Diluted axion star collisions with neutron stars. Issue 1 (20th January 2022)

• Record Type: Journal Article
• Authors: Bai, Yang; Du, Xiaolong; Hamada, Yuta
• Is Part Of: Journal of cosmology and astroparticle physics. Volume 2022:Issue 1(2022)
• Publication Date: 2022-01-20
• Subjects: axions -- dark matter theory; Cosmology -- Periodicals; Astrophysics -- Periodicals; 523.0105
• DOI: 10.1088/1475-7516/2022/01/041
• Languages: English
• ISSNs: 1475-7516

Abstract

Abstract: Diluted axion star, a self-gravitating object with the quantum pressure balancing gravity, has been predicted in many models with a QCD axion or axion-like particle. It can be formed in the early universe and composes a sizable fraction of dark matter. One could detect the transient radio signals when it passes by a magnetar with the axion particle converted into photon in the magnetic field. Using both numerical and semi-analytic approaches, we simulate the axion star's dynamic evolution and estimate the fraction of axion particles that can have a resonance conversion during such a collision event. We have found that both self-gravity and quantum pressure are not important after the diluted axion star enters the Roche radius. A free-fall approximate can capture individual particle trajectories very well. With some optimistic cosmological and astrophysical assumptions, the QCD axion parameter space can be probed from detecting such a collision event by radio telescopes.