There are a plethora of striking questions to ask about the universe we’re part of and many of them are in regard to the big ball of light that goes and comes around each day. I’d love to satiate these curiosities and try to inform you something about the gigantic, spinning, glowing sphere of hot gas, the Sun, we observe in our daily lives. We all are aware of the fact that the Sun is very crucial to us in every possible way, but we barely ponder about how it came into existence, or what is the future of it, & now is the time to explore more of these in detail.
When we look up at the night sky, we see millions of twinkling tiny diamond-like stars, and our Sun is one of them. It appears larger and brighter than the other stars because we are closer to it. The stars, along with planets and other astronomical objects, are formed when a nebula, a huge cloud of hydrogen gas, helium gas, and dust particles, collapses under the force of its gravity, which forms a Protostar, an early stage in the formation of a star. The gravity increases gradually, along with the mass. This not only creates the Sun, a ball of plasma, a very hot ionized gas with positive ions and free electrons that has no overall electric charge but also triggers the process of internal thermonuclear fusion reactions, in which hydrogen, present in the core of the stars, began to fuse to form helium; this fusion enables the creation of Solar Energy that is imparted in the form of heat and light, which is why our Sun shines and produces warmth.
Primarily, stars are big exploding balls of gas, mostly composed of hydrogen and helium. Our Sun is extremely hot that a large amount of hydrogen is undergoing a perpetual star-wide nuclear reaction, as in a hydrogen bomb. The nuclear reaction where the lighter elements’ nuclei (composed of protons and neutrons), in this case, nuclei of two hydrogen atoms, fuse within the core of a star to form heavier elements like helium, carbon, nitrogen, iron, etc is called the Stellar Nucleosynthesis. Inside the core, the pressure is extremely high and the temperature reaches about millions of Kelvins. Every second, millions of hydrogen atoms, are converted into helium. The process of fusion in the Sun is known as the proton-proton chain reaction, as four hydrogen nuclei (protons) come together to make a helium nucleus. This reaction releases a tremendous amount of energy in the form of heat and light, as the total energy of helium is less than the energy of the protons that formed it. The energy then moves out by a process called convection, and it could be felt through the sunlight and heat.
Even though the Sun is continually transforming hydrogen into helium, it will take another billion years for all the hydrogen to convert into helium, i.e. to utilize all the fuel in the star, as it is enormous in size. This is the same for most of the stars we encounter at night. The Hertzsprung–Russell diagram (H-R diagram), is a scatter plot of stars showing the relationship between the stars’ absolute magnitudes (size) or luminosities (brightness) vs. their effective temperatures and spectral class (color). It shows the stars at different stages of their life, a massive blue star would be hottest and brightest, a massive red star would be coolest and brightest, our Sun rests in the middle of the diagram (Main Sequence area), a blue tiny would be hotter and dimmer, and a red tiny star would be colder and dimmer. The star loses mass as they go through these phases, and when the star degenerates, the remnant of that star depends on the mass after the Main Sequence phase. The Sun is a Main Sequence star right now and the fusion of hydrogen will go on for billions of years. As hydrogen nuclei fuse to form heavier elements, the sequences get shorter. The Sun begins to die when helium starts to fusing into other elements like carbon, oxygen, etc and eventually when the iron is produced in the core, the fusion uses more energy than it releases, thus the star collapses, then gases at the star’s surface begin to burst out to form a Planetary Nebula, a halo of gases. Resulting in a hot carbon-oxygen core called a White Dwarf, as the Sun’s solar mass (solar mass = mass of the sun) is less than 1.4 solar masses, and if the star was massive than our Sun it results in a neutron star or a black hole.
Stars appear to have various colors like bluish-white, yellow, orange, and red this is primarily due to their composition and effective temperature, which is indicated in the H-R diagram.
At all times, stars emit light that is a combination of several different wavelengths. Different elements emit different wavelengths of electromagnetic radiation when heated. In the case of stars, this includes its main constituents, hydrogen, and helium, but also various trace elements that make it up. The color that we see is the melange of these different electromagnetic wavelengths, which are termed as the Planck’s curve.
The relationship between star temperature and star color is given by the black-body relation, which applies to any object that gives off light and doesn’t absorb light. So, the hotter an object is, the shorter its wavelength is and thus it imparts blue color (blue has the shortest wavelength in the electromagnetic spectrum). Whereas, the colder an object is, the longer the wavelength is and thus it imparts red color.
Initially, when the star is a Protostar (newly formed), it releases a lot of energy and is hotter, thus it imparts blue color. However, when almost all of the hydrogen in the sun’s core will have fused into helium and helium starts to fuse into even heavier elements, the Sun won’t be able to generate as much energy and will start to collapse under its weight. That weight can’t generate enough pressure to fuse the helium as it did with the hydrogen at the beginning of the star’s life. Yet, the hydrogen left on the core’s surface will fuse and produce additional energy, enabling the Sun to keep shining. Whereas the helium core will start to collapse in on itself and release energy, not through fusion, but through increased pressure, as compressing any gas increases its temperature. This release of energy will result in more light and heat, making our Sun even brighter, and it will also cause the Sun to bloat into a red giant, which is red in color as its surface temperatures are lower than stars like our sun. When stars start to get old, the nuclear reaction ceases, and they cool down, swell up, and shed off their outer layers producing Planetary Nebula. Some more massive stars than our Sun become unstable and explode in a supernova. A supernova is a fleeting astronomical object, the explosive death of a star, which unleashes a burst of light through the cosmos, eventually, this supernova turns into a black hole (if the star is more than 5 solar masses) or a neutron star (if the star is more than 1.4 solar masses and less than 3 solar masses), which is composed of closely packed neutrons.
Profound scientist Carl Sagan said “we are star stuff,” and indeed he was right, we are made up of stardust.
CHNOPS elements (carbon, hydrogen, nitrogen, oxygen, phosphorous, sulfur) are building blocks of all life on Earth. Hydrogen is one of the first elements to come into existence after the Big Bang, along with a little bit of helium, but soon the hydrogen atoms clustered and started forming helium, thereafter helium was converted into Carbon, Nitrogen, Phosphorous, Oxygen, Sulphur, and Iron, everything we’re made of. Our bodies are composed of remnants of stars and massive explosions in the universe, i.e. most of the matter that we’re made up of comes out of dying stars, or stars that have died in explosions. We have stuff in us as old as the universe itself. So, you wouldn’t be incorrect if you tell someone you are made of stars, everything on this planet is the derivative of the stars.
I hope I was able to satiate some of your curiosity and impart some knowledge about the mysteries above.
EUROfusion. “Research for Tomorrow’s Energy Supply.” Fusion on the Sun- EUROfusion, www.euro-fusion.org/fusion/fusion-on-the-sun/.
Nasa. “We Are Stardust-Literally.” We Are Stardust-Literally, 28 Jan. 2015, www.nationalgeographic.com/news/2015/01/150128-big-bang-universe-supernova- astrophysics-health-space-ngbooktalk/.
Nasa. “Sun Primer: Why NASA Scientists Observe the Sun in Different Wavelengths” 22 Jan. 2013, https://www.nasa.gov/mission_pages/sunearth/news/light-wavelengths.html
Cornell University. “Hertzsprung-Russell Diagram” http://hosting.astro.cornell.edu/academics/ courses/astro201/hr_diagram.htm