Two hours ago, he asked a question at the Physics Stack Exchange that made me LOL. He has already made all the important general plans and only asks the physics users to help him with a technical detail. So his question is:
What is the easiest way to stop a star?
No kidding. You're going to learn something about the mainstream science at the mainstream scientific institutes that do research into Earth sciences. ;-)
-->
What is the easiest way to stop a star?
I'm concerned that the stars are using up hydrogen nuclei at an unsustainable rate. If I was a sufficiently advanced civilisation I might want to do something about this, so that the hydrogen could be burnt in fusion reactors instead. That way, a much higher proportion of the available energy could be put to some use before it eventually becomes thermal radiation.
So my questions are:
- What would be the most energy-efficient way (using known physics) to blow apart a star or otherwise prevent or greatly slow the rate at which it performs fusion? We're assuming this civilisation has access to vast amounts of energy but doesn't want to waste it unnecessarily, since the aim is to access energy from the hydrogen the star would have burned. In order for this to be worthwhile, the energy gained from doing this would have to be substantially more than the energy the process takes.
- What would be the astronomical signature of such an activity? If it was happening in a distant galaxy, would we be able to detect it from Earth?
LM:
I emphasized the words "concerned" and "unsustainable" to make it clear that this Gentleman is firmly within the "mainstream" discourse of the Earth sciences that is currently fully controlled by the environmental whackos.
The idea that the Sun wastes too much energy so we should better extinguish it (almost all life on Earth would stop within weeks) is such a funny ramification of the environmentalist thinking (or, more precisely, the absence of it) that I didn't resist and had to repost the question here.
For the sake of completeness, here's my answer:
Burning (and fusion) is "unsustainable" by definition because it means to convert an increasing amount of fuel to "energy" plus "waste products" and at some moment, there is no fuel left.
I am not sure whether the word "unsustainable" was used as a joke, a parody of the same nonsensical adjective that is so popular with the low-brow media these days, but I have surely laughed (because it almost sounds like you are proposing to extinguish the Sun to be truly environment-friendly). The thermonuclear reaction in the Sun has been "sustained" for 4.7 billion years and about 7.5 billion years are left before the Sun goes red giant. That's over 10 billion years – many other processes are much less sustainable than that. More importantly, there is nothing wrong about processes' and activities' being "unsustainable". All the processes in the real world are unsustainable and the most pleasant ones are the least sustainable, too.
But back to your specific project.
When it comes to energy, it is possible to blow a star apart without spending energy that exceeds the actual thermonuclear energy stored in the star. Just make a simple calculation for the Sun. Try to divide it to 2 semisuns whose mass is \(10^{30}\) kilograms, each. The current distance between the two semisuns is about \(700,000\) kilometers, the radius of the Sun. You want to separate them to a distance where the potential energy is small, comparable to that at infinity.
It means that you must "liberate" the semisuns from a potential well. The gravitational potential energy you need to spend is\[
E = \frac{G\cdot M\cdot M}{R} = \frac{6.67\times 10^{-11}\times 10^{60}}{700,000,000} =
10^{41}\,{\rm Joules}
\] That's equivalent to the energy of \(10^{24}\) kilograms (the mass of the Moon or so) completely converted to energy via \(E=mc^2\), or thermonuclear energy from burning the whole Earth of hydrogen (approximately).
You may force the Sun to do something like the "red giant" transition prematurely and save some hydrogen that is unburned. To do so, you will have to spend the amount of energy corresponding to the Earth completely burned via fusion.
But of course, the counting of the energy which was "favorable" isn't the only problem. To actually tear the Sun apart, you would have to send an object inside the Sun that would survive the rather extreme conditions over there, including 15 million Celsius degrees and 3 billion atmospheres of pressure. Needless to say, no solid can survive these conditions: any object based on atoms we know will inevitably become a plasma. A closely related fact is that ordinary matter based on nuclei and electron doesn't allow for any "higher-pressure" explosion than the thermonuclear one so there's nothing "stronger" that could be sent to the Sun as an explosive to counteract the huge pressure inside the star.
One must get used to the fact that plasma is what becomes out of anything that tries to "intervene" into the Sun – and any intruder would be quickly devoured and the Sun would restore its balance. The only possible loophole is that the amount of this stuff is large. So you may think about colliding two stars which could perhaps tear them apart and stop the fusion. This isn't easy. The energy needed to substantially change the trajectory of another star is very, very large, unless one is lucky that the stars are already going to "nearly collide" which is extremely unlikely.
Physics will not allow you to do such things. You would need a form of matter that is more extreme than the plasma in the Sun, e.g. the neutron matter, but this probably can't be much lighter (and easier to prepare, e.g. when it comes to energy) than the star itself. A black hole could only drill a hole (when fast enough) or consume the Sun (which you don't want).
However, if you allow the Sun to be eaten by a black hole, you will actually get a more efficient and more sustainable source of energy. Well, too sustainable. ;-) A black hole of the mass comparable to the solar mass would have a radius about 3 miles. It would only send roughly one photon of the 3-mile-long wavelength every nanosecond or so in the Hawking radiation and it would only evaporate after \(10^{60}\) years or so. It would be so sustainable that no one could possibly observe the energy it is emitting. However, the black hole would ultimately emit all the energy \(E=mc^2\) stored in the mass.
If there are powerful civilizations ready to do some "helioengineering", they surely don't suffer from naive and primitive misconceptions about the world such as the word "sustainable" and many other words that are so popular in the mentally retarded movement known as "environmentalism". These civilizations may do many things artificially but they surely realize that the thermonuclear reaction in the stars is a highly efficient and useful way to get the energy from the hydrogen fuel. Even some of us realize that almost all the useful energy that allowed the Earth to evolve and create life and other things came from the Sun.
The Sun may become unsustainable in 7.5 billion years but according to everything we know about Nature, it's the optimum device to provide large enough civilizations – whole planets – with energy.
Concerning ambitious but less crazy plans in the outer space, look at NASA's plans to produce a "warp drive": HTML, PDF.
0 comments:
Post a Comment