By analyzing X rays generated by the rumblings of a neutron star 40,000 light-years from Earth, astronomers have estimated the thickness of the dense star's crust.
In December 2004, spacecraft including NASA's Rossi X-ray Timing Explorer detected the brightest X-ray flash ever seen from beyond the solar system (SN: 2/26/05, p. 132: Available to subscribers at Big Flash: Record-breaking explosion in outer space). The radiation came from an explosion on the neutron star SGR 1806-20.
Intensity fluctuations within the flash were probably generated by seismic vibrations traveling along different paths within the star's iron crust, according to astronomers led by Tod Strohmayer of NASA's Goddard Space Flight Center in Greenbelt, Md. X rays of some frequencies would have come from seismic waves on twisting paths around the star's circumference, while other X rays were probably generated by vibrations on a more direct path through the crust.