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


Features

More Features »

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: Self-Interacting Dark Matter Scores Again
Cosmology

Synopsis: Self-Interacting Dark Matter Scores Again

Dark matter that interacts with itself provides a better description of the speeds of stars in galaxies than dark matter that doesn’t self-interact. Read More »

Synopsis: Searching for Neutron Star Gravitational Waves
Astrophysics

Synopsis: Searching for Neutron Star Gravitational Waves

The first run of LIGO and Virgo’s gravitational-wave search shows no evidence of spinning asymmetric neutron stars, but recent upgrades could make the detection possible. Read More »

Synopsis: Strong Force Calculations for Weak Force Reactions
Nuclear Physics

Synopsis: Strong Force Calculations for Weak Force Reactions

Theorists have used lattice-QCD calculations to predict two weak-force-driven reactions—proton fusion and tritium decay. Read More »

More Articles