Astronomy Chapter 16 Flashcards

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Questions and Answers

What is a barred spiral galaxy?

A spiral galaxy in which the spiral arms begin from the ends of a bar running through the nuclear bulge.

What is a cluster of galaxies?

A collection of a few hundred to a few thousand galaxies bound by their mutual gravitational attraction.

What defines an elliptical galaxy?

A galaxy with an elliptical shape, little interstellar matter, and no spiral arms.

What is galactic cannibalism?

A collision between two galaxies of unequal mass and size in which the smaller galaxy is absorbed by the larger galaxy. Signup and view all the answers

What is a galactic merger?

A collision and subsequent merger of two roughly equal-sized galaxies. Signup and view all the answers

What is gravitational lensing?

The distortion of the appearance of an object by a source of gravity between it and the observer. Signup and view all the answers

What is the Hubble classification?

A system of classifying galaxies according to their appearance into one of four broad categories: spirals, barred spirals, ellipticals, and irregulars. Signup and view all the answers

What is the Hubble constant?

The constant of proportionality in the relation between the recessional velocities of remote galaxies and their distances. Signup and view all the answers

What does Hubble flow refer to?

The recession of the galaxies caused by the expansion of the universe. Signup and view all the answers

What is Hubble's law?

The relationship that states that the speeds of remote galaxies moving away from us are directly proportional to their distances from Earth. Signup and view all the answers

What is intergalactic gas?

Gas located between the galaxies within a cluster of galaxies. Signup and view all the answers

What is an irregular cluster of galaxies?

An unevenly distributed group of galaxies bound together by their mutual gravitational attraction. Signup and view all the answers

What defines an irregular galaxy?

An asymmetrical galaxy having neither arms nor elliptical shape. Signup and view all the answers

What is a lenticular galaxy?

A disk-shaped galaxy without spiral arms. Signup and view all the answers

What is the Local Group?

The cluster of about 40 galaxies of which our own Galaxy is a member. Signup and view all the answers

What is a poor cluster of galaxies?

A cluster of galaxies with only a few galaxies. Signup and view all the answers

What is a regular cluster of galaxies?

An evenly distributed group of galaxies bound together by mutual gravitational attraction. Signup and view all the answers

What is a rich cluster of galaxies?

A cluster of galaxies with many members. Signup and view all the answers

What is a spiral density wave?

A spiral-shaped pressure wave that orbits the disk of a spiral galaxy and induces new star formation. Signup and view all the answers

What defines a spiral galaxy?

A flattened, rotating galaxy with pinwheel-like spiral arms winding outward from the galaxy's nuclear bulge. Signup and view all the answers

What is a standard candle in astronomy?

An object whose known luminosity can be used to deduce the distance to a galaxy. Signup and view all the answers

What is a starburst galaxy?

A galaxy undergoing an exceptionally high rate of star formation. Signup and view all the answers

What is a supercluster of galaxies?

A gravitationally bound collection of many clusters of galaxies. Signup and view all the answers

What is a trailing-arm spiral galaxy?

A galaxy with its spiral arms pointing away from the direction of rotation, characteristic of all but one known spiral galaxy. Signup and view all the answers

What does the Tully-Fisher relation describe?

A correlation between the width of the 21-centimeter line of a spiral galaxy and its absolute magnitude. Signup and view all the answers

What are the least massive galaxies in the universe?

Giant ellipticals. Signup and view all the answers

Spiral density waves are directly responsible for what?

Promoting star formation. Signup and view all the answers

Which of the following statements about the motion of galaxies is correct?

Superclusters are all moving apart. Signup and view all the answers

What is the common name for the sonic boom created by lightning?

Supersonic boom. Signup and view all the answers

In spiral galaxies, what spectral classes of stars are only found in spiral arms?

Classes O and B are found only in spiral arms. Signup and view all the answers

What is the Hubble classification scheme?

A system that categorizes galaxies into spirals, barred spirals, ellipticals, and irregulars. Signup and view all the answers

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Study Notes

Key Galaxy Types

Barred Spiral Galaxy: Features spiral arms emerging from a central bar structure.
Elliptical Galaxy: Lacks spiral arms, has an elliptical shape and minimal interstellar matter.
Irregular Galaxy: Asymmetrical with no defined shape or structure.
Lenticular Galaxy: Disk-shaped, similar to spiral galaxies but without spiral arms.
Spiral Galaxy: Defined by its rotating, flattened shape and spiral arms originating from the nucleus.

Galaxy Collections

Cluster of Galaxies: Contains hundreds to thousands of galaxies held together by gravity.
Local Group: A cluster comprising approximately 40 galaxies, including the Milky Way.
Supercluster: A massive gravitational structure containing multiple galaxy clusters.
Rich Cluster: A galaxy cluster featuring a substantial number of member galaxies.
Poor Cluster: Composed of only a few galaxies.

Galaxy Interactions

Galactic Cannibalism: Occurs when a larger galaxy absorbs a smaller one during a collision.
Galactic Merger: Involves the merging of two galaxies of comparable size.

Galaxy Dynamics

Hubble's Laws: Describes the relationship between galaxy distance and recession speed, establishing that distances influence motion away from Earth.
Gravitational Lensing: A phenomenon where gravity distorts the view of distant objects.

Star Formation and Characteristics

Spiral Density Wave: A pressure wave in spiral galaxies that encourages new star formation.
Starburst Galaxy: Describes galaxies experiencing an exceptionally high star formation rate.
Standard Candle: An astronomical object with a known luminosity used to calculate distances to galaxies.
Classes O and B Stars: These high-mass stars are exclusively found in spiral arms, formed in actively star-forming regions.

Other Concepts

Hubble Constant: Vital for determining the universe's age based on galaxy recessional velocity.
Tully-Fisher Relation: Correlates the width of the 21-centimeter line in spiral galaxies with their absolute brightness.
Irregular Cluster of Galaxies: Characterized by an uneven distribution of galaxies, unlike regular clusters that are evenly distributed.

Miscellaneous

Gravitational Interactions: Superclusters are observed to be receding from one another, indicative of the expanding universe.
Supersonic Boom: Refers to the sound produced by lightning, analogous to the concept of a sonic boom.

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