S8GU1L3 - The life cycle of stars Part 3

S8GU1L3 - The life cycle of stars Part 3

White dwarfs

What happens to cause a red giant to become a white dwarf?

• Fusion stops within a red giant when the star has used up all the hydrogen and helium for fusion.

• The star’s atmosphere is ejected into space, leaving only the hot, white core.

What happens once there is no longer fuel for the fusion of nuclei within the core of a red giant star?

• Eventually all fusion stops, and the star’s atmosphere is ejected into space, leaving only the core.

• The core is called a white dwarf.

Multiple Choice

The sun is a medium-mass star. It is currently a main-sequence star. What stage will the sun enter next?

• Protostar

• T-Tauri Phase

• Main Sequence

• Red Giant

Explanation:

• When fusion slows in a medium-mass star such as the sun, the star’s atmosphere expands and the star becomes a red giant.

• This is the next stage in the sun’s life cycle. 

Life cycle of a low-mass star

How is fusion in a main-sequence star different from fusion in a red giant?

• A main-sequence star fuses hydrogen nuclei to form helium nuclei.

• In the core of a red giant, helium nuclei fuse to form carbon nuclei.

Fusion is the source of light in both main-sequence stars and red giants. When fusion stops, a white dwarf develops. What is the source of light in a white dwarf?

• Stored energy is the source of light in a white dwarf.

• As this energy is used up, the white dwarf becomes dimmer and dimmer.

Supergiants

Multiple Choice

What determines whether a star becomes a red giant or a supergiant?

• a star's density

• a star's mass

• a star's stage in its evolution process

• a star's origin

What determines whether a star becomes a red giant or a supergiant?

• A star’s mass determines whether it becomes a red giant or a supergiant.

• Low-mass and medium-mass stars become red giants, but high-mass stars become supergiants.

What does it mean when we say a supergiant has high luminosity?

• Luminosity is a measure of the actual brightness of a star.

• A supergiant is extremely bright.

DEVELOP SCIENCE CONCEPTS

What kind of fusion takes place in the core of a red giant? How is this different from a supergiant?

• A red giant fuses helium nuclei to form carbon nuclei.

• A supergiant is able to fuse different nuclei into elements that are heavier than carbon.

Neutron Stars and Black holes

DEVELOP SCIENCE CONCEPTS

What determines whether a star becomes a neutron star or a black hole?

• The mass of supergiant star determines whether it becomes a neutron star or a black hole.

• The most massive stars become black holes after fusion ends.

What is a neutron star?

• A neutron star is star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons. 

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Describe a supernova.

• When fusion ends in a supergiant, the star throws its outer layers into space in a huge explosion called a supernova.

Life cycle of a high-mass star

Multiple Select

What may happen after a high mass star experiences a supernova?

• the star becomes a white dwarf

• the star may develop into a black hole

• the star may become a neutron star

• the star turns into a supergiant

7 main stages of a star

a. giant gas cloud b. protostar c. T-Tauri d. main sequence e. red giant f. fusion of heavier elements g. supernova

EVALUATE

What happens after fusion slows down in a star with a mass similar to the sun’s mass?

• The sun is a medium-mass star. When fusion slows down, this kind of star becomes a red giant.

• When fusion stops altogether, the red giant ejects its outer layers into space, leaving behind the hot, white core. The remaining star is called a white dwarf.

What happens to the most massive stars after they experience a supernova?

• Stars that are at least 20 times as massive as the sun become black holes after a supernova.

• The cores of these stars collapse so much that gravity does not allow anything to escape.

EXTEND AND REFLECT

What is the difference between a white dwarf and a neutron star?

• Both white dwarfs and neutron stars are the leftover cores of old stars.

• When fusion ends in a red giant, the star releases its outer layers into space. A red giant becomes a white dwarf.

• A supergiant releases its outer layers in a huge explosion called a supernova.

• The remaining core is extremely dense because the electrons and protons have smashed together to form neutrons. This is called a neutron star. 

End of Part 3

To be continued