What is universe made up of?  It is always fascinating to look at the night sky and wonder where do all these stars come from and what are they made up of. Individuals from the past used constellation of stars for different purposes like navigation, determining seasons, analyzing personalities and making future predictions. Let’s analyze what universe is actually made up of?

The universe came into existence with a massive explosion known as the “Big Bang” about 13.7 billion years ago. This resulted in the creation of subatomic particles and fundamental forces acting in the universe which led to the formation of galaxies and stars. The visible universe which can be observed and seen is only 5% of the universe consisting of hundreds of billions of galaxies and hundreds of trillions of stars. The remaining 95% of the universe is dark universe. The observable universe is about 90 billion light years across. To comprehend the composition of universe we can categorize universe as atomic universe and dark universe. Let’s understand atomic and dark universe separately.

Atomic universe

Atomic universe is the part of universe which comprises of matter made of atoms. These atoms in turn are made up of electrons, protons and neutrons. The protons and neutrons reside inside the nucleus of an atom whereas, electrons are in the empty space surrounding the nucleus. Protons and neutrons are made up of quarks. There are four fundamental forces acting in the universe, which are gravity, electromagnetism, strong force and weak force. These fundamental forces and atoms give rise to the giants of the universe like galaxies and stars. Let’s understand galaxies and stars separately.

Galaxies

Galaxies are made up of star systems, planets, star clusters, gas and dust bound together by gravity. There are about 200 billion large galaxies in the observable universe, each containing about 100 to 200 billion stars. Galaxies are generally categorized as elliptical, spiral and irregular shaped. Our solar system resides in a galaxy called “Milky Way”. Milky Way galaxy contains about 200 billion stars. It would take light 100,000 years to reach at the edge of our galaxy. The nearest galaxy from our galaxy is “Andromeda” galaxy which is about 2.5 million light years away. Till the outermost planet of our solar system -Neptune- the diameter of our solar system is about 9 billion kilometers. If we go even further, where sun’s gravity still dominant enough to make objects orbit around it, then the diameter can be as large as 1.5 light years.

Stars

Stars are usually made up of lighter elements like hydrogen and helium and some other elements like carbon, nitrogen, oxygen and iron, mostly created by stars who exploded before. The fusion of lighter elements like hydrogen and helium give rise to heavier elements like carbon, nitrogen, oxygen and iron. The force of gravity is always trying to collapse the star by gravitational pull. The pressure created by the very hot star core, due to nuclear fusion of hydrogen and helium atoms, counteracts this force of gravity and prevent it from collapsing. When a star runs out of fuel, its inner layers start to collapse under the influence of gravity which increase the temperatures and pressures in the core, eventually making the core collapse. The outer layers of star expand outwards making star hundred times bigger, and is called “red giant”. The medium size star will shed its outer layers into space forming a gas cloud called nebula, whereas, core will shrink and cool leaving behind a hot ball called “white dwarf”. If the star is massive it will carry on nuclear reactions in its core and forming heavier elements like iron. At this point the temperature at core is about 100 billion degrees and it loses fight against gravity and explodes in the form of huge explosion called supernova explosion. The left over star core is converted into either neutron star or black hole depending on its mass.

Dark universe

Dark universe comprises of dark matter, dark energy and black holes. Let’s analyze each one separately.

Dark matter

Dark matter is an invisible matter present in the universe which does not interact with the electromagnetic force. It does not absorb or emit light therefore no body can see the dark matter. Scientists have discovered dark matter on the basis of gravitational effect it exerts on visible matter. According to scientists 27% of universe is comprised of dark matter whereas, the visible matter that we can observe in the form of galaxies and star is only about 5% of the universe.

Dark energy

Scientists found that a mysterious force is prevalent in the universe which is accelerating the expansion of universe, they termed this mysterious force as dark energy. Dark energy is an evenly distributed force in the universe which is causing the universe to expand at an accelerated speed. This accelerated expansion caused by dark energy is making galaxies move further away from each other. Dark energy comprises of about 68% of the universe.

Black holes

Black holes are mysterious entities in the universe which swallows everything which comes to them. Due to their strong gravitational pull, all the matter is squeezed into a tiny space. Their gravitational pull is so strong that even light can’t escape their pull. Therefore, nobody can see the black holes however, the effect of their strong gravitational pull on the stars around them can be observed. This is how scientist come to know if there is a black hole in action. Black holes are formed when massive stars which are about five times the mass of sun collapses upon themselves under the influence of gravity. The outer layers of these massive stars explode with a massive explosion called “supernova” whereas, their core implodes onto themselves due to gravity and is turned into black hole. Black holes can be of three types depending on their mass. Smaller black holes are called “primordial”, medium sized black holes are called “stellar” and are about 20 times the mass of sun. Whereas, larger black holes are called “supermassive” and are about one million times the mass of sun. There are supermassive black holes at the center of almost all galaxies.

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