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You may have heard about black holes. These enigmatic celestial objects are one of the most chewed over topics in the field of cosmology. They are powerful, extremely destructive, and are infinitely dense at their centre. But how do these mysterious voids come into existence? What makes them so powerful? And, what is their ultimate fate?
A Dead Star
Have you ever wondered what happens to the stars in the night sky? Well, like humans, stars die too, but they die in many different ways. We know one thing for sure; the outcome depends on the initial mass of the star. Theoretically, it is expected that stars similar to our sun will end up as white dwarfs and eventually, black dwarfs as a result of eons of nuclear fusion, the process of fusing atoms in high temperature and pressure into newer and heavier elements. This process ends as the core is unable to fuse heavier elements, and the star cools into a white dwarf. This is just one of the several outcomes that may unfold.
As we are talking about black holes, we will be discovering the lifecycle of gargantuan supergiant stars with masses tens of times greater than our sun’s. For scale, the masses of all the planets combined doesn’t even amount to ≈ 0.01% of the sun’s mass. In those stars, with masses around 8 times more than our sun’s, gravity is tremendously powerful. Throughout its lifecycle, the star continues the process of nuclear fusion, as its gases fuse into heavier and heavier elements. In this process, called Stellar Nucleosynthesis, where nuclei synthesize (come together) inside stars to form new elements, Hydrogen fuses into Helium, Helium to Oxygen, Oxygen to Silicon and finally, Silicon to Iron.
For millennia, stars have been in a state of hydrostatic equilibrium. This means that the star has been constantly providing enough outward gas pressure through nuclear fusion to counter the tremendous gravitational pull. This interaction keeps a star stable. However, the reason Iron declares the end of the star is simply because the reaction is now endothermic. Iron absorbs heat energy and is harder to fuse, and the star can no longer provide enough pressure to sustain itself. This causes the balance between the star’s gravity and the gas pressure to go haywire. The energy from nuclear fusion can no longer keep up with gravity, and the gravity far exceeds the gas pressure, resulting in a collapse. The star implodes with violent energy in the form of a supernova. It collapses on its weight and crushes inwards to form a black hole.
A New Life
The black hole continues to compress into an infinitesimally small point called a singularity. It surprisingly has an infinite density in its centre. The black hole is so densely packed together, that once an object passes the event horizon, a boundary line around the black hole, gravity becomes so overpowering, that nothing, not even light, can get away with its strong gravitational pull. The black hole violently spins at near-light speed and can uncontrollably engulf entire stars and other heavenly bodies. Black holes can also merge in violent collisions.
The black hole attracts all matter at a reasonable distance towards it and engulfs them. However, the falling matter descends at such high speed that it becomes luminous, making a ring around the black hole called an accretion disk. The celestial body spends eons continuing this process. Scientists theorize that billions of years into the future, there could be a time where the universe is made of nothing but black holes.
The Grand Finale
So, you are probably wondering what happens to these ferocious bodies after all! Earlier, it was believed that black holes were just the universe’s garbage collector. But, in 1974, Stephen Hawking released a ground-breaking paper that unified Einstein’s Theory of Relativity and Quantum Mechanics to establish the fact that Black holes do indeed die, but in the tremendous ordeal. Black holes die so slowly that it will take only about 1064 years to evaporate an average-sized black hole. That is 1 followed by 64 zeroes! For scale, our universe has only lived around 13.8 billion years.
However, Hawking Radiation, as this slow process was named, is a sizably vast topic on its own, and covering it in this chapter will not do any justice to it. Hawking Radiation deserves a wholly new article of explanation. In short, using small fluctuations in the quantum world that take place on a general basis, he was able to solidify the fact that over an eternity, black holes lose mass, atom by atom, until they evaporate with a flash into nothingness.
I hope this article proved beneficial in getting a picture of a black hole’s life cycle as we know it through modern physics. Black holes are still enigmatic and theoretically studied and there is still room to ameliorate the knowledge we possess about these perplexing and mysterious bodies.
Citations
1. NASA. “Black Holes.” Science Mission Directorate, 2021, science.nasa.gov/astrophysics/focus-areas/black-holes.
2. “NOVA | Birth of a Black Hole.” Public Broadcasting Service (PBS), www.pbs.org/wgbh/nova/blackhole/form-nf.html.
3. “How Much Mass Makes a Black Hole?” European Southern Observatory, 18 Aug. 2010, www.eso.org/public/news/eso1034.
4. Freudenrich, Craig. “How Stars Work.” HowStuffWorks, 7 Nov. 2020, science.howstuffworks.com/star6.html.
5. Fox, Ronald. “Origin of Life and Energy.” Elsevier Inc., vol. Encyclopedia of Energy, Volume 4, 2004, doi:10.1016/B0-12-176480-X/00054-1.
6. “Dying Stars and the Formation of Black Holes.” Encyclopedia, www.encyclopedia.com/science/technology-magazines/dying-stars-and-formation-black-holes.
Picture Courtesy
1. Nuclear Fusion. 2018, BBC https://www.bbc.com/news/business-46219656
2. Black Holes in Depth. 2019, Dark Space Central http://www.darkspacecentral.com/bh_in_depth_page.html
