"Creators of Worlds"

Our Sun, like all the other stars of our Universe, has at its heart a nuclear furnace where the battle between crushing gravity and erupting energy is delicately balanced and tuned to the single-minded task of fusing hydrogen into helium.

As four hydrogen atoms are squished to form a single helium atom a small amount of energy is released. It is the outward flow of this energy from the core that counteracts the oppressive crushing mass of the overlying layers of the star. Our Sun fuses about 600 million tons of hydrogen into helium (just a little less than 600 million tons helium) every second in order to maintain equilibrium and hold back the relentless force of gravity caused by itís own mass.

All stars hold this process in common; in fact it is this process of nuclear fusion that defines them as stars. That is where the similarities end however, as each star is "personalized" in size, temperature, colour, longevity and even shape by the mass of the precursor cloud of interstellar gas that goes into making it. Stars that form with the mass of our Sun (or less) will only create helium in their fiery nuclear furnaces while more massive stars will need to manufacture even heavier elements (working their way through the Periodic Table up to Iron) in order to combat the compressive gravitational force of their own mass.

This creation of consecutively heavier elements is called stellar nucleosynthesis. A small number of the largest stars will eventually run out of the nuclear fuel needed to combat gravity, and their subsequent collapse will initiate the largest explosion in our Universe, a supernova event. The increased pressure of the collapse and explosion of these giant stars is the engine of creation that manufactures the rich diversity of heavy elements we find in our universe.

Stellar nucleosynthesis and supernovae are the source of everything from the coins in our pockets to the ground we walk on! The presence of elements heavier than iron in our solar system speak to the distant past. These precious elements tell us that everything in Solís domain (including ourselves) has been recycled from an interstellar cloud made partly of supernova stardust that was likely compressed in the increased density of a galactic spiral arm, approximately 5 billion years ago. Dust to dust.

In addition to providing the raw materials required to create our solar system we must also give credit to supernovae events for providing a secure neighbourhood inside which the fledgling life forms of our solar system could evolve. Our Sun and its human cargo have been floating in a "safe" Local Bubble of low-density material that was probably swept clean by one or more supernovae events that occurred a few million years ago. This Local Bubble is an irregular cavity at least 300 light years across containing about one tenth of the density than that which is normally found in the interstellar medium (ISM). The Local Bubble appears to be an hourglass or peanut shape with the narrowest part on the galactic plane and the ends opening into the galactic halo as though they have punched through a weak point.

Our vacuous "rural"location in this safe bubble has protected us from the hustle and bustle interaction with the average "downtown" ISM community. We have been protectively sheltered from cosmic rays and nearby supernovae events, which could affect the atmosphere, climate and prospects for life on our planet. For example, a close brush with the Scopius-Centaurus interstellar cloud (now receding from us and 450 light years distant) may be linked to a mysterious die-off of many plankton, mollusks, and other UV-sensitive marine creatures on Earth during the boundary between the Pliocene and Pleistocene epochs 2 million years ago. The drift time through the echoing void of our safe Local Bubble has closely matched the evolutionary period of humankind, is this just coincidence?

This time of peace is about to end. Our solar system is nearing the end of its journey across the Local Bubble and it is poised to enter a dense cloud of interstellar medium (ISM) that may signal the return of harmful buffeting from the ISM and catastrophic supernovae extinction events. No need to panic yet though as we still have an estimated 50,000 years before we "hit the wall", leaving lots of time for other items on the shopping list of "really bad things" to make our day. In the meantime I think it is appropriate to take a moment for reflection and ponder the vital role of supernovae as creators and protectors of life environments.

As an amateur astronomer I have been fortunate to be able to observe supernovae events taking place in other galaxies with my telescope. Often the light of a single exploding star overwhelms the dim glow of the host galaxy, which could contain as many as 200 billion stars. Telescopically I have also observed many supernova remnants in our Milky Way, these are seen as very dim wispy clouds left over after a giant star obliterates itself.

When observing these diffuse, element-rich clouds I sometimes cast my thoughts into the distant future, to a time when these remnant clouds may again coalesce into a new solar system. Will they hold the genesis of yet another Klondike Gold Rush or galleons sailing an alien Spanish Main, as subsequent intelligent (?) life forms come to recognize the rarity of supernova elements, and the safe bubbles supernovae create?

I wonder.

I gaze upon the beauty of the stars that cover the face of the sky, and think of them as a garden of blossoms.

-- Moses Ibn Ezra (1070-1138)

Guy Mackie is the Director of Telescopes for the Royal Astronomical Society of Canada Okanagan Centre, and a keen amateur astronomer.