Black Holes: Space-Dust Donuts

    Black holes are not perfect vacuums— these space phenomena are notorious for having such intense gravity that even light cannot escape, but this characterization is only partially true. Black holes have a border of sorts, a line that must not be crossed, called the Schwarzschild radius, which formally defines when a black hole’s pull becomes inescapable, even for light. 

    Outside this radius, there is matter, sometimes dense enough to form a thick cloud that can hide the core of the black hole. Scientists call these donut-shaped clouds tori (singular: torus) and they are made primarily of hot, space dust. It sounds silly that the fearsome black holes that dominated the sci-fi industry for years could be hiding behind a big ring of dust, but these tori are essential to understanding several astronomical mechanisms.

    Recently, researchers have begun to develop a unified model to classify supermassive black holes like the one in the center of the Milky Way. These supermassive black holes vary from other kinds of black holes in that they produce jets of wind and light. Additionally, the large dust clouds that circle around them match the movement of the galaxies they occupy; hence, the Milky Way’s distinct spiral shape. 

Diagram of a supermassive black hole (active galactic nuclei) and its torus (TBH)

Also called active galactic nuclei (AGC), these supermassive black holes can be compartmentalized even further using the dust encircling them. Using thermal imaging, researchers have identified a thick, significant ring of dust that could change previous assumptions about the classification of AGC and confirm the unified model theory. 

How a torus can block the sight of a central black hole

When recent images surfaced of galaxy NGC 1068, researchers thought previous classifications of supermassive black holes would have to be changed. The torus displayed was too thin, and off-kilter from what would have been expected from a type-2 black hole. This contradiction quickly spurred debate over the classification system for active galactic nuclei, and how previous data needed to be reevaluated. 

Before any major edits could be made to the unified model, researchers from around the world worked in cohesion to reassess the torus around galaxy NGC 1068. Using three independent image reconstruction systems, and prior radio data, they were able to map out a different image of the galaxy (NGC 1068) and the torus wrapped around the supermassive black hole in question. They compared their findings, overlaying the infrared and radio images to form colorful blobs that corresponded to the positions predicted by the unified model.

Comparision of radio and infrared imagery from the research that reestablished the theory

This is good news for astronomers because it corroborates the long-held unified model. The pictured torus of the NGC 1098 galaxy is typical of a predicted type-2 supermassive black hole. The dusty shell around it is responsive to infrared technology as well, and when overlayed with radio imaging the process presents a new approach in evaluating the tori of supermassive black holes. The interaction between dust and radiation in the torus and the cloud formation that follows, are all now emerging as sources of classification, and the processes used can aid further research into understanding more about black holes.

Black holes are not perfect vacuums— and the matter that dances around them may very well lead to a better comprehension of one of space’s deepest mysteries.