S8GU1L3 - The life cycle of stars

The life cycle of stars

S8GU1L3

Compare and contrast luminosity, apparent magnitude, and absolute magnitude.

• Luminosity, apparent magnitude, and absolute magnitude are all measures of a star’s brightness.

• Luminosity and absolute magnitude are the actual brightness of a star.

• Apparent magnitude measures the brightness of a star as seen from Earth.

Vocabulary

No, not this Nebula

No, Not Eitri the Dwarf King

End of Vocabulary Presentation

Astronomers determine the surface temperature of a star by looking at its color. Which stars are the hottest—red, blue, or yellow stars?

• Blue stars have surface temperatures greater than 25,000 degrees Kelvin.

• Blue stars are the hottest stars.

Multiple Choice

Which star is the hottest?

• green star

• red star

• blue star

• yellow star

The sun is a medium-sized star. Why does it appear so large and bright when viewed from Earth?

• The sun is the only star in our solar system.

• It is the closest star to Earth.

What is a star?

• A star is a large celestial body that is made up of gas and emits light and other electromagnetic radiation.

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Multiple Choice

What is the star that has collapsed under gravity to the point that the electrons and protons have smashed together to from neutrons?

• Supernova

• Neutron star

• Nebula

• White Dwarf

Stars are born, grown and die

Where are stars born?

• Stars are born in regions called nebulae.

• A nebula is a large cloud of gas and dust in interstellar space.

Multiple Select

What is a Nebula?

• a large cloud of gas and dust in interstellar space

• a gigantic explosion in which a massive star collapses

• a region in space where stars are born

• a small, hot dim star that is the leftover center of an old sun-like star

How is a star’s life cycle similar to a human’s life cycle?

• Both humans and stars are born, grow old, and die.

• An average human life span is about 80 years. But a star goes through its life cycle in millions or billions of years.

N11 Nebula

The N11 nebula looks like cotton candy because of layers of gas and dust within the nebula. How did the process of star formation cause this appearance?

• During the birth and early life of stars, dust and clouds are blown away from the stars.

• Each generation of new stars developed farther from the center of the nebula.

• This process formed layers of gas and dust within the nebula.

Formation of a Star

Describe the formation of a star.

• In some areas of a nebula, gravity causes the gas and dust to collapse quickly.

• As the gas and dust condense, they form a hot, dense protostar.

• As the temperature in the protostar rises, fusion begins.

• Fusion releases huge amounts of energy, including light. 

A protostar is a developing star. Based on the definition of a star, what are some characteristics of a protostar?

• Like any star, a protostar is a celestial body that is composed of gas and that emits light.

• A protostar emits only infrared light.

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infrared light converted into energy

Fusion

What process takes place within the core of a main-sequence star?

• The fusion of hydrogen nuclei to form a helium nucleus takes place within the core of a main-sequence star.

• This process releases energy, including light and heat.

Nuclear Holocaust

Multiple Choice

Nuclear weapons and nuclear power plants use fission reactions. Is fission the same thing as fusion?

• Yes

• No

Nuclear weapons and nuclear power plants use fission reactions. Is fission the same thing as fusion?

• No. Nuclear fission is a reaction in which an atomic nucleus splits into two smaller nuclei.

• However, both fission and fusion release large amounts of energy.

Evaluate: What happens when the fusion process in a star slows?

• When fusion slows, stars release matter into space and lose mass rapidly.

• At this point, the star has reached the final stage of its life cycle.

Review Star Formation

Multiple Choice

You have learned a lot about stars. Which image shows an area where stars are forming?

Explain how fusion is related to the life cycle of a star.

• A young star is called a protostar until temperatures are high enough for fusion to begin.

• Fusion continues for millions of years. When fusion slows, the star enters the final stage of its life cycle.

Describe the process of fusion.

• Fusion is the process by which two or more atomic nuclei combine.

• In main-sequence stars, hydrogen nuclei fuse to produce helium nuclei.

Red Giants

DEVELOP SCIENCE CONCEPTS

Describe the changes that take place in a low-mass star as it ages.

Eventually, there is no hydrogen left in a star’s core. When this happens, the hydrogen fusion stops. The star’s core condenses, and its atmosphere expands. The temperature of the core rises, and the star begins to fuse helium nuclei to produce carbon nuclei. At this point, the star is called a red giant. When all fusion stops, the outer layers of the giant star are sent into space, leaving only the core. The exposed core of the star is called a white dwarf.

Compare and contrast nebula and planetary nebula.

Nebula and planetary nebula are layers of gases in interstellar space. Planetary nebulae are the remnants of the outer atmosphere of a dying star. They disappear when the star’s core cools. Nebulae, on the other hand, are areas where stars are born. Many young stars may exist within a nebula.

WHY IT MATTERS:

The sun is a main-sequence star. What process is currently taking place in its core?

Currently, hydrogen nuclei are fusing to produce helium nuclei. There are two forms, called isotopes, of hydrogen nuclei in the sun’s core. One isotope has two neutrons and a proton. The other has one proton and one neutron. The fusion produces a helium nucleus and a neutron. It also releases enormous amounts of energy.

EXTEND AND REFLECT

Astronomers determine the surface temperature of a star by looking at its color. During which stage of a star’s life cycle do you think it’s hottest—as a red giant or a white dwarf?

Red, orange, and yellow stars are on the lower end of the temperature spectrum. Although the core of a red giant is very hot, the surface is not as hot as the surface of a white dwarf.

End of Presentation

to be continued