Beyond Visible Light
The rainbow of light that the human eye can see is a small portion of the total range of light, known in science as the electromagnetic spectrum. Telescopes can be engineered to detect light outside the visible range to show us otherwise hidden regions of space. The James Webb Space Telescope detects near-infrared and mid-infrared wavelengths, the light beyond the red end of the visible spectrum.
Infrared light is important to astronomy in three major ways. First, some objects are just better observed in infrared wavelengths. Some bodies of matter that are cool and do not emit much energy or visible brightness, like people or a young planet, still radiate in the infrared. Humans perceive this as heat, while some other animals, like snakes, are able to “see” infrared energy.
These videos begin in visible light and end with an image in infrared light. Note what each wavelength reveals and conceals.
Visible light’s short, tight wavelengths are prone to bouncing off dust particles, making it hard for visible light to escape from a dense nebula or protoplanetary cloud of gas and dust. The longer wavelengths of infrared light slip past dust more easily, and therefore instruments that detect infrared light—like those on Webb—are able to see the objects that emitted that light inside a dusty cloud. Low-energy brown dwarfs and young protostars forming in the midst of a nebula are among the difficult-to-observe cosmic objects that Webb can study. In this way, Webb will reveal a “hidden” universe of star and planet formation that is literally not visible.
Finally, infrared light holds clues to many mysteries from the beginning of everything, the first stars and galaxies in the early universe, after the big bang. Through a process called cosmological redshifting, light is stretched as the universe expands, so light from stars that is emitted in shorter ultraviolet and visible wavelengths is stretched to the longer wavelengths of infrared light.
Observation of these early days in the universe’s history will shed light on perplexing questions of dark matter and energy, black holes, galaxy evolution over time, what the first stars were like, and how we arrived at the universe we experience today.