A spiral galaxy's magnetic field is global, but it likely acts locally to assemble huge clouds of gas and dust that then spawn stars. That's the upshot of a new study of M33, a nearby spiral galaxy located 2.8 million light-years away in the constellation Triangulum. As astronomers report online today in Nature, magnetic fields inside M33's six most massive giant molecular clouds—large concentrations of dense gas and dust that give birth to stars—line up with the spiral arms, suggesting the magnetic fields helped create the huge clouds  and that they regulate how the clouds fragment to form new stars. Although this finding pertains to M33, it likely extends to other spiral galaxies, too—including our own, which we'll never get to see from the outside.
See more ScienceShots .