Showing papers by "Charles H. Townes published in 1983"
TL;DR: In this article, it was shown that if generalized types of detection are considered, and if advantage is taken of the directivity of telescopes at short wavelengths, then somewhat less power is required for communication at infrared wavelengths than in the microwave region, and a variety of parameters other than power alone may be chosen for optimization by an extraterrestrial civilization.
Abstract: It has often been concluded that searches for extraterrestrial intelligence (SETI) should concentrate on attempts to receive signals in the microwave region, the argument being given that communication can occur there at minimum broadcasted power. Such a conclusion is shown to result only under a restricted set of assumptions. If generalized types of detection are considered—in particular, photon detection rather than linear detection alone—and if advantage is taken of the directivity of telescopes at short wavelengths, then somewhat less power is required for communication at infrared wavelengths than in the microwave region. Furthermore, a variety of parameters other than power alone may be chosen for optimization by an extraterrestrial civilization. Hence, while partially satisfying arguments may be given about optimal wavelengths for a search for signals from extraterrestrial intelligence, considerable uncertainty must remain.
47 citations
TL;DR: X-ray, gamma-ray and IR observations of the Galaxy's nucleus show that it contains the densest concentration of stars in the Galaxy, as well as a quantity of ionized gas and warm dust, which is clumped into a small number of rapidly expanding individual clouds whose velocities approach + or - 300 km/sec as mentioned in this paper.
Abstract: X-ray, gamma-ray and IR observations of the Galaxy's nucleus show that it contains the densest concentration of stars in the Galaxy, as well as a quantity of ionized gas and warm dust, which is clumped into a small number of rapidly expanding individual clouds whose velocities approach + or - 300 km/sec. The detection of electron-positron anihilation radiation, and a peculiar radio point source very close to the galactic center, add to the belief that the nucleus may contain some unusual object, such as a black hole, which is responsible for the cloud velocities and dust-heating radiation observed. Attention is given to IR intensity contours of the region, as well as a review of the observational evidence for the presence of a black hole. It is noted that a massive black hole fails to account for the unusual ionizing radiation field detected.
24 citations
TL;DR: In this article, a region in the Orion molecular cloud containing NH/sub 3/ and 3''.5 was examined with the high angular and spectral resolution of the VLA and it was shown that two small cloud fragments about 0.05 pc across that rotate rather rapidly and have masses approximating that of normal stars are likely candidates for a stage of cloud development shortly before the formation of low-mass protostars.
Abstract: A region in the Orion molecular cloud containing NH/sub 3/ and 3''.5 north of BN/KL has been examined with the high angular and spectral resolution of the VLA. Observations of the NH/sub 3/(1,1) and (2,2) inverison transitions reveal at least two small cloud fragments about 0.05 pc across that rotate rather rapidly and have masses approximating that of normal stars. Optical depth of the (1,1) transition is tau = 7 and the temperature is about 20 K. These clumps are likely candidates for a stage of cloud development shortly before the formation of low-mass protostars.
24 citations
TL;DR: In this article, the detection of the (J,K) = a(4,3)-s(3,3) rotation-inversion transition of ammonia at 1246 microns toward the center of the Orion-KL region is presented, and it is found to be in emission and has a FWHM greater than or equal to 30 km/s.
Abstract: Results of an investigation are presented which show the detection of the (J,K) = a(4,3)-s(3,3) rotation-inversion transition of ammonia at 1246 microns toward the center of the Orion-KL region The line is found to be in emission and has a FWHM greater than or equal to 30 km/s, while the far-IR ammonia line emission probably comes mainly from the 'hot core', a compact region of warm, very dense gas previously identified by the radio inversion lines of NH3 The a(4,3)-s(3,3) line is very optically thick and it is determined that radiative excitation of the (4,3) NH3 level by far-IR emission from dust within the source can be ruled out It is concluded that the (4,3) level is probably collisionally excited and the gas in the hot core region is warmer than the dust Densities of approximately 10 to the 7th/cu cm are high enough to explain the observations, while shock heating by the mass outflow from IRc2 may account for the high gas temperatures in the hot core region
14 citations