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Let's say an unknown cloud enters the Solar System and begins manipulating the Sun, destabilizing the magnetic fields. Could it end up causing the Sun to emit gamma ray bursts to render the system uninhabitable in say, a 5-10 year period?

And if this is not scientifically plausible, are there reality-based alternatives to this scenario?

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  • $\begingroup$ how massive is that cloud? Make it big enough and you won't need magic magnetism (to answer your last question, in our world, I don't think any astronomer would consider scientifically plausible any scenario that turns the sun in a murder machine in the matter of 10 years. So it depends on what you mean by that) $\endgroup$ Mar 8 at 12:46
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    $\begingroup$ "begins manipulating the Sun" - are those clouds intelligent? $\endgroup$
    – Alexander
    Mar 8 at 17:40
  • $\begingroup$ Manipulating the sun ? Nanites ? worldbuilding.stackexchange.com/questions/61675/… $\endgroup$
    – Goodies
    Mar 8 at 20:12

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I'd be a little surprised if the molecular cloud directly affected the Sun's magnetic field. The Sun's surface field is on the order of 1 Gauss, whereas molecular clouds have magnetic fields of at most $\sim10^{-3}$ Gauss, or maybe slightly higher - still higher than the typical interstellar magnetic field, but insignificant compared with the Sun's. I don't think the Sun's magnetic field will be affected. It might be interesting to see if it would induce any additional magnetic reconnection, but I'd bet that that would be miniscule.

That said, if the Solar System passes through a molecular cloud, some of that gas and dust will be accreted by the Sun. We could approximation the process as Bondi accretion; assuming typical molecular cloud properties gives us a sound speed of $c_s\sim0.3\;\text{km s}^{-1}$, which in turn implies an accretion rate of $\dot{M}\sim4\times10^{16}\;\text{kg s}^{-1}$. Making a crude approximation based on accretion disks (which are, yes, disk-shaped and not spherical), it might be reasonable to see temperatures higher than $\sim10^4$ Kelvin near the very center.

This would mean that there would be some gamma-ray emission - blackbody radiation implies emission across all wavelengths - but we'd see peak emission from that inner region at ultraviolet and x-ray wavelengths. I don't think it would be significant, since this is a fairly low accretion rate, but it could make things at least somewhat unpleasant on Earth. This is just a back-of-the-envelope estimation, of course.

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Strange Matter:

Strange matter is a hypothetical state of quark matter only formed in neutron stars that converts all other matter into strange matter. This may result in the release of a lot of energy (read radiation) and the conversion of everything into strange matter.

A cloud of strangelets (strange matter particles) colliding with the sun would be pretty terrible. Since they are purely hypothetical, the speed and pattern of the sun being converted to strange matter would be open to interpretation.

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