Beyond the Visible
Our view of the sky is shaped by what our eyes can detect. Yet there are many wavelengths of light beyond the colors we see. They let us observe star birth and death, peer into the dusty hearts of galaxies, and detect the otherwise invisible effects of black holes.
We can't tune our eyes to radio, microwave, infrared, ultraviolet, x-ray, or gamma-ray light. But we can extend our vision with detectors sensitive to such wavelengths. These instruments reveal a universe more detailed and understandable than we can see with only visible light.
Center of the Milky Way Galaxy in Each Wavelength
Radio waves open a window on black holes and jets of superheated gas streaming away from the hidden cores of galaxies. The center of the Milky Way Galaxy, which is hidden from our view by dust clouds, is populated by clusters of young stars, a glowing ring of gas, and a black hole. These all emit a whirlwind of radio waves.
The microwave universe looks very different from what we see with our eyes. The Milky Way Galaxy appears as a bar of hazy light emitted by warm dust clouds. This dust gives off heat, which our spacecraft detect as microwave radiation. Beyond the galaxy, all of space is permeated by a microwave glow left over from the Big Bang that created the universe.
Everything in the universe radiates heat. We detect it as infrared light. Infrared astronomy lets us peek into hidden nurseries where stars are being born and lifts the veils of dust that keep the hearts of galaxies from our view. Telescopes sensitive to infrared peer into the shrouded core of the Milky Way Galaxy and reveal the swarms of stars clustered there.
Millions of stars arc across our sky and define the visible shape of the Milky Way Galaxy. Yet, there is more to the universe than meets the eye. Even in visible light, there are places we cannot see. Clouds of dust obscure the heart of our galaxy, hiding a supermassive black hole surrounded by a ring of hot gas and clusters of bright stars.
The ultraviolet view of our galaxy's center is dark. We know this region has stars, superheated gases, and a black hole, but thick clouds of dust absorb the ultraviolet light they emit. The rest of the ultraviolet universe is easier to detect, but we must use telescopes orbiting above the thick blanket of air that protects Earth from this energetic radiation.
High-energy events shower the universe with x-rays. A solar flare, the interaction of a comet with the solar wind, the birth of a star, a supernova shockwave, and material falling into a black hole are all x-ray emitters. We know that the core of our Milky Way Galaxy is a hotbed of activity because its central black hole is a strong source of x-rays.
The most energetic things in the universe show up in the gamma-ray window. Super-hot, flashy events like galaxy collisions and supernova explosions send out huge bursts of gamma rays. The heart of our own Milky Way Galaxy is a strong gamma-ray source. There, the gravity of its supermassive black hole heats nearby gas being drawn in by the intense gravity.