# Density and B-field Evolution

## Mass Ratio = 1:1

We follow the evolution of the matter and magnetic fields of a gaseous disk. In the cavity of the disk are two black holes, with a mass ratio of q = 1:1. Green lines depict magnetic field lines within the disk. The seeding points used in drawing these fields lines were taken from a subset of fluid test-particles that were evolved during the simulation. By drawing magnetic field lines from these test-particles, we can visualize the evolution of the magnetic field lines, because they are attached ("frozen in") to the same particles for all time. White lines highlight the field lines threading the polar regions above the black holes. These field lines are drawn from fixed grid points above each black hole pole.

Here, we focus on the post-decoupling phase, during which $t_{vis} \gt t_{GW}$ and the binary decouples from the disk before the disk can relax. Note that the tidal field of the black holes carves out a cavity in the disk. However, two accretion streams from the cavity walls pour matter into the black holes, maintaining the luminosity from the region near the holes. Twin jets are also observed from the poles of the black holes. As the binary separation decreases, the two accretion streams diminish in strength and both the accretion rate and luminosity decline. This "pre-merger" effect is a signature of binary merger. After merger, gas pours into the cavity and onto the black holes, which generates "aftermath" radiation. Note that as the black holes merge so do their twin magnetic jets—another transient signature of the merger.

 Fig. 1-1 Fig. 1-2 Fig. 1-3
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