Chapter 17, Problem 1QFR

To determine

The three main types of galaxies and find the galaxy differ in their shape, stellar content, and interstellar matter.

Answer to Problem 1QFR

The three main types of galaxies are spiral, elliptical, and irregular galaxy.

The elliptical galaxy are elliptical in shape, it is formed through galactic collision. It has little star formation; there is no interstellar medium.

The spiral galaxy are spiral in shape, it is formed through collision of smaller galaxies. It has rotating flat disc of star, dust and gases. It has large amount of interstellar medium.

The irregular galaxy does not have specific shape; it is formed through external gravitational disturbances. They have large amounts of interstellar medium.

Explanation of Solution

Elliptical galaxy:

Elliptical galaxy formed through galactic collisions. Thus the elliptical galaxy contains between 10 million to 100 trillion stars.

Elliptical galaxies contain metal rich stars that appear orange and red in color. It has no interstellar medium and thus it has very little star formation.

Spiral galaxy:

Spiral galaxies have two or more windings from the center. These galaxies contains mixture of young and old stars, because to make a young star, a galaxy must contains dense clouds of dust and gas

Spiral galaxies have 15% of mass in their disk in the form of interstellar matter,

Conclusion:

Irregular galaxy:

An irregular galaxy is a galaxy that does not have a specific shape. These galaxies are formed from external gravitational disturbance such as another galaxy passing near to it, it has large amount of interstellar medium.