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View Full Version : 'Little' Gamma Ray Bursts Really Do Exist



Fraser
2008-Oct-13, 03:40 PM
Gamma-ray bursts (GRBs) are powerful blasts of energy that flash across the Universe. For a brief time, they are the brightest objects in the gamma-ray sky. Astronomers estimate that about 1,400 GRBs per year occur but because no one knows when and where they are going to appear, only a part of them happen [...]

More... (http://www.universetoday.com/2008/10/13/little-gamma-ray-bursts-really-do-exist/)

trinitree88
2008-Oct-13, 06:50 PM
Gamma-ray bursts (GRBs) are powerful blasts of energy that flash across the Universe. For a brief time, they are the brightest objects in the gamma-ray sky. Astronomers estimate that about 1,400 GRBs per year occur but because no one knows when and where they are going to appear, only a part of them happen [...]

More... (http://www.universetoday.com/2008/10/13/little-gamma-ray-bursts-really-do-exist/)

Fraser. Interesting. Note that the distribution is concentrated around the galactic plane of the Milky Way, all 11, unlike the relatively isotropic distribution of the strong bursts. There is a likely reason for that. Circulating neutron stars. Estimates of neutron star populations in the halos of galaxies runs to ~10,000 on up to ~ 100,000.
Like Cepheid variables, whose longitudinal axes of pulsation tend to be aligned, perpendicular to their host galaxy's plane, supernovae progenitors are similarly aligned. Type 2 core collapse supernovae only give a small proportion of their pulsars sufficient kick velocity to completely escape their host galaxies, so the remainder are gravitationally bound, circulating out to ~ 400 kiloparsecs, and then returning. During their collective orbits, they pass through the galactic plane where it's dustier and full of more small bodies. Interactions of neutron stars with such debris can create a fireworks show of small gamma bursts. These should occur most frequently where the debris is, and give a distribution concentrated around the galactic plane as is seen.
What's scarier...(approaching Halloween)...is that one of the pieces of debris, is us. Though statistically unlikely given the volume of "empty" space in the galaxy, and the relatively low frequency of pulsar passages, it is part of the physics of pulsar ejection velocities. What would confirm this scenario is a slow drift of position from a repeating weak burst emitter.
"Gamma Ray Bursts...A Halo of Neutron Stars at 400 Kiloparsecs?, Harvard University, AAPT Meeting, 1994, Olney Science Center. The Matt Damon & Ben Affleck in the back row talk. pete