Distributions and Collision Rates of ALP Stars in the Milky Way
arxiv(2024)
摘要
We apply current analytical knowledge on the characteristic mass and linear
evolution of miniclusters down to redshift z=0 to the hypothetical
minicluster distribution of the Milky Way. Using the mass-radius relation and a
core-halo relation for stable soliton solutions composed of axion-like
particles (ALPs), we connect the galactic minicluster mass distribution to that
of their ALP star cores. We consider different temperature evolutions of the
ALP field with masses in the range 10^-12 eV≤ m_a ≤
10^-3eV and infer the abundance and properties of QCD axion- and ALP stars
in our galaxy. We re-evaluate detection prospects for collisions of neutron
stars with both ALP stars and miniclusters as well as relativistic ALP bursts,
so-called Bosenovae. Our analysis shows that the collision rates between
miniclusters and neutron stars can become as large as ∼ 10^5yr^-1
galaxy^-1, but that the fraction of encounters that can lead to resonance
between ALP mass and magnetosphere plasma frequency is generally well below
∼ 1yr^-1 galaxy^-1, depending on the ALP model. We confirm
previous results that merger rates of ALP stars are extremely small <
10^-12yr^-1 galaxy^-1, while their host miniclusters can merge
much more frequently, up to ∼ 10^3yr^-1 galaxy^-1 for the QCD
axion. We find that Bosenovae and parametric resonance are much more likely to
lead to observable signatures than neutron star encounters. We also suggest
that a combination of accretion and parametric resonance can lead to observable
radio lines for a wide range of ALP masses m_a and photon-couplings
g_aγγ.
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