesSmaller and less common
11 StarsWhen heated to a sufficiently high temperature by gravitational attraction, stars begin nuclear reactions (NUCLEAR FUSION!), which convert matter to energy and fuse the lighter elements into heavier onesThese and other fusion processes in stars have led to the formation of all the other elements (heavier ones than Hydrogen and Helium)All of the elements, except for hydrogen and helium, originated from the nuclear fusion reactions of stars
12 Lifetime of a starThe overall lifespan of a star is determined by its massStars spend roughly 90% of their lives burning hydrogen into helium on the main sequenceMassive stars need higher central temperatures and pressures to support themselves against gravitational collapse, and for this reason, fusion reactions in these stars proceed at a faster rate than in lower mass starsIMPORTANT: The result is that massive stars use up their core hydrogen fuel rapidly and spend less time on the main sequence before evolving into a red giant star.
13 How to Classify StarsStars are classified by their color, size, luminosity and massA Hertzprung-Russell (H-R) diagram must be used to estimate the sizes of stars and predict how stars will evolveMost stars fall on the main sequence of the H-R diagramA diagonal band running from the bright hot stars on the upper left to the dim cool stars on the lower right
14 Hertzsprung-Russell Diagram SupergiantsWhere is our Sun?-Main SequenceBrightnessMain SequenceGiantsWhite DwarfsTemperature
15 Lifetime of a StarWhen hydrogen fuel is used up, nuclear fusion can no longer occur and the star begins to “die”Stages of a Low-mass star’s life:Nebula – star beginning, a cloud of gas and dust condense togetherMain Sequence – fusion causes pressure that is balanced-A star’s mass determines the star’s place on the main sequence and how long it will stay thereGiant – when hydrogen is exhausted, a balance no longer exists, star expands and coolsWhite Dwarf – after core uses up helium, expands more and outer layers escape into space, leaving a very hot, dense core (about the size of Earth)** If the star is a high-mass star, it could become a black hole