How was the sun formed and how does it emit light

Dr Irengbam Mohendra Singh *

Life is still an unfathomable mystery, probably blueprinted in a warm bubbling primordial soup.

There were days when I felt like checking my body into a left luggage locker. Shortly after holidaying at the Lakshadeep Island in the west coast of India in 1995, one day I was losing my eyesight so fast that I wondered whether I would be able to see the Sun next morning. I was admitted as an emergency at St Thomas' Hospital in London, on the bank of the River Thames, opposite the roof-top bar of the Houses of Parliament.

I did recover. Since then things change so fast in my life and I quickly forget that I had encountered such a serendipity. Like the computer's processing speed that doubles approximately every two years, modern life changes are faster than ever with digital technology

This story of the birth of our Sun is serendipity and its predicted demise follows the laws of nature. The Sun will also die one day, leaving behind a neutral star or black hole. Sunrise and Sunset have artistic value. Once, my wife, children and I stayed as guests at the Kerala Guest House on the beach of Kanyakumari in Tamil Naidu. At about 6 O'clock in the morning, it was a fantastic experience to watch both Sunrise and Sunset at the same time, when the whole skyline turned orange with its reflection in the Bay of Bengal as it rose, and as it set in the Arabian Sea. These are rhythms and patterns which are called Physical Laws or Laws of Nature.

The scientific origin of the Sun is still a hypothesis as the biblical origin of the Sun in Genesis, which gives a reference to an unnamed existence of the Sun before the Earth was formed from gas: "Now the earth was formless and empty, darkness was over the surface of the deep. And God said, "Let there be light, and there was light. And when the lights come on and everything is told to get fruitful and multiply". The Sun thus, gave light and energy for replication of plants and animals including humans.

The name "Sun" comes from "Sol", the ancient Roman Sun god, Sol Invictus (unconquered Sun). The planets are named from Greek and Roman mythologies, except Earth (modern English). In the first English translation of the Bible, 'Earth' was first used (Genesis 1:10). Roman names were adopted by European languages and culture, and became standard in science. Earth is 'Dunya' in Turkish and Urdu; Prthvee or bhoomi or Dhartee in Hindi; and Malem in Manipuri.

Because of its life-giving properties the Sun was worshipped by all the primitive people all over the world. Meiteis built their homes (yumjao) facing the Sun towards the east. Hindus believed 'Surya', the Sun, to be a he-god, and that Kunti's first son Karna in the Mahabharata, was born out of wedlock with Surya Bhagawan or the Sun god as his putative father. She became pregnant when she went for a bath in the River Ganges one morning, and was doing Surya-Namaskar (prayer to the Sun). Hindu women today, waist-deep in the water of a river, offer prayer to the Sun as it rises, on the day of Chath Puja, with the mantra: "Oh Surya who is the dispeller of darkness […] responsible for life, I pray to thee".

Human beings could not have evolved without the Sun though the earliest life did. The Sun gives plants energy to produce their food by photosynthesis in the beginning of the food chain. It's because the Sun is a middle-sized star. Had the Sun been too small our planet would have been dark, and had it been too big, the Earth would have been broiled.

Our Sun was born 4.5 billion years ago. Its date of birth agrees with the radioactive dating of meteorites in our solar system. It will begin to die 5 billion years from now. The Sun, when it dies, would become a 'Supernova' like any other star, as it explodes with a short-lived luminosity.

Likewise, astrophysicists can estimate the Sun's life expectancy by studying one particular star, named Messier 67, which is about the size of the Sun. They simulate its life cycle on a computer to ascertain how long it will live. They calculate that the Sun will have enough hydrogen to fuse with helium in its core, at about the same rate for another 5 billion years.

Investigative physicists believe that when the Sun runs out of its fuel it will still be able to continue giving the Earth its energy for some more years by burning reserves of hydrogen in the layers that surround its core.

Nuclear physicists say that all these things happen because of transfer of electrons that I discussed in previous columns, as it is in our life. Chemistry students will remember what is known as "Redox" reactions. This is a chemical reaction in which electrons are transferred between two species.

Plants make sugar (glucose) by the process of photosynthesis. And glucose combines with oxygen to produce carbon dioxide and water (glucose + oxygen -> carbon dioxide + water (C6H12O6 + 6O2 -> 6CO2 + 6H2O). In this reaction, electrons are transferred from a carbon molecule onto oxygen. During this process as in our respiration, some of the energy is released for plants and animals to live. This is done by the transfer of electrons between a series of atoms, usually iron, embedded in proteins. The process takes about 15 steps.

There is another complex system of producing energy in life, which is delivered by the respiratory chain and by the flow of electrons in molecules known as Adenosine Triphosphate (ATP). All undergraduate medical students have to be familiar with this. ATP transports chemical energy within cells for metabolism. Professor Brian Cox says: "ATP connects us for the great temporal sweep of the history of life on Earth. It points us back all the way to the 'little warm pond' of Darwin.

I digress… I recall that I am writing about the formation of the Sun and how it emits light for life to exist on Earth and carry on replicating. The origin of the Sun has now been thoroughly analysed. The Sun like any other star, began its life as clouds of hydrogen, helium, and the atomic nuclei, which were formed in the first three minutes after the Big Bang. Under the action of gravity the clouds collapse in on themselves. The collapsing clouds heat themselves up. When the temperature climbs to about 1000,000 degrees Celsius, the hydrogen and helium nuclei can no longer hold on to their electrons, and the cloud becomes hot gas of free electrically charged particles.

As the collapsing cloud continues, the temperature rises further, when the naked hydrogen nuclei containing a proton each, approach each other at high speed, despite the fact that each proton has a positive electrical charge. [normally opposite charges attract and similar charges repulse each other]. When some of them get very close to each other a transformation takes place under the influence of 'weak nuclear force'. This weak nuclear force can turn an 'up quark' into a 'down quark', and so a proton can be transformed into a neutron, along with the creation of a positron and neutrino. A proton is made up of two up quarks and one down quark, and a neutron is made up of two down quarks and an up quark.

Neutrons are electrically neutral and they can approach the proton close enough for the 'strong nuclear force' to take over and bind them together tightly. The resulting atomic nucleus that is made up of one proton and one neutron is called a deuteron. The formation of deuterons release a vast amount of energy. It's known as 'nuclear fusion'- a nuclear reaction. In this process, two or more atomic nuclei collide at a very high energy and fuse together into a new nucleus, by which the Sun and other stars generate light and heat.

Inside the core of the Sun the fusion process or nuclear reaction goes on at 15 billion degrees Celsius. At each stage, mass is transformed into energy, which heats it up. This super-heated energy also halts further gravitational collapse, balancing the inward pull of gravity. The Sun burns 600 million tons of hydrogen fuel every second into helium with the loss of four million tons of mass, which is released as energy.

When the Sun runs out of its fuel, it will begin to fuse helium into carbon and oxygen and will collapse into a fading ember known as 'white dwarf'. That's a dead Sun. Nuclear fusion produces Sun's energy, which we get as heat and light from its glowing surface temperature of 5500 degrees Celsius. It takes an average of 8 minutes and 20 seconds to reach us.

As we know, hot things like heated iron rods, emit light. The mechanism of this emission (electromagnetic radiation) led to quantum theory on which modern technological foundation rests. Matter is composed of electrically charged particles and when charged particle are shaken around, they emit light (photons). This is sunshine for you.

So, chemistry is about rearranging atoms. Nuclear physics is about rearranging nuclei.