Our Universe is vast, gigantic and its thought exceeds our imagination. It is infinite in size. If we explore more about our universe we understand many things that we have never seen in our widest dreams. Today, in the world of information technology, satellites and wireless communication, people of this generation have done immense research on this baffling topic i.e; "Our Universe". Our Universe is all the matter in space.   

Our  Universe is big. So we calculate the proximity of two stars in terms of light years.   Distance is too far to reach anywhere. Measurement in Kilo meters is too small to measure the distances between two celestial bodies in space.  So we measure in terms of light years. One light year is the time taken by the light to cover a distance in one year. Also, Light has uniform velocity. It travels at the velocity of approximately 6 lakhs kms per second. So we may wonder as to how much distance it covers for a year.   Some stars which were born billions of years ago are reaching us and we may wonder that even though they travel at a velocity of light, they take so much time to reach our planet earth and we see some of those stars today.

Our natural satellite moon, fascinates us and seems so mysterious in the night.  There is no air on the moon. and the gravity is approximately 1/6th of that of earth. Also, If, a person goes to moon he cannot talk to his friend unless he has any transmission device. There is no medium  through which our voice can pass to other person. The distance between the earth and the moon is equal to approximately four lakh kms. It takes 3 days to reach to moon with a fastest spacecraft. 

Gravity is a force which keeps all it's planets and stars move with its relative position. The planets are revolving  round the sun but what keeps it rotating around the sun. At the center of any celestial body, the force of gravity is maximum and that's why all bodies in space are attracted towards it's center.Even on earth we are all attracted towards our earth's center. The concept of gravity was known even in the past. Galileo, the man who moved the earth is among one of them who knew about gravity. Also, there was Newton, who knew about gravity. Before newton people had a wrong idea of our solar system. It was assumed that earth was in the center of the universe and all the plants and our star revolves round the earth. But we may wonder as to why all the planets are stars are almost spherical in shape. The reason was due to the fact that any celestial body always attract towards the center of any other celestial body and this is the reason as to why most of the bodies are almost spherical in shape. It's the gravitational force which keeps the planets revolving around the sun. Many scientists study the motion of planets and some other force like centripetal and centrifugal force. 

Our Universe was formed approximately about 20 billion years ago. It is assumed that our universe formed with a big bang.  There was a collision of Hydrogen, Helium atoms at that time and so gave a first glimpse of the birth of our universe. This theory was proposed by many people and so the assumption is still considered. This theory was named to be called big bang theory.  All the matter in our universe has energy.  Since any matter in our universe has energy, it is assumed that a massive energy is vibrating just as a musical string vibrates and so a theory known as "String" theory came into existence.  Further, it is assumed that our universe is expanding. Every matter is moving with a particular velocity. Even the stars, solar system, planets, galaxies are moving at a velocity. So we understand that our universe is expanding. All the matter is moving.  

Scientists  know more about our universe but it still remains a mystery. Perhaps, we sometimes feel that our life span is not enough to know all the things.  To unveil the hidden mystery, we have developed the most powerful telescopes and spacecrafts. Our universe is too big. We must spend 4 lights years approximately to reach to our nearest star. We have already sent messages or signals to a distant solar system assuming that we may one day find an alien life dwelling in a far off solar system, but it takes almost 25 light years to reach that destination.The most amazing hubble telescope has found a strange galaxy which is 45 million light years away from us.The name of the galaxy is NGC 660, also known as "polar ring galaxy". 

Further, Scientists have found free floating planets. These planets are isolated from other solar system and they do not revolve around any star. Also, Scientists have found a solar system which resembles our solar system. It has  a planet that as same as that of the earth. It has water too. The distance from the planet that is revolving around its star is almost same that of distance between our earth and sun. The name of the star has been kept as Star Gliese 581. This star is about 22 light years approximately from the earth. Scientists are closely studying this star to know if there is any alien life on this planet. There are trillions of galaxies in our universe and each galaxy has trillions of stars. Our galaxy is milky way. We have trillions of stars just in our own galaxy. The number of stars in our galaxy exceeds all the sand grains on all the beaches of our plant earth. Galaxies were born about more than 100 billion years ago. Even today there are birth to new galaxy. Many galaxies die and then they are reborn again. There is an endless cycle to birth and death. Two galaxies may collide and may give rise to a new galaxy and then gives rise to new solar systems, planets and so on. But in our universe we can assume that everything has an end. The star which is born will die in the future. Even our sun has a life span and has an end to it. Our sun was formed about  approximately 4.6 billions years ago. The average estimated life span of our sun is expected to be about 20 billion years. After this time everything in our solar system will be vanished. Then all the planets will be pulled towards the sun and the sun will become so small that the size of the sun might be approximately the size of a tennis ball and the mass will remain infinitely huge. All the stars will not end in the same manner as that of the sun. Some of them will become red giant before the end and some will become white dwarf and so on. 

What is the most powerful thing in the Universe? We can escape from any matter in this Universe but the one thing that you cannot escape is the most powerful thing in the Universe and that is black hole. Yes, The black hole is the most powerful thing in the Universe. Nobody can escape from this monster, black hole. If we go close to it then not even light can escape from it. Black holes are so powerful that it pulls any matter closer towards it. It does not pardon the giant stars too. Black holes have sufficient power to attract and pull the giant stars too. Black holes are usually dwelling at the center of the galaxy. Almost all the galaxies have black holes at it's center. Scientists have been observing this black holes till today. But it still remains a mystery. Some interesting things have been assumed on black holes. Black holes are also known as worm holes. It seems that worm holes offers cosmic shortcut to time and space and gives us the gateway to travel to some vast mysterious Universe.  The other question comes to our mind is as to how black holes are formed. Black holes are usually formed by a giant star . A giant star which is considered as a star which is more than 10 thousand times bigger than our own star "Sun". Such a star has massive gravitational field at the center of the star. At the center of star, the gravitation is so much that it starts colliding under its own gravity field and starts pulling itself towards it center and finally a huge violent supernova will occur and ultimately results in the formation of a black hole. One such star is the giant star named "Betelgeuse". The radius of this star is equivalent to 820700000 Km, the distance from the earth is 642.5 light years away from the planet earth, it's surface temperature is 3500 K and it's mass is equal to 15.31E0 Kg. This star is about to explode with a occurrence of a supernova. The center of the black hole has massive energy. Black hole shrinks everything towards it's center and this effect is so much that it becomes difficult to shrink further and the center point will have infinite density and  it is indefinitely small. This point is known as singularity. No light can escape at this point and our understanding of space and time breaks and therefore the laws of physics breaks down at this point.  

This Universe is full of mysteries. Though we have the most powerful telescopes and spacecrafts it's been a difficult task to unearth the most significant facts of our universe. Our Universe is big. It is bigger than our thoughts and dreams. We have billions of galaxies in our universe each with billions and trillions of stars. But the light of some of the stars may sometimes not reach us due to gas and dust in the cosmic space.