What Is the Diffuse Universe?

Abstract

Nowhere in the universe can we find a perfect vacuum. Around ordinary stars, a hot magnetized plasma seethes and bubbles outward in a thermally powered wind. Within the disks of spiral galaxies, dusty clouds of molecular gas continually coalesce and collapse under their self-gravity to form new stars. The light from these newborn stars heats and ionizes their placental cloud before finally dispersing it back into the galactic disk, ready to repeat the cycle (Fig. 1.1). Wherever there are stars, some will reach the end of their lives to explode as supernovae, hurling out the gas that has been transformed in their thermonuclear furnaces into heavy elements such as iron. The shocks of these events rumble their way through space, heating the interstellar, gas anew. Some is thrown up and far away from the galactic plane, while other parts are crushed into dense sheets and filaments which shine briefly as their shock energy is radiated away. In clusters of galaxies, heated gas glows softly in X-rays, cooling over billions of years before finally falling back into the bright galaxy cores to help feed the massive monster black holes that lurk at their centers. In intergalactic space, jets of plasma shot from the cores of active galaxies emit radio waves as relativistic charged particles circle in the magnetic fields, shedding their energy.

“Now entertain conjecture of a time When creeping murmur and the pouring dark Fills the wide vessel of the Universe”

— Shakespeare (Henry V, Act 4)