Black Hole

Whenever we talk about the universe, one thing that really blows our minds is how big it is. it's very hard to imagine how big it really is. There are billions of stars spread out in the galaxies, and each one is a different size and shape. It's like a huge playground in space, where everything are interconnected by gravity, which pulls everything together. 

There are plenty of black hole present in the universe. A black hole is a celestial body in space characterized by an intense gravitational force that prevents anything from escaping. Black holes are created through the process of giant massive star collapse, and possibly through other processes that remain unidentified. It acts like a cosmic vacuum cleaner, sucking in everything around it with its incredible gravitational force. These black holes are so powerful that they slow down time for anything nearby. Imagine being near one of these cosmic giants; time would appear to move very slowly. The black hole is invisible since it does not refflect any visible light.

Big Bang: The Formation of the Universe

In 1927, Georges Lemaitre proposed the Big Bang Theory.  Big Bang Theory is a scientific framework that explains the expansion of the universe from a densely packed and hot starting point. The universe originated from a singular point that was extremely hot and dense. This point rapidly expanded and stretched, initially at unimaginable rates and then at a more measurable rate, over a period of 13.7 billion years. As a result, we now have the continuously expanding universe that we are familiar with today. Current technological limitations prevent scientists from directly observing the creation of the universe. Therefore, our understanding of the Big Bang mostly relies on mathematical calculations and simulations. Astronomers are able to observe the reverberation of the expansion via a phenomena called the cosmic microwave background.

Approximately 13.7 billion years ago, all matter in the universe was compressed into an extremely small singularity, characterized by limitless density and heat. Suddenly, a rapid and forceful expansion commenced, causing our universe to rapidly expand outward at a velocity exceeding that of light. This was a brief moment of cosmic inflation that lasted for approximately 10^-32 second. After that event, when the temperature of everything was still extremely high, at approximately 10 billion degrees Fahrenheit an extensive flood of matter and radiation, referred to as reheating, commenced the process of building our universe with celestial objects such as stars and galaxies. The universe now contained an extensive amount of elementary particles, including neutrons, electrons, and protons, which served as the main building blocks for the formation of stars and galaxies.

At this moment, the unbound electrons would have caused light (photons) to scatter in the same way sunlight scatters from water droplets in clouds. Over time, the free electrons bonded with atomic nuclei, resulting in the formation of neutral atoms or atoms with balanced positive and negative electric charges.

After a period of about 380,000 years after the event of the Big Bang, light was finally able to glow. The term used to refer to this light is the cosmic microwave background.

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Bimal Kumar Dora

How big is our solar system?

According to scientists, there are around 2 lakh crores of galaxies in our visible universe. The galaxy we live in is known as the Milky Way. It is claimed to contain 25 to 40 thousand crores of stars, each of which is a solar system in itself.


Let us have a look at our solar system. Our star is known as the Sun, and it includes eight planets, moons, asteroids, and dwarf planets. Then a genuine question arises in our mind how big is our solar system?

Consider the sun to be the starting point for our solar system. The distance between the earth and the sun is now about 15 crore kilometers (i.e. one astronomical unit).

The time it takes for a light beam to travel from our sun to the closest planet, Mercury, is 3 minutes. The journey to Venus requires a duration of 6 minutes. The duration for the Sun's light to travel from the Sun to Earth is 8 minutes and 20 seconds. The duration of the journey to Mars is 13 minutes. It takes a duration of 15 minutes for the light to travel through the whole asteroid belt. The sunlight takes around 43 minutes to reach Jupiter. The duration for sunlight to travel from the Sun to Uranus is 2 hours and 40 minutes. The journey to Neptune takes a total of 4 hours and 10 minutes. When considering the planet Pluto's location in the Kuiper Belt, it takes a duration of 5 hours and 30 minutes for the Sun's light to travel and reach that destination.


The Kuiper Belt is a huge area of the outer solar system located beyond Neptune's orbit. The Kuiper Belt is named after Dutch astronomer Gerard Kuiper, who hypothesized its presence in the 1950s, and resembles a massive, doughnut-shaped disk made up of icy bodies, dwarf planets, and other small celestial bodies. The light takes around 1 hour and 10 minutes to traverse this quipper belt. We can reach interstellar space after traveling through the Sun's heliosphere for almost 12 hours. However, the adventure of our solar system does not finish here.


The outer portion of the solar system is called the Oort cloud. It takes about a year for sunlight to get over the Oort cloud. Proxima Centauri, located around 4.26 light years from the Sun, is the nearest star to our solar system. The Oort Cloud is believed to cover a distance a quarter of this distance, making it even farther than one light year. According to many scientists, our Sun's gravitational reach might extend beyond two light years. And after that, obviously, the solar system of Proxima Centauri will take place. This means that to get out of our solar system, we will literally have to enter another solar system.


(It may be claimed that Voyager 1 will enter the Oort cloud after 300 years. It will take at least 30,000 years to traverse the Oort cloud. The Parker Solar Probe is currently the fastest object created by human beings. It travels at a speed of around 430 kilometers per second. Now, if we attempt to reach Proxima Centauri, it will take at least 70,000 years.)

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Bimal Kumar Dora

If the universe is only 13.7 billion years old, How the diameter of the observable universe be 92 billion light years.

 1 Light Year = 9,500,000,000,000 km

Scientists have determined the age of the universe is 13.7 Billion years old. 

Then a question arises how big should be a visible universe?

Then a simple thing comes to our mind that we can't see before its beginning that is before the big bang. Therefore the observable universe consists of a sphere with a radius of 13.7 billion light years. Because when the big bang happened only light was there, which then traveled through the cosmos. Now we are seeing it arrive which means the light may travel 13.7 Billion light years before hits the earth. 

However, we are talking about the universe no logic in the universe is that simple.

The thing may be that simple if the universe is static. Then the distance between cosmic objects isn't changing.

However, the truth is the universe itself is expanding. After the very next seconds of the big bang the universe looks like microwave background radiation everywhere. Imagine the current location of Earth at that time. Let that be the point around which a sphere is there (Earth Point). The sphere is the origin of the cosmic microwave background radiation hitting the earth right now. That radiation moves towards the earth at the speed of light. In addition to this, it took 13.7 Billion years to get to the point. This may be called the critical sphere. 

If we take a sphere smaller than that sphere the light has already passed the Earth and we will be unable to see it. If we take a bigger sphere, then the light from it doesn't touch the earth's point yet. So we are unable to see it either.

When this light was emitted shortly after the Big Bang the sphere radius was about 43 Million light years away. In a simple way, we expected that the light would reach the earth point in 43 Million years. However, it took 13.7 Billion years to reach the earth point. The reason it took more time is the universe itself is expanding. One more thing the universe must travel much faster than the light. Because for a distance of 42 Million light years, light takes 13.7 billion years of time. 

Now remember the critical sphere from which the microwave background radiation is originally emitted also expanded its size and now the radius becomes 46 billion light years. That means that line is 41 Billion light years away from the earth point.

We can currently see object having a distance 46 billion light years away but we see them as they were in the past distance and in the form of how it was then. now those radiation or energy becomes starts we can't see those.

Any cosmic object that is currently outside of the sphere of radius 15 billion light years, we will never be able to see now no matter how long we wait. One more worst thing is we constantly lose approximately 20,000 stars per second. That means we are able to see the stars' emitted photons now but unable to see the stars' emitted photons after the very next seconds.

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Bimal Kumar Dora