This weeks image comes from a study of the* Collision of two Hopfians* from Universidad Rey Juan Carlos in Madrid, Spain. In their recent Journal of Physics A paper, M Arrayás and J L Trueba consider the collision properties for two Hopfians, or Hopf–Rañada electromagnetic fields. The results make for some spectacular images as well as allowing the authors to show that by controlling the angular momentum of such fields, they can control the topology of the flow associated with the field lines, as well as the energy distribution.

A hopfion, or Hopf–Rañada field, is an example of an electromagnetic knot. The Hopfians are solutions of Maxwell’s equations in a vacuum, where the electric and magnetic field lines form closed loops, each of which is linked to another.

**Read More: **

- Collision of two hopfions
- A class of non-null toroidal electromagnetic fields and its relation to the model of electromagnetic knots
- Motion of charged particles in a knotted electromagnetic field

This work is licensed under a Creative Commons Attribution 3.0 Unported License

Front and article image taken from M Arrayás and J L Trueba 2017 *J. Phys. A: Math. Theor.* **50** 085203 , © IOP Publishing, All Rights Reserved.

Categories: Journal of Physics A: Mathematical and Theoretical