The Universe in the Classroom

Stellar Evolution (a la Chez Stella)

There is something odd about this menu, you think. Something very odd. Baffled, you turn to the waiter. "I'm sorry," you confess, "but I'm new to this. Where I come from, menus are very different. Can you tell me what I should do?"

The waiter smiles. "But of course," he answers, "I wouldn't know how to order a hamburger." Then he looks carefully at the menu. "It is never easy. There is a saying: 'Always start with blues and follow with reds.' But everyone has different tastes. Some prefer small stars while others insist that the larger they are the better they are. I think, if I were you, I'd start with the largest and work my way through all of them."

You hesitate. There are no prices on the menu.

"Of course," he adds, sensing your concern, "you are the guest of Chez Stella. There is no charge."

"Then I'll do as you suggest," you smile.

"A 60-solar-mass star, type O5. Plump and ripe. An excellent specimen! Pity they don't last long." And as he speaks you seem to zoom towards the brightest star until you can easily see its shape. An apple from thirty meters would appear to be about the same size. No other stars are visible.

"How long do they last?" you ask.

"Four million years, maybe less."

"I'm afraid that's more time than I have."

"That is what this is for," he smiles confidentially, and pulls an enormous golden stopwatch out of his pocket and holds it up so you can see the handsome, old-fashioned face. "With this watch, I can compress any star's entire existence -- from the moment it starts burning hydrogen to the instant it dies -- into exactly sixty seconds."

You nod, wondering where you could get a watch like that. It would have been very useful on the blind date you had last Friday.

The waiter raises the watch. "Ready?"

You turn to the star. It is hanging alone in black and empty space. "Yes," you say softly.

Immediately you hear the "tock... tock... tock" of the stopwatch, and you gaze deep into the distant star. It is a brilliant blue, almost violet, like a blacklight at a party but more intense. From this distance it appears perfectly smooth. You blink. It dazzles and fascinates -- hard to look at but impossible to turn away from.

In spite of the waiter's claims, nothing seems to be changing. Maybe it grows a little brighter... maybe it turns a little less blue. It is definitely smoking. You hadn't noticed before, but it is giving off vast symmetric clouds of what looks like smoke or dust hanging in the space around the beautiful star.

Suddenly, after about 52 seconds, it reddens and inflates from the size of an apple to an enormous yellow-orange balloon eight meters in diameter. Then, just as suddenly, it collapses again into a hot blue core, leaving behind an expanding cloud of dust and gas. Something is clearly going on in the center, you think, because it changes from orange to bluish white once or twice as it puffs larger and then collapses. It almost seems to be tearing itself apart.

The flash is so brilliant you could have seen it with your eyes closed. You blink, dazzled, and stare into empty space. You blink again and realize the star is gone. There is nothing left at all, except a vast, dense, and expanding cloud of dust or smoke.

"Is it gone?" you ask.

"In a sense, no," the waiter smiles. "About ten percent of its original mass is still there, trapped in a black hole. The rest has, as you see, been blown away by the supernova. It isn't a star any more. But, a lot of the material it has blown off will eventually mix with other dust and gas and eventually end up in another star - though probably not so large as this was." He pauses a moment, thinking. "Or it could end up as a planet, or in a person. After all, the oxygen in you came from a supernova like this one."

"The oxygen in me?" you start to ask, but he has already turned to the second star.

"This one has 25 solar masses and you'll see about seven million years of evolution in one minute." The dust and debris from the first star disappears and is replaced with a bluish white star about the size of a golf ball seen from thirty meters.

"Tock... tock... tock..." you hear as you concentrate. It eventually seems to get a little brighter and maybe a little bigger. It smokes some in those nice symmetric puffs you saw the first time. Then, in the last six seconds it too puffs up, until it is a deep-red sphere maybe eight meters across. "How much of it is getting blown into space?" you ask.

Before the waiter can answer, the star dies in a brilliant flash that is indistinguishable from the death of the first star.

You blink, dazzled into silence for a moment, but soon the questions come flooding back. "Was it doing the same thing the first one did? Was it changing color in the beginning? Did it get brighter? And was it getting bigger?" you try to ask all these questions and more, but the waiter doesn't seem to hear. He has already started the clock.

This one is twelve times as massive as the Sun and looks about three centimeters across from where you are. It remains unchanged for about ninety percent of its life. Suddenly it balloons into a deep-red ball more than five meters in diameter. Then, almost as if the balloon had popped, it collapses and turns blue for several seconds. Finally, it expands, turns red, and dies in a terrible flash.

"That little gleam left over is a neutron star," the waiter says, but before you can get a really good look, the debris disappears and is replaced by a new star. And the clock is already ticking.

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