Galaxy

 Universe

All the galaxies are a part of one big unit that we call the Universe. This in turn means that all the stars, planets, dust, dark matter, interstellar gas, stellar remnants are a part of the Universe. It is made up of many millions of stars and planets separated by gigantic empty spaces, along with every form of matter and energy. The human beings and all the living organisms on Planet Earth also are a tiny part of this one humongous unit.

2. Stellar Remnants

Stellar remnants are the remains of stars that are diminishing or they are in their final stage of existence. There is very little nuclear reaction going on in these stars. They do not behave like matter i.e. any solid, liquid or gas. They are much smaller and denser in structure. Each star’s ending depends on its initial mass it was born with.

DO NOT WORRY: Our sun has a lot of fuel left in it. We can safely bask in the sun for the next trillions of years.

4. Cosmic Dust

 Space dust or extraterrestrial dust is the dust that exists in the outer space. They are formed from exploding stars. Most of these particles are very small in size, a few microns in measurement. Cosmic dust can be segregated by its astronomical location – intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust (as in a planetary ring e.g. Saturn). In some parts in space, we find small concentrated clusters of these dusts that are called stardust. In fact, every day, a bit of these cosmic dust rains on our planet earth too!

5. Dark Matter

Dark matter is in fact, the invisible material in the Universe. They are invisible as they do not emit or reflect light. Roughly 85% of the Universe consists of dark matter. Dark matter has been categorized into cold, warm and hot based on the size and velocity of these particles. Naturally, the hotter the particles, the lighter and faster they will be.

Milky Way Galaxy

Milky Way is the galaxy that houses our solar system. It is a spiral galaxy with a diameter of approximately 150,000 to 200,000 light-years. It is bar-shaped in the center composed mainly of stars.  It approximately contains 100 to 400 billion stars and over 100 billion planets! Studies in astronomy show that most of the matter in Milky Way is invisible by a telescope. The oldest stars of the Milky Way are nearly as old as the universe itself. The Milky Way appears as a band from within when viewed from Earth because of its disk-shaped structure. Galileo Galilei was the first person to resolve what this band of light was, with his telescope in 1610.

You must remember that there are many other galaxies aside from our Milky Way. Some scientists believe that there could be as many as a hundred billion galaxies in the Universe. Some of the known galaxies are Andromeda galaxy, Cartwheel galaxy, Cigar galaxy, Comet galaxy, Bode’s galaxy among others. Imagine we live on a planet called earth, which is a part of a solar system that is a tiny part of a galaxy called the Milky Way, which in turn, is a part of this humongous Universe with billion other galaxies!

Check Point

Fill in the blanks:

1. Our solar system is a part of a galaxy known as ______________.
2. The galaxies are believed to have supermassive __________at their centers.
3. _______is the star located at the center of the Solar System.
4. __________are the dying stars that are becoming very small and dense.
5. __________and _____________ are the two main gases present in interstellar gas.

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