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The Universe Chapter 20 “Recognize that the very molecules that make up your body, the atoms that construct the molecules, are traceable to the crucibles that were once the centers of high mass stars that exploded their chemically rich guts into the galaxy, enriching pristine gas clouds with the chemistry of life. So that we are all connected to each other biologically, to the earth chemically and to the rest of the universe atomically…It’s not that we are better than the universe, we are part of the universe. We are in the universe and the universe is in us.” - Neil deGrasse Tyson HUNTING THE EDGE OF SPACE What are Stars? 3 What are Stars? • The warthog was right… • Stars: huge sphere of very hot gas that emits light and other radiation • Formed from clouds of dust and gas, or nebulas, and go through different stages as they age 4 Light Years • Stars are located at various distances from the Earth • We measure this distance in light-years (ly) • Distance light travels in one year - 9.5 × 1012 km • UNIT OF DISTANCE, it would take us 10 million years to “drive” 1 light year 5 Stars are powered by nuclear fusion reactions • Remember: fusion is the combining of hydrogen in the creation of helium • A star is held together by the huge gravitational force created by its own mass • Because of this, the pressure INSIDE the star is immense (1billion times that of earths atmosphere) • The temperature of the core is more than 15 million Kelvins • http://www.youtube.com/watch?v=qe7mbv7v9Zg Studying Stars • Ancient Greeks classified stars by their color and brightness Telescopes allowed astronomers to study stars in more detail for the first time 7 Energy moves slowly through the layers of a star • Energy moves through the layers of the stars through a combination of radiation and convection. • Convection: hot gas moves away from the star’s core • Radiation: energy is transferred to individual atoms; the atoms absorb the energy and transfer it to other atoms in random directions; atoms near the surface give off the energy into space as electromagnetic radiation Studying Stars • Ancient Greeks: classified stars by their color and brightness • Telescopes allowed astronomers to study stars in more detail for the first time Traits of stars • Depends on the star’s temperature, size, and distance from the Earth. • Stars produce energy in different wavelengths of electromagnetic radiation other than visible light like high energy X rays and low energy radio waves Traits of stars continued • A star’s color is related to its temperature: hotter objects glow with colors that are more intense with shorter wavelengths (toward the blue end); cooler colors have longer wavelengths closer to red • The color that we see when we look directly at a hot object is determined mainly by the wavelength at which the object emits the most light • The sun appears yellow because that is the wavelength of light it releases the most of Spectral lines reveal the composition of stars • Light can be separated into a spectrum (like a rainbow shows all the colors) • When you pass light through a spectrograph it makes a unique pattern • The pattern is determined by what types of elements make up the gas that are emitted from the light • So each element has its own unique “fingerprint” when passed through this fancy prism • Comparing the known “fingerprints” to what gases the star emits will give the make up of a star Life Cycle of Stars • Like all things, stars have a natural progression from birth, through development, and then death • About 90% of the stars in our galaxy, including the sun, are around midlife • They are converting hydrogen into helium in their interiors (with nuclear fusion!). 16 Life Cycle of Stars • Nebula: thin cloud of gas and dust • Gravity causes nebula to collapse inward and begin spinning – creating a protostar • Hydrogen atoms begin fusing into Helium 17 Life Cycle of Stars • The onset of this fusion marks the birth of a star • Hydrostatic Equilibrium: The fusion reactions in the core of the sun produce energy and outward pressure, this balances the inward pressure from gravity • This creates the round shape of the sun 18 The sun will become a red giant before it dies • When all of the Sun's core supply of Hydrogen has been converted into Helium, nuclear fusion will stop. • With no outward pressure, gravity will crush the core smaller and smaller. • The pressure and temperature becomes so great that Helium is converted into Carbon and oxygen. Life Cycle of Stars • A star that is stable, like our sun, is called a Main Sequence Star • When the sun’s supply of hydrogen runs out, it begins to fuse heavier elements, all the way up to iron • The outer layers of dust and gas expand, and the star swells to a Red Giant – a large reddish star in its late life cycle 20 • When the core depletes the helium, it will get smaller again, but cause the outer layer of the star to expand • The Sun's outer photosphere expands to tremendous size, engulfing Mercury, Venus, and perhaps even Earth and Mars. Life Cycle of Stars • The outer layers eject themselves as a planetary nebula • In the sun’s case, these layers will engulf Mercury, Venus, and possibly Earth and Mars • The remaining core will shrink to an Earth-size ball – called a White Dwarf 22 • The formation of an iron core signals the death of a supergiant star • Why? It requires more energy to fuse heavier elements rather than releasing it so THE INWARD FORCE IS GREATER THAT THE OUTWARD FORCE Life Cycle of Stars • Stars larger than the sun will become supernovas • Supernova: a stellar explosion • The collapse of the core rebounds with a shock wave that violently blows the star’s outer layers away from the core. • A supernova can become a black hole or a neutron star 24 Life Cycle of Stars • A black hole consists of matter so massive and compressed that nothing can escape its gravitational pull, not even light. • The only way to detect one is by observing the radiation of light and X rays from the objects that revolve rapidly around them 25 Traits of Stars • Spectral lines reveal the composition of stars • When you pass light through a spectrograph, it makes a unique pattern • The pattern is determined by what types of elements make up the gas emitted from the light • Each element has its own unique “fingerprint” when passed through this fancy prism and comparing these will give the make up of a star 26 H-R Diagram (Hertzprung Russel) • Diagram that shows how stars evolve • This diagram doesn’t show where stars are literally, only their progression as they age • Y-axis (vertical): luminosity, or the brightness of stars. • X-axis (horizontal): surface temperature of the stars, with hotter temperatures on the left side • Once a star is stable it appears on a dotted line on the H-R diagram called the main sequence. 27 28 The Milky Way and Other Galaxies Section 2 29 Galaxies • Galaxy: a collection of millions to billions of stars • Grouped in clusters • The Milky Way and the Adromeda galaxy are two of the largest, with a cluster of more than 30 galaxies • Gravity holds galaxies together in space, and the solar system revolves around the center of the galaxy because of this gravity 30 Galaxies • Superclusters contain thousands of galaxies • They are the largest known structures in the universe • It takes our solar system about 226 million years to complete one orbit of our galaxy 31 Galaxies • Can be divided into three main types: • Spiral, Elliptical, and Irregular • Each has many stars, but differs in structure 32 Spiral Galaxies • Spiral arms made of gas, dust, and stars • Always growing with many new stars. • Milky Way • Has a lot of interstellar matter – • the medium needed to create new stars, mostly gas and dust 33 Elliptical Galaxies • Little gas or dust, no spiral arms– plainly round • Spherical or egg shaped • Often reddish in color 34 Irregular Galaxies • Lack regular shapes and well defined structures • Some have little interstellar matter while others have a lot • Young stars are hot • Gravity can be some of the cause of the irregular shape 35 Quasars may be infant galaxies • Quasi- stellar object named for its star-like appearance • They are the most distant and most radiant object in space • Might be the central parts of distant galaxies seen as they were when very young Galaxies Over Time • When a scientist observes a galaxy that is 1 billion years away, they are observing light that left the galaxy 1 billion years ago • Scientists don’t know what the galaxy looks like now, but can study similar closer galaxies to piece together the evolution of galaxies • The gas, dust and stars that make up galaxies is in constant motion, as they consume their gas/dust they can no longer make stars • Gravity changes the shapes of galaxies • The gas/dust from nearby galaxies can collide and set off rapid burst of new star formation 37 Origin of the Universe Section 3 38 The Universe • Universe: consists of all space, matter and energy that exists- now, in the past or in the future • Since distances are so far we use large units to express the distances between objects. • It takes time for light to travel in space • We see the universe now as it was in the past • The farther an object is, the older the light that we get from that object is • The sun is 8 light minutes away, that means we are seeing what the sun looked like 8 minutes ago 39 The Universe • Most of the universe is empty space • Space is a vacuum with no air and no air pressure 40 What happened at the beginning? • Scientists use telescopes to study the ancient light emitted by stars • Scientists have theorized that the universe formed during a cataclysmic event known as the big bang Edwin Hubble • 1929: Announced the universe is expanding based on observations of spectral lines in the light from other galaxies • He found these lines were almost always shifted toward the red end of the spectrum • THE SHIFTS showed the universe was expanding! 42 • Doppler effect: a change in the observed frequency of electromagnetic radiation when an object or observer is moving • Something moving closer to you appears to have a shorter wavelength (blue shift) • Something moving further away appears to have a longer wavelength (red shift) Edwin Hubble • The red shift can be explained by the Doppler Effect • Light waves from an object moving away would be stretched out • The faster the object moves, the longer the wavelength 44 The Big Bang • Scientists use telescopes to study the ancient light emitted by stars • Scientists have theorized that the universe formed during a cataclysmic event known as the big bang • The Big Bang Theory: States that the world began with a giant explosion 13 billion to 15 billion years ago (universe is believed to be about 13.7 billion years ago) 45 Cosmic Background Radiation • 1965: Arno Penzias and Robert Wilson were making adjustments to a radio antenna they built • There was a steady but dim signal they kept intercepting • They realized it was cosmic background radiation • The detected microwaves are remnants of radiation produced by the Big Bang 46 The Big Bang • According to this theory, before the big bang there was: • Nothing • No time • No space • But out of this big nothing came the vast system of space, time, matter, and pure energy that now makes up the universe 47 The Big Bang • According to the Big Bang Theory: • Immediately after, the universe was extremely hot and made up of pure energy • There was a period of rapid expansion that caused the energy to cool, and allowed electrons, neutrons and protons to form • Hydrogen nuclei started to form but it was still too hot for atoms to be stable • About 380,000 years after the big bang is when electrons could combine with atomic nuclei to form atoms • The first stars were born about 400 million years after the big bang 48 49 The Big Bang • There are several theories being tested, and as new information is found, we might revise what we believe • The Big Bang is the most supported by current evidence • cosmic background radiation and observation of the movement of distant galaxies 50 Future of the Universe • The future of the universe is uncertain • The universe is still expanding but it will not do this forever • The combined gravity of all the mass in the universe is also pulling the universe inward 51 Future of the Universe • Possible outcomes: • 1. the universe will keep expanding forever • 2. the expansion of the universe will gradually slow down and the universe will approach a limit in size • 3. The universe will stop expanding and start to fall back on itself 52 Future of the Universe • If there isn’t enough mass – gravity will not be strong enough to stop the expansion • Just right amount of mass – the expansion will slow down but not end completely • Too much mass – gravity will overcome the expansion and the universe will start to contract (the big crunch), becoming very hot and small, at this point the universe could end, or they cycle would start again 53 • It is possible that with too much mass the collapsing would become very hot and very small • Causing either the end • Or another big bang to happen • New technology helps scientists and astronomers test theories of the size of the universe • There is debate about dark matter (matter that is not visible) Planets, black holes, brown dwarfs • Dark matter contains dark energy– how do we even begin to observe this? • https://www.youtube.com/watch?v=QAa2O_8wBUQ Scientist use mathematics to build better models • Einstein expanded on Newton’s theory of gravity • Mass curves space (like your body curves a mattress if you sit in the bed) • In 1919 a total solar eclipse showed that stars (LIGHT) that could only be seen during the eclipse were in slightly different positions than expected • The larger the mass, the more distortion • Solar Eclipse