Ringing up another light echo.Ringing up another light echo A light echo is a phenomenon observed in astronomy. Analogous to an echo of sound, a light echo is produced when a sudden flash or burst of light, such as that observed in novae, is reflected off a source and arrives at the viewer some time after the initial flash. Although supernova supernova, a massive star in the latter stages of stellar evolution that suddenly contracts and then explodes, increasing its energy output as much as a billionfold. 1987A, located in the Large Magellanic Cloud Noun 1. Large Magellanic Cloud - the larger of the two Magellanic Clouds visible from the southern hemisphere Magellanic Cloud - either of two small galaxies orbiting the Milky Way; visible near the south celestial pole about 160,000 light-years from Earth, has been fading since the spring of 1987, astronomers Famous astronomers and astrophysicists include: Directory: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A
adj. Between or among the stars: interstellar gases. interstellar Adjective between or among stars Adj. 1. dust, taking a somewhat longer time to complete its journey than visible light coming directly from the supernova. Such a feature is known as a light echo. Last year, astronomers reported observing two glowing light-echo rings approximately centered on the supernova (SN: 6/18/88, p.388). Now, Howard E. Bond and his colleagues at the Space Telescope Science Institute The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST; in orbit since 1990) and for the James Webb Space Telescope (JWST; scheduled to be launched in 2013). in Baltimore report discovery of a third ring inside the other two. Whereas the previously discovered rings appear to correspond to two separate sheets of dust about 1,000 light-years and 400 light-years in front of the supernova as seen from the Earth, the newly observed ring suggests the presence of dust lying only 20 light-years from the supernova. Because there was no sign of the third ring in earlier observations, the researchers, conclude there is apparently a cavity or bubble in the material surrounding the supernova, at least in the direction of the Earth. Other astronomers have already confirmed the presence of this new light-echo feature and continue to monitor changes in the other two rings. Because the echoes have retained their near-circular shapes, astronomers suspect the interstellar dust must be highly concentrated into two layers. Furthermore, the very small deviations from a circular form impose tight constraints on the curvature and inclination of these dust sheets. |
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