A new Renaissance Computing Institute (RENCI) animation created from a mathematical model shows a black hole moving supersonically through an interstellar gas cloud. This phenomenon often occurs in multiple star systems, where a companion star provides the gas cloud. The gravity of the black hole pulls the gas inward. Early on in the process, a wake forms behind the black hole, much like the wake behind a motorboat. Unlike a motorboat wake, it begins to move back and forth after a while until it whips all the way around the black hole, forming an accretion disk of gas falling into the hole.

What has mystified scientists since 1988 is the seemingly erratic rotation of accretion disks in the computer-generated models. In some cases the model shows the disk rotating for a time in one direction, then suddenly switching directions. The disk’s spin may remain stable for a time and then abruptly reverse direction again. The reversal may repeat several times.

Astrophysicists refer to this accretion disk about face as “flip-flop instability” and have debated its possible causes for years. Some suggest the phenomenon doesn’t actually occur but is a flaw in the model itself. Yet flip-flop instability has shown up in numerous different studies, leading some scientists to suggest it is the cause of stellar flares and bursts of energy that haven’t otherwise been explained.

North Carolina State University researchers John Blondin and T. Chris Pope generated the data used to construct this visualization. Their computer simulations exploit the power of high-performance computers available through the National Science Foundation’s TeraGrid to explore flip-flop instability at an unprecedented level of detail and scientific sophistication. In a paper published June 30 in the Astrophysical Journal, they conclude that the flip-flop instability is real and not an anomaly of computer models.

In the animation, created by Steve Chall of the RENCI’s North Carolina State Engagement Center, the gas cloud swirls around the black hole at the center, creating an accretion disk around the black hole. At first, the disk spins counterclockwise and then very rapidly reverses to a clockwise direction. The background colors in the animation represent pressure, from green for low through blue, violet, red and finally pale yellow for the highest pressure. Spheres emitted from 10 equally spaced sources upstream from the black hole (far right) show the velocities of representative particles in the gas cloud. Pale yellow spheres exhibit the least velocity, through red, violet and up to blue for the fastest-moving particles.

Credits: Numerical simulation: Dr. John Blondin and T. Chris Pope, department of physics, North Carolina State University. Visualization: Steve Chall, Renaissance Computing Institute NC State. This research was supported in part by a grant from the National Science Foundation, by an NC State Undergraduate Research Award to T. Chris Pope, and by computing resources at the Texas Advanced Computing Center.

The NC State node of BEN, consisting of Infinera digital optical networking hardware, connects campus researchers to the experimental network through RENCI at NC State.

RALEIGH, NC, March 11, 2009—RENCI’s NC State engagement center recently completed upgrades to support the installation of the Breakable Experimental Network (BEN). BEN serves as a test bed for experimentation with new networking technologies that will help make networked communications faster, easier and more reliable. BEN is “breakable” because it is not meant to be a stable commercial network, such as those that keep the commercial Internet running. Instead BEN allows network researchers to experiment with disruptive technologies—those that are likely to have a major impact in the years to come and thereby disrupt standard operating procedures for networks.

The new network connects RENCI facilities at NC State, Duke University, UNC Chapel Hill, RENCI’s main office at Europa Center in Chapel Hill, and MCNC in Research Triangle Park. RENCI administers the network and provides access to the fiber for researchers at the Triangle area campuses through its engagement centers. With funding from the National Science Foundation, RENCI and Duke are using BEN as a test bed for the Global Environment for Network Innovations (GENI) project. GENI’s aim is to forge new solutions to problems facing today’s Internet including inadequate security, reliability, manageability and scalability.

RENCI at NC State also upgraded its 170-inch by 96-inch visualization display wall into a fully digital system that more accurately adjusts images on the screen. The display system uses 16 projectors and can display images at a resolution of 5,120 by 2,880 pixels.

The visualization wall allows researchers to view large-scale, time-dependent data as color-coded visual simulations of complicated processes, from astrophysical phenomena to the relationships among documents in a large data archive.

For more on BEN, see http://ben.renci.org.

For more on GENI, see http://www.geni.net

RENCI…Catalyst for Innovation
The Renaissance Computing Institute, a multi-institutional organization, brings together multidisciplinary experts and advanced technological capabilities to address pressing research issues and to find solutions to complex problems that affect the quality of life in North Carolina, our nation and the world. RENCI leverages its expertise and resources in leading edge computing, visualization, networking and data technologies to catalyze new collaborations and solve problems. Founded in 2004 as a major collaborative venture of Duke University, North Carolina State University, the University of North Carolina at Chapel Hill and the state of North Carolina, RENCI is a statewide virtual organization.