On average, the Universe today is an extremely cold place.
In intergalactic space, only the residual glow of the Big Bang warms matter noticeably.
At 2.725 K above absolute zero, only places that are actively cooling are colder.
However, many mechanisms warm the matter of the Universe.
Stars, for example, produce radiation that strikes nearby gas and dust.
Heated to tens of degrees above absolute zero, it radiates in the far infrared.
Closer to a newly formed star, the radiation sculpts protoplanetary structures.
Heated to hundreds of degrees, these protoplanetary disks radiate in all the infrared.
Higher energy phenomena, however, can have dramatic astronomical consequences.
The hottest, most massive young stars shine brightly in ultraviolet light.
The radiation heats the gas to thousands of degrees, ionizing many atoms and molecules.
As electrons roll down their energy levels, they emit a variety of emission signatures.
At a few thousand degrees, hydrogen ionizes, making nebulae pink with emission lines.
Above ~50,000 K, around dying stars, doubly ionized oxygen glows an eerie green.
The colliding galaxies heat the gas further, resulting in X-ray emissions.
But neutron stars and radiant black holes can shape entire galaxies.
Producing the most energetic gamma photons, even the Large Hadron Collider can’t compete.
Mostly Mute Monday tells an astronomical story in pictures, visuals and no more than 200 words. Talk less; smile more.