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Basis

We are in the universe we call our own, on the planet we call Earth, in the physics-set and known reality we assume. There is no flat-out "magic" or other things along those lines, so far as we know.

Concept

The universe we live in is occupied by more or less powerful beings with technology we can only barely understand. They have been at war with other beings for unfathomable time. And one of their strange and powerful weapons had its guidance system taken out. By colossal coincidence, it decided to head our way, and lock on to a nearby star within its detection range, Sol. Our sun. It's goal is simple, and used many times throughout a war long gone. Kill a star.

Limits

  • No wormholes
  • No FTL travel
  • Weapon no bigger than 0.3 times Sol's mass
  • No time travel
  • No warp drives
  • No black holes or singularities
  • No dark matter or antimatter
  • Must work in less than 3 years
  • Must be impossible to completely shut down via human effort

Question: How do you completely extinguish or destroy a star, using a weapon within the realm of known physics?

Note that this is not at all the same as: Is there a way to create a bomb to destroy a star?, because this is referring to the realm of known reality.

Also note that I'm not asking for you to question my basis.

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    $\begingroup$ You're not asking for a reality check, but constraining to known physics? Something has to give, because what you ask for is not possible given known physics. Also, note that "no larger than the moon" and "no bigger than 0.3 Sol's mass" is inconsistent. Thirty percent of Sol's mass is eight million times more than the mass of the moon. $\endgroup$ – Samuel Feb 26 '16 at 18:50
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    $\begingroup$ With parameters you described will be far easier just to destroy the main planet then to destroy the star. $\endgroup$ – Bryan McClure Feb 26 '16 at 19:07
  • $\begingroup$ Could you define what is meant by killing a star? $\endgroup$ – Schwern Feb 26 '16 at 20:43
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    $\begingroup$ I want to make everything science-based, instead of just a brainstorm of science fantasy. $\endgroup$ – Caleb Woodman Feb 26 '16 at 23:59
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    $\begingroup$ @CalebWoodman That's what the other question asks for, too, and gets it. See, for example, TimB's answer. But both questions themselves involve a certain degree of speculation, it seems. $\endgroup$ – HDE 226868 Feb 27 '16 at 0:35
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"Killing" a star is ambiguous. Does that mean blowing it apart? Making it go nova? Snuffing it out? Spoiler alert: it doesn't matter. There's more than enough wiggle room in this constraint, "Weapon no bigger than 0.3 times Sol's mass".

0.3 Sol's mass is extremely large. 6x1029kg is a lot of mass to work with. That's 200 Jupiters. That's a lot of mass. When you have that much mass, brute force works juuust fine. That much mass and the Sun's gravity combine to produce so much energy that we don't even have to throw it at the Sun, we can just drop it on the Sun.

It's impact on the Sun would be... well... massive. If allowed to simply free-fall from the outer solar system, its velocity at impact would be 6x105m/s (I'm estimating using the escape velocity of the Sun, please edit or comment with the full calculation) giving it a kinetic energy of 1x1041 J which, consulting my favorite page on Wikipedia, is 1/6 the gravitational binding energy of the Sun: that is, how much energy you need to blow the Sun apart "Death Star" style and prevent it from reforming.

The impact will blow apart the Sun and the weapon, sending the center of mass of the solar system flying off in the direction the weapon was traveling. Since we didn't overcome the Sun's gravitational binding energy a new star will eventually reform over a very long period of time, but I think that's pretty good approximation of "kill the Sun".


I used just the energy of falling into the Sun as a lower bound. Since you specify "must work in less than 3 years", how fast would it need to be going to get from detection range to the Sun in just three years? This depends on how far out it's detected. I'm going to assume the object will be radiating little energy to avoid direct detection, but an object that massive would likely begin to alter the orbits of the outer planets. We can assume conservatively we'll pick it up somewhere around the orbit of Neptune 31 AU or 4x1012 meters out.

To reach the Sun in three years that would require an average velocity of 5x104 m/s. I don't know the math necessary to calculate the average velocity of free fall into the Sun (please edit or comment if you do), but it seems feasible that the weapon will not need any great initial velocity and simply falling into the Sun will do.

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  • $\begingroup$ Your assumptions are somewhat faulty. If I wanted to affect earth via the sun, I would have said so. $\endgroup$ – Caleb Woodman Feb 26 '16 at 21:32
  • $\begingroup$ @CalebWoodman Well, it turns out they're not necessary after all. :) Your weapon killed the Sun just fine. I'll remove them as they're a distraction. $\endgroup$ – Schwern Feb 26 '16 at 21:34
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    $\begingroup$ Free fall directly towards the sun is just a special orbit. If you start stationary, the time to fall is half of an orbital period and the semimajor axis of the orbit is half the initial distance. So, we take the orbital period $T=2\pi\sqrt{a^3/\mu}$, divide by two and substitute $a\to r_0/2$, and you get $t=\pi\sqrt{\frac{r_0^3}{8\mu}}$. If we use canonical units, $\mu=1$ and $\frac{t}{\text{years}} = \frac{1}{4\sqrt{2}}\left(\frac{r_0}{\text{AU}}\right)^{3/2}$ (where we divided by $2\pi$ because $1~\text{year}=2\pi~\text{TU}$). $\endgroup$ – 2012rcampion Feb 27 '16 at 1:26
  • $\begingroup$ ...the upside of which is, if your free fall takes 3 years, your initial distance is $(3\times 4\sqrt{2})^{2/3}\approx 6.6~\text{AU}$. This may make the Sun seem surprisingly weak, but remember that at a distance of around 5 AU it takes the Sun about 12 years to pull Jupiter through a complete circle. $\endgroup$ – 2012rcampion Feb 27 '16 at 1:34
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    $\begingroup$ @DonielF No. The difference in scale is overwhelming between even our largest nuke and the energy required to move an object with 6e29 kg. To put an 18 orders of magnitude difference in perspective, if the energy required is the size of a person, the energy of the Tsar bomb is roughly the size of a single electron. Another way to look at it... we've exploded all sorts of nukes on Earth, above and below ground, and the Earth doesn't care. This object is 100,000 times more massive than the Earth. $\endgroup$ – Schwern Aug 3 '17 at 0:34
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I think there is only one way to achieve this result given known physics and without simply telling you it won't work.

One alien year = One orbit of a satellite galaxy of the Milky Way

The aliens designed the device to work within three years, if they count their years by the orbital period of one of Milky Way's satellite galaxies, one year could be several billion terrestrial years.

This way, in three alien years (more than six billion terrestrial years), Sol will die (probably sooner!). Let's go through the list:

  • No wormholes
    Check! Wormholes aren't part of known physics anyway, they're hypothetical!
  • No FTL travel
    Check! Already no FTL in known physics!
  • Weapon no bigger than 0.3 times Sol's mass
    Check! It can be the size of a single atom!
  • No time travel
    Check! Unless you count moving forward in time at the rate of one second per second.
  • No warp drives
    Check! Already no warp drives in known physics!
  • No black holes or singularities
    Check! Would have been cool, but oh well.
  • No dark matter or antimatter
    Check! Just the white regular matter here.
  • Must work in less than 3 years
    Check! Good thing aliens don't use terrestrial years!
  • Must be impossible to completely shut down via human effort
    Check! No chance we're going to stop this!

This is not a very devastating weapon, obviously. If a more devastating weapon is desired (or one acting on the order of three terrestrial years), we need to either break known physics or use a black hole that is thirty percent of the Sun's mass.

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  • $\begingroup$ This is very clever, but unsatisfying as it relies on word play. $\endgroup$ – Schwern Feb 26 '16 at 20:42
  • $\begingroup$ @Schwern I don't disagree. But given the OP's specific request for "not a reality-check" of an imaginary thing using real science, it's the best I can come up with. $\endgroup$ – Samuel Feb 26 '16 at 20:44
  • $\begingroup$ But you ignore the idea of having a weapon, namely one that points at the star and does something to it. There's nothing war-like about waiting for your enemies to die. $\endgroup$ – Caleb Woodman Feb 26 '16 at 21:35
  • $\begingroup$ using a weapon is part of the main question $\endgroup$ – Caleb Woodman Feb 26 '16 at 21:37
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    $\begingroup$ @CalebWoodman Are you familiar with the war tactic known as a siege? You wait for your enemies to die. Doing nothing to stop the death of the Sun can been seen as an attack if they have the capability to help. $\endgroup$ – Samuel Feb 26 '16 at 21:55
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All that's needed is a chunk of matter with a rest mass that's 0.3x the mass of Sol, but that's moving at 0.9999c. It doesn't really matter if it's neutronium, condensed matter or just regular matter -- hit the sun with it, and there won't be much left over. It will take a whole lot less than three years -- it will all be over in a matter of seconds (plus travel time, so we have to assume it's already in the right place and moving in the right direction, which is allowed for in your scenario).

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    $\begingroup$ Such a high velocity is overkill, and at 4x10^48 J would require 20 times the mass-energy of the Sun. To overcome the gravitational binding energy of the Sun (ie. blow it apart) you only need to solve the kinetic energy equation for v or sqrt(2F/m) = v. F is the desired gravitational binding energy of the Sun (7x10^41 J), m is the mass of the weapon (6x10^29 kg). So a velocity of "just" 1.5x10^6 m/s will do, a mere 0.005c. $\endgroup$ – Schwern Feb 26 '16 at 21:45
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    $\begingroup$ How, in known physics, do you accelerate that much mass to that velocity? $\endgroup$ – Samuel Feb 26 '16 at 21:50
  • $\begingroup$ @Samuel "With technology we can only barely understand", as stated in the question. It breaks no known laws of physics. $\endgroup$ – Mike Scott Feb 27 '16 at 6:35
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The moon-sized object approaches the solar system. As it nears the sun, it breaks apart into a vast set of mirrors with perfect wide-spectrum reflectivity. These proceed to surround the Sun, reflecting the Sun's light back at itself and darkening the star completely. To maintain position, and deter interference, the solar wind is gathered by each mirror and shot out at relativistic speeds away from the Sun, aimed at any object daring to approach within a few 10 millions of kilometers.

The Sun produces 3.8x10^26 Joules/sec, or ~10^34 Joules/year, so it won't destroy the Sun entirely in 3 years. However, if the shell failed after 3 years - perhaps in a designed manner, around the equator of the sun, the extra energy release would fry any nearby life-sustaining planets. And obviously, 3 years of darkness would have already killed off any ecosystems.

This gives an estimate of 1.8x10^26kg for a Dyson sphere at 1AU; our swarm of mirrors would be much closer (0.1AU or less); if the mass scales as the cube of the distance, then only 10^23kg or so of material would be required, roughly the mass of the moon.

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well, if you wanted something that didnt need obscene kinds of power to get up to light speed, it would be pretty easy to lob a big chunk of inert or heavy elements into the sun and make it unable to continue fusion. this is still a variation of the "bullet" idea, so how about something that could survive the destruction of a star relatively intact? how about a massive magnetic accelerator, able to hover a few thousand miles from the surface of the star, collecting solar energy and excess hydrogen (for fusion power and propellant mass) as it sucks up the plasma at the surface and ejects it far away from the solar system. eventually, the sun would run out of fusable material and die, while the weapon would be re-energized and full of reactant matter, free to once again drift through the empty expanse of space in search of new targets. to prevent it being shut down, perhaps it is able to divert some or all of the plasma stream at attackers as a self-defense mechanism? although, given current technology, just being that close to the sun would be a pretty good deterrent in and of itself...

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I would refer you to the grey bomb. This is a composition of self replicating nanobots designed only to reproduce. They would be programmed to utilize elements available. Upon reaching a planet surface they would then reassemble the entire planets into myriad copies of themselves thus reducing all to grey mush. Perhaps there could be nanobots designed to handle the extreme conditions on star surfaces, eating and cooling it to the core.

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    $\begingroup$ No known-feasible-science nanobots could survive anywhere near the sun... :( $\endgroup$ – Tim B Feb 26 '16 at 23:11
  • $\begingroup$ The problem with this is that the grey goo theory is total bunk anyway - it might work in the sun, but then you are relying on something that is either constructed of hydrogen, or somehow makes sustained fusion on command in a controlled fashion, neither of which are feasible by known science. $\endgroup$ – Emerson Feb 29 '16 at 6:29
  • $\begingroup$ I sorta like this idea. Here's hoping you guys are right, though. $\endgroup$ – Caleb Woodman Feb 29 '16 at 16:38
  • $\begingroup$ Welcome to WorldBuilding Thor! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – Sec SE - clear Monica's name Mar 21 '18 at 14:19

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