We are increasingly understanding supermassive black holes. And it is key to our knowledge of the universe

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Sometimes in science it is convenient to use the known in order to imagine the characteristics of the unknown. The problem with applying this logic to black holes is that they are not extremely different from anything we know. A new study carried out by researchers at the University of Dartmouth, in the USA, has managed to tackle this problem to better understand what happens in the vicinity of black holes.


The accretion torus.
The study focuses on active galactic nuclei (AGN), supermassive black holes located in the center of galaxies like ours, which are in a phase of rapid growth. These AGNs emit a broad spectrum of electromagnetic radiation, ranging from radio waves to X-rays.

AGNs typically have an accretion disk, a surrounding torus- or ring-shaped mass of dust and gas orbiting at high speed around the hole. This matter is the main responsible for the light emitted by black holes, but the amount of this light that reaches us from different AGN can vary considerably in intensity and color.

Astronomers have traditionally considered that the different light “signatures” of different black holes were related to the angle from which we viewed this disk. Thus, a disk with an axis of rotation pointing toward us would appear very bright, while a disk perpendicular to our perspective would appear darker.

We have detected a

A different perspective.
Researchers at Dartmouth College have offered a different hypothesis. They’ve made it through an article published in the magazine The Astrophysical Journal. According to this, the reason behind these different appearances would go further: they would be black holes at different stages of their life.

The key would be in the speed at which the holes absorb the matter that surrounds them. This speed would be associated with the amount of matter, dust and gas, around the AGN. The more activity of the hole, the more matter around it and therefore more light emitted by this toroidal cloud.

“This offers support for the idea that the toroidal structures around black holes are not always the same,” explained Ryan Hickox, one of the authors of the study. “There is a relationship between the structure and how it is growing.”

diversity in black holes.
The job offers according to their authorsthe strongest evidence to date of the existence of differences between the light emissions of the different black holes, and that these differences cannot be explained if we pay attention to the perspective from which we observe these toroidal disks that surround the AGN .

From assumptions to evidence.
“Over time we have made assumptions about the physics of these objects,” said Tonima Tasnim Ananna, who led the research. “We now know that the properties of strongly hidden black holes are significantly different from unhidden AGN.”

This work may also allow astronomers to estimate when black holes experienced their main growth phases. In this way they would be able to improve their understanding of the evolution, not only of the black holes themselves but also of the Universe as a whole.

Work still to be done.
In Annana’s words, “the light signature of these objects has mystified researchers for half a century.” Black holes are objects surrounded by mystery, and understanding their origin is among the main questions to be answered in the field of astrophysics. The authors hope that this study will facilitate this work.

The researchers also point out what they hope to be the next steps in this direction, such as specific analysis at certain wavelengths. This would allow the study to be extended to more distant regions of our Universe. Also understand what factors affect the accretion rate at which each black hole begins to absorb matter.

Only new studies will be able to answer these questions and clarify the extent of the diversity of black holes, objects that continue to be among the most intriguing that can be found in the observable Universe.

Image | POT

Sometimes in science it is convenient to use the known in order to imagine the characteristics of the unknown. The…

Sometimes in science it is convenient to use the known in order to imagine the characteristics of the unknown. The…

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