Stellar Lifecycles
PHY1000 SECTION 1
Monday, December 08, 2008
Jediah Logiodice
Contents
Introduction 3
Terra Mater – Surviving on Planet earth 3
Stellar Properties 5
Stellar Life 6
Conclusion 8
References 9
Introduction
One commonly held view of the creation of the universe states that “In the beginning, God created the heaven’s and the earth” (Gen 1:1 New International Version); another common view of the creation, while not contradictory, definitely less mystical goes a little something like this: “Bang!”.
Fast forward some 14 billion years, and zoom in billions of light years to this spiral galaxy called the Milky Way, into this cluster of planets within a solar system that surrounds a small, yellow dwarf sun, to a tiny little planet, that at first seems quite insignificant, and yet with a careful study of the universe it is found that creation has been tuned to bring about a species called humanity apparently for the very purpose of allowing humans to ask the most basic of fundamental questions like: “Where did we come from?”, “Why are we here?” and “Where are we going?”.
Terra Mater – Surviving on Planet earth
To begin our journey, we find that this planet maintains a very delicate harmony with aerated oxygen compounds, with nitrogen cycles, and with water cycles which provide a basic substance for life to flourish. These components all maintain coherence within an atmosphere that not only provides a base for these complex cycles, but also traps heat warming the surface and filtering out harmful radiation from bombarding the flora and fauna that has taken up residence.
On top of this atmospheric cocoon we find a magnetic shield also providing protection from harmful forms of radiation. We find a moon in harmonious dance, feeding into tidal waves that pull the oceans to and fro aerating the oceans and providing for a flourishing of oceanic life. And still, even further out, we have this star, called the sun that provides heat and warmth and the breath of life through photosynthetic planetary life. By whatever appropriate means you come to the final conclusion, it appears undeniable that the universe and everything within it was finely tuned to produce life. And thank goodness for that, or otherwise, I would not be here writing this paper, and you, in turn would not be reading it.
A further review of this tiny little planet would show that while most of these tiny little objects we call humans are busy scurrying around from day to day, unaware sometimes of how immaterial they really are, we also find that among these humans there are those that will pause, look up and think about what is out there, somewhere beyond the troposphere, beyond the stratosphere, the thermosphere, and even beyond the exosphere; far out in the dark night sky.
The story of this astronomical undertaking begins with such an individual; his name was Isaac Newton.
While there were many important names attributed to discoveries and classifications of astronomy long before Newton, like Johannes Kepler, who provided fundamental concepts around planetary motion, it was Isaac Newton who created three universal laws that explained motion on a grand scale. Newton’s laws were so fundamental to the understanding of the universe, that Newtonian Physics dominated the world of physics for a few hundred years, until the introduction of Quantum mechanics in the late 1800s.
Stellar Properties
While Newton’s version of Kepler’s third law of planetary motion was able to provide information about the mass of stars when found in a binary system, he had even more to offer within the world of astronomy than just the laws of motion, for it was Newton who first provided insights into the nature of light (Bennett, Donahue, Schneider, & Voit, 2007, p. 148).
Through advancements of the study of light (spectroscopy) that came later, scientists and astronomers found that through emission and absorption lines they could determine the chemical makeup of distant light producing objects (Bennett, Donahue, Schneider, & Voit, 2007, p. 162).
Additionally, by examining the spectrum provided by these objects in conjunction with observational laboratory studies of spectral lines of known chemicals, scientists could also determine if objects where moving towards our planet, or away from our planet, and could even determine how fast these objects were themselves rotating (Bennett, Donahue, Schneider, & Voit, 2007, p. 168). Another use for spectral lines was later found in categorizing the surface temperature of stars (Bennett, Donahue, Schneider, & Voit, 2007, pp. 508, 509).
Further investigations of stars provide detailed information about the stars luminosity and their apparent brightness. By measuring a stars visual brightness, and measuring a stars distance (e.g. through parallax) we can then determine how bright a star really is through the inverse square law.
And so, we find that Newton and his discoveries paved the way for understanding a stars luminosity, temperature, density, and chemical composition!
Stellar Life
As we look out into the night sky, we can tell, sometimes even with the naked eye, that not all stars are created equal. Based on a stars surface temperature, some stars produce reddish light, some stars produce white light, and some stars produce yellow light, and some stars may even produce blue light (Bennett, Donahue, Schneider, & Voit, 2007, p. 508). While some may be tempted to speculate that the more yellow and white stars are happier stars than the redder (angry) and bluer (sad) stars; for a star, brightness depends not on its cheery disposition, rather it depends on its most fundamental property at birth: mass.
From birth to death, a stars lifetime is strongly influenced by the mass it is first created with. The larger a star, the faster and hotter it burns, the heavier the elements it produces through its nuclear fusion process which are essential to life, and the more spectacular its final days of destruction will be.
While a massive star will end in a supernova that leaves behind a neutron star, smaller main sequence stars will most often outlast these stars by millions of years.
A main sequence star will begin by the compression of hydrogen and helium until the force of gravity heats the core enough to initiate nuclear fusion. The main sequence star will continue in this state through gravitational equilibrium for millions of years, which is the state that the sun is currently in.
Once the main sequence star has used up all of its hydrogen fuel, there is no longer enough outward pressure to keep the star from collapsing under the great gravitational weight. As the star begins to collapse inwardly, layers of hydrogen surrounding the collapsing core will heat up until the layers reach the point of nuclear fusion.
This will cause the star to expand becoming a red giant, which can, at its peak be “100 times larger in radius, and more than 1,000 times brighter in luminosity [than the sun] (Bennett, Donahue, Schneider, & Voit, 2007, p. 551).”
As the layers of hydrogen burn up, they will deposit helium into the shrinking core, which will continue to heat up. Once the helium core reaches 100 million Kelvin it will start nuclear fusion in the inner core as well.
Now that the star has both a helium nuclear active core and hydrogen nuclear active layers, eventually the star will undergo a helium flash, expanding the hydrogen layers, which will subsequently cool causing the star to produce less visible light.
Once the star has completely converted hydrogen to helium to carbon, nuclear fusion will cease, the star will cast off its outer layers in a brilliant show of lights called a planetary nebula, and all that will remain is a white dwarf. This white dwarf will continue to produce light until such time as it has cooled in the near distant future.
Both massive and not-so-massive stars have one thing in common: they create and recycle elements within the universe, and provide the building blocks that feed into the creation of existence of life on earth. They are a fundamental part of our circle of life.
Conclusion
In the end, we find that this massive beautiful universe as we can currently observe has played a significant role in the creation and maintenance of the very lives that we have been given. This very existence allows us to study and observe the universe, and should leave us within the fullness of wonder and awe.
However, without the capability to see beyond the stars and the universe as it exists, the scientific pursuit into origins ends at the moment of creation, and provides no further means to research these existential questions, and thus, within science alone, we are left in the state as if waking from “a bad dream (Jastrow, 1992, pp. 106,107).”
To build upon Einstein’s thoughts when he said: “the most incomprehensible thing about the universe is that it is comprehensible (BrainyQuote.com, 2008)”, I would leave you with the final question that remains unanswered and incomprehensible from a scientific perspective, and that question asks “why?”.
References
(2008). Retrieved December 08, 2008, from BrainyQuote.com: http://www.brainyquote.com/quotes/quotes/a/alberteins125369.html
Bennett, J., Donahue, M., Schneider, N., & Voit, M. (2007). The Cosmic Perspective 4th Ed. San Fransisco: Pearson Education, Inc.
Jastrow, R. (1992). God and the Astronomers. United States: Readers Library, Inc.
