Black hole formation from axion stars
Abstract
The classical equations of motion for an axion with potential V (φ)= m {sub a} {sup 2} f {sub a} {sup 2} [1−cos (φ/ f {sub a} )] possess quasistable, localized, oscillating solutions, which we refer to as ''axion stars''. We study, for the first time, collapse of axion stars numerically using the full nonlinear Einstein equations of general relativity and the full nonperturbative cosine potential. We map regions on an ''axion star stability diagram', parameterized by the initial ADM mass, M {sub ADM}, and axion decay constant, f {sub a} . We identify three regions of the parameter space: i) longlived oscillating axion star solutions, with a base frequency, m {sub a} , modulated by selfinteractions, ii) collapse to a BH and iii) complete dispersal due to gravitational cooling and interactions. We locate the boundaries of these three regions and an approximate ''triple point' ( M {sub TP}, f {sub TP}) ∼ (2.4 M {sub pl}{sup 2}/ m {sub a} ,0.3 M {sub pl}). For f {sub a} below the triple point BH formation proceeds during winding (in the complex U(1) picture) of the axion field near the dispersal phase. This could prevent astrophysical BH formation from axion starsmore »
 Authors:
 King's College London, Strand, London, WC2R 2LS (United Kingdom)
 Instituto de Física y Matemáticas, Universidad Michoacana de San Nicolás de Hidalgo, Ciudad Universitaria, CP 58040 Morelia, Michoacán (Mexico)
 Publication Date:
 OSTI Identifier:
 22679944
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 03; Other Information: Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; ASTROPHYSICS; AXIONS; BLACK HOLES; DECAY; EINSTEIN FIELD EQUATIONS; EQUATIONS OF MOTION; GENERAL RELATIVITY THEORY; INTERACTIONS; MASS; NONLINEAR PROBLEMS; QUANTUM CHROMODYNAMICS; SPACE; STABILITY; STARS
Citation Formats
Helfer, Thomas, Marsh, David J.E., Clough, Katy, Fairbairn, Malcolm, Lim, Eugene A., and Becerril, Ricardo, Email: thomas.1.helfer@kcl.ac.uk, Email: david.marsh@kcl.ac.uk, Email: katy.clough@phys.unigoettingen.de, Email: malcolm.fairbairn@kcl.ac.uk, Email: eugene.lim@kcl.ac.uk, Email: becerril@ifm.umich.mx. Black hole formation from axion stars. United States: N. p., 2017.
Web. doi:10.1088/14757516/2017/03/055.
Helfer, Thomas, Marsh, David J.E., Clough, Katy, Fairbairn, Malcolm, Lim, Eugene A., & Becerril, Ricardo, Email: thomas.1.helfer@kcl.ac.uk, Email: david.marsh@kcl.ac.uk, Email: katy.clough@phys.unigoettingen.de, Email: malcolm.fairbairn@kcl.ac.uk, Email: eugene.lim@kcl.ac.uk, Email: becerril@ifm.umich.mx. Black hole formation from axion stars. United States. doi:10.1088/14757516/2017/03/055.
Helfer, Thomas, Marsh, David J.E., Clough, Katy, Fairbairn, Malcolm, Lim, Eugene A., and Becerril, Ricardo, Email: thomas.1.helfer@kcl.ac.uk, Email: david.marsh@kcl.ac.uk, Email: katy.clough@phys.unigoettingen.de, Email: malcolm.fairbairn@kcl.ac.uk, Email: eugene.lim@kcl.ac.uk, Email: becerril@ifm.umich.mx. Wed .
"Black hole formation from axion stars". United States.
doi:10.1088/14757516/2017/03/055.
@article{osti_22679944,
title = {Black hole formation from axion stars},
author = {Helfer, Thomas and Marsh, David J.E. and Clough, Katy and Fairbairn, Malcolm and Lim, Eugene A. and Becerril, Ricardo, Email: thomas.1.helfer@kcl.ac.uk, Email: david.marsh@kcl.ac.uk, Email: katy.clough@phys.unigoettingen.de, Email: malcolm.fairbairn@kcl.ac.uk, Email: eugene.lim@kcl.ac.uk, Email: becerril@ifm.umich.mx},
abstractNote = {The classical equations of motion for an axion with potential V (φ)= m {sub a} {sup 2} f {sub a} {sup 2} [1−cos (φ/ f {sub a} )] possess quasistable, localized, oscillating solutions, which we refer to as ''axion stars''. We study, for the first time, collapse of axion stars numerically using the full nonlinear Einstein equations of general relativity and the full nonperturbative cosine potential. We map regions on an ''axion star stability diagram', parameterized by the initial ADM mass, M {sub ADM}, and axion decay constant, f {sub a} . We identify three regions of the parameter space: i) longlived oscillating axion star solutions, with a base frequency, m {sub a} , modulated by selfinteractions, ii) collapse to a BH and iii) complete dispersal due to gravitational cooling and interactions. We locate the boundaries of these three regions and an approximate ''triple point' ( M {sub TP}, f {sub TP}) ∼ (2.4 M {sub pl}{sup 2}/ m {sub a} ,0.3 M {sub pl}). For f {sub a} below the triple point BH formation proceeds during winding (in the complex U(1) picture) of the axion field near the dispersal phase. This could prevent astrophysical BH formation from axion stars with f {sub a}  M {sub pl}. For larger f {sub a} ∼> f {sub TP}, BH formation occurs through the stable branch and we estimate the mass ratio of the BH to the stable state at the phase boundary to be O(1) within numerical uncertainty. We discuss the observational relevance of our findings for axion stars as BH seeds, which are supermassive in the case of ultralight axions. For the QCD axion, the typical BH mass formed from axion star collapse is M {sub BH} ∼ 3.4 ( f {sub a} /0.6 M {sub pl}){sup 1.2} M {sub ⊙}.},
doi = {10.1088/14757516/2017/03/055},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 03,
volume = 2017,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2017},
month = {Wed Mar 01 00:00:00 EST 2017}
}

There is mounting evidence for the coevolution of galaxies and their embedded massive black holes (MBHs) in a hierarchical structure formation paradigm. To tackle the nonlinear processes of galaxyMBH interaction, we describe a selfconsistent numerical framework which incorporates both galaxies and MBHs. The highresolution adaptive mesh refinement (AMR) code Enzo is modified to model the formation and feedback of molecular clouds at their characteristic scale of 15.2 pc and the accretion of gas onto an MBH. Two major channels of MBH feedback, radiative feedback (Xray photons followed through full threedimensional adaptive ray tracing) and mechanical feedback (bipolar jets resolved inmore »

GALAXY FORMATION WITH SELFCONSISTENTLY MODELED STARS AND MASSIVE BLACK HOLES. I. FEEDBACKREGULATED STAR FORMATION AND BLACK HOLE GROWTH
There is mounting evidence for the coevolution of galaxies and their embedded massive black holes (MBHs) in a hierarchical structure formation paradigm. To tackle the nonlinear processes of galaxyMBH interaction, we describe a selfconsistent numerical framework which incorporates both galaxies and MBHs. The highresolution adaptive mesh refinement (AMR) code Enzo is modified to model the formation and feedback of molecular clouds at their characteristic scale of 15.2 pc and the accretion of gas onto an MBH. Two major channels of MBH feedback, radiative feedback (Xray photons followed through full threedimensional adaptive ray tracing) and mechanical feedback (bipolar jets resolved inmore » 
THE PROPERTIES OF HYPERVELOCITY STARS AND SSTARS ORIGINATING FROM AN ECCENTRIC DISK AROUND A SUPERMASSIVE BLACK HOLE
Hypervelocity stars (HVSs), which are observed in the Galactic halo, are believed to be accelerated to large velocities by a process of tidal disruption of binary stars passing close to the supermassive black hole (SMBH) which resides in the center of the Galaxy. It is, however, still unclear where these relatively young stars were born and what dynamical process pushed them to nearly radial orbits around the SMBH. In this paper we investigate the possibility that the young binaries originated from a thin eccentric disk, similar to the one currently observed in the Galactic center. By means of direct Nmore » 
Collapse of differentially rotating supermassive stars: Post black hole formation
We investigate the collapse of differentially rotating supermassive stars (SMSs) by means of 3+1 hydrodynamic simulations in general relativity. We particularly focus on the onset of collapse to understand the final outcome of collapsing SMSs. We find that the estimated ratio of the mass between the black hole and the surrounding disk from the equilibrium star is roughly the same as the results from numerical simulation. This suggests that the picture of axisymmetric collapse is adequate, in the absence of nonaxisymmetric instabilities, to illustrate the final state of the collapse. We also find that quasiperiodic gravitational waves continue to bemore »