Shakespeare in Space #4: The Heavens Themselves Blaze Forth

In about five billion years,
our Sun will die.

This infrared image reveals the Helix Nebula, residing about 700 light years from Earth, which formed as a result of the death of a sun-like star. Officially classified as a planetary nebula, this object actually has very little whatsoever to do with planets.

The term planetary nebula, coined in the 1780's by astronomer William Herschel, is a long-lasting misnomer. Because Herschel thought these sorts of round nebulae resembled planets like Jupiter when viewed through a telescope, he used the term 'nebula' (Latin for 'cloud') to describe them. The resulting phrase—planetary cloud—couldn't be further from the truth.

When an average-sized star depletes its hydrogen fuel near the end of its life (as our sun will do in about five billion years), it begins burning heavier elements at a more intense energy level. As these heavier elements are rapidly burned, the star expands exponentially in size and becomes what we know as a red giant. When our sun reaches this phase, it will expand to such a point that it will scorch and eventually engulf Earth. 

This rapid and intense burning of elements inside of the red giant creates an extremely hot core at the center of the star. Its outer gaseous layers are gradually ejected from the star by strong stellar winds. Intense ultraviolet radiation radiates from the core, blasting these ejected gases and forming a visible planetary nebula as imaged above. 

Left behind is the former red giant's core, now an extremely hot and dense ball of matter approximately the weight of the sun but compacted into the approximate radius of the Earth—an object known as a white dwarf

Despite this, the term planetary nebula stuck and is still used in astronomy to describe these glowing emissions of dead or dying stars. Perhaps in part because the man who coined the term is most famous for having discovered the planet Uranus, the first planet discovered since pre-history (the rest of the planets were easily visible to the naked eye). 

In the above image, the remaining white dwarf can be seen in the center of the red glow. Fascinatingly, astronomers have never observed two planetary nebulae that looked in any way similar. These objects typically form into extremely varied and complex structures, with no predictable pattern emerging.

The following quote originates from Shakespeare's historical play, The Tragedy of Julius Caesar, in which the assassination of the title character sparks a civil war in the Roman Republic. 

"When beggars die, there are no comets seen;
The heavens themselves blaze forth the death of princes."

These lines are uttered by Calpurnia, the wife of Julius Caesar, in reference to a soothsayer's earlier warning for Caesar to "Beware the Ides of March." Calpurnia presents Caesar with a superstitious argument in which she cites recent strange happenings within the city of Rome—such as ghostly apparitions and the dead rising from their graves—as proof that Caesar's life may be in jeopardy. 

Caesar retorts with the famous statement:

"Cowards die many times before their deaths;
The valiant never taste of death but once."

Just as the deaths of powerful leaders often shake the globe and either inspire or make way for the next generation of leadership to emerge, so too do the deaths of stars allow for new stars to emerge on the cosmic stage.

As gases ejected by dying stars spread out and form planetary nebulae, these gases eventually saturate the interstellar medium like fertilizer does to soil. Planetary nebulae are thought to play a crucial role in the chemical evolution of galaxies, as heavier elements (such as carbon and oxygen) formed in the hearts of red giant stars are subsequently pushed out into the cosmos to become the building blocks for more complex molecules—molecules which could eventually result in the formation of rocky planets and organic compounds. 

Astronomers are able to calculate the abundance of certain elements and measure the evolution of galaxies by observing the rate of planetary nebulae formation. As stars continue to die, discharging heavier and heavier elements into the cosmos, the rate of planet formation around new stars increases—as does the potential for the formation of complex life. 

Death of Caesar, by Vincenzo Camuccini (1771—1844)
Image Credit: Wikimedia Commons

From the ashes of Caesar rose a new era of Roman civilization led by Caesar's adopted son, who would eventually be known as Emperor Augustus—the first Emperor of the Roman Empire. Caesar's ambition for absolute power ultimately resulted in his assassination (which was an attempt to preserve the Republic), which in turn predicated a civil war in which a supreme ruler—the Emperor of Rome—was forged.

The Roman Republic had to die in order to make room for the Roman Empire. Similarly, stars go through a continuous cycle of death and rebirth. Every star in the observable universe exists as a culmination of a series of cosmic phenomena that occurred in the past.

It's only as a result of these past phenomena that the universe can achieve its current state, and the same could be said of modern civilization and human history. But, while the history of humanity has been written in books, the history of the cosmos has been written in the stars. 

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