Sunday, June 21, 2009

I'm the greatest star, I am by far, but no one seems to know

4.6 billion years ago in a galaxy called the Milky Way, there was a gargantuan molecular cloud of hydrogen and helium (and some trace amounts of heavier elements). This molecular cloud was a stellar nursery, where stars formed. Many of these stars lived short lives and died in cataclysmic explosions. In this violent place, a certain famous star would be born. 

In the molecular cloud some regions had become denser than others and it would be in one of these dense regions that our star formed. Gravity caused that dense region to collapse in to a pre-solar nebula and as it collapsed, it started to spin. The interplay of it's rotation, gravity, gas pressure and magnetic fields caused an almost-star to form at the centre of the spinning nebula. Surrounding the almost-star was a disc of matter that would later klump together and form planets, asteroids and comets. Over the next 50 million years the temperature and pressure of the core of our baby star increased and when it became hot and dense enough it began the fusion hydrogen into helium. A new star was born.

That star is, of course, the Sun. The star brightest in our sky. The star that the Aztecs used to sacrifice to by ripping out the still beating hearts of their enemies. The star that supports almost all living things, barring some extremophile bacteria and possibly  a bunch of aliens.    

The Sun will not be with us for all eternity, however. The Sun, too, will die, and it will not go out in a blaze of glory like it's more massive, live-hard-die-young kind of brothers and sisters. As the Sun age it will burn through it's supply of fuel faster and faster, growing hotter and hotter, becoming brighter and brighter. In about 5.4 billion years the Sun's core will be so hot that it's surrounding shell will start fusing hydrogen, like in the core. The Sun will now swell into a red giant, becoming about 250 times as big as it is now, incinerating the Earth. 

Indiffrent to this, the core of the Sun will gain in mass and temperature, and when it's dense and hot enough it will start fusing helium into carbon. This precipitate another drastic change, where the red giant Sun shrink to only eleven times it's current size. For a hundred million years the Sun will remain like this, furiously fusing helium. But eventually it will have to resort to burning it's reserves of hydrogen and helium present in the outer layers. Again, the Sun will swell up. But after 30 million years, only a quick moment in the galactic reckoning of time, the Sun's remaining outer layers will fall away, leaving the Sun a white dwarf. The shedded matter will form a planetary nebula, fuel for future generations of stars.     

Too old and too weak the sun will not have enough temperature to fuse the elements remaining to it.  The Sun will only grow cooler and dimmer. And because it now lack the gravity to retain them, the planets and other orbiting bodies will start to fall away. Two billion years later what remains is a largely crystalline structure with a frozen core of degenerete carbon and oxygen. 

Trillions more years later, the Sun shines no longer, having become a black dwarf. It's planets has long been stolen away by the gravity of other stars and the Sun is all alone. The Solar System is no more. 

Image of the Sun as viewed by the Soft X-ray Telescope courtesy of NASA

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