Accreting Neutron Stars

Background

Neutron stars are among the most fascinating and elusive astronomical objects. They are the densest form of matter naturally occuring in the cosmos - a tablespoon of neutron star matter has a weight comparable to about 3,000 aircraft carriers.

Accreting neutron star. more

The best natural laboratories to study neutron stars are X-ray binaries. X-ray binaries are stellar systems where a neutron star orbits a regular companion star, sucks matter from its companion onto its surface, and fuses this matter into a heavy element in huge thermonuclear explosions. The explosion creates a strong X-ray radiation that can be observed by space-based observatories (Fortunately, it is absorbed in the Earth's atmosphere).

Huge amounts of observational data are collected by new observatories like Rossi X-ray Timing Explorer or Chandra X-ray Observatory. This data might provide new clues about the nuclear reactions occuring on the neutron star surface or deeper in the neutron star crust where elements are transformed into neutrons. These nuclear processes generate the energy that can be observed as X-ray radiation. They might create a few Ruthenium and Molybdenum isotopes that might escape from the neutron star and, therefore, could explain the mysterious enrichment of these isotopes in our solar system and on Earth.

The Role of NSCL

However, to a large extent we don't know what these nuclear processes are like. The main problem in understanding the nuclear processes on and in neutron stars in X-ray binaries is that the nuclei involved are very exotic species. These exotic nuclei decay within fractions of seconds, so we know very little about them.

NSCL is able to produce many of the critical nuclei in larger quantities than can any other facility. This allows us to measure many of the properties that are needed to correctly model the nuclear processes, such as the decay rate, weight, and size.

NSCL scientists also are involved in running computer models of the thermonuclear explosions occuring on the surface of neutron stars. This allows us to determine the critical nuclei that need to be studied and to explore the consequences of our new experimental results.