Loyal readers may remember my very first column, when I wrote about an experiment using powerful lasers to rip apart matter into a hot plasma state, reproducing in the laboratory the same physics that occur in space during the aftermath of a supernova explosion. It demonstrated that turbulence – the chaotic motion of gases that causes a leaf to dance in the air – is the key to growing magnetic fields in astro-plasmas.
That was back in 2014. The team have since expanded and honed their craft of designing laboratory-based astrophysics experiments to focus in on this process, which is known as “turbulent dynamo”. This explains how magnetic fields observed in galaxy clusters – such as the Local Group, where our own Milky Way is located – have grown to be so strong. This is a key piece in the story of the Universe.
Their latest experiment has not only reproduced the physical process behind astrophysical magnetic field growth, but has this time managed to take snapshots of the process evolving over a time frame that spans a few billionths of a second. Their paper, published recently in Proceedings of the National Academy of Sciences, describes how two laser beams were focused down onto two targets to generate counter-propagating, super-hot plasma jets that collided head on, during which the turbulent mixing led to a rapid rise in magnetic field strength. At the exact moment of the collision, a third laser pulse was used to propel a beam of protons across the burning plasma.
The protons deflected as they travelled through the magnetic fields, imprinting the field structure onto the beam, which then projected onto a stack of imaging film. This created a series of blown up maps of the tiny magnetic structures, allowing the team to visualise them and deduce the strength of the fields. The film pack they used rolled out like a flip-card movie, showing the field strength increasing at a rate that was, to their surprise, above the theoretical predictions – the first time this process has been seen and measured in such detail.
This article is from the Witness section of the New Humanist summer 2021 edition. Subscribe today.
