Researchers at Imperial College have created a spinning disk of plasma in a laboratory, mimicking the disks found around black holes and forming stars.
The experiment more accurately models what happens in these plasma disks, which could help researchers figure out how black holes grow and how collapsing matter forms stars. As matter approaches black holes, it heats up and turns into plasma, a fourth state of matter consisting of charged ions and free electrons. It also begins to spin, in a structure called an accretion disk. The rotation causes a centrifugal force that pushes the plasma outward, which is balanced by the gravity of the black hole that pulls it.
These glowing rings of orbiting plasma pose a problem: how does a black hole grow if material is stuck in orbit rather than falling into the hole? The leading theory is that instabilities in the plasma’s magnetic fields cause friction, causing it to lose energy and fall into the black hole. The main way to test this has been to use liquid metals that can be rotated and see what happens when magnetic fields are applied. However, since the metals must be contained within the pipes, they are not a true representation of free-flowing plasma.
Now, Imperial researchers have used their Mega Ampere Generator for Plasma Implosion Experiments (MAGPIE) machine to spin plasma into a more accurate representation of accretion disks. Details of the experiment are published May 12 in the journal Physical Review Letters.
The first author, Dr. Vicente Valenzuela-Villaseca, completed the study during his PhD at the Department of Physics at Imperial. “Understanding how accretion disks behave will not only help us reveal how black holes grow, but also how gas clouds collapse to form stars, and even how we might better create our own stars by understanding the stability of plasmas in them.” fusion experiments,” he said in a statement.
The team used the MAGPIE machine to accelerate eight plasma jets and collide them, forming a spinning column. They found that the closer to the interior of the rotating ring it moved the faster, which is an important feature of accretion disks in the universe. MAGPIE produces short pulses of plasma, which means that it was only possible around one rotation of the disk. However, this proof-of-concept experiment shows how the number of rotations can be increased with longer pulses, allowing for better characterization of disk properties. A longer experiment run time would also allow applying magnetic fields to test their influence on the friction of the system.
More information: V. Valenzuela-Villaseca et al, Characterization of Quasi-Keplerian, Differentially Rotating, Free-Boundary Laboratory Plasmas, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.195101