Physics is so dear to me, although many students and science teachers alike do not feel good with it. To some, it is boring and full of Maths. Others just do not find it attractive to their intellect, I should say. But to me, it is full of wonders and an endless chain of discoveries. One of my favourite topics in this field is Space and the Universe. It appeals to me differently because I feel like watching a movie and doing some reflection at the same time.
Just like the stars that we glimpse in the sky on quite nights, they are full of excitement. They are part of the history that unfolds before our senses, because the stars that you see were actually there many years ago. Stars are light years away from the Earth, and so it would take years for its emitted light to reach us. A light year is a distance that light can travel in one year. If a ray of light travels in a vacuum in approximately 3x108 m/s, the ray of the sun which distance from the Earth is approximately 150 million kilometres could reach the Earth in eight minutes, how much more for distant stars?
They are simply stars, but it is fascinating to learn that they have a life cycle. And the process is extremely long, explosive, but amazing. Like us, they are born, they live, and will eventually die.
The theory is that the birth of the star begins after the Big Bang. This tremendous explosion produced a massive cloud of gas and dust particles. Much of these huge clouds are NEBULAE. Gravity plays a very significant role to gradually pull this gas and dust particles together creating a denser ball of gas in the cloud. They grow in size over time and form a core over millions of years. As it gets larger and larger, the core temperature increases incredibly, and the pressure mounting so high, producing an intense brightness and eventually becomes white hot. Most of its energy stay trapped inside whilst some are emitted as infra red radiation. The ball of gas begins to look like a massive dark red glow hanging in space. For another millions of years the mass of the gas changes and a star is slowly coming into life. This is now called a PROTOSTAR.
The protostar continues to be unstable due to nuclear reactions within. For another series of changes, the very hot core produces a violent flow of particles scattering outwards blowing away gas and dust in the banks of cloud around. Slowly the core collapses, and nuclear fission starts releasing enormous amount of energy. As temperature further increases, the mass of the REAL STAR begins to emerge.
The sun in our solar system is a star and it has its life like any other stars in the universe. Our very own sun is nearly 5 billion years old and is believed to be in its midlife. There is really no serious reason to fear about it dying, because it would still take billions of years and this generation of humanity and surely hundred more generations could still enjoy the benefit of its life. Hydrogen fuel as a main gas component of stars is responsible for its life. However, a star continues to lose mass in the form of energy like how Albert Einstein predicted in his familiar energy equation. As its mass decreases so as its gravitational power, and this causes the instability of the inner radiation pressure and the pull of gravity. But, for as long as there is enough of this hydrogen fuel, the star continues to shine and provide us bright nights of diamond-like glitters.
That is true, stars will die eventually. Depending on the size of the star, two possibilities would happen. It may either become a black dwarf or a black hole. Our very own sun is a medium-sized star which after millions of years, all its hydrogen fuel would run out. The mass of the sun would decrease and so the inner radiation pressure would become higher than the gravity. The effect would lead the star to expand and becomes a red giant. As it expands, the core temperature decreases then as it cools down the red giant would sooner or later contract. As the pressure decreases, the gravity gets the upper hand to pull back the red giant into itself and after many more years, it would collapse into a so called white dwarf. And as it cools further, the hot white dwarf becomes a black dwarf. For very massive stars, they do have a more interesting death. Yes, the hydrogen fuel be all used up and its gradually becomes a red supergiant, it cools down, quickly contracts and collapses, making its core very dense. This speedy contraction, with a very high gravity increases the temperature to unimaginable level.
Finally, the star would explode to what is called SUPERNOVA, releasing an enormous amount of energy. Aside from blasting off massive surface layers, some elements are formed at this explosion. A neutron star would emerge which turns into pulsar, and if it has enough mass, its gravity would crumple it still further to become a black hole.