Dark matter effect on the weak deflection angle by black holes at the center of Milky Way and M87 galaxies
Reggie C. Pantig , Physics Department, De La Salle University, Philippines
Ali ﾃ-vgﾃｼn Physics Department, Eastern Mediterranean University, Cyprus
The European Physical Journal C volume 82, Article number: 391 (2022)
https://link.springer.com/article/10.1140/epjc/s10052-022-10319-8
Several decades ago, the existence of a black hole was a mystery and only was explored as a mathematical construct . Until recently, the Event Horizon Telescope collaboration unveiled the first image of the shadow of a black hole in the electromagnetic regime. On the other hand, there are recent studies on this specific direction, using perhaps the most important yet mysterious astrophysical environment - the dark matter. Dark matter constitutes about 85% of the total mass of the Universe and is used to explain the strange behavior of stars and galaxy dynamics.
In our recent paper, we investigated the effect of dark matter on the weak deflection angle by black holes at the galactic center by considering three known dark matter density profiles such as the Cold Dark Matter, Scalar Field Dark Matter, and the Universal Rotation Curve from the Burkert profile. Using the current observational data in the Milky Way and M87 galaxies, we find interesting behaviors of how the weak deflection angle varies with the impact parameter, which gives us some hint on how dark matter interacts with the null particles for each dark matter density profile. We conclude that since these deviations are evident near the dark matter core radius, the weak deflection angle offers a better alternative for dark matter detection than using the deviation from the black hole shadow. With the dark matter profiles explored in this study, we find that the variation of the values for weak deflection angle strongly depends on the dark matter mass on a particular profile.
Let us list some space technology that can potentially detect the deviation in the weak deflection angle or the Einstein ring caused by the dark matter density profiles. First, we have the Event Horizon Telescope that can achieve an angular resolution of 10-15 ﾎｼas within 345 GHz in the future. In addition, while the ESA GAIA mission is also capable of providing around 20-7ﾎｼas of angular resolution , a more powerful space-based technology called the VLBI RadioAstron can obtain an angular resolution ranging from 1-10 ﾎｼas. We then conclude that they are within the capability of extracting information from the dark matter profiles herein, especially for high dark matter density. Although the weak deflection angle is small for Sgr. A*, the angular radius for the Einstein ring is detectable.