Supernovae – Without them we wouldn’t be here!

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A Cosmic Calendar

Whether plant or animal, it is necessary for us to end life so we can continue to exist; it is part of the very natural cycle that has been going on for a long, long time. However, in the grand scheme of things, our existence is almost trivial. The life of something else much bigger and older had to end so that we could even exist.

This is the Cosmic Calendar, depicting the entire span of the Universe’s existence as a single year. It was popularized by the astronomer Carl Sagan, in his book THE DRAGONS OF EDEN (1977), and then on his widely acclaimed television series Cosmos (1980). Those 13 one-hour-long documentary episodes did more to increase awareness of our place in the Universe than anything that had come before.

It’s perfectly understandable to be fascinated by human history; on our personal timescale, we have been here “forever”. If the entire history of the universe were laid out, as the Cosmic Calendar above, a 100-year human lifetime would only be 0.23 seconds on this scale.

If the current time, right now, was the last second of the last day on this calendar, humans and chimpanzees split from our common ancestor less than four hours ago at 8:10pm; we walked upright at 9:25pm; our brains tripled in size at 10:30pm; and at just 8 minutes before midnight, modern humans finally evolved…but absolutely none of that would have happened if not for Supernovae (or Supernovas, if you prefer).

In the beginning…

The Big Bang occurred, of course, followed by the expansion of the Universe. Eventually things settled down enough to create electrons and protons and then some elemental hydrogen and helium. Due to slight variations in density here and there, these gases condensed out into blobs forming proto-galaxies, and further condensed to form stars.

These early stars, the oldest in the universe, had no metals in them (for convenience, astronomers consider anything more complex than helium to be a metal). They were pure, clean, simple stars. As the nuclear fusion process began, they started to become contaminated with more complex atoms. Hydrogen fused to become helium; helium fused to become beryllium; and this carried on up the table of elements until (if the star was big enough) it made an iron core for itself.

The Irony of Iron

Unfortunately, that iron core is a star’s death knell. No matter how big they are, stars cannot maintain a fusion reaction beyond the point where they create iron. The mighty fusion reaction which creates the pressure to balance the immense gravity of the star’s outer envelope comes to an end. It radiates away the last of this energy and then begins to rapidly shrink.

This massive collapse signals the end of that star’s life; however, the immense force of this collapse is the kick-off point for the creation of all the other elements. Once the star reaches maximum density it explodes with the force of 1,000,000,000,000,000,000,000,000,000 (10^27) atomic bombs. For comparison there are 7,500,000,000,000,000,000 (7.5 x 10^18) grains of sand on Earth.

Elementary, my dear Watson

The energy release creates more than half of all the remaining elements of the periodic table. Spewed out with all this incredible energy these elements trigger disturbances in other gas clouds, causing them to condense and make new stars, but this time with a whole array of elements that have never existed before.

Now, finally we can have solid bodies, planets, with argon, calcium, carbon, chlorine, hydrogen, oxygen, phosphorus, potassium, scandium, silicon, sodium, sulphur, titanium, iron, and so much more. You can finally have water and chemicals that could become bioactive. With just the right amount of ionizing radiation biosynthesis can begin, et voila: life!

Novae and Supernovae

SN 1994D (bright spot on the lower left), a Type Ia supernova out-shining its home galaxy NGC 4526

photo: wikipedia

In about five billion years when of our Sun runs out of its primary nuclear fuel, it will start to expand. It will blow off its outer layer of gas, leaving just its small core radiating at a temperature of 100,000 Kelvin. It will be a White Dwarf star, and it will soon wind down and burn out.

On the other hand, many white dwarfs have companion stars. The little thieves like to steal gas from their companion. When they collect enough they like to create a massive explosion called a nova which can generate millions of times the light ordinarily generated by the binary pair. The white dwarf can do this repeatedly, as long as it can steal fuel from its companion.

Supernovae, on the other hand, come in two flavours, Type I and Type II. The first type, as we understand it, is essentially an ordinary nova taken to an extreme. It steals so much hot gas so quickly that it turns into a runaway thermonuclear explosion, completely obliterating the star and leaving nothing behind.

The second type is the sort that forms the iron core. Once it blows away it’s outer layer (at several percent of the speed of light), it collapses to become a neutron star, or if it’s big enough, a black hole.

The Takeaway

It doesn’t much matter which course a supernova follows. All Supernovae are good for the Universe because they create brand new materials, stimulate gas clouds to condense and form stars, and help to push the “last days of the universe” a little further into the future.

It was just a little over 4.5 billion years ago today that a nearby supernova caused our own star to condense; it tipped the balance so that our stellar accretion disk started to become denser in many spots; solids began to form and gather together and eventually made our rocky and watery little home.

Take a look at a supernova visualization

Thanks, Supernovae!

feature image: devian art


David Carter

David Carter

David Carter, a Canadian science writer, SF writer, and software engineer, who delights in clarifying complex science issues for the general population—a talent he acquired from his acquaintance with Isaac Asimov. He has been providing on-line content in all areas of science, commercial endeavour, and learning for decades.
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