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.

1. 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.

2. Under the right conditions, even visible light can be dangerous. Can you describe one such condition?

Blue. Red.

3. 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…

4. 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.

5. Which color refracts the most? Least?

Blue. 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.

6. 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.

7. 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…

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.

9. 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.

10. 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.

11. After our sun burns up all of its usable hydrogen, 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 will compress itself. This will cause it to heat back up and turn from red to white.

13. Eventually, our sun will turn into a black dwarf. Why?

The compression that heats up a white dwarf is the last energy source for the sun. After this energy is radiated into space, there will be no more. The sun will become cold and dark.

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.

16. Immediately after running out of fuel, a massive star’s temperature will ________.

Decrease

17. The temperature change of #16 will cause the volume of the star to ________.

shrink

18. 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, the outside layers 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 16-18

New nebulas that can turn into new solar systems like ours

Black Hole Neutron 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.

18.5 Where were the heaviest (heavier than iron) elements in our bodies created?

Supernova explosions

19. Why does the material from dying stars sometimes form “neutron stars?”

shrinkThere is so much pressure that the positive protons and the negative electrons fuse to become neutrons.

20. 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.

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.

Evidence supporting the Big Bang Theory:

1) Microwave 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.