Του Αντώνη Καπετάνιου μαθητή της Β τάξης
You have heard the word universe in TV shows and radio broadcasts many times, but have you ever wondered what the universe really is? Well the answer lies here, it is pretty much everything. To be more specific the universe contains all matter, energy, planets, stars and galaxies.
And for many here the question arises: “How was the universe created?”. Even astronomers and astrophysicists have difficulty in explaining this. Most of them claim that around 14 billion years ago the universe was condensed in an extremely small point and the next moment the biggest explosion in the history of the universe happened. At a temperature of approximately 5.5 billion degrees Celsius, there was no matter, just huge amounts of energy.
Nevertheless, the cosmos as we know it today began to develop gradually. After this explosion, the universe started cooling and matter was formed. It was dark, there was no light. It started shining about 380,000 years after the Bing Bang. And that was when it started taking its current form.
Earth: The Blue Planet
As we all know, Earth is a planet. Planets are huge astronomical objects which have a round shape. Also they orbit around a star or a stellar remnant. Earth was formed 4,54 billion years ago.
The most amazing fact about Earth is that it meets the requirements in order to be able to host life as we know it. Its right distance from the sun, its climate and water are the most important specifications that are required for life to develop.
Moreover, 70% of earth’s surface is covered by oceans (this is the reason why it is called the blue planet). Last but not least, it has a nickel-iron core which provide a magnetic field. This magnetic field protects life from solar winds which can be harmful.
The Sun
It is common knowledge the fact that without the sun there wouldn’t be life on earth. The sun is a star, but what exactly is a star?
Well, it is a large sphere of gas that emits huge amounts of heat, radiation and energy. The main difference between stars and planets is their size. Although both stars and planets in the very beginning of their life are hot spheres, what defines whether this object is going to be a star or a planet is its size. Stars are larger than planets. Because of their mass it is impossible to cool down and for this reason they remain hot and shinny for the rest of their life.
Stars begin to form when a disturbance, such as a shock wave by a nearby supernova (an exploding star), causes gas clouds to collapse. Then the gas heats up until it turns to plasma. However, this cool interstellar gas needs about 10 million years to gather, heat up and eventually transform into a star.
There is a large variety in the size and color of the stars. In particular, the cooler stars give off a reddish color and the warmer ones a bluish color.
In addition smaller red stars (called red dwarfs) such as Proxima Centauri, use less energy and “live” longer, about 10 trillion years. On the other hand, bigger blue stars (called blue super giants) such as Rigel use the most energy, emit large amounts of radiation and die out much faster than the other stars.
Our star, the sun, is a yellow dwarf. It has a diameter of approximately 1,392,684 kilometers and was formed about 4.57 billion years ago and it has about 5 billion years to go.
Galaxies
The word galaxy is derived from the Greek word “galaxias” (γαλαξίας) and literally, it means “milky”. Galaxies are jumbo clusters of stars, gas, planets, dust. Astronomers don’t know exactly how many galaxies exist, but they have estimated that just in the observable universe there are about one hundred billion galaxies.
There are three major types of galaxies depending on their shape: spiral, elliptical and irregular galaxies.
The galaxy which hosts our solar system is called Milky Way and belongs in the category of spiral galaxies. They look like flat disks with spiraling arms and a bulbous center where some of the oldest stars reside. All of the stars, planets, dust, black holes and nebulae (interstellar clouds of ionized gases) revolve around this center. Spiral galaxies spin around their bulbous center at hundreds of kilometers per second.
The second type is elliptical galaxies. They are believed to form when two spiral galaxies collide (a process that takes billions of years). Some of them are almost a perfect circle and some other are more elongated. They also have a center but their stars tend to move more randomly than those in spiral galaxies.
Finally, we have irregular galaxies. These galaxies do not have a certain pattern like spiral and elliptical galaxies. Most of the times this is caused by gravitational influences from nearby galaxies.
The Milky Way
Milky Way is a Spiral Galaxy. Actually it belongs in a subcategory called Barred Spiral Galaxies. Planet Earth resides in one of Milky Way’s spiral arms. It has more than one hundred billion stars. Some decades ago, scientists believed that earth was located near the center of our galaxy. After many years this state was proven wrong.
Furthermore, the nearest galaxy, Andromeda, is moving towards our galaxy at about 110 kilometers per second. But there is no need to worry because the collision is not likely to happen for at least another four billion years.
Black Holes
To begin with, there is a big misconception concerning black holes. Most people believe that black holes can transfer you to another dimension. I am sorry, but I have to disappoint you, this is just a myth. Black holes are defined regions of compact mass. They are called black due to the fact that even light cannot escape from them.
Black holes vary in size. They can have extremely small size but the ten times the mass of the sun. They are classified to supermassive and stellar.
Supermassive black holes are found in the center of every large galaxy and as their name suggests they are enormous.
Stellar black holes are tiny but their mass is huge.
Exploration Of The Universe
One last question. How do we know all these things? Astronomers and astrophysicists using telescopes and satellite can collect images from the farthest edges of the universe and study them. Additionally, manned missions to the moon and robots sent to Mars and other nearby planets help us collect more information. Finally, scientists create mathematical models which allow them to understand the universe and many astronomical phenomenons better.
«When I look up at the night sky and I know that yes we are a part of this universe, we are in this universe, but perhaps more important than both of those facts is that the universe is in us… Many people feel small cause they’re small and the universe is big, but I feel big because my atoms came from those stars. There’s a level of connectivity.»
— Neil deGrasse Tyson, Astrophysicist, Time magazine, 2012
Sources
https://sway.com/universe_cheatsheet
https://en.wikipedia.org/wiki/Black_hole
https://en.wikipedia.org/wiki/Galaxy
