Microwave Astronomy Helps Astronomers Explore the Cosmos

Detailed full-sky map of the oldest light in the universe captured by the Wilkinson Microwave Anisotropy Probe

NASA / Wikimedia Commons / Public Domain 

Not many people think about cosmic microwaves as they nuke their food for lunch each day. The same type of radiation a microwave oven uses to zap a burrito helps astronomers explore the universe. It's true: microwave emissions from outer space help give a peek back at the infancy of the cosmos. 

Hunting Down Microwave Signals

A fascinating set of objects emits microwaves in space. The closest source of nonterrestrial microwaves is our Sun. The specific wavelengths of microwaves that it sends out are absorbed by our atmosphere. Water vapor in our atmosphere can interfere with the detection of microwave radiation from space, absorbing it and preventing it from reaching Earth's surface. That taught astronomers who study microwave radiation in the cosmos to put their detectors at high altitudes on Earth, or out in space. 

On the other hand, microwave signals that can penetrate clouds and smoke can help researchers study conditions on Earth and enhances satellite communications. It turns out that microwave science is beneficial in many ways. 

Microwave signals come in very long wavelengths. Detecting them requires very large telescopes because the size of the detector needs to be many times greater than the radiation wavelength itself. The best-known microwave astronomy observatories are in space and have revealed details about objects and events all the way out to the beginning of the universe.

Cosmic Microwaves Emitters

The center of our own Milky Way galaxy is a microwave source, although it's not so extensive as in other, more active galaxies. Our black hole (called Sagittarius A*) is a fairly quiet one, as these things go. It doesn't appear to have a massive jet, and only occasionally feeds on stars and other material that pass too close.

Pulsars (rotating neutron stars) are very strong sources of microwave radiation. These powerful, compact objects are second only to black holes in terms of density. Neutron stars have powerful magnetic fields and fast rotation rates. They produce a broad spectrum of radiation, with the microwave emission being particularly strong. Most pulsars are usually referred to as "radio pulsars" because of their strong radio emissions, but they can also be "microwave-bright."

Many fascinating sources of microwaves lie well outside our solar system and galaxy. For example, active galaxies (AGN), powered by supermassive black holes at their cores, emit strong blasts of microwaves. Additionally, these black hole engines can create massive jets of plasma that also glow brightly at microwave wavelengths. Some of these plasma structures can be larger than the entire galaxy that contains the black hole.

The Ultimate Cosmic Microwave Story

In 1964, Princeton University scientists David Todd Wilkinson, Robert H. Dicke, and Peter Roll decided to build a detector to hunt for cosmic microwaves. They weren't the only ones. Two scientists at Bell Labs—Arno Penzias and Robert Wilson—were also building a "horn" to search for microwaves. Such radiation had been predicted in the early 20th century, but no one had done anything about searching it out. The scientists' 1964 measurements showed a dim "wash" of microwave radiation across the entire sky. It now turns out that the faint microwave glow is a cosmic signal from the early universe. Penzias and Wilson went on to win a Nobel Prize for the measurements and analysis they made that led to the confirmation of the cosmic microwave background (CMB).

Eventually, astronomers got the funds to build space-based microwave detectors, which can deliver better data. For example, the Cosmic Microwave Background Explorer (COBE) satellite made a detailed study of this CMB beginning in 1989. Since then, other observations made with the Wilkinson Microwave Anisotropy Probe (WMAP) have detected this radiation.

The CMB is the afterglow of the big bang, the event that set our universe in motion. It was incredibly hot and energetic. As the newborn cosmos expanded, the density of the heat dropped. Basically, it cooled, and what little heat there was got spread over a larger and larger area. Today, the universe is 93 billion light-years wide, and the CMB represents a temperature of about 2.7 Kelvin. Astronomers consider that diffuse temperature as microwave radiation and use the minor fluctuations in the "temperature" of the CMB to learn more about the origins and evolution of the universe.

Tech Talk About Microwaves in the Universe

Microwaves emit at frequencies between 0.3 gigahertz (GHz) and 300 GHz. (One gigahertz is equal to 1 billion Hertz. A "Hertz" is used to describe how many cycles per second something emits at, with one Hertz being one cycle per second.) This range of frequencies corresponds to wavelengths between a millimeter (one-thousandth of a meter) and a meter. For reference, TV and radio emissions emit in a lower part of the spectrum, between 50 and 1000 Mhz (megahertz). 

Microwave radiation is often described as being an independent radiation band but is also considered part of the science of radio astronomy. Astronomers often refer to radiation with wavelengths in the far-infrared, microwave, and ultra-high frequency (UHF) radio bands as being part of "microwave" radiation, even though they are technically three separate energy bands.

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Millis, John P., Ph.D. "Microwave Astronomy Helps Astronomers Explore the Cosmos." ThoughtCo, Feb. 16, 2021, thoughtco.com/microwave-radiation-3072280. Millis, John P., Ph.D. (2021, February 16). Microwave Astronomy Helps Astronomers Explore the Cosmos. Retrieved from https://www.thoughtco.com/microwave-radiation-3072280 Millis, John P., Ph.D. "Microwave Astronomy Helps Astronomers Explore the Cosmos." ThoughtCo. https://www.thoughtco.com/microwave-radiation-3072280 (accessed May 30, 2023).