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The most detailed simulations of black holes solve many years of riddles



  The most detailed simulations of the black hole solve a long-standing mystery.
This image shows how the inner area of ​​the accretion disk (red) is aligned with the equatorial plane of the black hole. The outer disc is tilted away. The inner disc (where the black curve drops off) is horizontal, signaling the long-awaited Bardeen-Petterson alignment. Picture credits: Sasha Tchekhovskoy / Northwestern University; Matthew Liska / University of Amsterdam

An international team has created the most detailed simulation yet of a black hole with the highest resolution. The simulation proves theoretical predictions about the nature of accretion disks – the matter that orbits and eventually falls into a black hole – that have never been seen before.

The study will be published on June 5 in the Monthly Notices of the Royal Astronomical Society .

The team of computer astrophysicists at Northwestern University, the University of Amsterdam, and the University of Amsterdam Oxford found that the innermost region of an accretion disk faces the equator of the black hole.

This discovery solves a long-standing mystery revealed in 1975 by Nobel laureate John Bardeen and astrophysicist Jacobus Petterson. Bardeen and Petterson argued that a spinning black hole would cause the inner area of ​​an inclined accretion disk to align with the equatorial plane of its black hole.

The simulation of the team showed that while the outer area of ​​an accretion disk remains inclined, the inner area of ​​the disk is aligned with the black hole. A smooth chain connects the inner and the outer area. The team solved the puzzle by thinning the accretion disk to an unprecedented degree, including the magnetized turbulence that causes the disk to grow. Earlier simulations have made a substantial simplification by merely approximating the effects of turbulence.

"This groundbreaking discovery of the Bardeen-Petterson alignment closes a problem that astrophysicists have been following for more than four decades," said Alexander Tchekhovskoy from the Northwest. who accompanied the research. "These details about the black hole may seem small, but they have a tremendous impact on what happens throughout the galaxy, controlling how fast the black holes spin and what effects they have on their entire galaxies." 19659009] The simulation shows that the inner area of ​​the accretion disk is aligned at the equatorial plane of the black hole, signaling the long-awaited Bardeen-Petterson alignment. Picture credits: Sasha Tchekhovskoy / Northwestern University; Matthew Liska / University of Amsterdam

Tchekhovskoy is Assistant Professor of Physics and Astronomy at the Weinberg College of Arts and Sciences in the northwest and a member of the CIERA (Center for Interdisciplinary Research and Research in Astrophysics), a focused research center in the northwest promoting astrophysics with a focus in interdisciplinary contexts. Matthew Liska, a researcher at the Anton Pannenkoek Institute for Astronomy at the University of Amsterdam, is the first author of the work.

"These simulations not only solve a 40-year-old problem, but have also shown that it is possible to simulate the brightest accretion disks in full relativity," Liska said. "This paves the way for a next generation of simulations that will hopefully solve even more important problems with luminous accretion disks." learned by studying accretion discs. Without the bright ring of gas, dust, and other stellar debris whirling around black holes, astronomers could not make out a black hole to study it. Accretion discs also control the growth and rotational speed of a black hole. Understanding the nature of accretion disks is therefore crucial for understanding the development and function of black holes.

"The alignment affects how accretion disks turn their black holes," Chekhovskoy said. "So it affects how the spin of a black hole develops over time and triggers outflows that affect the evolution of their host galaxies." Two main problems have acted as a barrier for computer astrophysicists. For one thing, accretion disks get so close to the black hole that they move through distorted spacetime, which crashes into the black hole at tremendous speed. To make matters worse, the rotation of the black hole forces space-time to spin around it. To properly explain these two crucial effects, a general theory of relativity is required. Albert Einstein's theory predicts how objects affect the geometry of space-time around them.

<img src = "https://3c1703fe8d.site.internapcdn.net/newman/csz/news/800/2019/5cf8bf8f7e776.jpg" alt = "The most detailed simulations of the black hole solve the long-standing puzzle Tchekhovskoy / Northwestern University, Matthew Liska / University of Amsterdam

Second, astrophysicists had no computational power to explain magnetic turbulence or agitation within the accretion disk. This agitation causes the particles of the disc to stick together in a circle, and eventually gas will fall into the black hole.

"Imagine, you have this thin disk, then you have to resolve the turbulent movements in the disk," said Chekhovskoy. "It's going to be a really difficult problem."

Without being able to solve these functions, computer scientists could not simulate realistic black holes.

Cracking the Code

Developing a code that is capable Liska and Tchekhovskoy used GPUs instead of central processors (CPUs) to simulate accretion discs with titles around black holes. GPUs are extremely efficient at processing computer graphics and image processing and speed up the creation of images on a display. They are much more efficient than CPUs for computational algorithms that process large amounts of data.

Tchekhovskoy compares GPUs with 1,000 horses and CPUs with a Ferrari with 1,000 horsepower.

  The most detailed simulations of black holes solve the long-standing mystery
Photo credit: Sasha Tchekhovskoy / Northwestern University; Matthew Liska / University of Amsterdam

"Suppose you have to move into a new apartment," he explained. "With this powerful Ferrari you have to do a lot of driving because it's not suitable for a lot of boxes, but if you could put a box on each horse, you could move it all at once – that's the GPU – it has a lot." of elements, each of which is slower than the ones in the CPU, but there are so many. "

Liska also added a method called Adaptive Mesh Refinement, which uses a dynamic mesh or grid that changes and adjusts the motion flow during simulation, saving energy and computing power by focusing only on specific blocks in the grid,

The GPUs significantly accelerated the simulation and the adaptive mesh increased the resolution, allowing the team to simulate the thinnest accretion disk with a height-to-radius ratio of 0.03 Was simulated thinly, the researchers could observe an alignment directly next to the black hole.

"The thinnest previously simulated slices had a ratio of height to radius of 0.05, and it turned out that this is all of interest things pass at 0.03 ", said Chekhovskoy.

Even with these incredibly thin accretion disks emit Surprisingly, the black hole still emits strong rays of particles and radiation.

"Nobody had expected that these discs would produce jets at such low thicknesses," said Chekhovskoy. "People expected the magnetic fields that created these jets to simply break through those really thin slices, but there they are, and that actually helps us solve observation puzzles."


The computer model shows that strong magnetic fields can alter the alignment of black hole accretion disks and plasma jets


Further information:
M Liska et al., Bardeen-Petterson alignment, jets and magnetic truncation in GRMHD simulations of inclined thin accretion disks, Monthly Notices of the Royal Astronomical Society (2019). DOI: 10.1093 / mnras / stz834

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Northwestern University




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The most detailed simulations of black holes solve many years of mystery (2019, June 6)
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