How Stars Live Out Their Lives

~From Birth To Death~

Stars- magnificent objects hurtling out in outer space in enormous numbers. The Milky Way Galaxy alone contains an estimated number of some 100–400 billion stars! They were the first ever stellar objects to form in our cold and dark universe. They are all different from one another; some enormously large stars and some little, faint red dwarves. But what they all have in common is that they have all witnessed the dazzling cosmos and hidden within them are our very origins. In a way we have descended from them; the matter that makes up stars has made us. Maybe that is the reason that we are told as children that those stars are actually our ancestors. Though however childish it may sound, deep down there is some meaning attached to this statement. Maybe this is what makes us look at them in awe, open-mouthed, overflowing with questions and in their midst we forget our worries. Sadly though, not all wonderers out there bother to get the answers to their questions. Generally, it is young children with a lot of curiosity within them about their world that ask these questions, but they are mostly made to shut up by adults who get irritated by such questions because they don’t know the answers to them. Apart from children, there are few people (and I count myself in) who tend to bother about these questions.

When the universe was young, it was overflowing with its only present element: hydrogen. As expansion after the big bang followed, some areas of the universe were not uniform. The concentration of matter in those areas was more than in the surroundings. As a result, gravity attracted more matter and as a result hot and dense hydrogen clouds began to spin about their axes. As they collapsed in on themselves after rapidly spinning, they formed the first stars! Inside these stars, nuclear fusion takes place as hydrogen burns to produce helium molecules. This keeps the star stable against the pressure of gravity and also helps it emit-heat and light. Over time, as stars exhaust their hydrogen fuel they are left with helium which too undergoes nuclear fusion. As the new forming elements exhaust and are replaced by heavier elements, the balance of the star becomes feeble. Finally when stars are left with no more matter to fuse, they end their lives and they can do so in a variety of ways depending upon their size.

Our Sun is a medium sized star. It was formed almost 5 billion years ago and will not die out for another 5 billion years. It has lived only half of its lifetime and has been a witness to numerous spectacular events. Stars that have planets orbiting them are rare and the ones that have a planet around them that harbours life are surely very, very rare. So for us at least our Sun which will be considered average sized on the scale of the universe is very special and unique. But how is it to end its life? Stars the mass of our Sun end their life in a fashion which is short of spectacular. As the nuclear fusion within them comes to a halt, their outer layers expand outwards into their surroundings, in case of our Sun, as it ends its life it will destroy and swallow all the planets in the course of doing so. Sure enough, humanity isn’t going to survive until then and maybe our planet will be completely destroyed by us: lifeless like its fellow companions. When in a star’s life its outer layers expand outwards as nuclear fusion comes to a halt it is called a Red Giant. This process may last for some time until the red giant finally explodes in a miniature supernova. The remnants of the star left behind along with the debris of the explosion is a Nebula and what remains of the star is a white stellar corpse known as a White Dwarf. The light emitted by white dwarves is very faint, just as much as the Moon will emit on a clear full moon night. It is a very dense object indeed. The white dwarf is indeed in fact the star’s core that couldn’t undergo nuclear fusion anymore. White dwarves may rarely help life to thrive around them as they cannot be a reliable source of heat and light. But we cannot surely say as there are an infinite number of possibilities for our universe. Scientists predict that given enough time, white dwarves too will lose their remaining energy and reach their final stage: Black Dwarf. They will not emit any sort of heat or light. As per predictions, there can not be any black dwarfs in our universe right now because it takes considerably a very long time for white dwarfs to reach this stage.

The Orion Nebula housing the remnants of a dead star

So now, what about stars that are larger than the mass of our Sun? Well, their fate as they end their lives is really awe striking!

Indian physicist and Nobel Laureate, Sir Subrahmaniam Chandrashekhar was travelling to Cambridge from his native land India when he developed some calculations regarding stars of a certain mass. He found out that stars almost twice the mass of our sun and even larger would end their lives in a very different fashion. Stars that were almost twice our Sun’s mass would too at first become red giants, plummeting their boundaries and then end in a spectacular supernova much much more powerful than that of stars like the Sun. Such supernovae have the capacity to outshine billions of stars in their galaxy! So what will happen after that?

As we discussed earlier, stars burn hydrogen fuel within them to keep themselves stable against the force of gravity. Once this power source extinguishes, the force of gravity takes over the body of the star. The core of the stars that remains after the supernova explosion starts collapsing onto itself due to gravity. Its dense mass gets shrinked into space that becomes more and more tighter. At this stage every proton and electron are squeezed within the stars to produce neutrons. Thus these stars( more precisely dead stars) are called Neutron Stars. These are fascinating objects. They are small; some have a radius of around 10 miles or so. But they are extremely dense due to the huge density of matter shrinked to a tiny space. One teaspoon of such a star can weigh around 10 trucks or even higher. Added to this, they have a very strong magnetic field. Some of these neutron stars have an exceptionally huge magnetic field which gives them the name Magnetar. They gain their energy due to magnetic field decay powered by the weak nuclear force. If our sun were to be replaced by a magnetar, it would totally rip us apart. Their magnetic field will cause disturbances in the electron clouds of atoms that make us up. Another such variant of a neutron star is a rapidly rotating magnetar known as Pulsar. Their magnetic poles emit electromagnetic radiation which can be detected when such an emission takes place in the direction of the Earth. Fascinating right?

Now as told earlier, there can be another fate of massive stars. If the stars are larger than a certain limit, they continue their collapse surpassing the Neutron Star stage. This limit named after the scientist who devised these calculations is known as the Chandrashekhar Limit. As these stars continue their collapse, not only protons and neutrons but all subatomic particles and even quarks are shrinked into a very small area of space. The immense density of these objects provide them with an exceptionally powerful gravitational field from which nothing can escape- not even light! The curvature of space-time is infinitely great because of their super powerful gravitational field. Even time slows down immensely around these objects. These stellar monstrous objects are what we know as Black Holes. There is no escape from them once you have crossed what is known as the event horizon of a black hole. As you enter the black hole, your body will slowly get stretched due to gravitational pull as the black hole keeps getting denser and denser and finally you reach a point of singularity where time presumably comes to a halt and the laws of physics break down. This is the space where the immense curvature of space-time comes to a halt. These are deeply mysterious objects and may hide immense secrets about our universe’s past and its upcoming future.

Sir Subrahmanyam Chandrashekhar

(Note: The bigger the size of the star, the faster it will exhaust its hydrogen fuel)

There are stars out there in huge numbers and throughout ages we have enjoyed viewing them. Since hunter-gatherer times, stargazing has been very prominent. As seen from the earth, some of these stars join together to form certain shapes that resemble earthly objects. These patterns and shapes are called Constellations. Some of the most prominent constellations include Orion which is formed by eight stars, two of which are very prominent- Rigel and Betelguese.It is in the shape of a hunter This constellation can be located towards the northern and north-eastern sky in winter. Another prominent constellation includes Ursa Major (Saptarshi Mandal) in the shape of a bear and can also be seen as a big ladle which gives it another name Big Dipper whose handle points in the direction of Polaris (pole star). This constellation is prominent in the northern sky in winter and in summer its sort of twin constellation, Ursa Minor remains prominent. Another prominent constellation is that of Phoenix which houses the brightest star in the earth’s sky Sirius A. The southern sky now in summers is decorated by the constellations Scorpio, Virgo, Libra, Ophiuchus and towards the South-east and east are Hercules, Bootes, Corona Borealis, Serpens Caput etc, and in this part we can locate another huge star Arcturus in the constellation of Bootes.

Stars have always remained significant parts of our lives. Whether it be a hunter or a civilised human, whether it be a stressed out person or the world’s most happy person, whether it be an ignorant person or an educated person, poets or scientists, astrologers or astronomers, rich or poor; the sky is what unites us all. As we all look up at the night sky, we are overwhelmed by the sensation of the vastness of the universe and the role we are playing in it. We may have different ideologies, principles, opinions etc, but we are all descendants of the same stars that brighten our nights. Next time, looking up at the night sky, admire your origins, embrace them, feel the warmth of the cosmos that calls out to you for the sky will speak to you if you are ready to listen.

The band of stars here is the Milky Way Galaxy seen on a clear night away from light pollution

~Puja Krishnatraya.

“Absence of evidence is not the evidence of absence” — Carl Sagan