[ Diagram of MWC 349 Disk ]

Radio Star MWC 349

Circumstellar disk surrounding the hot star MWC 349. Maser emissions are thought to occur in outer regions while lasers are operating nearer the central star. (Courtesy Strelnitski et al., 1995)

The first "natural" laser in space was detected by scientists on board NASA's Kuiper Airborne Observatory (KAO) as they trained the aircraft's infrared telescope on a young, very hot, luminous star in the constellation Cygnus.

Discovery of this naturally occurring laser provides scientists with a powerful tool for probing the conditions in disks of gas and dust surrounding young stars, according to Principal Investigator Vladimir Strelnitski of the Astrophysics Laboratory, National Air and Space Museum (NASM), Washington, DC, who made the discovery. Scientists believe that many of these circumstellar disks are regions where planets are forming.

The laser is created as intense ultraviolet light from the star "pumps" or excites the densely packed hydrogen atoms in the gaseous, dusty disk surrounding the star. Then, when the infrared light shines on the excited hydrogen atoms, it causes the atoms to emit an intense beam of light at exactly the same wavelength, creating the circumstellar laser, according to Sean W. J. Colgan of the Search for Extraterrestrial Intelligence (SETI) Institute, Mountain View, CA, a co-investigator in the discovery.

The discovery was made as the KAO, the world's only flying observatory, returned to Moffett Field, CA, from observing missions based in Hawaii. Co-investigators in the discovery are Howard A. Smith, also of NASM; Michael R. Haas and Edwin F. Erickson, Ames Research Center, Mountain View, CA; and Colgan.

Strelnitski used a sensitive liquid helium-cooled spectrometer attached to the KAO telescope to search for selected "lasing lines" in the infrared region of the spectrum between 50-500 microns (100 to 1000 times the wavelength of visible light).

The natural laser was detected at 169 microns as the scientists viewed the nearly edge-on gas and dust disk surrounding the peculiar star known as MWC 349. The "lasing line" has an intensity six times brighter than non-amplified spontaneous emissions at the same wavelength, Strelnitski said.

The existence of natural lasers was predicted more than 15 years ago, following the successful amplification of both microwave and visible light wavelengths in laboratory experiments, and the discovery of amplified microwaves in space.

(COMMENT: This statement is not exactly correct, stellar lasers were predicted more than a quarter of a century ago by the astrophysicist D.H. Menzel in a remarkable paper on Laser Action in Non-LTE Stellar Atmospheres)

American physicist and Nobel laureate Charles Townes first proposed the practical amplification of electromagnetic radiation by stimulated emission in 1951. In 1954, his group at Columbia University created the first laboratory amplifier of microwaves, calling it a MASER (Microwave Amplification by the Stimulated Emission of Radiation.)

In 1960 Theodore Maiman at Hughes Research Laboratories developed a device to amplify visible light, creating the first LASER (Light Amplification by Stimulated Emission of Radiation.)

Not long after the invention of laboratory masers and lasers, the first natural masers were discovered in interstellar and circumstellar gas clouds. Townes, a frequent investigator onboard the KAO, was among the discoverers of the first strong astrophysical water masers.

Astrophysical masers, due to their extremely high intensity and spectral purity, are valuable tools in studies of the birth and death of their associated stars. On Earth, many scientific and industrial applications of masers and lasers have been developed, such as keeping exact time, bar-code reading in supermarkets and performing "bloodless surgery."

Astrophysical masers can be observed from the ground with special instruments, but the major part of the infrared spectrum where potential lasers might be seen is hidden from the ground observer by Earth's absorbing atmosphere.

This long awaited discovery of a natural laser was made on the last scheduled flight of the KAO instrument -- the Ames Cryogenic Grating Spectrometer. The instrument permits sensitive detection of emission from atoms and molecules throughout the mid- and far-infrared spectral domain.

The KAO is scheduled for retirement this fall. NASA plans to begin development of the follow-on airborne observatory SOFIA in 1996, with first flight scheduled for the year 2000.

Don Savage
Headquarters, Washington, DC      August 29, 1995
(Phone:  202/358-1547)

Diane Farrar
Ames Research Center, Mountain View, CA
(Phone:  415/604-3934)

RELEASE:  95-148


Laser line spectral profile

H-26-alpha microwave laser

Spectral line profile of the H-26-alpha maser transition in MWC 349 (Strelnitski et al., 1995) The shape of this microwave laser line (354 GHz) is similar to the H-15-alpha infrared laser line at 169 microns (1775 GHz). These velocity profiles are typical of microwave laser emissions in many other sources and probably indicate high velocity outflows towards and away from the observer.


The lower and upper levels of this far infrared laser are high Rydberg states, i.e. the H-15-alpha laser transition is taking place between levels with quantum number in the mid teens. In the historical review of astronomical spectroscopy section we mentioned that metastable states become overpopulated in the extended atmospheres of shell stars : In a low density plasma, the high Rydberg (large n) states of Hydrogen and other atoms can have very long lifetimes. Experimental studies demonstrate that the lifetime increases approximately as the cube of the effective principal quantum number, in agreement with hydrogenic theory. It is obvious that, in practical terms, high Rydberg states with long lifetimes will behave as metastable states. The high Rydberg states are considered metastable because of their relatively longer lifetime in a low density plasma as compared to the lower quantum levels. For example, the H-alpha-15 transition has an effective lifetime hundreds of time longer than spontaneous Balmer radiation.

Radio Stars

In a recent paper Strelnitski et al. (1995) called the star MWC349A a 'radio star' due to the strong emissions of radiation in the low frequency part of the electromagnetic spectrum. In the 1960's quasars were also known as 'radio stars', then in the 1970's Varshni discovered laser action in quasars. With the recent discovery of a laser in the stars Eta Carinae and MWC 349 and also in the central star of planetary nebula NGC 7027; it seems that laser action is common to many of these 'radio-active' objects. Is is therefore no wonder that the radio morphology and behavior of quasars is related to other jet emitting stars such as SS433 and Young Stellar Objects (YSO) which are very similar to quasars such as Cygnus-A, 3C 345 they are all objects within the galaxy. In fact their properties are so similar that two recent 'radio stars', GRS 1915-105 and GRO J1655-40 have been nicknamed 'mini-quasars' by their discoverers. It is also not surprising many quasars appear to be 'Naked'.


  1. Strelnitski,V.S., Smith,H.A., Haas,M.R., Colgan,S.W.J., Erikson,E.F., Geis,N., Hollenbach,D.J., Townes,C.H.: 1995, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust (N96-13618 02-88), Astronomical Society of the Pacific, Volume 73 p 271-274. A search for hydrogen lasers in MWC 349 from the KAO
  2. Thum,C., Strelnitski,V.S., Martin-Pintado,J.: 1995, AA., 300, 843. Hydrogen recombination {beta}-lines in MWC 349.
  3. Ponomarev,V.O., Smith,H.A., Strelnitski,V.S.: 1994, ApJ., 424, 976. Modeling of the Hydrogen Maser Disk in MWC 349
  4. Smith,H.A., Strelnitski,V.S., Thum,C., Matthews,H.E.: 1993, Bull.Amer.Astron.Soc., 183, 4401. Detection of the First beta-line Hydrogren Maser in MWC 349
  5. Strelnitski,V.S., Smith,H.A., Ponomarev,V.O.: 1992, Bull.Amer.Astron.Soc., 181, 1705. Modeling of The Hydrogen Maser Disk in MWC349
  6. Ponomarev,V.O., Strelnitski,V.S., Chugal,N.N.: 1990, Astron.Tsirk., 1545, 37. Radio recombination line maser in MWC 349 : how does it work ?
  7. Ponomarev,V.O., Smirnov,G.T., Strelnitski,V.S., Chugal,N.N.: 1989, Astron.Tsirk., 1540, 5. Kinematical interpretation of the maser radio recombination lines from MWC 349.
  8. Doel,R.C., Gray,M.D., Field,D., Jones,K.N.: 1993, AA, 280, 592. FIR lasers from dense OH maser regions
  9. Laser Focus World, Oct 1995 : MWC 349, Natural laser discovered in space
  10. Sky and Telescope, Weekly News Bull., Sep.8, 1995 - A Laser in Space
  11. Scientists Discover First 'Natural' Laser in Space, (An Unlimited Vision On-Line Publication)
  12. High Rydberg metastable states in circumstellar envelopes and shell stars.
  13. Star Formation Newsletter

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