1. STARS
Essential Questions

2. LEARNING OBJECTIVES:
SC.912.E.5.3: Describe and predict how the initial mass of a star determines its evolution

3. What Are Stars Made Of?
The chemical composition of stars is nearly three quarters hydrogen and over twenty percent helium
Other elements include carbon, oxygen, neon, silicon and iron, all of which are created in stars by nuclear fusion
Scientists analyze light spectra to determine the chemical composition of astronomical objects.
Use the link below to learn how scientists use spectroscopy to study stars.

4. How are Stars “Born”?
Nebula contain all the material necessary to create a star.
When these materials are disturbed by an interstellar occurrence such as a comet or a gravity wave, the gas and dust particles of the nebulae collide and coalesce.
Gravity then begins to pull more material inwards, heating it up in the process.
The star is “born” when the density and heat become so great that thermal nuclear fusion starts to take place and the star lights up.
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Use the link to watch a video more about star formation.

5. What are the Properties of Stars?
Stars are typically characterized by size, mass, color, temperature and luminosity (brightness).
A star’s brightness is measured two ways: Apparent magnitude (how bright it is from Earth) and Absolute magnitude (how bright a star appears at a standard distance).
Scientists use the H-R Diagram (right) to classify stars based on these properties.
Hertsprung-Russell (H-R) Diagram
Use the link below and complete the interactive activity to learn about the difference between apparent and absolute magnitude.

6. How are Stars Classified?
Stars are classified by their spectra (chemical elements they absorb) and temperature
There are seven primary classifications of stars
Use the link below and click on the stars to learn about the characteristic of each star classification.

7. What are the Different Kinds of Stars?
Most stars in the universe are Main Sequence stars. These stars include blue giants, red dwarfs and medium yellow-white stars like our sun.
Stars nearing the end of their life are red giants and red super giants.
Stars that have reached the end of their life cycle, or “dead” stars, are white dwarfs and neutron stars.
Brown dwarfs, are considered to be “failed” stars, as they do not have enough mass for nuclear fusion.
Use the link below to learn about the different types of stars in the universe.

8. How Does a Star “Die”?
The life, death and ultimate fate of a star is determined by its size
As stars burn off their hydrogen fuel, they begin fusing helium, becoming hotter and expanding
As average stars expand, they “throw off” their outer layers (planetary nebula) and the remaining core is a white dwarf
Massive stars, fuse elements until no more fusion can occur, which results in a massive explosion called a supernova.
Depending on the size of the star, either a neutron star or a black hole will be left behind.
Use the link below to learn about the life and death of stars.

9. What are Gamma Ray Bursts?
When a supermassive star dies, it will sometimes form a black hole
On some occasions, when too much material is pulled into the black hole, some of the energy is ejected out into space in the form of a gamma ray burst
Gamma ray bursts are the brightest things in the universe and can be seen throughout the universe
Use the link to learn about gamma ray bursts.

10. What are Pulsars and How are They Formed?
Pulsars (short for pulsating star) are rapidly rotating neutron stars
Their rapid rotation creates powerful magnetic fields that send out alternating beams of energy, which appear as lights flashing on and off from a distance.
Use the link below to learn what pulsars are and how they are formed.

11. What is a Black Hole?
A black hole is an area in space where gravity pulls so much that even light can not get out.
The gravity is so strong that the matter surrounding it has been squeezed into a tiny space.
Black holes are formed after supermassive stars die and become supernovas.
Use the link below to learn about black holes and what would happen if you fell into one.