Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Journey to the Limits of Spacetime

Black hole simulations on XSEDE supercomputers present new view of jets and accretion disks
Voracious absences at the center of galaxies, black holes shape the growth and death of the stars around them through their powerful gravitational pull and explosive ejections of energy.

"Over its lifetime, a black hole can release more energy than all the stars in a galaxy combined," said Roger Blandford, director of the Kavli Institute for Particle Astrophysics and Cosmology and a member of the U.S. National Academy of Science. "Black holes have a major impact on the formation of galaxies and the environmental growth and evolution of those galaxies."

Gravitational forces grow so strong close to a black hole that even light cannot escape from within, hence the difficulty in observing them directly. Scientists infer facts about black holes by their influence on the astronomical objects around them: the orbit of stars and clumps of detectable energy. With this information in hand, scientists create computer models to understand the data and to make predictions about the physics of distant regions of space. However, models are only as good as their assumptions.
"All tests of general relativity in the weak gravity field limit, like in our solar system, fall directly along the lines of what Einstein predicted," explained Jonathan McKinney, an assistant professor of physics at the University of Maryland at College Park. "But there is another regime—which has yet to be tested, and which is the hardest to test—that represents the strong gravitational field limit. And according to Einstein, gravity is strongest near black holes."

This makes black holes the ultimate experimental testing grounds for Einstein's theory of general relativity.

While black holes cannot be observed, they are typically accompanied by other objects with distinctive features that can be seen, including accretion disks, which are circling disks of superhot matter on our side of the black hole's "event horizon"; and relativistic jets, high-powered streams of ionized gases that shoot hundreds of thousands of light years across the sky.

In a paper published in Science in January 2013, McKinney, Tchekhovskoy and Blandford predicted the formation of accretion disks and relativistic jets that warp and bend more than previously thought, shaped both by the extreme gravity of the black hole and by powerful magnetic forces generated by its spin. Their highly detailed models of the black hole environment contribute new knowledge to the field.

For decades, a simplistic view of the accretion disks and polar jets reigned. It was widely believed that accretion disks sat like flat plates along the outer edges of black holes and that jets shot straight out perpendicularly. However, new 3D simulations performed on the powerful supercomputers of the National Science Foundation's Extreme Science and Engineering Discovery Environment (XSEDE) and NASA overturned this oversimplified view of jets and disks.

The simulations show that the jet is aligned with the black hole's spin near the black hole but that it gradually gets pushed by the disk material and becomes parallel to (but offset from) the disk's rotational axis at large distances. The interaction between the jet and disk leaves a warp in the accretion disk density.

"An important aspect that determines jet properties is the strength of the magnetic field threading the black hole," said Alexander Tchekhovskoy, a post-doctoral fellow at the Princeton Center for Theoretical Science. "While in previous works it was a free parameter, in our series of works the field is maximum: it is as strong as a black hole's gravity pull on the disk."

In the simulations, the twisting energy grows so strong that it actually powers the jet. In fact, the jet can reorient the accretion disk, rather than the other way around, as was thought previously.
"People had thought that the disk was the dominant aspect," McKinney said. "It was the dog and the jet was the wagging tail. But we found that the magnetic field builds up to become stronger than gravity, and then the jet becomes the dog and the disk becomes the wagging tail. Or, one can say the dog is chasing its own tail, because the disk and jet are quite balanced, with the disk following the jet — it's the inverse situation to what people thought."

What does this have to do with Einstein and his theory of general relativity?

Astronomers are closer than ever to being able to see the details of the jets and accretion disks around black holes. In a September 2012 paper in Science, Sheperd Doeleman of MIT reported the first images of the jet-launching structure near the supermassive black hole, M87, at the center of a neighboring galaxy, captured using the Event Horizon Telescope, a very long baseline interferometry (VLBI) array composed of four telescopes at three geographical locations. It constituted a small sliver of a vast skyscape, yet the results give astronomers like McKinney, Tchekhovskoy and Blandford the hope that they will get their first comprehensive glimpse into the black hole's neighborhood in the next three to five years.

"We'll see the gases swirl around the black hole and other optical effects that will be signatures of a black holes in spacetime that one can look out for," said Blandford.

The observations will either match models like theirs, or they will be different. Both outcomes will tell researchers a lot.

"If you don't have an accurate model and anything can happen as far as you understand, then you're not going to be able to make any constraints and prove one way or another whether Einstein was right," McKinney explained. "But if you have an accurate model using Einstein's equations, and you observe a black hole that is very different from what you expected, then you can begin to say that he may be wrong."

The model Blandford and others generated using supercomputing simulations will help serve that comparative role. But they need to add one crucial element to make the simulations meaningful: a way of translating the physics of the black hole system into a visual signal as it would be seen from the vantage point of our telescopes, billions of light years away.

"We're in the process of making our simulations shine, so they can be compared with observations," McKinney said, "not only to test our ideas of how these disks and jets work, but ultimately to test general relativity."
Supported by NASA, the Princeton Center for Theoretical Science and NSF Extreme Science and Engineering Discovery Environment (XSEDE).

Aaron Dubrow, Science and Technology Writer
February 13, 2013
The Texas Advanced Computing Center (TACC) at The University of Texas at Austin is one of the leading centers of computational excellence in the United States. The center's mission is to enable discoveries that advance science and society through the application of advanced computing technologies. To fulfill this mission, TACC identifies, evaluates, deploys, and supports powerful computing, visualization, and storage systems and software. TACC's staff experts help researchers and educators use these technologies effectively, and conduct research and development to make these technologies more powerful, more reliable, and easier to use. TACC staff also help encourage, educate, and train the next generation of researchers, empowering them to make discoveries that change the world.

Aaron Dubrow | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht Hope to discover sure signs of life on Mars? New research says look for the element vanadium
22.09.2017 | University of Kansas

nachricht Calculating quietness
22.09.2017 | Forschungszentrum MATHEON ECMath

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

All Focus news of the innovation-report >>>



Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

Latest News

Rainbow colors reveal cell history: Uncovering β-cell heterogeneity

22.09.2017 | Life Sciences

Penn first in world to treat patient with new radiation technology

22.09.2017 | Medical Engineering

Calculating quietness

22.09.2017 | Physics and Astronomy

More VideoLinks >>>