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In the Marvel Universe Mjolnir is said to be forged in the heart of a dying star. Neil deGrasse Tyson mistakenly assumes it was forged out of the heart of a dying star in this video.

But what if there was a weapon that was actually made this way and magically enchanted to only transfer the generated force when applied as a tool or weapon. In other words it has a "true mass" of an object with density of star's core and a "fake mass" with mass and gravitational pull of a regular warhammer.

True mass applies to the force(power) equations only on succesfull strikes that land on the intended target. If the wielder misses, drops the hammer or hangs it on a coat rack it behaves according to its' fake mass.

How much force a regular blow would apply? What about Thor's signature move?

If there are negative effects like recoil(Newton's Third Law) consider them being magically nullified(behaves like fake mass) - the goal is to determine how powerfull as a weapon or tool it could be with only practical applications being possible.

Neil posts that a White Dwarf core has a density of 1 tonn per cubic cm, while a Neutron Star of 1 trillion per cubic cm. I'd be content with a White Dwarf but Neutron Star is also appreciated.

Bonus question: if the magic is dispelled what havoc such an object would wreak on a Earth-like world just by lying on the ground.

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    $\begingroup$ Do you mind summarizing what Mjolnir is to those like me who have no clue? $\endgroup$
    – L.Dutch ♦
    Aug 1, 2018 at 19:06
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    $\begingroup$ Bonus question: it would explode with nuclear-bomb level energy (or more?). The critical mass required to compress matter into electron-degenerate matter is called the Chandrasekhar limit, and it is roughly 1.44 solar masses. A body of electron-degenerate matter that weighs less than this would revert to normal matter, which occupies a MUCH greater volume. With the magic dispelled, Mjolnir would instantly revert to normal matter, liberating more than enough energy to turn itself and anything around it into plasma. Out to how far? I don't know...maybe someone can calculate the energy released? $\endgroup$
    – Qami
    Aug 1, 2018 at 19:14
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    $\begingroup$ Force is simply mass times acceleration: I'm sure plenty of people have discussed the mass of the hammer, and the acceleration of swinging something is pretty easy to find. The only possibly tricky question here is the effects of a superdense object being placed on the Earth, but like most physics-defying questions the answer is probably "bad stuff". $\endgroup$
    – Giter
    Aug 1, 2018 at 19:14
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    $\begingroup$ Victim is probably turned to plasma. Might be useful for controlled executions as the quickest, most painless death ever. $\endgroup$
    – user39548
    Aug 1, 2018 at 19:19
  • $\begingroup$ I am pretty certain that "force" is the wrong word here. Momentum, maybe, kinetic energy, possibly. Hint: projectiles don't "transfer force". They just don't. $\endgroup$
    – AlexP
    Aug 1, 2018 at 19:50

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Lets say it is made of neutronium and has a mass of $2\times10^{15}$ kg

It is swung like a hammer and strikes at 1ms$^{-1}$ so it carries about a million gigajoules of energy.

Now its not very clear how to model the collision between the hammer and its target. Does it behave like a chunk of neutronium or does it magically behave like regular matter. This matters because when something heavy hits something light, only a small fraction of the kinetic energy is transfered (a train hits a fly, the train isn't slowed down by much). But if something small hits something large, a large proportion of the kinetic energy is transferred.

In the first case, if the hammer hits a person (mass 100kg), that person will be accelerated to the same speed as the hammer, the hammer won't be significantly slowed down.

In the second case, if the hammer magically transfers all its kinetic energy to a human (mass 100kg) they will be accelerated to about 4 million m/s, and instantly converted to a fireball

Energy is proportional to mass, so if this were white dwarf degenerate material, the effects would be a lot less. The hammer would have a mass comparable with a locomotive and being hit by it would be similar to being hit by train. I.e. you die, but you don't explode.

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    $\begingroup$ The answer sounds something like the Relativistic Baseball question on XKCD: what-if.xkcd.com/1 $\endgroup$
    – Thucydides
    Aug 2, 2018 at 1:20
  • $\begingroup$ I think that magically transferring kinetic energy would be more likely to simply blow a hole through a person. Unless the hammer also provides the recipient with magical energy distributing armor... $\endgroup$
    – Matej Lieskovsky
    Aug 2, 2018 at 7:48

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