The average lifespan of a human being is approximately 80 years. This number pales in comparison to the lifespans of celestial bodies such as the stars, luminous spheres of plasma that illuminate the night sky (Figure 1).
The lifespan of a star depends on its mass. Interestingly, it is found that the more massive the star, the faster it fades away. The Sun, for example, is about 4.6 billion years old, and will last another 9 billion years. Stars that are 10 times the mass of the Sun burn only for 100 million years. On the other hand, stars one-tenth the mass of the Sun burn 100 billion years or longer. Those are some large numbers being thrown about, but in astronomy, these orders of magnitude are quite common. To put this in perspective, our ancestors have been around for about six million years, but the modern form of humans, or homo sapiens evolved only about 200,000 years ago. Human civilization is a recent enterprise of 6000 years, with industrialization beginning only in the 1800. Our existence is a fleeting instance compared to the lives of stars, a rich history woven through several evolutionary stages of enormous extravagance, which begs the question, what happens when a star dies?
Colors of an Explosion
Stellar evolution is the process by which a star changes over the course of time. As mentioned earlier, the more massive a star, the faster it burns out. All stars are born from nebulae, clouds of gas and dust, and over the course of millions of years, these proto- or infant stars settle down, and transform into what is known as a main-sequence star. The Sun is a typical main-sequence star (Figure 2).
The death of a star is intrinsically related to the energy source that powers a star for most of its life: nuclear fusion. If one were to peel open a star, they would find a ring structure like that inside an onion. Initially, the energy generated by a main-sequence star is through the fusion of hydrogen atoms at its core. Hydrogen atoms fuse to produce Helium resulting in an abundance of the latter, and the depletion of the former fuel. Eventually, the star begins to fuse the Hydrogen fuel along a spherical shell surrounding a mostly Helium core. This process causes the star to grow in size, and evolve into what is known as a Red Giant. Stars with half the mass of the Sun can also generate Helium fusion at their core, while more massive stars fuse heavier elements in a series of concentric shells. In general, the more onion rings, the more massive the star (Figure 3).
Once this nuclear fuel has been exhausted, a star like the Sun collapses into a dense, small body known as a white dwarf, with much of the outer layers of the Sun being expelled into a planetary nebula (Figure 4).
We learn about the stars by receiving and interpreting the messages which their light brings to us. The message of the Companion of Sirius when it was decoded ran: “I am composed of material 3,000 times denser than anything you have ever come across; a ton of my material would be a little nugget that you could put in a matchbox.” What reply can one make to such a message? The reply which most of us made in 1914 was—”Shut up. Don’t talk nonsense.” – Sir Arthur Eddington
The word “planetary nebula” is a misnomer. It does not mean clouds of gas and dust consisting of planets. The word originated in the 1780s when astronomer William Herschel viewed these objects through his telescope, naming them so because they resembled the rounded shapes of planets.
Stars more massive than the Sun can explode in a supernova releasing much of the material that they were composed of in a shock-wave into the vacuum that is space. By releasing the bulk of the chemical elements that they had originally sustained in their core (the list includes: Hydrogen, Helium, Carbon, Neon, Oxygen, Silicon, and Iron), stars enrich the interstellar medium. The resulting shock-wave produced from a supernova also helps trigger the formation of new stars. The cores of such massive stars collapse into an extremely dense neutron star, and in certain cases, a black hole (Figure 5).
A normal-sized matchbox containing neutron-star material would have a mass of approximately 13 million tonnes, or a 2.5 million m3 chunk of the Earth (a cube with edges of about 135 metres).
The decisive factor is always the mass of the star, which in simple terms, is proportional to the strength of its gravity.
Gravity is a one-dimensional force, in that it is always attractive, and tries to pull things together. We are held to the surface of the Earth by the planet’s gravitational force. A black hole is born when an object is unable to withstand the compressing force of its own gravity. Stars use their nuclear fusion to maintain a tremulous balance, for several million years, in an exhaustive fight against gravity. The Sun will never become a black hole, as its gravity isn’t sufficient to overpower the force produced by its nuclear furnace. But in more massive stars, gravity ultimately wins.
Then what are hypernovas?
Even Bigger Explosions
Simply put, hypernovas are pretty much the same thing as supernovas, just on a much grander scale. Hypernovas are extremely energetic supernovas, and though their formation is similar, they are both distinct phenomena (Figure 6).
In a supernova, a star sheds its outer matter leaving behind a dense core in a neutron star. In a hypernova, the force of the explosion tears the inner star apart as well. Hypernovas only occur in stars with greater than 30 times the mass of the Sun. Like in a supernova, the star runs out of fuel, unable to support itself under the weight of its own gravity. As it collapses, the star subsequently explodes, spewing matter in all directions. The energy released within mere seconds of this explosion is greater than the energy that the Sun will release in its entire lifetime.
Time for an analogy. The sun radiates ~ 3.83 x 1026 W of energy. The standard light bulb for a table lamp has a wattage of 60 W. Thus, the sun radiates energy equivalent of 7 x 1024 light bulbs. Supernovas shine with the brightness of 10 billion suns (1 sun = 7 x 1024 light bulbs, then 10 billion suns = 10 x 109 x 7 x 1024 light bulbs = 7 x 1034 light bulbs), their total energy output being ~ 1044 J, which is the total energy output of the sun in its 10 billion year lifetime. Hypernovas release energy in excess of this amount. That’s a lot of light-bulbs!
Two plausible reasons currently conceived on the formation of a hypernova include:
A massive star (rotating at a very high speed or encased in a powerful magnetic field ) exploding, resulting in the inner core being ripped apart.
Two stars in a binary system colliding, forming one gigantic mass, and exploding.
The result is ultimately clear: a black hole is produced, and a huge amount of energy is released in the form of a gamma-ray burst, one of the brightest known events in the universe. The light released in a hypernova is several million times greater than all the light of the stars in the Milky Way galaxy put together.
Introducing the Universe
The world is very old, and human beings are very young. Significant events precede our appearance on Earth in what is an awesome vista of time. But in our vanity, we find the stubborn pride which motivates our claims, and actions as a higher organism on this planet. Thus, we are blind to the overwhelming reality that our existence on Earth, and the very existence of the planet itself, is nothing more than a single thread woven into the rich tapestry that is the universe. There, beyond the confines of our world and among the stars, lies unfathomable mysteries of great wonder. Hypernovas are a small shade of that enormous spectrum of amazing phenomena in our universe.
“What seest thou else in the dark backward and abysm of time?” – William Shakespeare
Time is a component quantity of our daily lives. It is symbolic of the indefinite progress of existence, and events that are generally considered to occur in an apparently irreversible sequence from the past, to the present, and onto the future.
The concept of time has been central to the growth, and evolution of human civilizations. It has also served as an important facet of knowledge that has been studied to a great effect in religion, philosophy, and science. But, to this day, an absolute definition of time still evades scholars.
In The Dragons of Eden, Sagan does not extend his arguments toward an extensive discussion on the concept of time, but rather focuses on its use as a metaphor to describe humanity’s place in the cosmos. To infer the future, it is necessary for us to understand our origins. This is the basis of Sagan’s approach.
Now, it is argued that the predecessors of modern-day human beings, the Homo sapiens¸ evolved somewhere between 250,000, and 400,000 years ago. This number pales in comparison to the appearance of the first primitive humans, such as the Australopithecines, which happened somewhere between 8-9 million years ago. But, even these events, are preceded by an even greater “vista of time” reaching far back into the history of our planet, the solar system, and the universe. Very little is known about these periods of time, and even with the numbers mentioned earlier, we still struggle to grasp the immensity of these time intervals (Figure 1).
Nevertheless, science has found success in the establishment of specific methods that have allowed us to date events from the remote past, such as geological stratification (Figure 2), and radioactive dating (Figure 3).
These two methods have provided information on archaeological, paleontological, and geological events. Astrophysical theory has provided for the same on a grander scale involving the dating of stars, planetary surfaces, galaxies, and the even the age of the universe (Sagan states this to be 15 billion years old, though recent results from the Wilkinson Microwave Anisotropy Probe (WMAP) puts the number somewhere at 14 billion years old). The earliest event known in record is called the Big Bang, an intense explosion from the universe is said to have formed, but rather than a beginning, the Big Bang is generally considered to be a discontinuity in time where the earlier history of the universe was destroyed.
To put this further into perspective, Sagan introduces the Cosmic Calendar, where he compresses the 14-billion-year-old chronology of the universe, into the span of a single earth year. In this manner, one billion years of Earth history is the equivalent of twenty-four days of our cosmic year, and one second of the cosmic year is the same as 475 real revolutions of the Earth about the sun. The Cosmic Calendar is a humbling account of humanity’s place in the universe, with all our recorded history occupying the last few seconds of December 31.
Though a short chapter, Sagan’s use of the Cosmic Calendar is quite analogous to a common argument used in astronomy to provide a picture of our place in the universe (Figure 4).
While the major premise of Sagan’s book focuses on discussions on the evolution of human intelligence, this introductory chapter is a necessary prelude that helps to symbolize the significance of the subject matter. While it may be true that humanity occupies an insignificant instance in the face of cosmic time, we are now embarking on a new cosmic year, one which is highly dependent on our ability as a species to come together, use our wisdom, and unique sensitivity to the world for our survival, and a greater future.
Sagan, Carl. The Dragons of Eden: Speculations On The Evolution of Human Intelligence. Ballantine Books, 1977.
I’m yet to successfully defend my thesis before the supervisory committee, and as such can make no claims to having completed my thesis. Nevertheless, this won’t stop me from relishing the relief that follows having “hammered” out a 100 page first draft detailing my work over the past two years.
My personal treat on the eve of this achievement was to go to my first movie premiere. It was a Tamil movie, titled ‘Kabali.’ The movie features the actor Rajinikanth, who is possibly one of my favorites among various others in the South Indian film fraternity.
Along with Leina, and a good friend, we attended the premiere last Thursday. While we enjoyed the movie, our night ended with partial deafness, and loss of hearing, from the raucous cheering, and entertainment that the audience (about 300 other Tamilians) provided throughout the outing.
The entire event was reminiscent of the chaotic fun that results in the premiere of every Rajinikanth movie in India, and it was a once in a lifetime experience for the three of us.
All of which leads me back to where I am now. Come September 2016, I will have lived in Edmonton for a total of 7 years. Time has certainly flown by! It still feels like yesterday when I was sitting in an old lecture hall, voraciously digesting the lecture notes for a Physics 101 course.Having recently turned 25, I feel an even greater sense of responsibility, and ambition that I intend to carry over to the next phase of my life.
Much of August will focus on editing my thesis, and making the necessary preparations for my defense. I’m hoping that everything will go according to plan. And now, I shall leave you all with this brief update, as I contemplate the subject of my next blog post. I intend to have it up by this weekend, along with an “info” sheet on the various new additions that will be made to the blog, and its structure. Until then, toodles!