Simon Candelaresi id
Poster Title
Stabilizing effect of magnetic helicity on magnetic cavities in the intergalactic medium
University of Glasgow
Abstract (short summary)
We investigate the effect of magnetic helicity for the stability of buoyant magnetic cavities as found in the intergalactic medium. In these cavities we insert helical magnetic fields and test whether or not helicity can increase their stability to shredding through the Kelvin-Helmholtz instability and with that their life time. This is compared to the case of an external magnetic field which is known to reduce the growth rate of the Kelvin-Helmholtz instability. By comparing a low and high helicity configuration with the same magnetic energy we find that an internal helical magnetic field stabilizes the cavity. This effect increases as we increase the helicity content. Stabilizing the cavity with an external magnetic field requires a significantly stronger field.
Plain text (extended) Summary
Observations have shown that above some galactic disks there exist hot under-dense bubbles in the intergalactic medium. Due to their low density, they rise and seem to survive for tens of millions of years. However, the Kelvin-Helmholtz instability should lead to a break up at a much shorter time scale.

We test if an internal magnetic field with helicity can stabilize the bubbles. This is motivated by the realizability condition that imposes a lower bound for the magnetic energy in presence of magnetic helicity. We compare the non-magnetic case with two cases with a internal helical magnetic field. Both magnetic fields have the same energy, but different helicities by a factor of 4. We run numerical simulations that clearly show that a highly helical magnetic field can stabilize the bubbles for several of tens of millions of years. The energy required is much lower than for a stabilizing external magnetic field.