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When light in the microwave part of the spectrum shines on gas, sometimes the molecules respond by amplifying it, producing a dramatically brighter object called a “maser”. Naturally-occurring masers are found near stars and supermassive black holes, as well as in the atmospheres of Jupiter and other Solar System objects. Researchers also build masers in the lab to serve as extremely reliable clocks for many experiments.

Our Work

Center for Astrophysics | Harvard & Smithsonian scientists and engineers are involved in both artificial and natural maser research:

  • Using masers to measure the size and structure of the Milky Way. The far side of the galaxy is largely obscured by gas and dust, but masers shine through the mess. Using virtual observatories made up of many smaller telescopes, researchers compared the position of a water maser associated with a star-forming region to that of a distant black hole. That provided a precise measurement of the distance to this maser, and as a consequence a better measurement of the size and shape of our galaxy.
    Measuring the Distance to the Far Side of the Galaxy

  • Identifying and studying astronomical masers around stars using the CfA Submillimeter Array (SMA) and other observatories. That includes discovering some of the first known naturally-occurring hydrogen masers, which are much rarer than those produced by other molecules.
    Hydrogen Masers in Space

  • Comparing the way masers on Earth and on satellites behave, to test fundamental predictions of the theory of relativity. This theory says there should be no difference in the behavior of clocks based on the orientation of the experiment, and masers provide some of the most accurate clocks to use for testing.

Hubble image of megamaser IRAS 16399-0937

This galaxy's serene appearance hides the fact that it is actually two galaxies merging. This collision has given birth to a "megamaser" called IRAS 16399-0937, where rapid star-formation produces intense microwave radiation.

Credit: ESA/Hubble & NASA, Judy Schmidt

Lighting Up in Sync

Each type of atom or molecule absorbs and emits light of specific wavelengths, giving them a unique spectrum. In some cases, shining light on atoms or molecules can stimulate the emission of photons of the same wavelength — color — as the original light. This creates a cascade effect, resulting in a lot of light of a very pure color, often beamed in one direction. That’s the principle behind lasers, familiar from many everyday items.

That’s the principle behind both lasers and masers. In fact, the words were originally acronyms for “Light” or “Microwave Amplification by the Stimulated Emission of Radiation”, though that use isn’t common anymore. Masers are the lower-energy form, and occur naturally throughout the universe.

The most powerful masers, known as megamasers, are found near supermassive black holes at the centers of galaxies. Molecules of water embedded in matter falling onto the black hole are powerful masers, emitting in radio wavelengths. That provides details about the black hole’s environment, as well as a way to measure its distance. Other masers occur around forming and dying stars, in the remnants of supernovas, and in the atmospheres of Solar System worlds.

The unique colors and brightness of masers also allow scientists to identify the chemical composition of interstellar clouds. The first astronomical maser discovered was used as evidence for the existence of molecules in space, which some researchers at the time didn’t think could exist. Since then, astronomers have found masers from water, hydroxyl, hydrogen, ammonia, methanol, silicon monoxide, and many other molecules.


Laboratory Masers in Astronomy

Artificial masers work the same basic way as the naturally-occurring versions, only with dedicated power supplies and amplification chambers to contain the gas. Astronomers use the very precise frequency at which molecules in masers absorb and emit light as a clock. Hydrogen masers are used to coordinate telescopes separated by thousands of miles, the observation method known as Very Long Baseline Interferometry (VLBI).

Masers can also be used in tracking spacecraft and for testing fundamental physics, as part of space-based experiments to test Einstein’s theory of relativity.