http://www.spacedaily.com/news/gamma-04h.html
The universe was regarded even until the early 20th century as a stable and eternal place, but evidence collected in the intervening years has shown the cosmos is anything but placid. It is seething with activity, some of it entirely hostile to life. One piece of that evidence concerns phenomena known as gamma-ray bursts, which are extremely powerful explosions now thought to be detonated by the birth of black holes. Just as particle accelerators can produce more energy in a microsecond than the electric power the entire country uses in a year, for a brief time, gamma-ray bursts - or GRBs, as astronomers call them - shine more brightly than entire clusters of galaxies. As powerful as they are, GRBs are elusive. They often last less than 1 second and no longer than a few minutes - a characteristic that has presented a challenge to astronomers wishing to study them. The problem involves communication and reaction time. Earth-based observers must first communicate to the world's astronomy instruments - telescopes and detectors of every wavelength - that a GRB has been spotted. Then the instruments must separate from their current objectives and refocus on the appropriate area of the sky. Because the burst disappear so quickly, the process is rarely successful. So, NASA has launched a nimble spacecraft called Swift that is designed to help capture data about GRBs and their possible relationship to black holes. Blasting off atop a Boeing Delta II rocket from Cape Canaveral, Fla., last Saturday, Swift is a multi-wavelength observatory - meaning it can watch for GRBs and afterglows in the gamma-ray, X-ray, ultraviolet and optical wavebands simultaneously. Swift will use three onboard telescopes that can quickly identify and monitor the wavelengths of gamma-ray bursts, which are estimated to occur somewhere in space at least once a day. The spacecraft can respond within about a minute or less after it detects a GRB. First, it rotates to the proper position so its onboard telescopes can view the burst. Then it monitors the afterglow, which can continue emitting X-rays, optical light and radio waves for periods lasting up to several weeks. Swift also notifies several other companion telescopes worldwide that can react quickly to join the study. Swift caps off a 30-year hunt to understand the nature of gamma-ray bursts, flashes of light that burn as brightly as a billion-billion suns, said Anne Kinney, director of NASA's Universe Division in Washington. We expect to detect and analyze over 100 gamma-ray bursts a year, said Neil Gehrels, Swift's principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Md. What scientists eventually will find from those detections and analyses remains speculative. The link between some GRBs and black hole formation seems solid, but the bursts also could be caused by two neutron stars merging or even a pair of black holes orbiting each other. Hence, one of Swift's missions is to determine whether GRBs produce different energy levels. Some bursts likely originate from the farthest reaches, and hence earliest epoch, of the universe, said John Nousek, Swift's mission director and a professor of astronomy and astrophysics at Penn State University. Swift's Mission Operations Center is located at PSU campus in University Park, Pa. They act like beacons shining through everything along their paths, including the gas between and within galaxies along the line of sight, Nousek said. Another of Swift's primary missions will be to watch for GRBs that might originate within the Milky Way galaxy. On that question, the interest might be more than purely scientific. Astronomers suspect that a powerful burst occurred here just a few thousand years ago, from W49B, a supernova remnant only 35,000 light-years away. At one time, W49B was a supermassive star that blew itself up, then collapsed into a black hole. The question is whether it, too, created a burst in the process. The nearest known gamma-ray burst to Earth is several million light years away -- most are billions of light years distant - so the detection of the remnant of one in our own galaxy would be a major breakthrough, said William Reach of the California Institute of Technology. W49B is barrel-shaped and ringed by bright, hoop-like structures that can be seen in the infrared range of light. It also exhibits intense X-ray emissions produced by concentrations of iron and nickel ions along the axis of the barrel. This makes it a prime candidate for being the remnant of a gamma-ray burst, said Jonathan Keohane of NASA's Jet Propulsion Laboratory in Pasadena, Calif. At this distance, the structure is a comfortable curiosity. That would not be the case if Earth's solar system was located, say, within a few hundred light-years of W49B. Then, the X-ray jets would blind observers on Earth and orbiting spacecraft alike with radiation equivalent to 10 quadrillion suns. Which raises the question: What if a burst did happen that close to Earth? History provides one clue. A paper presented earlier this year by Adrian Melott of the University of Kansas Department of Physics and Astronomy, suggests a mass extinction that occurred during the late Ordovician period, about 440 million years ago, could have been caused by a GRB. Due to expected severe depletion of the ozone layer, intense solar ultraviolet radiation would result from a nearby GRB, Melott wrote. Some of the patterns of extinction and survivorship at this time may be attributable to elevated levels of UV radiation reaching the Earth. In addition, a GRB could trigger the global cooling which occurs at the end of the Ordovician period that follows an interval of relatively warm climate. Intense rapid cooling and glaciation at that time, previously identified as the probable cause of this mass extinction, may have resulted from a GRB. A discussion of such effects is hardly academic, because there is at least one nearby star that might be big enough to collapse into a black hole someday. Betelgeuse, located about 400 light-years away and occupying the constellation Orion's right shoulder - and easily visible in the sky in the fall and winter in the northern hemisphere -- is a red giant more than 600 times wider than the sun. If the two switched places, Betelgeuse's surface would swallow up Earth and the inner planets and reach almost to Mars. Though a relatively young star, Betelgeuse also is aging very rapidly. The sun has an estimated remaining life expectancy of 4 billion or more years, but Betelgeuse may not make it through the next 5 million. As red giants do, it is consuming its nuclear fuel so fast it will not be able to resist the pull of gravity much longer. When that happens, Earth-based observers will know, because Betelgeuse will destroy itself in a supernova explosion, which will be visible here even in daylight. The question is whether Betelgeuse has enough mass to collapse into a black hole and cause a gamma-ray burst. It is an important distinction. Debris - in the form of gas and particles - from the supernova could cause problems on Earth, but not for hundreds or thousands of years after the light from the explosion arrived. Humanity would have some time to prepare. In the case of a GRB, however, the radiation would arrive at the same time as the light. Unless deep space outposts of the time gave some warning, the event could come as a rude awakening. A case of severe disruption in the stellar neighborhood. xponent Ouchies Maru rob _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
