The life cycle of stars
In the article – origin of elements in stars – I describe how stars are formed. Stars are formed when a cloud of hydrogen and helium gas collapses under its own gravity. This collapse releases energy which heats up the cloud until when a critical temperature is reached, thermonuclear reactions are ignited and the star turns on. These reactions involve the fusion of hydrogen to produce helium. Fusion releases energy creating an outward pressure which is balanced by the opposing gravity exerted by star matter. The body of the star is therefore maintained by two opposing forces- heat pressure trying to explode the star and gravity trying to implode the star. Stars do not have an unlimited supply of hydrogen. When the hydrogen stores dry up, the star suffers an energy crisis. Thermonuclear reactions are temporarily disrupted and energy production stops. With dwindling outward heat pressure the implosive force of gravity dominates and the initial collapse resumes. This consequent contraction of the star exerts a compressive force which generates extra heat and pressure causing the outer layer of the star to expand. This will be the fate of our sun.
Some three to five billion years from now when its nuclear fuel becomes exhausted, our sun will increase by two hundred times its present size becoming a bloated red giant. It will fill the entire sky engulfing an incinerating nearby planets, the moon and probably the earth. Hopefully be then we would have ventured elsewhere in the cosmos.
The sun will gradually cool over the aeons, losing its outer layers to the surrounding medium, its size steadily decreasing. With little heat and energy to support its structure, overwhelming gravity will shrink the remnant of the sun to a white dwarf. Our sun which could initially accommodate a million earths in its volume will then be the size of the earth only. Further shrinkage of the white dwarf will be blocked by electron forces. Note that since our sun is an average size star, the above events describe the fate of all such stars. When a star becomes a red giant, what happens next depends on the initial mass of the star. Average size stars like our sun as explained ends up as a white dwarf.
Stars ten times the mass of our sun have enormous gravitational power and their collapse cannot be stopped by electron forces. They do not end as white dwarfs. Within a second, its core at that moment the size of the Earth, is reduced to a neutron star the size of a city about ten kilometres across. Further collapse of the neutron star is prevented by nuclear forces.
The neutron star phase is not the end of the story for much larger stars. Super giant stars have a much more dramatic fate. After going through the red giant and neutron star phase, the collapse of the interior leaves the inner star with no support. The result is the outer layer with its colossal weight comes crushing down onto the solid dense newly formed neutron star. This violent encounter sends out a cosmic force of unimaginable power which literally blows the star apart (the “inner” neutron star remains). During this cataclysmic period lasting a few seconds, the star temporarily shines brighter than a billion suns. The intense heat generated by the collapse gives rise to elements heavier than iron such as gold, silver, lead and so on. Such violent explosions are known as supernovae.
Although stars that end their lives as supernovae are many times more massive than our sun, they are not massive enough to exert sufficient gravitational power to overcome the nuclear forces exerted by the neutron star. The result is a stable neutron star. However, much larger stars (25 times more massive than our sun) have stupendous gravitational power. When such stars collapse at the end of their lives and blow up as supernovae, they do not become neutron stars. They have a bizarre fate. Relentless gravitational forces squeeze the stellar fragment to smaller and smaller volumes. It does not stop at a nuclear star level, but the stellar fragment is compressed further and further until it catastrophically implodes to a point of zero size, the gravitational field so intense that even light cannot escape from it, hence the term black hole. If light is imprisoned by a black hole, how do scientists detect and study them? Black holes reveal their physical presence through an effect on surrounding structures called gravitational lensing. For example, an intervening black hole can bend light from a distant galaxy on its way towards earth. Scientists can detect such bending caused by the black hole. The immense gravitational force at the centre of a black hole causes an infinite distortion of space-time. This has led to the exciting idea that black holes may be gateways (known as worm holes) to other regions of space-time. With this basic background of the life cycle of stars, we can now turn our attention of what the Quran has to say about this fascinating subject.
Red Giant and White Dwarf phase
As stated above about five billion years from now, our sun will suffer an energy crisis. The sun will become a bloated red giant swelling to two hundred times its present size. Gradually over time it will lose material to the surrounding interstellar space, its size gradually diminishing. The Quran describes these events in the following manner: (keep in mind that the lifecycle of medium-sized stars and their fate are similar to that of our sun) “(When) the sun and the moon are united into a single mass” (75-9). There are two interpretations to the verse: a) disruption of the orbital paths of the sun and moon. A stray celestial object may dislodge the moon sending it on a collision course towards the sun or b) reference to the red giant stage of the sun. The sun will grow many times its original size and will engulf the moon and thus also the nearby planets. Since the sun is gigantic compared to the moon, the much larger giant sun will simply consume the moon. The next two verses favour the latter interpretation: (1) “(When the sky) becomes red inclining towards yellow and other colours” (55-37). The distended sun will fill the sky, creating a burning red halo around Earth. It is plausible to concede that the colour changes in the sky are meant to reflect the transformations of the giant sun since the latter will cover a large portion of the sky. An alternate explanation for the red sky is the following: Normally the light emitted by the sun is deflected by the particles in the earth’s atmosphere. This scattering of light and the thickness of the atmosphere together cause the blue appearance of the sky. During the red giant phase of the sun, the atmosphere will evaporate and there will be no light scattering. If there are any humans around, they will witness a blazing red sky caused by the giant sun radiating predominantly in the red region of the EM spectrum. What is the significance of the colour changes referred to in 55-37 above? Stars, at the end of their lives undergo a series of temperature changes. These changes can be detected as variations in the pattern of the light colours emitted by the star. This phenomenon – where temperature changes produce a difference in the colour spectrum of the star – is hinted at in the verse. This fact was only discovered 150 years ago. The verse could also refer to the changes in colour of the cosmic background radiation to be discussed later. (2) “(When) the oceans boil over” (81-6). Extreme temperatures generated by the massive swollen sun will heat the planet’s seas to boiling point.
The external layers of the bloated sun at this stage predominantly contain helium, which will be lost to the surrounding interstellar medium. The loss of helium and over-powering gravity compressing the sun will cause it to gradually diminish in size. The shrinking process is referred to in verse 81-1: “When the sun is folded up and losing its light.” When something is folded up, it becomes more compact and dense and this is precisely what will happen to the dying sun. The latter part of the verse indicates that the folding up will occur towards the end of the sun’s lifecycle when its light and energy reserves dry up. In the meantime with almost no fuel supplies, the sun will gradually cool over the aeons until it is no longer hot enough to glow. This stage, characterised by its loss of brilliance and its eventual transformation to a cold dead star, is described in verse 81-2: “When the stars lose their lustre”. The end of the lifecycle of an average star is therefore marked by a number of spectacular happenings and breaking up processes. The latter may also be alluded to in the following verse: “I call to witness the falling down of parts of stars” (56-75). The verse may apply to the disintegration of massive stars as well (explained shortly).
Almost all commentators, because of lack of insight and influenced by early translators, view these verses as a sign of the end of the universe. Cosmic events are playing themselves out throughout the cosmos. Through the telescopic eye, scientists are witnessing stars in various stages of their lifecycles, which have been described in the above verses.
On the 23rd of February 1987, star gazers saw a bright new object in the Large Magellanic Cloud – a small nearby galaxy consisting of about 30 billion stars. The magnificent sight was not visible the night before. Now the newcomer could be seen with the naked eye in the southern skies. Astronomers map the sky just like geographers map countries on Earth. From previous observations it was clear that the brilliant new starry body appeared at the exact site of a massive star about 50 times the diameter of the sun. The massive star was present at the same location before the 23rd of February 1987, as determined by telescopic observations. Subsequent observations (i.e. after the 23rd of February 1987) of the same region containing the bright object showed that the large star had disappeared. The bright object that appeared in its place somehow caused it to vanish. There is only one explanation consistent with such a sequence of events – the newcomer was a supernova. The star had blown itself up in a titanic explosion, hence the “disappearing act” of the massive star and the appearance of the brilliant object signifying the explosion. Of course the actual event took place 170 000 years ago, as the Large Magellanic Cloud is a 170 000 light years away. It took light signals from the explosion 170 000 years to cross the intervening space and reach Earth. The first ever recorded supernova dates back to the 11th Century when Chinese astronomers saw a bright new object in the constellation of Taurus. Supernovae leave tell-tale signs. The explosive ejection of matter sweeps up the interstellar material in its surroundings until its momentum is slowed down by the resistance of the built up dense material. Rather like one forceful sweeping motion with a broom that causes an instantaneous clean region and further away a pile of dirt. Thus the supernova creates a kind of vacuum around it, which in turn is surrounded by a shell of compressed matter. Now many centuries later modern astronomers bear witness to the unusual cosmic event. Clearly visible through the telescope is a remnant of that ancient happening, a shell of dust known as the Crab Nebula where once existed one of the brightest stars. Ancient astronomers did not know what these brilliant heavenly objects were. Today we not only know their true nature and why they explode, but also what role they play in shaping the cosmos.
Bear the following facts in mind:
1.) The first supernova sighting dates back to the 11th Century and its full significance was only realised in recent times (only in 1930 did the Bulgarian astrophysicist who coined the word supernova write an article providing key insights as to the true nature and formation of supernovae); and 2.) The 7th Century (the time the Quran arrived), inhabitants viewed stars only as feeble lights in the sky (the Bible describes them as small objects – Daniel 8-10), the Quran has this to say about the extraordinary cosmic occurrence: “Consider heavenly space and the night-visitant (therein) which suddenly (appears after) a cataclysm. And what would make thee conceive how great the night-visitant is? (It is) a star of piercing brightness” (86-1, 2, 3) – a fitting description of a supernova. It is referred to as a night-visitant due to its brilliant appearance when darkness comes. More significant is the term “visitant” (also means newcomer). It appears suddenly and unexpectedly like a visitor in the night sky where none has been detected before, then fades and disappears. It is not a permanent resident, but leaves like a guest after a brief visit (relatively speaking in terms of astronomical standards). The supernova’s sudden appearance follows the cataclysmic event. The Arabic word attâriq describes the suddenness and violent nature of the supernova. The whole process of implosion and explosion happens within a few seconds. This is no ordinary star the Quran is describing, hence the rhetorical question in the verse referring to its greatness. Its colossal energy output lights up the skies and it shines brilliantly, therefore the phrase: “A star of piercing brightness”. My insertions are based on context and the following verse: “It is He alone that sustains the star that appears at the time when intense heat and energy (is generated within its core) giving it its bright appearance” (53-49), a reference to a supernova. Supernovae become visible after the explosion and astronomers observe them as bright objects in the sky. Ordinary stars appear as feeble lights. The bright star described in 53-49 is therefore more likely to be a supernova. The mentioning of the fact that it is God who sustains the supernova is to impress upon the reader that its power, spectacular destiny and critical function of creating the atoms you and I are made of, is ultimately His handiwork and cannot be accounted for by mindless nature. All commentators understand the bright star to be Sirius, a star that is prominent in the sky due to its closeness to Earth, and which was widely worshipped in pre-Islamic Arabia. It is wise not to interpret Quranic words as proper nouns. The reason is obvious; proper nouns are likely to change. The Quran is a timeless Book and its words must possess permanence.
The Quranic word ash-shi’râ describes a supernova in 53-49 and has therefore no connection with Sirius. The verse: “I swear by the coming down in parts of the stars” (56-85) has been discussed. It may also refer to the breaking or blowing up of a supernova. Before rounding off the discussion on supernovae I would like to quote the following: “He knows all that enters the Earth and all that comes out of it, as well as all that descends from the skies and all that ascends to them” (34-2). While a 7th Century resident may have conceived rain coming down from the skies, his knowledge about anything ascending from the Earth would have been rudimentary. Today we know the verse can refer to the innumerable physical phenomena on Earth and include those interactions between it and the sky above. The average mind may think of showering meteors, descending rain, water disappearing into the Earth and vapours arising from it and so on. The more discerned will be aware of EM waves, cosmic waves as well as elusive neutrinos from space bombarding the Earth. Neutrinos have penetrating power and are produced in enormous numbers in supernovae, stars and of course our sun. They cross the vast distances with tremendous speeds and shine down on us during the day, and at night when the sun is on the opposite side, they penetrate that side of the Earth with ease shining up on us. Not a single neutrino, according to 34-2, escapes the knowledge of the All-Knower.
Verse 15-16 in the Quran may refer to black holes: “Indeed We have set up (unseen) structures in space (derived from) large stars that become manifest through their great (gravitational) force, and which are gateways.” If the structures referred to make their physical presence felt through a force as indicated, and not visually, then they most likely must be invisible, hence my description of unseen. The celestial objects that best fit the above description are black holes. . Since they do not emit light, they are telescopically invisible. However, black holes betray their existence indirectly, they ‘become manifest’ through their powerful gravitational influence on surrounding structures. They are also considered to be a means of exit or entry, a ‘gateway’, a kind of intergalactic tunnel to other space-time regions.
The stars that we see as flickering lights in the sky – are they really distant suns? Are some of them really 20 – 100 times greater compared to the diameter of the sun and shine ferociously thousands of times greater than the sun’s luminosity? To appear as mere dots in the sky stars have to be very far away. Indeed they are. Scientists have devised means to measure their distances.
How real are black holes, red giants and neutron stars? Do these strange objects exist or are they just scientific speculation? Astronomers turn their telescopes upwards and scan the skies. These instruments are extremely reliable and millions of times more sensitive than our eyes. They faithfully record the evidence they “see”. Scientists are observing distinct phases of star formation. The various stages of their lifecycles are spelt out across the heavens. A hundred light years from Earth is the Orion Nebula, a glowing cloud of gas. Telescopic analysis reveals parts of it in the process of collapsing, marking the birth of stars. A red giant star called Betalgeuse has been identified. A star becoming a white dwarf has been observed in the Ring Nebula of Lira. Such observations and our calculations on the blackboard demonstrate that we really do know something of the real world. The intriguing astronomical objects already discussed are not figments of a scientist’s imagination. They do exist out there.