Unit 5 Critical Thinking Dropbox: Exploring Types of Galaxies

Which of the following is a characteristic feature of spiral galaxies?

• They have a smooth, featureless appearance.

• They contain a central bulge and spiral arms.

• They lack a defined shape and structure.

• They are primarily composed of older stars.

Answer explanation

Spiral galaxies are characterized by their distinct structure, which includes a central bulge and prominent spiral arms. This feature differentiates them from other galaxy types, making the second choice the correct answer.

What is a common similarity between elliptical and irregular galaxies?

• Both have well-defined spiral arms.

• Both can contain older stars.

• Both have a central bulge.

• Both are primarily composed of gas and dust.

Answer explanation

Both elliptical and irregular galaxies can contain older stars, as they are not defined by a specific star formation rate. This contrasts with spiral galaxies, which typically have younger stars in their arms.

Which of the following statements best describes a difference between spiral and elliptical galaxies?

• Spiral galaxies have a more defined shape compared to elliptical galaxies.

• Elliptical galaxies have spiral arms, while spiral galaxies do not.

• Spiral galaxies are generally older than elliptical galaxies.

• Elliptical galaxies contain more gas and dust than spiral galaxies.

Answer explanation

Spiral galaxies have a distinct structure with defined spiral arms, while elliptical galaxies have a more rounded, less defined shape. This makes the first statement the best description of their difference.

Identify a key difference between spiral and irregular galaxies.

• Spiral galaxies have a central bulge, while irregular galaxies do not.

• Irregular galaxies have spiral arms, while spiral galaxies do not.

• Both have a smooth, featureless appearance.

• Both are primarily composed of older stars.

Answer explanation

Spiral galaxies are characterized by a central bulge and distinct spiral arms, while irregular galaxies lack this defined structure. This key difference helps in classifying the two types of galaxies.

Which of the following is a characteristic of elliptical galaxies?

• They have a well-defined spiral structure.

• They are often rich in gas and dust.

• They have a smooth, featureless appearance.

• They are primarily composed of young stars.

Answer explanation

Elliptical galaxies are characterized by their smooth, featureless appearance, lacking the defined structure seen in spiral galaxies. They typically contain older stars and are not rich in gas and dust.

What is a common feature of irregular galaxies?

• They have a central bulge and spiral arms.

• They lack a defined shape and structure.

• They are primarily composed of older stars.

• They have a smooth, featureless appearance.

Answer explanation

Irregular galaxies are characterized by their lack of a defined shape and structure, distinguishing them from spiral and elliptical galaxies, which have more organized forms.

Which of the following is a similarity between spiral and irregular galaxies?

• Both have a central bulge.

• Both can contain regions of active star formation.

• Both have a smooth, featureless appearance.

• Both are primarily composed of older stars.

Answer explanation

Both spiral and irregular galaxies can contain regions of active star formation, making this a key similarity. In contrast, the other options do not accurately describe both types of galaxies.

Which of the following is a difference between elliptical and irregular galaxies?

• Elliptical galaxies have a defined shape, while irregular galaxies do not.

• Irregular galaxies have a central bulge, while elliptical galaxies do not.

• Both have spiral arms.

• Both are primarily composed of young stars.

Answer explanation

Elliptical galaxies are characterized by their smooth, rounded shapes, while irregular galaxies lack a defined structure, making the first choice correct.

Which of the following best describes the composition of spiral galaxies?

• They are primarily composed of older stars with little gas and dust.

• They contain a mix of older and younger stars, with significant gas and dust.

• They are primarily composed of young stars with no gas and dust.

• They have a smooth, featureless appearance.

Answer explanation

Spiral galaxies are characterized by a mix of older and younger stars, along with significant amounts of gas and dust, which are essential for star formation. This distinguishes them from other galaxy types.

What is a defining characteristic of irregular galaxies compared to spiral and elliptical galaxies?

• They have a central bulge and spiral arms.

• They have a smooth, featureless appearance.

• They lack a defined shape and structure.

• They are primarily composed of older stars.

Answer explanation

Irregular galaxies are characterized by their lack of a defined shape and structure, unlike spiral galaxies which have central bulges and arms, and elliptical galaxies which are smooth and featureless.