The Life and Death of Stars

How do we gather information about distant stars?

Answer explanation

We gather information about stars using the light that is produced by each star.

When is a white dwarf formed?

Answer explanation

At the end of the life cycle of medium and small stars.

Why is a light-year a more useful measurement in astronomy than a meter is?

Answer explanation

The enormous size of the galaxy and universe necessitate a much larger unit of measure than is provided by the meter. If meters were the standard unit of measure, numeric representations of distances between celestial bodies would be so large as to be impractical.

Describe how astronomers determine the composition of a star.

Answer explanation

When a light passes through a prism, the light is broken up into different colors. Each color corresponds to a specific wavelength in the electromagnetic spectrum. Each element produces a unique pattern of spectral lines, which includes dark lines where light is missing at specific wavelengths. By comparing the spectral line patterns of known elements to those produced by stars, scientists can deduce the chemical composition of stars.

What are the products and reactants in the primary fusion reaction carried out within the sun?

Answer explanation

Two hydrogen nuclei are fused to produce a helium nucleus and energy.

What conditions, common to most stars including our sun, appear to be necessary in order for fusion reactions to take place?

Answer explanation

Nuclear fusion occurs under conditions of extremely high temperature and pressure.

Name two properties that are used to characterize a star.

Answer explanation

Two defining properties used to characterize a star are color and brightness. Another property is composition and the fact that stars are driven by nuclear fusion reactions.

Describe the birth of a star.

Answer explanation

A star begins to form when a cloud of gas and dust collapses inward as a result of gravitational forces. When the temperature at the center of the cloud reaches approximately 15 million Kelvins, electrons are stripped from hydrogen atoms, leaving positively charged protons. At these very high temperatures, protons can fuse to form helium atoms. Once nuclear fusion begins in the cloud, a star is born.

What information can be derived from the color of a star?

Answer explanation

Each color is associated with a specific temperature. Therefore, the surface temperature of a star can be estimated using color.

How is the death of a very large star different from the death of smaller stars?

Answer explanation

Late in their lives, smaller stars become red giants that fuse helium into carbon and oxygen. Then they die out as white dwarfs. Instead of red giants, large stars form supergiants that can produce iron through fusion. When the core of a supergiant is entirely iron, fusion stops, which causes the core to collapse. This collapse results in a violent rebound explosion called a supernova.