Image: TRAVIS MITCHELL/NIST
A tiny crystal lattice may help determine whether certain stars experience shifts in their crusts, new research suggests. Writing in the October 29 issue of Physical Review Letters, Travis Mitchell of the University of Delaware and colleagues describe how a crystal structure reacts under intense pressure that mimics the conditions some scientists predict are present in neutron stars.
The researchers cajoled 15,000 beryllium ions into a disk-shaped crystal lattice (see image), which was cooled to slightly above absolute zero using magnetic and electric fields. Once the disk formed, the team adjusted the surrounding magnetic fields to prevent it from spinning. Next they applied a force to the disk using a laser beam and watched the outcome unfold through a digital camera. Under the additional torque, the crystal lattice cracked, twisted slightly, regenerated and once again locked in place. Such "stick and slip" behavior, the authors write, is found in a variety of systems, including avalanches and earthquakes.
The crystal the team compiled is believed to be structurally similar to the outer crust of a neutron star. According to one astrophysical theory, such stars may experience what scientists have termed starquakes¿very large-scale stick-slips¿as a result of intense magnetic fields pushing outward against their crusts. Soft gamma-ray emissions from neutron stars have recently been reported as evidence for this theory, the authors write, noting that the distribution of the slips seen in their experiment corresponds to those of the gamma-ray observations.