Question

A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction are called_______.
a.Galaxies
b.Comets
c.Collection of stars
d.None of the above

Answer 1

Hint: The Solar System is the gravitationally bound system which consists of the Sun, the eight planets , meteors and asteroids. the objects that orbit it, either directly or indirectly. Beyond the solar system, there are thousands of planetary systems revolving around other stars in the Milky Way.

Complete answer: Looking at the above options:
Option a: A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a supermassive black hole in the middle. When you look up at stars in the night sky, you're seeing other stars in the Milky Way. This option is correct.
Option b: Comets are cosmic snowballs of frozen gases, rock and dust that orbit the Sun.When a comet's orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. There are a total 6619 comets in our solar system. This option is incorrect.
Option c: The collection of stars seen in the sky are called constellations and a group of stars that forms a pattern in the sky is called an asterism.
Option d: This option stands irrelevant.

Hence, the correct answer is option 'a'.

Note: - Our galaxy is called the Milky Way because it seems as a milky band of light in the sky when one sees it in a really dark region.
-Astronomer Edwin classified galaxies according to shape. The three major categories are: elliptical, spiral and irregular.