EVEN a material 10 billion times as strong as steel has a
breaking point. It seems neutron stars may shatter under extreme
forces, explaining puzzling X-ray flares. Neutron stars are
dense remnants of stars gone supernova, packing the mass of the
sun into a sphere the size of a city. Their cores may be fluid,
but their outer surfaces are solid and extremely tough - making
graphene, the strongest material on Earth, look like tissue
paper by comparison. These shells may shatter, though, in the
final few seconds before a pair of neutron stars merges to form
a black hole - a union thought to generate explosions known as
short gamma-ray bursts. David Tsang of the California Institute
of Technology in Pasadena and colleagues have calculated how the
mutual gravitational pull of such stars will distort their
shape, creating moving tidal bulges. As the stars spiral towards
each other, orbiting ever faster, they squeeze and stretch each
other ever faster too. A few seconds before the stars merge, the
frequency of this