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Neutron Star Swaps Lead To Short Gamma-Ray Bursts
Cambridge MA (SPX) Feb 01, 2006 New research suggests that short gamma-ray bursts can be caused by the rematching of pairs of neutron stars. Gamma-ray bursts are the most powerful explosions in the universe, emitting huge amounts of high-energy radiation. Though the phenomena have mystified scientists for a long time, recent studies have shown they seem to originate from two causes: from hypernovas-the explosions of giant stars-or from the collision of neutron stars, either with each other or with a black hole. The new work, however-by Jonathan Grindlay of the Harvard-Smithsonian Center for Astrophysics, and colleagues Simon Portegies Zwart of the Astronomical Institute of The Netherlands and Stephen McMillan of Drexel University in Philadelphia-indicates that neutron star activity within globular clusters is another potential source of the titanic events. "As many as one-third of all short gamma-ray bursts that we observe may come from merging neutron stars in globular clusters," Grindlay said in a statement. Globular clusters contain some of the oldest stars in the universe crammed into a tight space only a few light-years across. Such tight quarters can provoke many close encounters, some of which actually lead to partner swaps. If a neutron star with a companion, such as a white dwarf or Sun-sized star, exchanges its partner with another neutron star, the resulting pair eventually will spiral together and collide explosively, creating a GRB. "We see these precursor systems, containing one neutron star in the form of a millisecond pulsar, all over the place in globular clusters," Grindlay said. "Plus, globular clusters are so closely packed that you have a lot of interactions. It's a natural way to make double neutron-star systems." GRBs occur in two forms: bursts lasting a minute or more, which seem to be caused by hypernovas, and short bursts, sometimes of only a millisecond, which probably originate from neutron-star merges. Grindlay's team performed about 3 million computer simulations to calculate the frequency with which double neutron-star systems can form in globular clusters. Knowing how many have formed over the galaxy's history, and approximately how long it takes for a system to merge, they then determined the frequency of short gamma-ray bursts expected from globular cluster binaries. They estimate between 10 and 30 percent of all short gamma-ray bursts may result from such systems. Community Email This Article Comment On This Article Related Links - Stellar Chemistry, The Universe And All Within It
Two Exiled Stars Are Leaving Our Galaxy Forever
Cambridge MA (SPX) Jan 27, 2006TV reality show contestants aren't the only ones under threat of exile. Astronomers using the MMT Observatory in Arizona have discovered two stars exiled from the Milky Way galaxy. Those stars are racing out of the Galaxy at speeds of more than 1 million miles per hour - so fast that they will never return. |
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