The Death of the Sun
Published on Jun 5, 2006 at 1:24 pm.
1 Comment.
Filed under Sun.
The Sun is dying. Oh, it won’t happen tomorrow, or the next day, but it will happen. Nothing lasts forever. Despite what the ancients believed, the heavens are not unchanging and eternal.
Currently, the Sun is sort of stable. It maintains this stabilty through energy releaed in nuclear fusion in its core. This energy ballances the gravity that is trying to compress the Sun. At present, the Sun is fusing hydrogen into helium. It can keep this up for about 10 billion years before it gets too little hydrogen in its core to maintain fusion at the rate needed. The Sun is about 5 billion years old, so it is halfway done.
But, we won’t be here for 5 billion years. Yeah, I am sure that my students, when taking the final exam, think that it lasts 5 billion years, but it isn’t so. Actually, we’ve got no more than a billion or so years, perhaps only a few hundred million at best. For you see, all that fusion in the Sun’s core is producing helium, which is simply getting in the way. Helium is heavier than hydrogen, so it stays in the core. That means that the fusion rates would tend to slow down from the interference of the helium. That would not ballance against gravity, though, so the core gets a bit hotter and the fusion rates go up again to maintain ballance. The net effect, though, is that the Sun apears slightly larger and brighter as seen from Earth. This warms Earth.
Right now, Earth is is a nice thermal ballance. We get as much thermal energy from the Sun as we radiate into space. In the distance past, the Sun provided Earth with less thermal energy, so that would make Earth cooler, right? Well, in the past, Earth had more of certain gasses in the atmosphere, and these gasses make Earth less efficient at radiating energy into space — the so-called greenhouse effect. This made Earth warmer than it should have otherwise been, allowing life to develop. Combined natural processes on Earth have been steadily reducing the greenhouse gasses as the Sun has warmed up. The net effect has been pretty close to a nice ballance of temperature. However, we are very near the end of how much of the greenhouse gasses can be removed from the atmosphere. There are still some, and that is good. Without any greenhouse effect, Earth’s average temperature would be well below freezing. However, we can’t take many more greenhouse gasses from the air, so eventually the Earth will quit becoming more efficient radiating heat, but the Sun will continue to provide more. Earth will warm. Eventually, in a few hundred million years, perhaps, on the polar regions of Earth will be habitable. In under a couple billion years or so, the oceans will likely evaporate away. By that time, Earth will have long since become uninhabitable, perhaps as soon as a billion years from now. The Sun won’t be dead, but Earth will be. Maybe by then, Congress will have finished debates on whether or not to fund NASA to develope space colonies. Maybe, but I doubt it. They’ll still be haggling.
Finally, in about 5 billion years, the Sun will simply not be able to sustain fusion in its core anymore, and the core will begin to collapse. As it collapes, it heats, and this causes the outer layers of the Sun to expand and cool. The Sun becomes a red giant, with its outer portions out beyond the orbit of Mercury. Earth is pretty well toatsted to a crisp. It will be so hot that the atmosphere will distend and much will be lost into space. The surface will be hot enough to melt lead.
The end isn’t quite there yet. The Sun will then go through more changes. It will begin to fuse helium and contract. It will then run out of helium and expand again to a bigger red giant — what we call an asymptotic giant branch star. At this point, the outer edge of the Sun will be somewhere near where Earth is now. Now, the Sun will have lost some mass by that time, so Earth’s orbit would have moved out a bit. It isn’t really clear if Earth will be swallowed by the Sun or not. If it isn’t, then it will be a molten, airless, blob of material. Eventually, the Sun will pulsate, shed its outermost layers and what’s left will collapse to a small object about the size of the Earth called a white dwarf. If by some miracle Earth survives, it will freeze. The white dwarf will not provide hardly any heat, and Earth will cool to near what Pluto is today. The white dwarf, mostly carbon, will cool and crystallize, and Earth will cool to only a few degrees above absolute zero. The Sun and Earth will then be truly dead. Not much will then ever happen again unless we get eaten by a black hole.
Of course, an asteroid or comet will likely wipe us out long before all of this.
-Astroprof
Johnny Pelayo on June 2, 2008 at 3:53 pm: 1
Pretty harsh, but could be possibly true inevitable end for all of us, but we should make some colony on some other planet before all this happens, we should eventually come up with some really high tech technology or something or aliens will save us hopefully anyways we all go to the heavens with God because like religion says heaven exists, and God created everything and we will go there and live in harmony forever, because there has to be an unexplainable reason why we exist in this place and have reason and understanding mind, only God knows what he is doing, thats if he exists and we worship nothing but our own beliefs, and everything is an unexplainable, and unsolvable mystery…