Life of the stars

Life of the stars:

Whenever we gaze at the night sky, we see infinite numbers of stars twinkling in the sky. At childhood, our parents told us that, after death of any person they became star and watched every events occurring in the earth. They also told that there were many angels in the stars who sometimes visited earth. These were just some stories. Now we know that these stories were just some imaginary sequences and not real. Now, we have scientific evidences about stars and its formation. So what is life of the stars and how did they form?

First we have to know what actually a star is. A star is a kind of large chamber or nuclear reactor which emits energy in the form of heat and radiation by nuclear fusion reaction. In nuclear fusion reaction; one or more atomic nuclei combine to form one or more different atomic nuclei. In our host star SUN, nuclear fusion is taking place which is called Proton-Proton fusion in the core portion. The hydrogen particles fuse together to form helium. This fusion process radiate sufficient heat and energy which is necessary for the solar system. Simply, nuclear fusion is the heart reaction for creation of stars.

Formation of the stars:

Stars forms when dense concentration of the interstellar gas and molecular clouds collapse due to their own gravity. The major gases of interstellar gas are carbon monoxide, hydrogen, oxygen etc. The molecular clouds are often known as Stellar nursery which are actually some interstellar clouds, commonly consist of molecule hydrogen (H₂).

When the gravity becomes the dominant force, then the cloud and gases collapse and implode to the center forming a protostar. Protostar is the early version of formation of star which gathers mass from its parent molecular clouds. This process takes many many years (almost 10 millions years).

The nuclear fusion process takes place in the core of the star and it emits energy in the form of heat and radiations. The host star of our solar system "sun" also produces heat and radiations by nuclear fusion process. radiations are very harmful for humans specially the UV ray, but the atmosphere filters out the UV radiation and allow only the needed radiation and heat. So, we should thank our earth's atmosphere.

Color does matter:

Color of a star is so important in astronomy. It defines the age, temperature and many other factors of a star. Even the distance from the earth can also be calculated by understanding the color of the star.

Temperature of a body can be measured by observing its color. Each color has its own wavelength. Among the visible light, red has the lowest wavelength and blue has the highest wavelength. Hence, red color is coolest and blue is the hottest color. That means, if a star is reddish in color (absolute color, not for the observer), then it can be assumed that the star is comparatively cooler than other stars and if a star is bluish in color (absolute color, not for the observer), then obviously it is hotter than the other stars.

Age of a star can also be calculated through these colors. The astronomers have divided the stars to define their ages with some letters of english alphabets. They are O-B-A-F-G-K-M-N. This is the ascending order of stars from creation to death. That means, the newly born stars are classified under the O group and the old aged stars which are about to die are classified under the M-N group.

The colors of the stars also deal with this classification. The O grouped stars are bluish in color, B grouped stars are almost bluish white, A grouped stars are white, F grouped stars are yellowish white, G grouped stars are yellow, K grouped stars are orange and M grouped stars are purely red. When the stars reach the N stage, they are destroyed completely.

The O grouped stars have temperature of almost 35,000 to 40,000°C, the B grouped stars have 12,000 to 26,000°C, the A grouped stars have 7,000 to 11,000°C, the F grouped stars have 6,000 to 7,500°C, the G grouped stars have 4,200°C for yellow giants and 5,500°C for dwarfs, the K grouped stars have 3,000 to 4,000°C, the M grouped stars have 3,000°C for red giants and 3,400°C for dwarfs. Our sun have been categorized under G group which is almost yellowish white in color. In almost 5 billion years the sun will become a red giant due to helium burning process and it will end its life.

Destruction of the stars:

Nothing is permanent in this universe. The stars also get destroyed at the end of its lives. The destruction of a star mainly depends on its mass. Greater the mass, shorter its life. For example, let A and B are two stars which ages are equal. But star A has greater mass than B, then the gravity of star A will also be greater than B. So, A will end its life more quickly compared to B.

1. Supernova Explosion:

When the stars reach to M-N category, burning of helium takes place and this process ends their life. For a star like our sun, the force from the core portion dominates the gravity and hence it blows up its surface. This state is called red giant, because it can eat up all the internal planets. After almost 5 billion years, when the sun will become a red giant, it will eat up all the internal rocky planets from mercury to mars. When the reaction almost overs, then due to its gravity it again implodes and becomes a white dwarf.

But here comes a condition. Not all stars become white dwarf. An Indian scientist Subrahmanyan Chandrasekhar proposed a theory in 1935 which was universally known as Chandrasekhar Limit. According to this theory, if a star weighs more than 1.4 million solar masses (2.765×10³⁰ kg) then the gravity overcomes every forces of the star and its core suddenly collapses resulting a supernova explosion. Supernova explosion is one of the biggest explosion in this universe. It is so strong that even some explosions were observed from the earth. After supernova explosion, the resulting clouds and dust gives birth nebulae. Crab Nebula, Eagle Nebula, Helix Nebula are some of the examples of supernova explosion.

Binary stars can also cause supernova explosion. If one of the two stars of binary star system becomes a white dwarf, then it starts absorbing the energy of its neighbouring star and when its capacity reaches a certain point, it explodes with a large supernova explosion. This explosion creates many elements including iron. In fact we are also the children of supernova explosion.

2. Neutron stars:

Some giant stars do not end its life with supernova explosion. Because of its giant size and mass, some portion of the star remains safe after the supernova explosion. This is a neutron star. These neutron stars are too dense and dangerous for us. They emit some electromagnetic radiation which can be observed from the earth. When these neutron stars spin and emit such kind of radiation, then they are called Pulsars. Most of the pulsars rotate once per second which are called Slow Pulsars. Those pulsars which rotate 100 times per second are called Millisecond Pulsars, but according to recent discovery; the fastest millisecond pulsars can rotate up to 700 times per second.

3. Black Hole:

When an explosion occurs on a giant star which is almost 100 times larger than our sun, then that explosion is called Hypernova Explosion. After hypernova explosion, its mass and density becomes infinite and hence it warps and bends its nearest space-time in such a way that gravity becomes so strong and the matter got squeezed to Schwarzschild radius. Then a black hole forms. The center of a black hole is known as Singularity. The gravitational pull of a black hole is so strong that even light cannot escape from it. A black hole has capability to eat up all heavenly bodies. That is why they are also called as Monster of space.

As, black holes eat up everything, that is why a dangerous cosmic event occurs. They emit some dangerous radiations to space which is called Gamma Ray Burst. The gamma ray burst is the most dangerous cosmic event in this universe. If a pulse of gamma ray travels through earth, it will destroy the whole life within a second. But fortunately, we do not have to worry about this, because it is not going to happen with us till yet.