Chapter 26, Problem 1E

Describe the main distinguishing features of spiral, elliptical, and irregular galaxies.

To determine

The differences between spiral, elliptical and irregular galaxies.

Explanation of Solution

The differences between spiral, elliptical and irregular galaxies are stated in the table below.

Characteristics	Spiral galaxy	Elliptical galaxy	Irregular galaxy
Mass	The mass of the spiral galaxy is ${10}^9$ to ${10}^{12}$ times of the mass of the sun.	The mass of the elliptical galaxy is ${10}^5$ to ${10}^{13}$ times of the mass of the sun.	The mass of the irregular galaxy is ${10}^8$ to ${10}^{11}$ times of the mass of the sun.
Diameter	The diameter of the spiral galaxy is $15,000$ to $150,000$$\text{light-years}$ .	The diameter of the elliptical galaxy is $3,000$ to $>700,000$$\text{light-years}$ .	The diameter of the irregular galaxy is $3,000$ to $30,000$$\text{light-years}$ .
Luminosity	The luminosity of the spiral galaxy is ${10}^8$ to ${10}^{11}$ times of the luminosity of the sun.	The luminosity of the elliptical galaxy is ${10}^6$ to ${10}^{11}$ times of the luminosity of the sun.	The luminosity of the irregular galaxy is ${10}^7$ to $2\times {10}^9$ times of the luminosity of the sun.
Stars	The spiral galaxy consists of a large population of old and young stars.	The elliptical galaxy consists of a large population of old stars.	The irregular galaxy consists of a large population of old and young stars.
Interstellar material	The spiral galaxy consists of gas and dust as interstellar material.	The elliptical galaxy consists of a little amount of gas and almost no dust as interstellar material.	The irregular galaxy consists of gas and dust as interstellar material
Mass to light ratio in the visible part	The mass to light ratio in the visible part of the spiral galaxy is 2 to 10.	The mass to light ratio in the visible part of the elliptical galaxy is 10 to 20.	The mass to light ratio in the visible part of an irregular galaxy is 1 to 10.
Mass to light ratio for galaxy	The mass to light ratio for the spiral galaxy is 100.	The mass to light ratio for the elliptical galaxy is 100.	The mass to light ratio for the irregular galaxy is not defined.