Revisiting the Great Attractor: The Local Group's streamline trajectory, cosmic velocity and dynamical fate

TL;DR

This study uses digital simulations to reassess the Great Attractor's role in Local Group velocity, revealing it is not a dominant structure but an artifact of the current velocity field, with multiple influences shaping cosmic motion.

Contribution

The paper introduces a new suite of simulations that challenge the traditional view of the Great Attractor as the primary source of Local Group velocity.

Findings

Mass within 155 Mpc accounts for only 72% of the Local Group velocity.

No single structure, including the Great Attractor, dominates the velocity budget.

The Local Group's future motion is primarily towards Virgo, but no single attractor governs its trajectory.

Abstract

We revisit the Great Attractor using the Manticore-Local suite of digital twins of the nearby Universe. The Great Attractor concept has been proposed as an answer to three distinct questions: what sources the Local Group velocity in the cosmic microwave background frame, where present-day velocity streamlines converge, and where the Local Group is moving to. Addressing the original motivation of the Great Attractor -- explaining the Local Group cosmic velocity -- we find that mass within $155~h^{-1}\mathrm{Mpc}$ accounts for only ${\sim}72\%$ of that velocity magnitude with ${\sim}38\,\deg$ directional offset. We show that even in the purely linear regime convergence within this volume is not guaranteed, particularly when also accounting for small-scale contributions to the observer velocity; no single structure, including the proposed Great Attractor, would be expected to dominate the velocity budget. Streamline convergence is smoothing-scale-dependent, transitioning from Virgo at small scales through the Hydra--Centaurus region at intermediate scales to Shapley at large scales; at intermediate smoothing the convergence point lies near Abell 3565 with an asymmetric basin of mass $\log( M / (h^{-1} \mathrm{M}_\odot)) = 16.4 \pm 0.1$ that excludes Norma. To address the third question, we evolve the Manticore-Local realisations to scale factor $a = 10$ in a new Beyond-Present-Time simulation suite and identify the asymptotic future location of the Local Group. We find that the dominant motion is towards Virgo, but even it contributes at most one third of the Local Group velocity. Our results demonstrate that the classical Great Attractor is not a dynamically dominant structure but an artefact of the instantaneous velocity field, and that no single attractor is likely to account for the Local Group motion in the cosmic rest frame.