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Following on from this question, here is a high-speed photograph of a nuclear explosion, taken about 1 ms after detonation: (source) As anna v pointed out, several similar images can be seen in a Google image search for "high speed nuclear explosion photos".

enter image description here

The spikes at the bottom are know as "rope tricks" - they're caused by cables being heated by the radiation. But what causes that weird-looking structure in the fireball itself?

My suspicion is that the explosion at this stage is an expanding ball of air that's being ionised by the radiation coming from the nuclear chain reaction. If some regions of the surrounding air are ionised more easily due to differences in their temperature (or density or moisture content) prior to the explosion then perhaps this would explain the structure. The explosion is probably taking place in a desert, meaning that there could be quite a bit of turbulence in the ambient air due to thermal convection. However, this is just a wild guess, and I'd be interested to know if anyone has any knowledge or insight about this structure.

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    $\begingroup$ This looks to me like bread dough rising too fast in the oven, anisotropies appear and bubbles . It could be that the original anisotropies in the solid medium before the critical point is reached are amplified as the plasma forms after it runs away. $\endgroup$
    – anna v
    Jan 2, 2013 at 7:01
  • $\begingroup$ Related: physics.stackexchange.com/q/233798/2451 $\endgroup$
    – Qmechanic ♦
    May 8, 2018 at 7:32
  • $\begingroup$ @Qmechanic same photo, different question. I know what the spikes are (and say so in the question). I was asking about the structure in the spherical part. $\endgroup$
    – N. Virgo
    May 8, 2018 at 8:49
  • $\begingroup$ @Qmechanic and in any case, this question is a good three years older than the proposed duplicate. $\endgroup$
    – N. Virgo
    May 8, 2018 at 8:53

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There is a description on Wikipedia accompanying this picture that seems to indicate the mottled surface is the leading edge of a compression shock propagating through the air. In particular, it carries the imprint of the irregularities in the casing surrounding the bomb.

I am inclined to agree. While I admit there is no scale to indicate what the different levels of brightness mean, it seems there is considerable variation, and this seems difficult to attribute to the percent-level differences in air temperature and composition you might get at those scales (20 meters across). Furthermore, there seems to be far too little time for the wavefront to develop large-scale turbulence of its own given the densities involved - the time since detonation is quoted as "less than one millisecond," which is about a percent of the sound crossing time of something that large in the ambient air.

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  • $\begingroup$ Thanks, I didn't spot that explanation on Wikipedia. I agree that the uneven distribution of material from the bomb casing is a more plausible one than mine. $\endgroup$
    – N. Virgo
    Jan 2, 2013 at 11:05
  • $\begingroup$ @Nathaniel To make such a horrible bomb more powerful it has to be added more nuclear material. This material is radioactive and with a too big concentration starts a fusion process. To prevent this at the beginning two half spheres were shoot together. Later they shoot more units together. Knowing for this bomb how many units they use one can proof Chris Whits explanation, which seems very reasonable. $\endgroup$
    – HolgerFiedler
    Feb 5, 2016 at 5:21

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