As Big as They Get

Mighty Betelgeuse (beetle-juice), the red supergiant marking the shoulder of Orion the hunter, will rise by 8:00 tonight. The planet Mars also red, though brighter, rises at about the same time, to the north of Betelgeuse.

Betelgeuse is one of the largest stars in the galaxy. It is as big as the entire orbit of Jupiter, with a diameter five hundred times that of the Sun.

There is a downside to its being so large, though. Its mass, a mass just twenty times that of our Sun, must fill a region a hundred million times larger than the Sun. It is a blazing ball of almost nothing. The thin mountaintop air that climbers struggle to breathe is a brick wall by comparison.

Still, it is one of the brightest stars in the sky. It is further away than most of the stars we can see. The light we see left Betelgeuse over three hundred years ago. At that distance our sun would be invisible without a telescope. What a strange star! Brilliant, huge, and as tenuous as the finest smoke.

Like the dully glowing embers in a fireplace, its ruddy hue tells us that the surface of Betelgeuse is cool, only half the temperature of the surface of the Sun. While the Sun's energy comes from a giant nuclear furnace at its center, Betelgeuse has used up most of the fuel in its core.

What is being consumed now in Betelgeuse are the gasses in its outer layers. As the outer layers warm, they expand: Betelgeuse becomes a supergiant. But since the energy now has to be distributed over such a vast surface, this surface is relatively cool.

Betelgeuse is dying. Its outer layers, so far from the central core, are drifting off into space. For a hundreds of millions of years the fantastic weight of its gasses have been supported by outward pressure from the fires in its core.

Now, as the fires in this core die out, the core contracts and gets hotter.- The star expands. Additional elements are fused in the core. And then, Betelgeuse will die in a tremendous supernova explosion.

In this explosion, the elements needed for life - elements like sodium, potassium, mercury - the "heavy" elements - are created. We come from the stars.

(11/14/07)