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Earth is made mostly of metals and rocks. Where did this material come from?

It was produced by nuclear fusion in stars.

What is nuclear fusion?

the process of combining lightweight nuclei to make heavier nuclei

What's the sun mainly made of?

hydrogren and helium

By studying distant galaxies in the 1920s, Hubble made the following important discovery that led us to conclude that the universe is expanding

All galaxies outside the Local Group are moving away from us,and the farther away they are, the faster they're going.

The core of the sun is

hotter and denser than the surface.

How does the Sun generate energy today?

nuclear fusion

At the center of the sun, fusion converts hydrogen into

helium, energy, and neutrinos

Suppose you put two protons near each other. Bcause of the electromagnetic force, the two protons will

repel each other

Sunspot cycle

-the number of sunspots peaks approximately every 11 years
-the number of solar flares peaks about every 11 years
-the cycle is truly a cycle of magnetic activity, and variations in the number of sunspots are only one manifestation of the cycle
-with each subsequent peak in the number of sunspots, the magnetic polarity of the sun is the reverse of the previous peak (the first 11 years the North and South poles have 1 polarity, and the second 11 years they switch)

What observations characterize solar maximum?

We see many sunspots on the surface of the sun. Solar max is when the sun is most active, so there are more solar flares.

Since all stars begin their lies with the same basic composition, what characteristic most determines how they will differ?

mass they are formed with

If you were to come back to our Solar System in 6 to 7 billion years, what might you expect to find?

a red giant star

How would you describe the axes of a Hertzsprung-Russell (H-R) diagram?

surface temperature on the horizontal axis and luminosity on the vertical axis

On an H-R diagram, where would we find stars that are cool and dim?

lower right

How did Hubble measure the distance to the Andromeda galaxy?

He applied the period-luminosity relation to Cepheid variables.

On the main sequence, stars obtain their energy by

converting hydrogen to helium

What happens when a star exhausts its core hydrogen supply?

Its core contracts, but its outer layers expand and the star becomes bigger and brighter.

Stages of life for a low-mass star

protostar, main-sequence, red giant, white dwarf


-Stars 1.4-3 solar masses turn into neutron star
-More massive create black hole

Suppose the star Betelgeuse were to become a supernova tomorrow. What would it look like to the naked eye?

Betelgeuse would remain a dot of light but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.

Which event marks the beginning of a supernova?

the sudden collapse of an iron core into a compact ball of neutrons

From a theoretical standpoint, what's a pulsar?

a rapidly rotating neutron star

How does a black hole form from a massive star?

During supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole.

Neutron star

ball of neutrons the size of a city

What happens as the corona expands into space?

It becomes solar wind

Sun layers

core, radiative zone, photosphere, chromosphere, corona

Sun's core temperature

15 million K

Sun's surface temperature


Necessary temperature to fuse hydrogen into helium


How do stars replenish energy given off through fusion?


Brown dwarves

-Objects that contract but don't have nuclear fusion
-Cool, dim, and small
-Contract until electron degeneracy pressure forms
-13 to 80 Jupiter masses
-Give off infrared radiation

Electron degeneracy pressure

-Keeps stars from contracting so much that they explode
-In a fully degenerate electron state, all electrons are in their lowest possible energy levels


-don't like to touch each other or be in the same quantum state


-like being together in the same quantum state


-form from clouds of dust and gas that collapse due to their own gravity
-young star
-once it's dense enough that the ocllisions cause agitation and heating, it's a pre-main sequence star
-once fusion starts, it's a main sequence star

What will happen to the sun?

It will run out of hydrogen in its core to fuse into helium and turn into a red giant star. The gas will expand and cool off, giving it a red color. At 100 million degrees, helium in the core will fuse into carbon and oxygen. Eventually, the core of carbon and oxygen will have 2 shells which will bloat the star and it will become a white dwarf star. There will be no fusion since carbon and oxygen repel each other.The white dwarf star will cool off.

Planetary nebula

-Structure of white dwarf star
-Dying stars lose most of their material

White dwarf stars

-No new energy
-Small and dim
-Only thermal energy that was there during creation
-Electrons are piled up in all possible quantum states so they can't lose energy
-If mass is added, they contract and become more dense because of added gravity
-If too much mass is added, it collpases

.08-8 solar masses

main sequence-red giant-white dwarf-black dwarf

Chandrasekhar Limit

As white dwarfs accumulate mass, the radius shrinks and the electrons approach the speed of light which is difficult, so the electrons' ability to exert pressure decreases. When a star reaches this, it collapses into its core.


-As the star is collapsing, its density bounces back and forth
-If stuff around the core hits the core while it's bouncing it's propelled outwards
-Protons and neutrons collide to form neutrinos

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