Strange behavior of ferrofluid exposed to flame

monotonic

The Living Force
So, I don't want to give the impression I think something radical is happening here, but there is something that will make you think. If you look closely, whenever the ferrofluid is exposed to flame, the hexagonal grid of spikes changes to a square grid. How do you explain that?

https://www.youtube.com/watch?v=Fw-PemqRN3A
 
Are you referring to the part around the 7:51 - 8:16 mark?


https://youtu.be/Fw-PemqRN3A?start=471

I think it's the heat profile of the match projected onto a convex plane. As the match continues to burn, the flame spreads out in a straight line. This accounts for 2 corners of the square as they are parallel with the match. The two remaining corners, that are perpendicular to the first 2 mentioned, are aligned with the highest/hottest part of the flame, albeit it is a bit difficult to see the exact orientation the matchstick holds in relation to the sphere and resulting square pattern.

Also, if I am looking at the correct part of the video this is most prominent around the 8:15 mark.
 
Each spike concentrates the field moving through it and they separate into spikes because surface tension and gravity prevent them from making one big spike. Since the spikes have a minimum corner radius due to surface tension, perhaps the heat lowers the viscosity/surface tension of the oil, allowing them to make sharper corners and create a more space-efficient square pattern?

Or perhaps the plasma from the flame causes a change in the magnetic field?
 
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