Angular momentum and the absence of vortices in the cores of fuzzy dark matter haloes
- Author(s)
- Sonja Ornella Schobesberger, Tanja Rindler-Daller, Paul R Shapiro
- Abstract
Scalar field dark matter (SFDM), comprised of ultralight (≳ 1022 eV) bosons, is distinguished from massive (≳GeV), collisionless cold dark matter (CDM) by its novel structure-formation dynamics as Bose–Einstein condensate (BEC) and quantum superfluid with wave-like properties, described by the Gross-Pitaevskii and Poisson (GPP) equations. In the free-field (‘fuzzy’) limit of SFDM (FDM), structure is inhibited below the de Broglie wavelength λdeB, but resembles CDM on larger scales. Virialized haloes have ‘solitonic’ cores of radius ∼λdeB that follow the ground-state attractor solution of GPP, surrounded by CDM-like envelopes. As superfluid, SFDM is irrotational (vorticity-free) but can be unstable to vortex formation. We previously showed this can happen in halo cores, from angular momentum arising during structure formation, when repulsive self-interaction (SI) is present to support them out to a second length scale λSI with λSI > λdeB (the Thomas–Fermi regime), but only if SI is strong enough. This suggested FDM cores (without SI) would not form vortices. FDM simulations later found vortices, but only outside halo cores, consistent with our previous suggestion based upon TF-regime analysis. We extend that analysis now to FDM, to show explicitly that vortices should not arise in solitonic cores from angular momentum, modelling them as either Gaussian spheres, or ( n = 2)-polytropic, irrotational Riemann-S ellipsoids. We find that, for typical halo spin parameters, angular momentum per particle is below ℏ, the minimum required even for one singly-quantized vortex in the centre. Even for higher angular momentum, however, vortex formation is not energetically favoured.
- Organisation(s)
- Department of Mathematics, Department of Astrophysics
- External organisation(s)
- University of Texas, Austin
- Journal
- Monthly Notices of the Royal Astronomical Society
- Volume
- 505
- Pages
- 802–829
- ISSN
- 0035-8711
- Publication date
- 05-2021
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 103004 Astrophysics
- Keywords
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/c5dad982-e940-4546-b005-b6f78b41435a