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Been There, Sun That

Despite our acknowledgement and stated appreciation of the role that the Sun plays in our lives, we are generally unaware of the history of its existence and the details of its very being. I hence took it upon myself to explore the the very lifeblood of the solar system (from the comfort of my bedroom of course), and begged the famous preschool question: what exactly is the Sun?

The Sun is a yellow dwarf star, and is essentially a pulsating ball of gases and plasma at the heart of our orbit. Its massiveness exerts a strong gravitational force that acts as centripetal force for all celestial bodies in our solar system, ergo pulling all of us into a nearly circular orbit around the star.

About 4.6 billion years ago, our solar system was an unfathomably large cloud of gas and dust (dubbed our ‘solar nebula’), consisting of relatively light elements (such as hydrogen). An unexplained phenomenon then caused this cloud to collapse inwards on itself, and the accumulation of matter at the very core of this cloud began to exert a gravitational force, pulling more matter inwards until the center of the cloud was a dense ball under extremely high, inward-directed pressure. Coupled with the heat at the center, the high pressure provided the perfect conditions for nuclear fusion to occur, a rough 100,000 years later. Soon enough, the atoms at the centre of this cosmic cloud fused to form elements of increasing mass, starting with hydrogen (and its isotopes), helium, oxygen, and so on. The violent expulsion of energy during nuclear fusion reactions occurs due to difference in mass of the products and reactants (i.e. of the mass difference between the initial atoms and the heavier atom(s) they fused to form) of the said nuclear reaction can be described with the rather iconic equation E = mc2, where m is the mass difference, c is the speed of light and E represents the energy that accounts for the Sun’s scorching heat and immense brightness.

A few million years later, the Sun has evolved to become what we know it as today: a main sequence star. Main sequence stars are the most popular kind, accounting for approximately 90% of all stars in the known universe.  Existing as the largest object in our solar system, the Sun boasts an inscrutable surface temperature of about 5505 °C and an even higher core temperature of around 15,000,000 °C.

A spectacle that continues to be exhibited by the Sun is what we’ve come to call a solar flare. These flares are radiation discharges from the Sun’s surface due to the interference of the celestial body’s intense magnetic fields with each other. The emitted radiation is observed at a multitude of wavelengths, often accompanied by heavier subatomic particles that are emitted and accelerated too, the likes of which are electrons and protons. All the while, nuclear fusion still continues to occur in the Sun, with scientists detecting heavier elements such as carbon, magnesium, and even traces of iron in the star’s core today.

However, this continued nuclear fusion builds up the inward pressure that is exerted on the Sun’s core, which in turn causes the acceleration of nuclear fusion at the core (to expel energy to counteract the inwards pressure). The increased nuclear fusion gradually increases the luminosity of the Sun, at the current rate of 1% every 100 million years. In 3.5 to 4 billion years, the luminosity of the Sun would have increased by about 40%, subsequently causing all water in Earth’s oceans to boil and all of our ice caps to melt. Moreover, all trapped water vapour would exit the atmosphere of the Earth, overall effectively deeming any form of planetary life dead.

The process of nuclear fusion will continue to increase, insinuating the star’s eventual exhaustion of hydrogen. This occurs in about 5 billion years, and as it occurs, the Sun evolves into a red dwarf. Its atmosphere then commences its terrifying expansion, which is predicted to continue until it reaches the Earth, ergo nonchalantly digesting Mercury and Venus in the process.

At this point, the Sun has about 120 million years of life left in it. The initial 100 million years see the celestial body lose its mass, luminosity and volume through helium flashes as it continues to fuse helium in its core until exhaustion, while the following 20 million see a staggering increase in luminosity, thanks to a series of relatively frequent thermal pulses. Nuclear fusion continues with heavier and heavier elements until it is only left with the heaviest possible element for main sequences – iron. Since the fusion of iron does not actually produce any energy, the inward pressure finally wins, consequently causing the Sun to cave in and implode, resulting in an instantaneous wave of energy that reverberates through the solar system (or at least what remains of it). This occurrence leaves behind a superdense ball of matter: a neutron star. It exists in this state for an incomprehensible amount of time and continues to cool as it bears witness to innumerable other celestial phenomena that our universe boasts.

If this article made you consider relocation to an extrasolar planet, don’t worry; you still have a few billion years to pack.

Key terms:

  • Yellow dwarf: A main sequence star, with a surface temperature of up to 6000K.
  • Plasma: Superheated matter where atoms exist without orbiting electrons (hence forming an ionized gas)
  • Centripetal force: Resultant force that acts perpendicular to the velocity of an object in circular motion, causing said body to continue its circular path
  • Nuclear fusion: the fusion of two or more atoms/nuclei to form heavier nuclei, expelling energy in the process
  • Red dwarf: Main sequence stars of low luminosity and surface temperature
  • Helium flash: Rapid conversion of helium into carbon via nuclear fusion in red dwarves

Works cited:

  • Choi, C. Q. (2021, June 9). Earth’s sun: Facts about the sun’s age, size and history. Space.com. Retrieved October 29, 2021, from https://www.space.com/58-the-sun-formation-facts-and-characteristics.html.
  • Evolution of our Solar system – Gallery. Lunar and Planetary Institute (LPI). (n.d.). Retrieved October 29, 2021, from https://www.lpi.usra.edu/education/timeline/gallery/#formation.
  • NASA. (2021, October 15). Solar System: In Depth. NASA. Retrieved October 29, 2021, from https://solarsystem.nasa.gov/solar-system/sun/in-depth/.
  • Published: Friday, S. 18. (2020, September 18). What will happen to the planets when the Sun becomes a red giant? Astronomy.com. Retrieved October 29, 2021, from https://astronomy.com/magazine/ask-astro/2020/09/what-will-happen-to-the-planets-when-the-sun-becomes-a-red-giant.
  • Redd, N. T. (2018, February 24). Main Sequence Stars: Definition & Life Cycle. Space.com. Retrieved October 29, 2021, from https://www.space.com/22437-main-sequence-stars.html.
  • Sharp, T. (2017, November 4). What is the Sun made of? Space.com. Retrieved October 29, 2021, from https://www.space.com/17170-what-is-the-sun-made-of.html.
  • Solar System Timeline. The Planetary Society. (n.d.). Retrieved October 29, 2021, from https://www.planetary.org/worlds/solar-system-timeline.
  • Williams, M. (2016, September 24). What is the life cycle of the sun? Universe Today. Retrieved October 29, 2021, from https://www.universetoday.com/18847/life-of-the-sun/.
  • Zell, H. (2015, March 6). What is a solar flare? NASA. Retrieved October 29, 2021, from https://www.nasa.gov/content/goddard/what-is-a-solar-flare
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