Constraining ultralight bosonic dark matter with Keck observations of S2's orbit and kinematics

Constraining ultralight bosonic dark matter with Keck observations of S2’s orbit and kinematics

Guan-Wen Yuan, Zhao-Qiang Shen, Yue-Lin Sming Tsai, Qiang Yuan, and Yi-Zhong Fan

Phys. Rev. D 106, 103024 – Published 18 November 2022

Abstract

Ultralight bosonic dark matter is expected to be able to form a cloud surrounding the supermassive black hole (SMBH) in the Galactic center. With increasing precision of the observations of the stellar kinematics around the SMBH, tiny effects from such a dark matter cloud, including its gravitational perturbation and the direct coupling with the ordinary matter may be detectable. In this work, we search for possible evidence of the scalar cloud using accurate orbital measurements of the S2 star around Sgr $A^{*}$ . We solve the first order post-Newtonian equation, considering simultaneously the extended mass distribution of the scalar cloud and the frequency shift induced by the additional coupling via Higgs portal or photon portal interaction. Furthermore, we also investigate the impact of an astrophysical power-law component from the gas and stellar remnants. We find that the astrometric and spectroscopic data of the S2 star are well consistent with the scenario of a pointlike mass of Sgr $A^{*}$ . We thus derive upper limits of the coupling of the new interaction and the extended mass, with and without the contribution from the astrophysical component. The limits of the Higgs/photon coupling and the extended mass of the scalar cloud are the most stringent ones for the scalar mass window between $3.2 \times 10^{- 19} eV$ and $1.6 \times 10^{- 18} eV$ .

Received 16 May 2022
Accepted 31 October 2022

DOI:https://doi.org/10.1103/PhysRevD.106.103024

Physics Subject Headings (PhySH)

Particle dark matter

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Guan-Wen Yuan ^1,2, Zhao-Qiang Shen ^1,*, Yue-Lin Sming Tsai ^1,†, Qiang Yuan ^1,2, and Yi-Zhong Fan ^1,2

¹Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China
²School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, China

^*zqshen@pmo.ac.cn
^†smingtsai@pmo.ac.cn

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 106, Iss. 10 — 15 November 2022

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
The density distribution of scalar cloud around Sgr $A^{*}$ . Gray region is the distance covered by the S2 orbit, and the scalar field mass $μ_{s} = 3.2 \times 10^{- 19}$ , $5.0 \times 10^{- 19}$ , $1.0 \times 10^{- 18}$ , $1.6 \times 10^{- 18}$ , $3.2 \times 10^{- 18} eV$ are also shown with blue, red, purple black, and green lines, respectively. The vertical black dotted line shows corresponds to the innermost stable circular orbit of Sgr $A^{*}$ . We fix the mass of the scalar cloud as $4 \times 10^{3} M_{⊙}$ (corresponding to $κ \sim 0.001$ ).
Reuse & Permissions
Figure 2
Definition of the coordinate systems, whose axes originate from Sgr $A^{*}$ , and projection of S2 orbit onto the plane of the sky. The picture shows an illustration of the S2 star orbital parameters: $θ$ is the azimuth angle of the spherical system of coordinates associated with the $x$ , $y$ , and $z$ Cartesian coordinates. For an elliptic motion in the $x - y$ plane, the two coordinates (red and blue) associated with each other via three Euler rotations: $I$ is the angle of inclination between the S2 orbit and the observation plane, $Ω$ is the angle of the ascending node, and $ω$ is the argument of pericenter. It is worth mentioning that the $Z$ -axis of the coordinate system is defined by the vector pointing from the Galactic center to the solar system.
Reuse & Permissions
Figure 3
The theoretical and observed orbit of S2 star around Sgr $A^{*}$ . The theoretical fitting models are calculated by solving the equation of motion Eq. (30). The upper left panel presents the 45 astrometric measurements of the S2 star orbit around Sgr $A^{*}$ , overlaid with our best-fitting projected orbit in the plane of the sky. The black star is the place of Sgr $A^{*}$ , and the axes of R.A. and Dec. correspond to offset in right ascension and declination, respectively. The upper right panel shows RV measurements and the best-fitting RV model using 115 RV measurements from 2000–2018. Residuals from the best-fitting RV model and error bars indicate $1 σ$ uncertainties. The two panels at the bottom show the R.A. and Dec. as a function of time and their respective residuals. Here, we use the observational data reported by Keck Observatory in [31], and the best-fit parameters of the Higgs portal given in the third column of Table 1. The corner of parameters has also presented in Fig. 6 in the Appendix.
Reuse & Permissions
Figure 4
The 95% credible exclusion upper limits of the Higgs portal and photon portal coupling constants, without (solid) and with (dashed) the additional power-law astrophysical component. The left and right $y$ -axis are for the photon portal coupling $g$ and the Higgs portal coupling $β$ for different scalar field mass $μ_{s}$ . The green and blue lines present the constraints from the supernova energy loss [66] for the photon portal coupling and the ATLAS for the Higgs portal coupling [100], respectively.
Reuse & Permissions
Figure 5
The 95% credible upper limits of the extended mass from the scalar DM enclosed within the S2’s orbit for different scalar field mass $μ_{s}$ , without (solid) and with (dashed) the additional power-law astrophysical component. The Keck [101] and GRAVITY [36] excluded regions on the extended mass are larger than $\sim 10^{4} M_{⊙}$ and $\sim 4000 M_{⊙}$ within the radius of S2 orbit, as shown by purple and orange shaded regions.
Reuse & Permissions
Figure 6
The corner plot of 18 free parameters obtained from a MCMC sample. All parameters are well constrained, including mass ratio of scalar cloud $κ$ and coupling $β$ . To ease comparisons, parameters measured in identical units are plotted with identical axes lengths.
Reuse & Permissions

Physical Review D

covering particles, fields, gravitation, and cosmology