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07-06-2024

Black hole disks are unexpectedly 'fluffy' as they grow and evolve

The thought of black holes can send shivers down our spines. The idea of a region in space where gravity is so strong that nothing (not even light) can escape, is both awe-inspiring and chilling.

Yet, black holes occupy a pivotal position in the cosmos. Recently, scientists at the California Institute of Technology (Caltech) have unveiled new insights into these mysterious entities. Thanks to a revolutionary computer simulation, the team has provided a look into the evolution of a black hole and its disks.

The research was led by Phil Hopkins, the Ira S. Bowen Professor of Theoretical Astrophysics at Caltech. Over the years, Profeesor Hopkins has led multiple projects, with this simulation being the apex of intense collaborative efforts.

Simulation and its surprising findings

The researchers have successfully simulated the journey of primordial gas from the early universe, tracking its path until it gets caught up in the vortex towards a supermassive black hole.

This stellar project represents an unprecedented leap in resolution – over a thousand times greater than the previous record in the field!

The team’s work has stirred up the world of astrophysics. Why? Because the results turned the existing theories around accretion disks – those swirling, galactic disks that feed black holes – on their heads.

“Our theories told us the disks should be flat like crepes,” said Hopkins. “But we knew this wasn’t right because astronomical observations reveal that the disks are actually fluffy – more like an angel cake. Our simulation helped us understand that magnetic fields are propping up the disk material, making it fluffier.”

Supermassive black holes and their fluffy disks

Chances are, you’ve heard about supermassive black holes before. These beasts lie at the heart of most galaxies, our Milky Way included, and they’re absolute gluttons for cosmic matter.

They attract and devour gas and dust, forming a swirling accretion disk as material gets pulled towards them. Just before plunging into the black hole, this material emits a vast amount of energy, making these cosmic objects shine brighter than almost anything else in the universe.

The problem? We still know very little about these fascinating systems. While black hole disks in our own galaxy and Messier 87 have been imaged, these are far tamer than the disks around distant, more active black holes. This is where computer simulations come in handy.

Power of black hole disk simulation

Simulations offer researchers a way to recreate these cosmic activities. They incorporate all the physics at work in these galactic settings – from the basics of gravity to the behavior of dark matter and stars – into computing algorithms.

These algorithms allow scientists to model complex phenomena, like star formation or the behavior of galaxies, with great detail. However, Hopkins noted that it’s not as simple as saying “gravity pulls everything down.”

For a simulation to truly work, it needs to account for the complicated ways stars interact with their surroundings.

For instance, they emit radiation that can heat up or push the surrounding gas. They blow stellar winds that can sweep up material, and they can explode as supernovae, dramatically altering their surroundings.

So, the team at Caltech developed a simulation that could cover all the relevant scales, from larger galactic scales to the level of a single accretion disk around a supermassive black hole. This ambitious project was a monumental computational challenge.

Unexpected discovery

The researchers discovered that the pressure from the magnetic fields of the accretion disks was actually 10,000 times greater than the pressure from the heat of the gas.

In simpler terms, the magnetic fields were doing most of the work in supporting the disks, reshaping our understanding of their structure and function.

The team’s discovery opens a new chapter in the exploration of black holes and galaxies. Their simulation enables us to delve deeper into complex questions about galactic collisions, the formation of diverse types of stars, and even the nature of the universe’s first generation of stars.

So, what’s next in the incredible world of cosmic research? Only time will tell. But you can bet that the dedicated scientists at Caltech will be at the forefront, bridging the mysteries of the cosmos with our earthly understanding.

The study is published in The Open Journal of Astrophysics.

Video Credit: California Institute of Technology

Image Credit: Caltech/Phil Hopkins group

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