New insights into pion condensation and the formation of neutron stars

December 21, 2018, RIKEN
Credit: CC0 Public Domain

In 1973, Russian physicist A.B. Migdal predicted the phenomenon of pion condensation above a critical, extremely high—several times higher than that for normal matter— nuclear density. Although this condensation has never been observed, it is expected to play a key role in the rapid cooling process of the core of neutron stars. These city-size heavy stellar objects are so dense that on Earth, one teaspoonful would weigh a billion tons.

Recently, researchers from the RIKEN Nishina Center for Accelerator-Based Science and Kyushu University, performing an experiment at the RIKEN RI Beam Factory on a very -rich tin isotope, investigated whether this process could really occur in neutron stars having the mass of about 1.4 times that of our sun. Similar investigations were conducted previously on , such as 90Zr or 208Pb, but this time the researchers decided to study the case of 132Sn, an isotope of tin. This doubly magic unstable nucleus has a fairly simple structure that makes the theoretical calculations easily compared to other with similar mass. Furthermore, 132Sn with its large neutron excess (it consists of 50 protons and 82 neutrons) provides better conditions than the stable isotopes for extending this study toward the pure neutron matter in the .

A secondary cocktail beam containing 132Sn was produced by projectile fragmentation of a uranium primary beam colliding with thick a beryllium target. Then, a liquid hydrogen target was irradiated with 132Sn. Resulting in the collective excitation of the neutrons and protons of the tin nuclei, with the neutron spin and proton spin oscillating out of phase. This excitation mode, called "giant resonance," is suitable for studying the short-range interactions that, while being crucial in the onset of pion , are complex and extremely difficult to measure.

According to Masaki Sasano from RIKEN Nishina Center, who is one of the first authors of this study, their result, which was published in the Physical Review Letters journal, shows that the pion condensation should occur at around two times normal nuclear density, which can be realized in a neutron star with a mass of 1.4 times that of the sun. Sasano said that in order to understand the possibility of the pion condensation fully, they plan to extend these unique studies of giant resonances to other neutron-rich nuclei that are far beyond the stability line, having large neutron-proton asymmetry.

Explore further: Proton scattering reveals the secrets of strongly-correlated proton-neutron pairs in atomic nuclei

More information: J. Yasuda et al. Extraction of the Landau-Migdal Parameter from the Gamow-Teller Giant Resonance in Sn132, Physical Review Letters (2018). DOI: 10.1103/PhysRevLett.121.132501

Related Stories

ISOLDE mints isotopes of chromium

July 6, 2018

CERN's nuclear physics facility, ISOLDE, has minted a new coin in its impressive collection of isotopes. The facility has forged neutron-rich isotopes of the element chromium for the first time, and in prodigious quantities. ...

Tests confirm nickel-78 is a 'doubly magic' isotope

September 5, 2014

The stability of atoms can vary considerably from one element to the next, and also between isotopes of the same element (whose nuclei contain the same number of protons but different numbers of neutrons). While many isotopes ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

Physicists reveal why matter dominates universe

March 21, 2019

Physicists in the College of Arts and Sciences at Syracuse University have confirmed that matter and antimatter decay differently for elementary particles containing charmed quarks.

ATLAS experiment observes light scattering off light

March 20, 2019

Light-by-light scattering is a very rare phenomenon in which two photons interact, producing another pair of photons. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.