The Remains of the Sun
The Aztecs believed, that one day the Sun will fall from the sky and the stars will be shaken from the heavens. They foretold a time “when the Earth has become tired… when the seed of Earth has ended”, and this time will certainly come one day in the future.
Eventually the time will come when the solar interior is all carbon and oxygen and when at the prevailing pressures and temperatures no further nuclear reactions can occur. The central helium will be used up and the interior of the Sun will continue its collapse. The temperatures will rise again, triggering a last round of nuclear reactions and expanding the solar atmosphere a little.
In its death throes, the Sun will slowly pulsate, expanding and contracting once every few millennia, spewing its atmosphere into space in one or more concentric shells of gas. The hot exposed solar interior will flood the shell with ultraviolet light, inducing a red and blue fluorescence extending beyond the orbit of Pluto. Half the mass of the Sun will be lost in the way. The solar system will be filled with an eerie radiance the ghost of the Sun, outward bound.
The remains of the Sun, the exposed solar core at first enveloped in its planetary nebula, will be a smaller hot star, cooling to space, collapsed to a density unheard of on Earth, more than a ton per teaspoonful.
Billions of years hence, the Sun fill become a degenerate white dwarf, cooling like all those points of light we see at the centers of planetary nebulae from high surface temperatures to its ultimate state, a dark and dead black dwarf.
When we look around us in our little corner of the Milky Way, we see many stars surrounded by spherical shells of lowing gas, the planetary nebulae (they have nothing to do with planets, but some of them seemed reminiscent in inferior telescopes of the blue-green discs of Uranus and Neptune).
Every planetary nebula is a token of a star in extremis. Near the central star there may be a retinue of dead worlds, the remnants of planets once full of life and now airless and ocean-free, bathed in a wraithlike luminance.
In the meantime, human beings will have evolved into something quite different. Perhaps they will merely pick up and leave for Mars or Titan or seek out an uninhabited planet in some young and promising planetary system near enough to reach out and settle.
But perhaps our descendants will be able to control or moderate stellar evolution. They may be able to reuse Sun’s stellar ash for fuel only up to a point.
We had the sky, up there, all speckled with stars, and we used to lay on our backs and look up at them, and discuss about whether they were made, or only just happened (Mark Twain, Huckleberry Finn). Image: © Megan Jorgensen Image: © Megan Jorgensen
Voir aussi :