Synopsis: Weighing Models of Neutron Stars

A precise mass measurement of an exotic zinc isotope gives new insight into the composition of the crust of neutron stars, the possible birthplace of heavy elements.
Synopsis figure
NASA/CXC/M. Weiss

Nuclear fusion reactions in stars produce many elements found on Earth, but only those with atomic numbers up to that of iron. Heavier elements may have been created during previous supernova explosions of massive stars, or they may have been somehow ripped from the outer crust of superdense neutron stars that those explosions left behind.

If neutron stars indeed provide the heavy elements, their abundance should reflect the composition of the kilometer-thick crust, which varies rapidly with depth because increasing neutron density favors heavier nuclei. Now, in Physical Review Letters, researchers report precision measurements of the mass of short-lived zinc isotopes, which modify the predicted crust composition. The international team of scientists running the ISOLTRAP experiment at CERN’s radioactive ion-beam facility, ISOLDE, measured the mass of zinc-82 (Zn-82), a neutron-rich isotope that existing models predict is prevalent in the crust of neutron stars. The researchers exploited a new technique to rapidly separate the few desired zinc ions created in a pulse from thousands of others with almost the same mass. They then measured the Zn-82 mass relative to a reference with an accuracy of 40 parts per billion. All of this must be done very quickly, because Zn-82 decays with a half-life of only a quarter of a second.

The new mass measurement supports a revised model of neutron-star crusts in which the zinc-82 is in fact no longer present, but is instead replaced by nickel-78. The revised model also fits nicely with the recent discovery of a particular neutron star that is heavier than would be possible using earlier models. – Don Monroe


Announcements

More Announcements »

Subject Areas

AstrophysicsNuclear Physics

Previous Synopsis

Next Synopsis

Particles and Fields

Waiting for Dark Matter to Light Up

Read More »

Related Articles

Synopsis: Spatial Tests of Dark Matter
Astrophysics

Synopsis: Spatial Tests of Dark Matter

Maps of merging galaxy clusters could help find signatures of dark matter based on its decay into photons. Read More »

Viewpoint: Cavity with Iron Nuclei Slows Down X Rays
Optics

Viewpoint: Cavity with Iron Nuclei Slows Down X Rays

Slow light effects have been measured for x rays using a cavity filled with iron nuclei, where the speed of light was reduced by a factor of 10,000. Read More »

Synopsis: Quakes in Neutron Stars
Astrophysics

Synopsis: Quakes in Neutron Stars

Simulations of the magnetic field of a neutron star show that shear stresses induced by the field are strong enough to fracture the star’s crust. Read More »

More Articles