The First Robust Evidence Showing a Dark Matter Density Spike Around the Supermassive Black Hole in OJ 287
Man Ho Chan, Chak Man Lee
Abstract
Abstract Black hole dynamics suggests that dark matter would redistribute near a supermassive black hole (SMBH) to form a density spike. However, no direct evidence of a dark matter density spike around an SMBH has been identified. In this Letter, we present the first robust evidence showing a dark matter density spike around an SMBH. We revisit the data of the well-known SMBH binary OJ 287 and show that the inclusion of the dynamical friction due to a dark matter density spike around the SMBH can satisfactorily account for the observed orbital decay rate. The derived spike index <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>sp</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.351</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.045</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.032</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> gives an excellent agreement with the value γ sp = 2.333 predicted by the benchmark model assuming an adiabatically growing SMBH. This provides a strong verification of the canonical theory suggested two decades ago modeling the gravitational interaction between collisionless dark matter and SMBHs.