A dust grain in interstellar space is like a tiny compass. Inside it sit inclusions of magnetic minerals that make the grain rotate along invisible magnetic field lines. How obediently the grains align determines how they polarize the light of distant stars and what radiation they emit.

For a long time, these magnetic inclusions were thought to be uniform in size, like sand grains sifted through a single sieve. But nature doesn't work that way. The authors of the new study allowed the grains to vary, from very small to large, and observed what changes. It turned out that the magnetic response of a dust grain no longer drops sharply at slow rotation, as in the old model. Instead, it stays nearly constant: small grains respond to fast oscillations, large ones to slow ones, and together they cover the entire range.

Such a flat response means that dust grains will align with the magnetic field equally well in dense cold clouds and in hot rarefied regions. This changes calculations of light polarization and magnetic emission from dust across the entire Galaxy.

The compass-dust grain now points more accurately: its needle doesn't tremble but smoothly follows the magnetic field, whatever the rotation tempo.