Fate of Our Sun – A Diamond!?

Believe it or not here it comes!  If we ask others, which is the biggest diamond in our planet Earth, the right answer will be The Great Star of Africa or The Golden Jubilee Diamond  or The Cullinan Diamond, which has 546 carats and at its crude stage (uncut) it had 3,107 carats!  Now coming to Cosmos, we have everything big and the biggest diamond which has been discovered and confirmed by Astronomers is a giant star Lucy about 50 light-years away from Earth in the constellation of Centaurus.  It is about 4,000 Kms across and this has a diamond at its core which is about 10 billion trillion trillion carats!!  A tea-spoon size white dwarf diamond will weigh about 5 tonnes!  Twinkling in the sky is a diamond star of 10 billion trillion trillion carats, astronomers have discovered. "Our Sun will become a Diamond that is truly forever", says Mr. Metcalfe, who discovered this star Lucy.

A diamond that is almost forever

Star Lucy

Star Lucy was once as bright as our Sun and went through its maturity and dying stage and now it is a white dwarf with its core containing solidified carbon interior to form our galaxy?s largest known diamond so far. This huge cosmic diamond star known by the name BPM 37093 is one of the fascinating facts of astronomy.  This white dwarf is not only radiant but also rings like a gigantic gong, undergoing constant pulsations.  The astronomer Travis Metcalfe who discovered this star states, "By measuring those pulsations, we were able to study the hidden interior of the white dwarf, just like seismograph measurements of earthquakes allow geologists to study the interior of the Earth."

We have learnt in our previous article how a star is born or formed.  Now awaits the biggest surprises of all that each one of us ought to internalize, how stars end their life in our cosmos.  All living being have a fate to die and so does our active celestial objects.  We have heard the song, "Twinkle, Twinkle Little Star", the twinkling stars will cease one day (just a term) to exist what they are now.  For living creatures it might be few years to couple of hundred years but when it comes to stars it is millions to billions of years! This millions to billions of years is based on how much bigger or massive the star is.

We might have a false conception that bigger and robust stars live longer.  In reality larger and hotter (absolute luminosity) the stars are, more energy they consume and they exhaust primary fuel of hydrogen much more rapidly than cooler and less massive ones.  Once core?s ready supply of hydrogen is gone, nuclear process ceases. This in turn, limits the outward pressure generated by the fusion reaction and leads to the enormous gravitational pull. This will lead to the collapse of the outer layers into the core.  The temperature of pressure increase to higher than when the star was formed and as a result fusion of helium atoms into carbon is initiated.  This fusion begins when the core temperature is about 100 million Kelvins.  All this and further reactions is dependent on star mass.

As we know there are varieties of stars in our galaxy starting from Red dwarfs.  As per recent astrophysical models red dwarfs having 0.1 solar masses may stay on the main sequence for almost six trillion years, and take several hundred billion more to slowly collapse into a white dwarf.  Our nearest star is Proxima Centauri, which is a red dwarf.  We can see its companion stars alpha and Beta Centauri to the naked eye near the horizon.  From Mangalore we can see these stars as a bright object and through a small telescope you can separate the alpha and beta into bright objects, which shine just like headlights of a car during night time.  We cannot see our nearest through smaller (laymen version) telescopes.  Unfortunately, we cannot see this star from United States.

The average stars of our galaxy and the universe have a fate quite similar which awaits to our Sun.  A medium-size star 0.5-3.0 solar mass, once it exhausts the helium fuel the star?s size changes drastically and its outer layers go on expanding to hundreds of its initial size.  This phase of the star is known as red giant phase.  When our Sun attains red giant phase it will not only engulf the inner planets but also may  cover the orbit of Earth.  The fate of our Sun to attain this red giant phase is about 5 billion years from now.  Our Sun is just an average star with an age of 4.5 billion years (main sequence star).  This phase (red giant phase) of life of a star is called Late type stars. 

Star Betelgeuse ? comparison of size

The most common red giants that we can see are Betelgeuse and Aldebaran in Orion and Taurus constellations respectively.  To identify the star Betelgeuse, just see three prominent stars in a line (theg rai or three kings in Konkani) at the center of the constellation Orion and one on each side of those stars is Betelgeuse (reddish in color) and Rigel (bluish in color) and they collectively form a shape of a compass needle.  Each end point of the needle represents the Rigel and Betelgeuse.  For all the readers who want to start exploring the night sky and its constellations, start with this Orion constellation.

Orion Constellation ? Betelgeuse is at the top and Rigel is at the bottom

The outer layers implode to initiate accelerated form of hydrogen fusion and then helium fusion reaction.  This helium fusion reaction is very sensitive to temperature fluctuations at the core, which leads to huge pulsations (immense force of gravity and outward pressure of fusion reactions) at the center.  As these huge pulsations build up, it gives enough kinetic energy for the out layers to be shot out or ejected as a planetary nebula.  At the center of the nebula remains the core of the star, which cools down to form a small but dense white dwarf, typically weighing about 0.6 solar mass, measuring about the diameter or size of the Earth.  All white dwarfs can have a critical mass of less than 1.44 solar masses (Chandrashekar Limit) not more.  Our Sun will remain at this stage for thousands of millions of years, until there is no more fuel to burn and will extinguish as a black dwarf.  This black dwarf is nothing but huge dense highly condensed carbon core, which we call a diamond!  So, our Sun awaits the fate of turning itself into a diamond in about 5-7 billion years to come!

Comparison of red giant star Antares with that of our Sun, a minute spec at the top

Let us explore the fate of super-massive stars.  Any stars massive than 4 solar masses awaits another fate, which is most violent and unbelievable.  In these supergiant stars the inner core of carbon fuses to burn heavier elements and as a result counteracts the forces of gravity.  This extends to until silicone is fused to iron.  The fusion of silicone to iron does not radiate energy rather iron fusion absorbs energy!  This means there is no outward pressure and in split of a second the entire outer layers fuses with the core.  This is known as supernova.  A typical supernova in a split second ejects an energy equivalent to billions of Suns.  More than the energy that Sun can generate in its lifespan.  What happens next is not clearly understood.

There are two possibilities for this stellar evolution:  Once the star on white dwarf stage and are heavier than 1.44 (Chandrashekar Limit) to 3-5 solar masses, the force of the supernova forces the electrons into the nuclei, where they combine with the protons to form neutrons. The electromagnetic forces which keep the nuclei separate are gone.  A neutron star is formed.  The neutron stars have a radius of anywhere 20-10 kms (they shrink as their mass increases.  This is 30,000 ? 70,000 smaller in size than our Sun.  Its weight roughly, 1-1.5 million masses of Earth.  Due to its smaller size and high density, the neutron stars have very high rotational speed, as one revolution can take anywhere one-seven hundredth to 30 seconds.  Some spin at over 600 revolutions/sec.

Neutron star

The escape velocity of neutron star is about 150,000 Kms/second.  To put this in perspective, if an average human were to encounter a neutron star, he or she would impact with roughly the energy yield of a 100 megaton nuclear explosion (the power equivalent to twice the size of the tsar bomba, the biggest nuclear weapon ever built by humans).

On the right hand side is the blue giant companion star and on the LHS is the blackhole engulfing the outer layers of the star.

For more massive (4-15 solar masses) stars very strange fate takes over.  The implosion of a star is so immense practically all the particles turned into singularity.  The immense gravity takes over any moving particles and not even light can escape from its event horizon.  The escape velocity is far beyond the speed of light.  If the Earth becomes a blackhole, its diameter will be just about 4 millimeters!  Supermassive blackholes are believed to exist in the center of most galaxies, including our own Milky Way galaxy.  This type of blackhole contains millions to billions of solar masses. The location of X-ray source Cygnus X-1(in Cygnus, The Swan constellation, also known as Northern Cross, Deneb, a blue giant, the most powerful star close to us heads this constellation and forms the top starting point of a cross-shape), which is widely accepted to be a 10 solar mass black hole orbiting a blue giant star (which has 20-30 solar masses).

So, readers wake up!  Where are we in this universe and do we pay any attention to the heavens up above?  

Author: Stany DSouza- USA