# Strange Matter and Stars

I am researching some stuff for a WorldBuilding.SE question, which asks if there is a true scientific method (not necessarily at our current technology level) to create a bomb capable of destroying a star. In one of the comments to the question, a user suggests using strange matter, which would cause the star's nuclear matter to be absorbed into itself until it yields a larger strangelet. The comment quotes this article:

http://www.physics.rutgers.edu/~jholden/strange/node17.html

The comment text itself says:

"Simplest" way might be impacting the star with a proper strange matter bomb. "The resulting exothermic reaction would simply produce a larger strangelet."

I have since looked up strange matter, quark stars and strangelets on WikiPedia. I could understand that theoretical physicists posit strange matter as a possible most stable state of matter under certain critical conditions (critical density and pressure), where our normal nuclear matter is only metastable, but with a very long lifetime, close to the lifetime of the universe.

Coming to the question, is it indeed possible for what the commenter posited to happen (implying, is it possible for a normal star to become a strange star on interaction (contact) with strange matter)? And if so, under what conditions? (Forgoing mathematics more complicated than integration would be favoured!)

• In principle this kind of question is what WorldBuilding is for, and the fact that it doesn't reward careful physics (or any science) enough that you feel you have to leak it's questions back here is a great disappointment. – dmckee Feb 18 '16 at 15:10
• @dmckee you are very correct. If the commenter there had posted an answer, he might have been rewarded. As it stands, I did not understand his implication so I asked about it on a hard-science site – Tamoghna Chowdhury Feb 18 '16 at 15:13

A nucleon is a bound state of (on average) three quarks, and like all bound states it has a zero point energy. If you could make the quarks heavier this would reduce the zero point energy and therefore decrease the energy of the nucleus. However making the quarks heavier costs energy, because to increase the mass of the quarks by some amount $m$ requires adding an energy $E=mc^2$.

You can't just make quarks heavier, but what you can do is turn a quark into a heavier quark. For example a proton contains up and down quarks, and in principle you could add enough energy to turn these into strange quarks. Because the strange quarks are heavier, the process would reduce the zero point energy and thereby reduce the total energy of the nucleus. If the reduction of the nucleus energy is greater than the energy required to turn up and down quarks into strange quarks then overall the process would be energetically favourable and should happen spontaneously.

There have been various attempts to calculate whether this process is energetically favourable or not, but results differ. Part of the problem is that calculating the properties of bound states of quarks is exceedingly difficult. You could argue that since the nuclei around us haven't all turned into strange matter the process can't be energetically favourable, but this could simply mean there is a large potential barrier and the reaction would occur spontaneously if we waited long enough.

So if strange matter is more stable than normal matter and if it's just a potential barrier that prevents the reaction then we could make the reaction go if we could find a catalyst that eliminates the barrier. And this brings us to the idea of the strangelet bomb. If we could make a chunk of strange matter then it should catalyse the conversion of normal matter to strange matter, so the argument is that if we drop our strange matter into a star it would convert the whole star to strange matter.

But ...

The chunk of strange matter wouldn't attract normal matter, or at least not over any great distance, so the strange matter would sweep up and convert and matter it ran into. But:

1. stars are big, and it's going to take a long, long time for our small chunk of strange matter to convert the whole star

2. the reaction must be exothermic (other it would go) and is likely to be violently exothermic and the released heat would inhibit accretion of normal matter onto our chunk of strange matter.

It's like the old idea of destroying a star by dropping a small black hole into it. The smallness of the black hole and the Eddington accretion limit mean that in practice it would take a very long time to turn the whole star into a black hole.

You ask how a chunk of strange matter can catalyse the conversion. Well a single nucleon cannot change into a stable strange particle. We know that because the particle with three strange quarks exists - it's called the Omega and it's actually unstable with a lifetime of around $10^{-10}$ seconds. It decays back to a proton (and several mesons).

The argument is that while three strange quarks on their own aren't stable, a large number of them would be. But that means to form a strangelet would require lots of nucleons to simultaneously transform to strange matter then aggregate together. The probability of this happening is effectively zero (which is just as well for us! :-).

However if you have a chunk of stable strange matter then a nucleon can hit the surface and transform quark by quark, whith each quark transformation releasing a burst of energy to help the next quark on its way. But this requires the nucleon to hit the surface of the strangelet, and nucleons even a few proton radii away from the strangelet surface wouldn't be affected.

• Well, as absurd as the original proposition was, the chunk of strange matter might not necessarily be very small, even in comparison to a star. – Tamoghna Chowdhury Feb 18 '16 at 12:09
• @TamoghnaChowdhury: strange matter would at least as dense as neutronium, and in practice far denser because the strange quarks are heavier than up and down quarks and more densely packed. To make a strangelet big enough to present a serious danger to the star would require a mass comparable to or greater than the mass of the star itself. If you could handle such large masses wouldn't it be easier to crash another star into your target? – John Rennie Feb 18 '16 at 12:13
• Well, it was in fact a joke. Missed an emoji somewhere :P – Tamoghna Chowdhury Feb 18 '16 at 12:16
• @John Rennie Can you back up your claim 1)? From this paper e.g. it seems that this could happen rather fast, in the ms regime. arxiv.org/pdf/1304.6884v2.pdf – Noldig Feb 18 '16 at 12:24
• @Noldig: that paper describes conversion of a neutron star into strange matter, not a normal star. – John Rennie Feb 18 '16 at 12:25