Dec 02 2011
Gamma Ray Burst of Christmas Day 2010
As a comet approaches a neutron star, areas of an intensely strong magnetic field can dissolve parts of the comet. A comet on a direct path that actually collides with the neutron star may penetrate into the neutron lattice, first as a tidal disruption, and then passing through the neutron star and smashing much of it into pieces of a neutron star, along with free neutrons, as it goes. Each free neutron would decay into a proton, an electron, and an antineutrino, around 15 minutes after gaining its freedom. In the case of the sustained gamma ray burst which reached earth on December 25, 2010 from the direction of the Andromeda constellation, before which “a comet or asteroid crashed into a neutron star” [1], antineutrinos would have been among the electromagnetic waves reaching the NASA Swift Burst Alert Telescope [2]. This particular gamma ray burst lasted about one half hour.
Gamma rays emitted as antineutrinos from free neutron decay are often between 15 and 340 keV in energy [3]. The gamma rays that BAT read were in the keV range and have nothing to do with gravity at 313 MeV. The collision would likely have been due to a coincidence of independent path and time since a neutron star that is made up only of neutrons would have no gravitational pull.
[1] http://www.csmonitor.com/Science/2011/1130/The-mystery-of-the-humongous-Christmas-space-explosion
[2] http://swift.gsfc.nasa.gov/docs/swift/about_swift/bat_desc.html
[3] http://www.nature.com/nature/journal/v444/n7122/abs/nature05390.html