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Transcript
Can you guess why I am showing you this picture? Electromagnetic Waves, Stars, and The Universe Contents: • How we know what’s in a star (emission spectra) • Nuclear Fusion • Star life cycles (our sun versus massive stars) • Supernovae and creation of heavy elements • Black Holes • Big Bang Theory, with Evidence Longer wavelengths (left side) have less energy. Think of these waves a Which of being shaken. Rapidly shaken (high energy) strings look like strings type that are electromagnetic radiation is the ones on the right. typically most dangerous? What color are the hottest Why? stars that we can see? The coolest stars? Gamma rays. Shorter wavelengths have more energy. Blue. Red. Under the right conditions, even visible light can be dangerous. Can you describe one such condition? Laser light. When visible light is amplified and brought “into phase,” it can become intense enough to burn things. These shorter wavelengths have more energy. That’s why they’re dangerous. The Electromagnetic Spectrum •Visible light is just a small segment of the continuum. •The “red end” of the spectrum has longer wavelengths. The “blue end” has shorter wavelengths. •Shorter wavelengths have higher energy, so we know that a red star is cooler and a blue star is hotter. Blue stars – 40,000 degrees These green stars are bogus! The stars in the middle of the “rainbow” actually look white, because they’re a mix of the colors on either side. When you mix all the colors of light, you get white. Red stars – 3,000 degrees Why are there no green stars? If a star’s radiation output Why there are is centered on green, that no green star produces all colors of stars… the spectrum. A star that produces every color will appear white. •Stars emit many different wavelengths of “light.” •Light refracts (turns) when it passes through materials of different density (such as a glass prsim. Which color refracts the different so a most?amounts, Least? •Different wavelengths refract prism can separate light into a color spectrum. Violet. Red. Correct Refraction Incorrect Refraction,but it shows light from a star. A spectroscope separates radiation into its component wavelengths in an organized way that can be easily analyzed. •When elements are in gas state, they absorb or emit specific wavelengths of radiation. •The wavelengths of radiation an element emit or absorb depend on their electron configurations. •Those wavelengths can be used as a “fingerprint” to identify elements in distant stars. In the•When diagram,gases which part Why do differentorbit elements absorb light, their electrons faster, shows emission of light? absorb and emit different causing them to jump out to more distant energy levels Which part shows colors? (orbiting farther from the nucleus). absorption of light? •When electrons release energy (by giving off light), they Each element has a themdifferent to fall arrangement inward to of an orbit The bottom diagram, “deslow shows down. This causes excitation,” emission (giving off) of light. closer to the nucleus. The top diagram, “excitation,” shows absorption of light. electrons. Some electrons fall farther, giving off light with more energy (and a different color). “Fingerprints” of different elements Are these absorption spectra or emission spectra? Emission Example •The black lines are wavelengths of radiation that are absorbed by Neon. •If we see these black lines when we analyze starlight with a spectroscope, we know that neon is in the star. Neon Absorption Spectra In the sun, nuclei fuse. When they do this, the products of fusion have less mass than the nuclei that fused. This “lost” mass is actually converted to energy, according to Einstein’s famous equation… E = Energy produced by nuclear fusion C = Speed of light M = Mass that’s “lost” when nuclei fuse. Most stars are “Main Sequence” stars. These stars are powered by hydrogen fusion proceeding at a steady pace. Luminosity vs. Surface Temperature Luminosity = energy radiated each second In an average star,get like our Why will the sun bigger sun, its energy as itmost gets of older? comes from the fusion of Fusion produces helium Hydrogen. Hydrogen (heavier than Hydrogen), produces helium when it which sinks to the sun’s fuses. core and displaces This heliumoutward. is heavier, so it hydrogen sinks to the sun’s core and Why willthe the sun turn pushes hydrogen redder as it gets older? outward. As ages, this outward Asour thesun fusing hydrogen movement of fusing moves outward, it Hydrogen willless cause the sun encounters pressure, to soexpand. fusion slows down. Temperature drops. This outward movement also causes the rate of hydrogen fusion to diminish (due to lower pressure away from the core), thus cooling the sun. Cooling will turn it red. 11. AfterAtour sun point, burns fusion up all of andsun’s core. The sun some willitsnousable longerhydrogen occur in the helium (some helium also fuse),will why will itit shrink? will cool, andwill that cooling cause to shrink. This shrinkage will whichshrink will, in turn,they cause the sun to heat back It will coolcreate down.compression, Things generally when cool up (and turn from a cooler red to a hotter white). This stage is down. called a white dwarf. 12. Shrinking will cause the sun to turn white (becoming a white dwarf). Why? As the sun shrinks, it compresses itself. This causes it to heat back up and turn from red to white. 13. Eventually, our sun will turn into a black dwarf. Why? The energy it has as a white dwarf will slowly be lost to space. There is no new energy source. This stage is called a “planetary nebula.” The super hot core creates a “solar wind” that blasts away and “lights up” the outer layer of gases. With no fuel remaining, the star will eventually radiate its heat into space and turn to a cold, dark “black dwarf.” In the beginning, the massive star on the right was mostly _________. Hydrogen In a massive star, there is enough pressure to layers cause of a massive star come from? Where do the inner more fusion. Simply the elements Fusion put, of the outer layersin the inner layers come from fusion of the elements in the Why does the “ash” that is created by fusion move to the outer layers. It all starts with center of the sun? hydrogen fusion… When atoms fuse, their product is a heavier, denser The fusion process continues material. Denser materials sink. until iron is created. Even in a massive star there is not enough pressure for iron nuclei to fuse. Lifea massive Cycle of massive star (25 times size of thematerial sun) When stararuns out of fuel, it collapses. Thethe collapsing outer Immediately after running out of fuel, a massive star’s speeds toward the star’s center at an extremely high velocity. This outer material temperature will ________. then slams into the core and “bounces” back outward. This bounce is an explosion Decrease called a supernova. The temperature change of #16 will cause the volume of the star to ________. shrink When a massive star runs out of fuel and collapses on itself, its mass collides at its core and bounces back in an explosion called a ____________. As a result of this explosion, parts of the massive star fly away into space, where they can form _____________. If the mass remaining in the dead star’s core is 3 times our sun’s mass, it will form a ____________. If it is less, a __________ may form. supernova New nebulas that can turn into new solar systems like ours Black Hole Neutron Star Click mouse for questions 16-18 Life Cycle of a massive star (25that times theeven sizeheavier of thethan sun) A supernova produces such high pressures elements iron are formed by the fusion. Many(heavier of thesethan elements are scattered Where were heaviest iron) elements in into space and “recycled.” form new nebulas that create new stars. our bodiesThey created? Supernova explosions Scientists believe that all of the earth’s heavy elements were created in a massive star that exploded long ago. Why does the material from dying stars sometimes form “neutron stars?” Our solar system formed shrink There is so like much that the positive protons and from a nebula thispressure one, the negative electrons fuse to become neutrons. but smaller. Two characteristics of Neutron stars are: Extreme density (3 suns compressed into the size of a city --one spoonful would have the same mass as all of the cars on the earth) and very rapid spinning. Scientists believe the heavy elements in our solar system came from a supernova. Lifeouter Cycle of aofmassive The portions the star arestar blasted outward and scattered through space. (25 times the size of the sun) Ultimate Fate of A Massive Star (Greater than 25 Solar masses) The core becomes so compressed that protons (+) and electrons (-) fuse to create neutrons… If the material remaining in the core is less than 3 solar masses, a very dense “neutron star” is created. If the material remaining in the core is greater than 3 solar masses, its gravitational force is strong enough to cause the collapse of neutrons. The mass compresses itself into an infinitely small point whose gravity is so intense that not even light can escape from it. Our Sun is an average star like this one. What can this graphic be used to illustrate? What do “main sequence” stars have in common? Their energy is being produced by fusion of hydrogen into helium What percentage of stars are main sequence stars? About 90% The “Singularity” The “Event Horizon” The Big Bang Theory suggests that the universe exploded outward from an infinitely small point, called the “cosmic singularity” – and that the universe has been expanding ever since. As the universe expands, that Today, the wavelength of that radiation is so long that it corresponds to matter at about 3 degrees Kelvin (degrees above absolute zero). This is the most distant light that we can see. As space has expanded, this radiation has stretched along with space. radiation (emitted by the early 2000 degree universe) stretches with the universe, so its wavelength lengthens and energy decreases. Universe is now transparent to light, so suddenly, light can travel. Temperature of matter filling the universe is 2000 degrees Kelvin. Universe is a plasma, which is opaque to light. Radiation emitted just after the big bang has stretched along with the expanding universe. 13.7 billion years ago, the background radiation was consistent with radiation from a 2000 K degree body. Today, the background radiation has a longer wavelength, consistent with radiation from a 2.73 K degree body. Evidence supporting the Big Bang Theory: 1) Cosmic Microwave Background Radiation: Space is filled with low-energy microwave radiation of same temperature that scientists predicted would be left over from the Big Bang. More Big Bang Evidence: The Doppler Effect •Waves emitted by a moving object are compressed in front of the object and stretched out behind the object. •When a star moves toward us, we see shortened wavelengths. This is called a “blue shift,” because the blue end of the light spectrum has shorter wavelengths. 2) All distant galaxies, and most nearby galaxies, have redshifts (stretched waves), indicating that they are moving away from us, and that, therefore, the universe is expanding. Hubble’s Law •The farther away a galaxy is, the faster it is moving away from us. We can tell this by applying knowledge of the Doppler effect. Is this diagram showing an emission spectrum or an absorption spectrum? Absorption – the dark areas show the wavelengths of light that are being absorbed by the star. http://periodictable.com/Properties/A/Unive rseAbundance.ssp.log.html Balloon Model of The Universe’s Expansion (coins = galaxies; balloon surface = universe.) •The universe is inflating like the surface of a balloon. •Galaxies (pennies in diagram) are not moving through space, the space between them is expanding. •The space within galaxies is not expanding, because gravity is holding it together.