"Dark Matter" in Accretion Disks

TL;DR

This study reveals that accretion disks in binary systems contain a large, invisible dust ring surrounding the gaseous disk, which significantly alters the understanding of their structure and composition.

Contribution

It introduces the discovery of an asymmetric, dusty outer ring around the gaseous accretion disk in WZ Sge, highlighting a new component previously undetected at optical wavelengths.

Findings

Detection of a large, asymmetric dust ring around the gaseous disk

The dust ring is invisible at optical and near-IR wavelengths

The dust ring's radius is approximately 15 times larger than the gaseous disk

Abstract

Using Spitzer Space Telescope photometric observations of the eclipsing, interacting binary WZ Sge, we have discovered that the accretion disk is far more complex than previously believed. Our 4.5 and 8 micron time series observations reveal that the well known gaseous accretion disk is surrounded by an asymmetric disk of dusty material with a radius approximately 15 times larger than the gaseous disk. This dust ring contains only a small amount of mass and is completely invisible at optical and near-IR wavelengths, hence consisting of "dark matter". We have produced a model dust ring using 1 micron spherical particles with a density of 3 g/cm$^3$ and with a temperature profile ranging from 700-1500K. Our discovery about the accretion disk structure and the presence of a larger, outer dust ring have great relevance for accretion disks in general, including those in other interacting binary systems, pre-main sequence stars, and active galaxies.