Stars are the source of thousands of vibrating light points in the distant sky, somewhat clear and somewhat obscure. The planets-satellites-comets are all glowing for the stars, capturing our eyes with infinite beauty and immense wonder. Not only that, new theories and information are revealed in space science. It opens a lot of unknown truths with data.
But we must know the life story of the star which is constantly serving the science-minded and curious people of the world with such a modern scientific truth. We need to know its birth-history, active life and finally their consequences.
Whether a star is small, medium or large in size, the life of each of them begins with the grace of Hydrogen (H), the mother of all the elements in the universe. After the Big Bang, when matter was scattered all over the universe, it contained dust and hydrogen molecules. However, these substances did not spread evenly everywhere. As a result of this unequal distribution, parts of the universe had no matter present, some had less while some parts had significant amount of matter present.
According to the space science, the Nebula is the place where dust and hydrogen are located in large quantities. In this region, the dust and hydrogen come closer to each other under the influence of the force of attraction and continue to rotate around each other and gradually form the lumps. This process causes to increase the size of the lumps further. According to the laws of physics, as the mass of matter increases, so does the force of attraction. As a result, the lumps naturally attract the dust and hydrogen around it more intensely and increase its volume over time. As this process is continued, the pressure in the centre of the dust and hydrogen lumps increases, and as the pressure increases the density of the material inside the lumps increases. Due to this increase in density, the temperature inside the lumps gradually increases. However, the process of Nuclear Fusion, known as the main driving force of the star, has not yet begun. For this, dust and hydrogen lumps have to meet at least one condition. That is, the mass of the lumps must be at least 8 percent of the mass of our sun otherwise the process of nuclear fusion will not begin. Lumps whose mass are less than 8 percent of the mass of the sun, the growth or improvement of those lumps cease thereafter. As their colour is brown, they are called Brown Dwarf Star (BwDS) or Failed Star. Although here we have recognised them as stars but actually they are not stars at all. Scientists speculate that Jupiter in our solar system may be somewhat a failed star. At this point, the lumps whose mass is equal to or greater than 8 percent of the solar mass begin the process of nuclear fusion and these lumps are called baby star or Proto-Star. In the future, these baby stars will develop into full-fledged stars. This baby star is the initial stage of a star.
As the process of nuclear
fusion begins in the Proto-Star, two hydrogen molecules combine to form a
helium molecule. This reaction releases a lot of energy as light and heat. That heat acts as trigger for the next hydrogen molecules to participate
in this reaction. Thus, the chain of reactions continues and the mass of the Proto-Star continues to increase for the production of helium. As a result, Proto-Stars are more intensely attracted to the surrounding dust and hydrogen
molecules, increasing their mass and volume, to become mainstream stars known
as Main Sequence Star (MSS). Our sun is now going through exactly this phase.
It is a common certainty that all small, medium or large stars come to this
stage in their life cycle.
It has already been mentioned that energy is generated in stars through the process of nuclear fusion. This energy is radiated from stars in the form of heat energy and light energy. The point to note here is that the heat and light radiation of a star acts as an inversely consistent force against its intense gravitational force and gives the star stability. From this it is clear that as long as the energy radiation from the star continues, the center of the star will not collapse despite the intense gravitational force. Here the gravitational force acts as the Centripetal Force and the radiation as the Centrifugal Force.
But over the time, the star's fuel, hydrogen, will gradually run out. Only the center filled with helium will remain. As the mass increases, the gravitational force of the star will increase and the center will continue to compress more. The contraction of the center will increase the pressure and density of the helium which will cause the temperature of the star to rise so much that the process of nuclear fusion of helium will begin. For this event the radiation of the star will take on a more intense shape and the outer layer of the star will increase and giving the star a monstrous shape. It has been calculated that when our sun reaches this stage, the outer layer of the sun will reach almost to Jupiter. During this time, a new element, carbon (C) is formed at the center of the star through the process of nuclear fusion of helium. At this time the temperature of the star will decrease naturally and it will turn red.
This low-temperature star is called the Red Giant Star (RGS). The closest red giant star to Earth so far discovered is the Gamma Crucis or Gacrux, which is located 88 light-years from earth. During this time ionized particles are thrown into space from the extended outer layer of the star. This state is called Planetary Nebula. During this time the star rapidly loses its temperature. It is worth noting that by studying these types of planetary nebulae it is possible to get a clear idea about the chemical structure and evolution of galaxies. The planetary nebula is also one of the brightest objects in the galaxy. It provides the galaxy more heavenly beauty.
Later the star appears in a
new form. During this time the star radiates heat and light, albeit in small
quantities. This phase is called White Dwarf Star (WDS). The closest white
dwarf star ever discovered to earth is Sirius-B, located 8.6 light-years from
earth. It can be said that this is the last illuminated phase of the star. During this time the concentration of star is very high. It is assumed that
stars like the sun will actually take the shape of the earth at this stage.
Since no nuclear fusion process takes place at this stage, the star has no
energy source. The star will continue to cool as it slowly radiates the
accumulated heat inside its centre.
Eventually a situation will
arise when the star will not be able to radiate a significant amount of heat
and light. This form is called Black Dwarf Star (BDS). In other words, this
stage is the corpse of the star. During this time the star turns into dark
black lumps. Later, after some more time, that black lumps will disintegrate
according to the eternal laws of nature and spread in space, which is called
nebula. After this previous situation will return and new stars will be born.
But not all stars follow the same path. The first correct explanation of the separation of the path was given to us by eminent Indian physicist Dr. S. Chandrasekhar for which he was awarded the Nobel Prize in Physics in 1983 and in recognition of his successful research, the only condition based on which stars adopt separate path towards its maturity, is called Chandrasekhar Limit. According to his theory, the remaining mass of the red giant star will select the next stage of the star. In that case, if the mass of the star is less than or equal to 1.4 times the mass of our Sun, then the phenomenon has already been mentioned. But if the mass of a star is more than 1.4 times of the solar mass, then new events will appear.
In the second event also the star will get the aforementioned red phase. But due to their size, scientists have identified them with a new name and that is the Red Super Giant Star (RSGS). The closest ever discovered red giant star to earth is Betelgeuse which is located 434 light-years from earth. In order to be huge in size, a series of slightly different events can be seen in the center of this class of stars. Here, Carbon is formed through the process of nuclear fusion of Helium too. Subsequently, in the process of nuclear fusion of carbon, it produces Neon (Ne) and Neon to Oxygen (O), Oxygen to Silicon (Si) and Silicon to Iron (Fe). In the case of stars, the last element produced by the process of nuclear fusion is iron because iron is a very compact and stable element. Therefore, it is never possible for the process of nuclear fusion to take place. As a result of this phenomenon, as the mass of a star will increase drastically and the gravitational force intensify, so does the process of nuclear fusion will stop and light along with heat radiation will be affected. As a result, the balance between the two opposite forces will suddenly collapse and a repulsive force will be created in the center of the iron molecule or in the nucleus. This energy will come out from the star in the form of shock wave. The amount of energy, generated through the repulsive force inside the stars will be million times more than the energy, released from the star. Eventually a situation will be created when the star can no longer hold the pressure of that energy and the energy will release through a terribly intense explosion. This explosion is called Supernova Explosion. This explosion emits so much energy that the total amount of energy emitted from the billions of stars in the galaxy is nothing compared to the energy of a supernova explosion. Evidence of this information it is said that the combined brightness of all the stars in the galaxy is completely dimmed by the brightness of a supernova explosion. The last supernova explosion that has caught our eye is SN-1016aps. Discovered from the Hawaii Island in the United States on February 22, 2016, the supernova explosion occurred in the Draco Constellation which is 360 crore light-years away. However, the name of the galaxy of that constellation is still unknown.
After the explosion, if some part of the center of the star remains and its mass is 1.40 to 2.17 times the mass of the sun, some events will occur but if the mass of the rest of the centre of the star is equal or more than 2.17 times of solar mass, different incident will happen.
We will first discuss what happens if the mass of the remnants of the center of the star after a supernova explosion ranges from 1.40 to 2.16 times the mass of the Sun. After a supernova explosion, the electrons and protons in the nucleus of the iron present in the center of the star combine with each other to form neutron particles, forming a dense centre of neutrons. That is why such a star is called a Neutron Star. This type of star can have a maximum diameter of 25 km but it is a very dense type of star. Giving a simple comparison will make the subject easier to understand. If we were able to collect one tea-spoon of matter from a neutron star, the mass of that tea-spoon would be greater than the mass of any high peak in the Himalaya. Another significant property of a neutron star is that such a star begins to rotate on its own axis as soon as it is born and scatter different types of waves. As time goes on, the speed of rotation of neutron stars increases. According to the observation till date, the speed of rotation of a neutron star on its own axis is 10 to 716 times per second. Normally, other objects around such a star are attracted by the intense rotational speed of the star and its mass gradually increases. But neutron stars are never black holes. Their structure and nature are different. However, the actual relationship of the black hole with the neutron star is not yet clear, so it is a matter of research.
Different types of neutron stars have been discovered with the help of various scientific methods and telescopes. Some of the most well-known types of neutron stars are:
Radio Pulsar Neutron Star, Non-Pulsating Neutron
Star, Recycled Pulsar Neutron Star, X-Ray Pulsar Neutron Star,
Anomalous Pulsar Neutron Star, Low Mass X-Ray Binaries Neutron Star,
High Mass X-Ray Binaries Neutron Star, Intermediate Mass X- Ray
Binaries Neutron Star, Soft Gamma Ray Repeater Neutron Star, Magnetar
etc
What is the last consequence with neutron stars is not clear to us yet, it is still shrouded in a cloud of mystery. However, it is hypothesized that neutron stars themselves gradually lose energy in the course of time and disappear into the impenetrable darkness of space, or become black holes by excessively increasing their mass through the surrounding matter under the influence of a super-gravitational force. However, more detailed observation, research and study is required to know the actual fact.
Now we will discuss what happens if the mass of the remnants of the center of the star, after a supernova explosion, is 2.17 times the mass of the Sun or more. But one thing is for sure before the discussion that this form of the star is probably the most heard, spoken and discussed in the general public mind compared to other forms of the star. Yes, this time we will discuss another mysterious phase of the star, the Black Hole.
A black hole is an object in space that attracts all the matter around it, even light, to itself through its strong gravitational force, and matter can no longer get out of here. Light is not reflected from here so it is pitch black darkness like space and we cannot see it with our eyes. Here in a small place so much mass is gathered that a very strong gravitational force is formed. Probably the black hole is the only known place in universe where the traditional laws or formulae of physics do not work; perhaps there is other set of rules which are completely unknown to us. So we cannot explain it perfectly through the knowledge gained. Even with today's advanced technology, we have not been able to unravel the mystery inside the black hole for ages. This form of star has been given such a name probably because of the inviolability of the mystery.
The idea of a black hole was first introduced to us by Dr. John Michell, a famous geologist of nineteenth century, and later by Dr. Pierre Simon Laplace, a mathematician, and later by Dr. Albert Einstein, a world-renowned physicist. In 1916, he predicted the presence of black hole through his Theory of Relativity. A few years later, Dr. Karl Schwarzchild was the first to tell the world about the existence of black hole in space. The word black hole was first introduced to the public in 1967 by Dr. John Wheelar. Earlier this type of star was called Dark Star.
The black hole usually
consists of two parts. The core of the middle is called Singularity and the
imaginary line around it that marks the boundary of the black hole is called
Event-Horizon. The area between the event horizon and the singularity is called
the Schwarzchild-Radius. On the basis of Schwarzchild-Radius, four types of
black holes have been found. These are the Stellar Black Hole, the Intermediate
Black Hole, the Super Massive Black Hole, and the Miniature Black Hole. However,
at present some people do not consider the last type of black hole as such
because this black hole was formed for a short time, shortly after the Big
Bang.
The black hole begins with the Event-Horizon. In other words, the Event-Horizon is the entrance to the black hole. It is a region or imaginary boundary outside which the influence of the black hole is not so intense. The Event-Horizon is the last frontier to return from the black hole Singularity is a place or point where all the objects coming from outside the black hole come and accumulate and multiply the density of the black hole many times. Such is its gravitational pull that even the most powerful time comes to a stop in front of it. If it would be possible to observe the outer space from the black hole, the rest of the space would seem very fast and dynamic. Again, if the black hole is observed from outside the black hole, then it would seem exactly the opposite. If an object crosses the event horizon of the black hole and moves to the singularity, then the escape velocity, required for that object to come out of the black hole or to cross the Event-Horizon again must be greater than the speed of light (108 crore kilometer/ hour) which is practically an impossible event.
Till date, many black holes have been discovered. The nearest black hole from the world has been found in 2020. The black hole of HR-6819 alias HD-167128 alias QV-Telescopii star of Telescopium constellation is 1050 to 1120 light years away from us. The largest black hole ever discovered is called TN-618, which has a mass 6.6 X 1010 times the mass of the Sun. This star is located 1036 crore light years away from us. In 2019, a vague image of a black hole was first captured using advanced technology. We have seen the image of a black hole of a star in the galaxy of Messier-87 alias M87 alias Virgo-A alias NGC-448, that is situated 5 crore 19 lakh to 5 crore 51 lakh light-years from Earth. The first star to be thought to have a black hole is Cygnus X-1. This star is 14 to 16 times larger than the Sun and is located 5,600 to 6,500 light-years from Earth. At the center of our galaxy, there is a super massive black hole. Thousands of stars along with their own star-system are rotating around this black hole. The black hole at the center of the galaxy is called Sagittarius-A* and its distance from the earth is 25,640 light-years. Its mass is 4 lakh times heavier than that of sun.
At the end of this discussion, the question should arise in our mind that what is the end result of the black hole ? The famous British mathematician and cosmologist Dr. Stephen Hawking showed in mathematics in 1974 that when the black hole did not get anything to swallow, it began to lose its energy little by little because of the continuous radiation of electromagnetic wave with high velocity. Radiation of electromagnetic wave is a very regular occurrence. But electromagnetic radiation, emitted from a super massive black hole is the most talked about. The radiation of electromagnetic waves emitted from a very large black hole is called a Quasar. These electromagnetic waves travel far and wide in space. So far, more than 5 lakh different types of quasar have been found. Evidence of the brightness of these quasars is that, the combined brightness of thousands of galaxies, like our Milky Way, fades in comparison to the brightness of the brightest visible quasar ever discovered. The black hole itself provides the energy needed to release these electro-magnetic waves. The phenomenon of intense electromagnetic wave radiation from a black hole is called Hawking Radiation. Since the source of the energy of this radiation is the black hole, so every time the wave radiates, the energy of the black hole will decrease to some extent, that is, through this process the evaporation of the black hole will continue. According to Einstein's Mass-Energy Equation, mass and energy are interrelated (E = mc2). So the loss of energy in the black hole means a slight decrease in mass, and if the radiation continues, the black hole will theoretically merge into space at certain point of time. However, this is a very slow process that goes on for a long time. It can take 2 X 10100 to 2 X 10106 years for a star to turn into a black hole and evaporate completely in the space. However, it is not yet possible to say exactly what happens after that. A group of scientists say that White Holes, Warm Holes may be created through black holes. Another group of scientists says that it will be possible to reach another universe by Time-Travel through the black hole, that is, Multi-Verse Hypothesis or Parallel-Universe Hypothesis may be clearly and accurately established in near or far future through the black hole. With the help of modern technology, we may inform our existence in future to new universe through black hole.
We do not know the future, but if we will like to know, mankind has to wait patiently because human do not breathe a sigh of relief until success is achieved. What seems imaginary, unrealistic or impossible to us today, it may be established as real through research and study in the next few decades or centuries. So all we have to do is study, research and wait patiently. The star that gives us light in its life, gives us the strength to live in life, shows the way will surely show the way to the new world even after its own death.
