August 28, 2011
Of all the great cataclysms that can happen in the Universe, almost nothing compares to the death of even a small star like our sun.
We can predict with a fair amount of certainty that our sun will die in about five billion years, and we can also predict just exactly how it will die.
We cannot, of course, watch the entire 10-billion-year lifespan of a star.
However, we can wander through the forest where there are many oaks going through various stages of life. Here we will see acorns on the ground, the saplings they produce, the tall, mature oak and its decaying corpse on the ground.
The Milky Way galaxy contains in excess of 300 billion stars. You’re bound to see every kind of star at every stage of its life from even casual observations.
As it turns out, stars about the size of our sun often leave beautiful emblems of their deaths — fitting funeral wreaths to the graves of giant thermonuclear reactions that exploded for billions of years.
Our own sun has settled comfortably into the prime of its life, a respectable and long-lasting middle age. The sun is a stable inferno fusing hydrogen into helium and releasing the energy that gives light and heat to the earth.
It will not always be that way, and we can look to objects like the Ring Nebula to give ourselves an inkling of what is in store.
Look almost straight overhead, and you’ll see the bright star Vega. Hanging almost straight east is a small parallelogram of stars. You’ve found the constellation Lyra.
Visible in binoculars halfway between the two stars farthest from Vega in the parallelogram is a fuzzy, star-like point of light. At medium magnification through a telescope, that point will expand into a smoke ring in space called the Ring Nebula (M57 in the Messier catalog).
The Ring is really a shell of gas and dust surrounding what is left of a star that has reached the end of its life cycle.
They are called planetary nebulae because their disk-like appearance bears a superficial resemblance to planets in small telescopes.
They got that way because a star ran out of hydrogen fuel to burn, swelling to 1,000 times its former size. Planets as far as the earth is from the sun would be exposed to the thousands of degrees temperature of the star’s atmosphere. The planet would remain but its water and atmosphere would vaporize into space. In five billion years our planet will French fry.
Soon thereafter (in millions, not billions of years), stars like our sun then eject about 10 or 20 percent of their substance into space at up to 15 miles per second to form a shell of gas like the Ring Nebula. The star that remains collapses to a super-dense ball only the size of Earth but with a mass almost as great as the original star. That so-called white dwarf eventually fades to cold blackness.
In the meantime, the shell of gas continues to expand. After a mere 100,000 years or so, it is too faint to be seen.
Our own sun will die soon, in only 5 billion years or so. A typical species on Earth is lucky if it survives 100 million years. It’s hard to imagine humans lasting any longer than that.
Still, we’re the ones with the big brains. If our intelligence doesn’t kill us first, it might eventually ensure our survival for a long time.
I know it’s presumptuous of me, but I would like to think that humans will have solved their problems and still be around in five billion years.
If we do, surely we will have developed the ability to leave our doomed solar system to find a new home among the stars.
Perhaps some day, a human mother, unimaginably in advance of our puny notion of what is human, will show her children a faint smoke ring of light and say, “There is the place where humans first trod, from which the human seed first spread among the stars.”
Jupiter peeps above the eastern horizon by 10:30 p.m. or so, but you should wait until it’s a bit higher — at least midnight or so — to look at it in binoculars or a telescope. Binos show two to four of its brightest moons lined up close to the planet. A telescope reveals the planets parallel cloud bands.
Mars, the sort-of-red planet, rises in the northeast around 2:50 a.m. Look for it low in that direction just before morning twilight.
Rarely seen Mercury makes an appearance next week. Stay tuned for details.