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Suppose there is a Sirius A based alien civilization, but their planet is heavily defended, so direct attack is useless. Could we use some kind of weapon to detonate the Sirius B and cause a disaster for that civilization?

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    $\begingroup$ Yes, it's easy, just make a bomb that make the same energy the Sirius is making. Of course if you can make a bomb that is equivalent of Sirius why care about any defence? $\endgroup$ – SZCZERZO KŁY Mar 14 at 10:40
  • $\begingroup$ Welcome to the site SWM, please take the tour and read up in our help centre about how we work: How to Ask With our curent level of technology we haven't even put people on a different planet or sent a spacecraft near any other stars yet, what makes you think it could be possible? $\endgroup$ – Chickens are not cows Mar 14 at 11:05
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    $\begingroup$ "Can we use some kind of weapon...". If you take we as the human civilication today, the answer is no. Otherwise, please ellaborate on we. $\endgroup$ – DarthDonut Mar 14 at 11:47
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    $\begingroup$ Personally I'd just strap Bussard ramjets to a bunch of handy asteroids & accelerate them to near light speed directly at the planet (there's not a lot that could plausibly be able to really stop those & pretty much anything that could is going to be able to protect the sun from them too), but if you really want to you might throw them at the sun instead ~ you'd have to hand-wave the density of interstellar hydrogen for that though. $\endgroup$ – Pelinore Mar 14 at 14:03
  • $\begingroup$ ^ if you want to remain plausible on the time-frame that one would probably take (lots of) decades between launching the attack & it hitting if they start out from Earths local asteroid belt ~ you'd have to do some math there that I can't be bothered with :) $\endgroup$ – Pelinore Mar 14 at 14:10
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No, not in any effective way Getting a star to explode requires masses on the order of solar masses. If you have the ability to move stars as weapons, you may more effectively use them as kinetic energy weapons.

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    $\begingroup$ Agreed. Any weapon that could effectively cause a start to explode would make any other defence trivial. Any defence that could protect from something that could make a star explode could likewise protect their star. Causing targeted solar flares might be a more viable option. $\endgroup$ – Ynneadwraith Mar 14 at 11:43
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    $\begingroup$ I'm not so sure I buy this. Degenerate stellar remnants like white dwarfs can be unstable to nuclear detonations (which is why we have Type Ia supernovae). I don't know quite how much mass you'd need to add, but it definitely wouldn't be on the order of solar masses (and Sirius B is a fairly massive white dwarf, compared to the universal average). Plus, if you actually detonated a nuclear weapon of your own, you could very well trigger runaway fusion. $\endgroup$ – HDE 226868 Mar 14 at 13:52
  • $\begingroup$ @HDE226868 white dwarves are what they are because they're "out of gas" -- any remaining fusion in its core is a negative-energy reaction. It takes a bunch of hydrogen building up on the surface to produce the type Ia supernova (see my answer). $\endgroup$ – Zeiss Ikon Mar 14 at 15:01
  • $\begingroup$ @ZeissIkon They've lost their hydrogen, but not other elements - chiefly carbon and oxygen. When a Type Ia supernova occurs - or a nova, or some related detonation - it's almost always dominated by runaway carbon fusion. Hydrogen isn't really a key player. $\endgroup$ – HDE 226868 Mar 14 at 19:46
  • $\begingroup$ @HDE226868 True, but it's my understanding that in Type 1a, the trigger is a (re)start of hydrogen fusion in the accreted layer sitting on the surface of the dwarf. Key being that this then compresses the core enough to start the carbon runaway, which couldn't happen in a star this mass without such a trigger event. $\endgroup$ – Zeiss Ikon Mar 15 at 11:50
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A white dwarf is what's left when a star too small for a type II supernova runs out of fuel (our sun is in this category): it will go through a red giant phase, shed a fraction of its mass into a planetary nebula, then when fusion ends, shrink to a hot degenerate matter white dwarf (not heavy enough to form a neutron star).

If you have a white dwarf that's within years (or possibly decades) of a type Ia supernova explosion, it might be just possible to trigger the supernova early with a large enough compression event over a large enough fraction of the star's surface.

This kind of star is one that has collected hydrogen from a companion star over a long period, until the collected hydrogen (which lies on the surface of the degenerate matter stellar corpse) becomes deep enough for the lower layers to start to fuse; the reaction apparently occurs rapidly enough and symmetrically enough to push the remainder of the white dwarf into fusing elements like carbon and nitrogen, which in turn provides the energy to fuse iron and heavier elements (producing even trans-uranics, as happens in a classic type II supernova of a star of several solar masses), and the resulting energy literally blows the entire white dwarf apart, accelerating most of the mass beyond the star's escape velocity.

Triggering this kind of event early is a somewhat "hand-waving" situation, as it's not scientifically clear whether it's actually possible or what would need to be done. One method I'd suggest (as a thought experiment or plot device) would be to somehow bathe the entire surface of the star evenly in the correct variety of muons to trigger "cold" fusion in the surface layers (which are already plenty hot, just below fusion parameters), which would then compress the deeper hydrogen layers.

There might be other methods that would work, and are "easier" to accomplish, depending on the technology available. Bombarding the surface with anti-hydrogen or anti-protons, perhaps even a patterned application of very large fusion explosions would be enough if the star is close enough to the type Ia event.

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  • $\begingroup$ Are white dwarves not remnants of explosions? I don't think Sirius B has anything feeding it mass. $\endgroup$ – Whitecold Mar 14 at 11:57
  • $\begingroup$ A white dwarf is what's left when a star too small for a type II supernova runs out of fuel (our sun is in this category): it will go through a red giant phase, shed a fraction of its mass into a planetary nebula, then when fusion ends, shrink to a hot degenerate matter white dwarf (not heavy enough to form a neutron star). $\endgroup$ – Zeiss Ikon Mar 14 at 11:59
  • $\begingroup$ And no, I don't think Sirius B is close enough to Sirius A to collect hydrogen, at least at a rate that would allow a type Ia event within the life of the larger star. $\endgroup$ – Zeiss Ikon Mar 14 at 12:01
  • $\begingroup$ All very good, but can I direct you to the other answer by @Whitecold if you haven't already looked at it :) any weapon of sufficient magnitude to be capable of persuading a star to "detonate" almost certainly doesn't need to worry about any defense that's insufficient to protect the titular civilization from an exploding sun, so might plausibly be more usefully deployed directly against said civilization. $\endgroup$ – Pelinore Mar 14 at 13:31
  • $\begingroup$ Question as I read it is "can it be done and how", not whether it makes sense to do it. $\endgroup$ – Zeiss Ikon Mar 14 at 13:39
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If you're looking for an "explosive", a sufficiently large chunk of anti-matter will do nicely. If you're looking for something more exotic, I refer you Charles Stoss's Iron Sunrise

For this exercise, a field encompasses a volume of the star's core, and time is enormously sped up inside the field. Eventually, the volume becomes degenerate, and when the field is removed, with no radiation pressure to maintain the outer layers they free-fall into the center, then the collision produces a supernova.

Stross did rather finesse the question of what happened to all of the energy emitted during the "decay" process, but you can't have everything.

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