In a disk of gas and dust around a young star, dust particles behave like sand grains in a stream of water: the gas flows faster, the dust lags behind, and friction arises between them. This friction can rock the magnetic waves that run through the disk. The galaxy is full of such disks: it is precisely in them that planets are born.
Scientists examined how dust and magnetic fields interact when the gas is partially ionized (that is, some atoms have lost electrons and can conduct electricity). It turned out that dust dampens certain types of disturbances — oblique waves that would otherwise tear the disk apart. But in return, dust triggers another mechanism: resonance between the dust drift and the magnetic wave. The wave begins to grow, like a swing that is pushed in rhythm.
This resonance works even where there is very little dust and it is strongly coupled to the gas. It gathers dust grains into clumps — future planetesimals (planetary embryos). Thus, dust bypasses the sticking stage: instead of slow accretion, particles are pulled together into clumps by the force of magnetic waves.
So, in cold, weakly ionized disks, where rapid growth was not expected before, dust can gather into planets. This changes the picture of how often and where in the universe new worlds appear.
The resonant instability in question is similar to the mechanism that drives a swing: if you push it in time with its natural oscillations, the amplitude grows. In the disk, the role of 'pushes' is played by the drift of dust relative to the gas.