WHAT ARE STAR-SYSTEMS

A STAR SYSTEM

A star-system (galaxy) is like an independent star-city with millions of stars, gas and dust in it. The force of gravity holds them all together. Galaxies were formed soon after the universe had come into being about 10-20 billions years ago. To begin with, they were just huge clouds of gas-mainly hydrogen. By and by the huge gas-clouds took the shape of smaller gas-lumps due to gravity and begin to shine as stars.

Astronomers do not know how many galaxies there are in the universe, though they have photographed millions of them with their telescopes. Still it is believed that they are in billions. They are unevenly scattered throughout the universe. Small galaxies have stars in millions while the big ones have in billions and trillions.

TYPES OF GALAXIES

The galaxy; whereof our solar system is a part, is called the Milky Way. Besides it, three other galaxies can be seen from the earth with the naked eye on dark clear nights. They are:

1. Andromeda which can be seen in the northern hemisphere,

2. Large Magellanic Cloud } they can be seen in the southern hemisphere

3. Small Magellanic Cloud }

Galaxies fall into four types in respect of their shapes:

(a) Spiral (Disc) Galaxies

(b) Barred Spiral (Disc) Galaxies

(c) Elliptical Galaxies

(d) Irregular Galaxies

Galaxies occur in small and big clusters that may number in two or three digits. These clusters may belong to super-clusters. These clusters and super-clusters are speedily flying away from one another because the universe is ever expanding.

Galaxies give off several kinds of radiation (light rays etc.) in space. Some scientists believe that all galaxies are about the same age as they were formed soon after the Big Bang. But others believe that new galaxies keep forming constantly as the old ones move apart.