An international team of astronomers has found that extraordinary large loops of matter around the galaxy NGC 5907 are the relic of a gigantic collision between galaxies of similar sizes, which would have occurred 8 to 9 billion years ago.
NGC 5907 galaxy (left) and result of the simulations (Jay Gabany, cosmotography.com / Observatoire de Paris / CNRS / Pythéas / NAOC)
NGC 5907 is a spiral galaxy lying in the constellation Dragon, showing gigantic loops and currents of stars in its surrounding halo.
Previously these 150 000 light-years loops were believed to be associated with the capture of a very small satellite galaxy that would have lost its matter relatively recently.
Now, on the basis of simulations with 200 thousands to 6 million particles, astronomers of the Paris Observatory, National Astronomical Observatories of China (NAOC) and Aix-Marseille Université has proposed new scenario.
Their results, published online in the journal Astronomy and Astrophysics, suggest that these loops are the relic of a gigantic collision between galaxies of similar size.
Numerical simulations have been made using 32- and 196-core computers at the Paris Observatory Center and the 680-core Graphic Processor Unit supercomputer at Beijing NAOC with the capability to run 50000 billion operations per second.
“This study shows that a major merger scenario for the formation of giant loops in NGC 5907 may explain the observations, as well as the infall of a minor merger with a mass ratio lower than 12:1,” the team wrote.
“Together with the rebuilding of a thin disc in an almost bulge-less galaxy, a gas-rich major merger forms gigantic loops, within which stars may orbit in loops for several billion years. Low-mass ratios down to three are particularly efficient in removing the residuals of the secondary interloper, and are still consistent with the observational uncertainties on the bulge-to-total mass ratio. This is especially true when high order loops are considered, several billion years after the merger.”
“Interestingly, our model of NGC 5907 can be falsified by new and extremely deep observations of a wider field surrounding this galaxy,” the astronomers concluded. “If NGC 5907 has been formed by a major merger, there should be faint and extremely large structures at hundred kilo-parsecs or more, coinciding with lower order loops.”
