The possibility of occurrence of a small galaxy GRB.

<P Align=center> </ P> <P> 4.4 billion years ago, no one knows exactly how the terrible events occurred, so that about 85% of species disappeared from the earth. .Astronomers put forward the hypothesis of lethal radiation, and now the unprecedented predicament. .</ P> <P> "In fact, the galaxy's environment may protect the earth, so that life on Earth from radiation caused by disaster." NASA's Swift Number (Swift) detector Nepal, chief scientist .Seoul • Gairui Si (Neil Gehrels) 7 月 18 at the 36th World Conference on Space Science, said. .He said that when the earth around the GRB occurred within 6000 light years, the radiation may have on Earth caused a fatal blow, but fortunately, such a gamma ray burst is unlikely to occur in the Milky Way .. .</ P> <P> GRB is called "Supernova," the objects in the course of the outbreak of two poles from the high-energy gamma rays given phenomenon. .Or, when two neutron stars collide, they may produce GRBs. ."For the short GRBs, we believe that from the neutron star collision, although it is less certain." Gai Ruisi said. .</ P> <P> astronomer at the University of Kansas Adelaide Lee • Mak steam drian Melott Feng years ago suggests that the Earth's mass extinctions may be the first to attack from the GRB. .He believes that, 4.4 billion years ago destroyed a GRB of biological protection of Earth's ozone layer, so that the intensity of ultraviolet light under normal conditions reached more than 50 times, which killed many animals living in shallow water. .Moreover, this further induced ice age creatures living environment makes matters worse, a large number of species could not escape unscathed. .</ P> <P> Although Mak insisted today his views, but more and more evidence seems to reduce the possibility of this happening is zero. .</ P> <P> disaster possibilities </ P> <P> astronomical, which lasted more than two seconds of the GRB is known as long GRBs. .Gairui Si and his colleagues found that, if issued by the supernova magnetic GRB lasted just 10 seconds of exposure to the earth, the world's stratospheric ozone by 35%, some height up to 55%, and this reduction of at least .In the five years will not be restored. .At this time, by the ultraviolet radiation on the ground under normal circumstances will reach three times, which is likely to cause widespread extinction. .</ P> <P> the other hand, Swift lifted off more than a year's observation of GRB seems to imply that such events hardly occur in the earth. .Because, Swift number of long gamma-ray observations mainly from the low-metallicity galaxy, the Milky Way is not included. .</ P> <P> Astronomers usually hydrogen, helium and lithium as the metal elements other than the elements, while the star or galaxy is metal elements to their metallic content. .</ P> <P> "I do not know how the metal of the work, but our observations do suggest that the GRB and the link between the metal." Gai Ruisi said after the meeting. .As the metal of the Milky Way is much higher than those long GRBs occur in galaxies, so this may be a safe signal. .</ P> <P> "Swift observations of the number of all GRBs of people working in the field." Ohio State University astronomer Christopher • Vista Naik (Krzysztof Stanek) 7 .24 said, "For example, there are many more GRBs are well defined position." </ P> <P> three months ago, Starr and his colleagues have published papers Nike said .They are four long GRB studies show that these GRBs occur in low-metallicity galaxies, and this GRB in the Milky Way in the probability of occurrence of less than 0.15%. .</ P> <P> "at least in the past few billion years, the Milky Way's metal too rich, so can not produce long GRBs." Vista Naik writes in the paper. .</ P> <P> </ p>.