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

These shorter wavelengths have more energy. That’s why they’re dangerous. Longer wavelengths (left side) have less energy. Think of these waves a strings that are being shaken. Rapidly shaken (high energy) strings look like the ones on the right. Which type of electromagnetic radiation is typically most dangerous? Why? Gamma rays. Shorter wavelengths have more energy. Laser light. When visible light is amplified and brought “into phase,” it can become intense enough to burn things. Under the right conditions, even visible light can be dangerous. Can you describe one such condition? Blue. Red. What color are the hottest stars that we can see? The coolest stars?

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 Red stars – 3,000 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.

Why there are no green stars… Why are there no green stars? If a star’s radiation output is centered on green, that star produces all colors of 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. Different wavelengths refract different amounts, so a prism can separate light into a color spectrum. Correct Refraction Incorrect Refraction,but it shows light from a star. Which color refracts the most? Least? Violet. Red.

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.

When gases absorb light, their electrons orbit faster, causing them to jump out to more distant energy levels (orbiting farther from the nucleus). When electrons release energy (by giving off light), they slow down. This causes them to fall inward to an orbit closer to the nucleus. In the diagram, which part shows emission of light? Which part shows absorption of light? The bottom diagram, “de- excitation,” shows emission (giving off) of light. The top diagram, “excitation,” shows absorption of light. Why do different elements absorb and emit different colors? Each element has a different arrangement of 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

E = Energy produced by nuclear fusion M = Mass that’s “lost” when nuclei fuse. C = Speed of light 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…

Luminosity vs. Surface Temperature Luminosity = energy radiated each second Most stars are “Main Sequence” stars. These stars are powered by hydrogen fusion proceeding at a steady pace.

In an average star, like our sun, most of its energy comes from the fusion of Hydrogen. Hydrogen produces helium when it fuses. This helium is heavier, so it sinks to the sun’s core and pushes the hydrogen outward. As our sun ages, this outward movement of fusing Hydrogen will cause the sun to expand. 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. Why will the sun get bigger as it gets older? Fusion produces helium (heavier than Hydrogen), which sinks to the sun’s core and displaces hydrogen outward. Why will the sun turn redder as it gets older? As the fusing hydrogen moves outward, it encounters less pressure, so fusion slows down. Temperature drops.

At some point, fusion will no longer occur in the sun’s core. The sun will cool, and that cooling will cause it to shrink. This shrinkage will create compression, which will, in turn, cause the sun to heat back up (and turn from a cooler red to a hotter white). This stage is called a white dwarf. With no fuel remaining, the star will eventually radiate its heat into space and turn to a cold, dark “black dwarf.” 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.planetary nebula 11. After our sun burns up all of its usable hydrogen and helium (some helium will also fuse), why will it shrink? It will cool down. Things generally shrink when they cool down. 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.

In a massive star, there is enough pressure to cause more fusion. Simply put, the elements in the inner layers come from fusion of the elements in the outer layers. It all starts with hydrogen fusion… The fusion process continues until iron is created. Even in a massive star there is not enough pressure for iron nuclei to fuse. In the beginning, the massive star on the right was mostly _________. Hydrogen Where do the inner layers of a massive star come from? Fusion of the outer layers Why does the “ash” that is created by fusion move to the center of the sun? When atoms fuse, their product is a heavier, denser material. Denser materials sink.

Life Cycle of a massive star (25 times the size of the sun) When a massive star runs out of fuel, it collapses. The collapsing outer material speeds toward the star’s center at an extremely high velocity. This outer material then slams into the core and “bounces” back outward. This bounce is an explosion called a supernova. Immediately after running out of fuel, a massive star’s temperature will ________. Decrease 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 Click mouse for questions New nebulas that can turn into new solar systems like ours Black HoleNeutron Star

Life Cycle of a massive star (25 times the size of the sun) A supernova produces such high pressures that elements even heavier than iron are formed by fusion. Many of these elements are scattered into space and “recycled.” They form new nebulas that create new stars. Scientists believe that all of the earth’s heavy elements were created in a massive star that exploded long ago. Our solar system formed from a nebula like this one, but smaller. Scientists believe the heavy elements in our solar system came from a supernova. Where were the heaviest (heavier than iron) elements in our bodies created? Supernova explosions Why does the material from dying stars sometimes form “neutron stars?” shrink There is so much pressure that the positive protons and the negative electrons fuse to become neutrons. 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.

Life Cycle of a massive star (25 times the size of the sun) The outer portions of the star are blasted outward and scattered through space. 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. Ultimate Fate of A Massive Star (Greater than 25 Solar masses)

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. Universe is a plasma, which is opaque to light. Universe is now transparent to light, so suddenly, light can travel. Temperature of matter filling the universe is 2000 degrees Kelvin. This is the most distant light that we can see. As space has expanded, this radiation has stretched along with space. As the universe expands, that radiation (emitted by the early 2000 degree universe) stretches with the universe, so its wavelength lengthens and energy decreases. Today, the wavelength of that radiation is so long that it corresponds to matter at about 3 degrees Kelvin (degrees above absolute zero).

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. Radiation emitted just after the big bang has stretched along with the expanding universe.

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 red- shifts (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.

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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.