Probing Dark Matter Using Precision Measurements of Stellar Accelerations

Abstract

Dark matter comprises the bulk of the matter in the universe but its particle nature and cosmological origin remain mysterious. Knowledge of the dark matter density distribution in the Milky Way Galaxy is crucial to both our understanding of the standard cosmological model and for grounding direct and indirect searches for the particles comprising dark matter. Current measurements of Galactic dark matter content rely on model assumptions to infer the forces acting upon stars from the distribution of observed velocities. Here, we propose to apply the precision radial velocity method, optimized in recent years for exoplanet astronomy, to measure the change in the velocity of stars over time, thereby providing a direct probe of the local gravitational potential in the Galaxy. Using numerical simulations, we develop a realistic strategy to observe the differential accelerations of stars in our Galactic neighborhood with next-generation telescopes, at the level of 10 −8 cm/s 2 . Our simulations show that detecting accelerations at this level with an ensemble of 10 3 stars requires the effect of stellar noise on radial velocity measurements to be reduced to <10 cm/s. The measured stellar accelerations may then be used to extract the local dark matter density and morphological parameters of the density profile.

Precision and consistency of astrocombs

“…A servo controller ("secondary guiding") ensures that the object image is always centered in the object fibre. In order to ensure light entrance stability and proper mode mixing in the fibres, a dynamical fibre scrambler that shakes the fibres was added to the setup, adding a temporal scrambling of light (Probst et al 2020).…”

“…where f o and f r are the "offset" and the "repetition" frequencies, and n is the mode number (a large positive integer). Both f o and f r are radio-frequencies referenced to an atomic clock and known with precision of ∆ f / f = 5.6 × 10 −12 over the timescale of several hours (Probst et al 2020). The frequency, and the wavelength, of each line can therefore be determined with the same precision.…”

“…Relevant information about the two astrocombs are tabulated in Table 1. See Probst et al (2020) for a more comprehensive description of the astrocomb design and the setup during the April 2015 campaign. 3 DATA…”

“…the fine strucure constant, α, Dzuba et al 1999;Webb et al 1999Webb et al , 2011King et al 2012, and others). It is also the method proposed to measure the expansion of the Universe in "real time" and in a model-independent way (also known as the Sandage test or the "redshift drift" measurement, Sandage (1962); Loeb (1998); Liske et al (2008)) and to map the gravitational potential of the Galaxy (Ravi et al 2019;Leão et al 2019). These science goals are important drivers for all 30-meter class telescopes planned for the 2020s, i.e.…”

“…The first one was to understand whether the precision of a single astrocomb is confirmed by an independent system, and the second one was to assess zero-point offsets in the wavelength calibration introduced by switching between the two astrocombs. Probst et al (2020) analyses the same dataset, but with a focus on describing the experimental setup, astrocomb hardware and its optimisation during the campaign before the astrocomb's deployment in May 2015. This paper, on the other hand, focuses on data analysis techniques and advanced algorithms that will provide wavelength calibration precision required by the ELT projects discussed above.…”