The 2,070th Meeting of the Society

February 21, 1997

The Controversy on the Distance to Gamma Ray Bursters

Jay Norris

NASA Goddard Space Flight Center


President Lettieri called the 2070th meeting to order at 8:20 p.m. on February 21, 1997. The Recording Secretary read the minutes of the 2069th meeting and they were approved. The speaker for the 2070th meeting was Jay Norris, from the NASA Goddard Space Flight Center. The title of his talk was, “The Controversy on the Distance to Gamma Ray Bursters.” With our sky now known to be filled with X-rays, infrared radiation, ultra-violet light and radio waves as well as visible light, Mr. Norris described another element, gamma ray bursters for us. Gamma rays are the most energetic form of radiation and have the shortest wavelength, ranging from 10-11 to 10-13 meters. Imagine looking through a modern astronomical detector as you would look through an old-fashion telescope or set of binoculars. The sky appears utterly black because you are looking into the gamma ray universe and it appears to be empty. Suddenly, there is a brilliant pinprick flash that is gone in an instant. Then nothing is noted for hours, until suddenly you see another flash from somewhere else. After a while you see another from still somewhere else and on and on. These are gamma ray bursters. Mr. Norris advised that astronomers are utterly perplexed by them and they remain one of the great unsolved mysteries of the cosmos. Gamma ray bursters were discovered serendipitously in the 1960's during attempts to detect violations of the Nuclear Test Ban Treaty. The reason they remained undetected for so long is that gamma ray bursters do not make it to the ground and require an orbital detector to be observed. Gamma ray bursters are the brightest, spectrally hardest, celestial transients. They are chaotic and unpredictable, allowing no convincing prediction of coming from a source. As a result, the huge Gamma Ray Observatory, twice as heavy as the Hubbell Telescope and measuring 30' x 15' x 15', was built and launched. It contained a myriad of instruments to detect and monitor gamma ray bursters. The instruments have wonderful names like BATSE (Burst and Transient Source Experiment), GLAST (Gamma Ray Large Area Space Telescope) and EGRET (Energetic Gamma Ray Experiment Telescope). All bursters are different but some have been categorized into specific types such as a fast type that has a rapid 4 millisecond rise and a slower 5 second exponential decay. Bursters that have more structure are brighter and ones that have less structure are dimmer. To date, no known physics can account for gamma ray bursters. Mr. Norris also stated that we probably will not be able to account for them thirty years from now either. They are coming from everywhere and whatever caused a burster must have been destroyed by it. They are not neutron stars and are not galactic. If they are cosmological, they are on the order of the “Big Bang” in power — although not in energy nor in density — and the mystery continues. The ongoing scientific work is directed at finding some counterpart to the gamma ray bursters in one or more of the other radiation spectra. Mr. Norris then closed his presentation and kindly responded to questions from the audience. President Lettieri thanked Mr. Norris for the society and announced the next meeting. He then made the usual parking announcement and adjourned the 2070th meeting to the Social Hour at 9:31 p.m. Attendance: 41 Temperature: 18.1°C Weather: Warm and cloudy Respectfully submitted, Bill Spargo Recording Secretary