A galaxy is a collection of stars and other astronomical bodies, including planets, comets and asteroids, held together by gravity.

There are many different physical forms and measurements of galaxies. These include the spiral, barrel-spiral and elliptical. Our galaxy, called the Milky Way, is approximately 100,000 light years in width and contains over 100 billion stars.

The centre of galaxies can contain many young, very hot stars as well as older stars. Swirling clouds that have been energized by magnetic forces also exist in the centre. At this point in time, no one knows the exact number of galaxies in the universe. Astronomers are, however, learning more and more about them everyday.

From the text we know that …. 

A. gravity holds galaxies together in this universe

B. the number of our universe is limited in size

C. astronomers cannot study about galaxy anymore

D. there are some forms of galaxies that we know

The Correct answear is A. gravity holds galaxies together in this universe.