Electromagnetic interaction refers to the fundamental force by which charged particles exert forces on one another through electric and magnetic fields. This force is one of the four fundamental interactions in physics and is responsible for most phenomena observable in everyday experience, from chemical bonding to light itself.
Electromagnetic Interaction and Dark Matter
Dark matter differs fundamentally from ordinary baryonic matter in its interaction with electromagnetic forces. While normal matter—composed of electrons, protons, and neutrons—is electrically charged and readily interacts through electromagnetic fields, dark matter appears to be electrically neutral. This means dark matter cannot radiate away energy through electromagnetic radiation, nor can it be held up against gravitational collapse by electromagnetic pressure in the way that ordinary matter can.
Ordinary stars and planets resist complete gravitational collapse because the electromagnetic forces between electrons in their material create outward pressure that balances inward gravitational pull. Dark matter lacks this electromagnetic support. However, dark matter does not form black holes in large quantities because it is extremely diffuse and distributed across vast regions of space. Its low density means gravitational attraction remains too weak to overcome the slight random motions of dark matter particles. The absence of electromagnetic interaction therefore does not cause dark matter to catastrophically collapse, but rather leaves it distributed as a diffuse halo around galaxies without the condensed structures that electromagnetic forces help create in ordinary matter.