Black holes come to the big screen 6 November 2014, by Daniel Stolte

UA's new supercomputer—nicknamed El Gato—the researchers combined knowledge from mathematical equations and astronomical observations to generate visualizations of an object known by astronomers as Sagittarius A* ("Sagittarius A star"), a supermassive comprising the mass of 4.3 million suns.

Located 26,000 light-years from Earth at the center of our galaxy, Sagittarius A* is tiny to the eyes of astronomers. Smaller than Mercury's orbit around the sun, it appears about the same size as a

grapefruit on the moon. A black hole as depicted in the movie "Interstellar." Credit: Paramount Pictures The team just published the first major science results obtained using El Gato's unique, massive, parallel-computing capabilities to create visualizations of what a space traveler might see The new movie "Interstellar" explores a upon approaching SgrA*. The results, published in longstanding fascination, but UA astrophysicists two reports in the Astrophysical Journal—one are using cutting-edge technology to go one better. focusing on the imaging and the other on the They're working on how to take pictures of the computing—provide some of the groundwork for the black hole at the center of the galaxy. Telescope, or EHT, a huge undertaking involving scientists and observatories What does a black hole look like up close? around the world to take the first-ever picture of SgrA*. When the sci-fi movie "Interstellar"—hitting theaters this week—wows audiences with its computer- The film "Interstellar," starring Matthew generated views of one of most enigmatic and McConaughey and Anne Hathaway, prominently fascinating phenomena in the , University features a black hole, touted as the first visual of Arizona astrophysicists Chi-kwan Chan, depictions based on the actual science and Dimitrios Psaltis and Feryal Ozel are likely to nod mathematics of Einstein's Theory of General appreciatively and say something like, "Meh, that Relativity. On some of the renderings, a special- looks nice, but check out what we've got." effects team of about 30 experts reportedly spent up to 100 hours of running calculations to create "We want to know what happens near extremely each frame. compact objects such as black holes and neutron stars," said Psaltis, a professor of astronomy and "Our team of four here at the UA can produce physics in the UA's Department of Astronomy and visuals of a black hole that are more scientifically Steward Observatory. "We want to watch as matter accurate in a few seconds," said Ozel, also a fed onto a black hole crosses the event horizon, professor of astronomy and physics at Steward the point of no return, and disappears." Observatory.

To find answers, the group created a monster in "It's a bit like gaming on steroids," she explained. the basement of the UA's high-performance "El Gato uses a massively parallel architecture of computing facility. Harnessing the power of the hundreds of graphic processors working side by

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side, with each node functioning as a renderer in makes the black hole easier to find than if we were real time." looking for complete blackness. These simulations also help us find ways to distinguish this signature As part of a collaboration that includes the papers' from all this swirling plasma around the black hole." first author, postdoctoral fellow Chan, and researchers at Harvard University and MIT, the By imaging the glow of matter swirling around the husband-and-wife research team of Psaltis and black hole before it goes over the edge and Ozel developed software algorithms capable of plunges into the abyss of space and time, scientists calculating the paths of millions of individual can see only the outline of the black hole, also photons in mere seconds as they shoot toward the called its shadow. black hole. In addition to providing groundwork for the EHT, the Funded by the National Science Foundation and simulations will support NICER, a new NASA NASA, the computer simulations are a crucial step mission involving an instrument that will be before astronomers can start to look for the black attached to the International Space Station, to help hole using the EHT, functioning as a sort of field ID scientists better understand neutron stars and to guide of what astronomers should look for once the test navigation methods for future spacecraft using EHT is up and running. neutron stars as extremely accurate clocks.

The EHT will combine radio telescopes across the Until EHT is ready to take the first images of what globe to create a virtual telescope the size of the lurks at the center of our , astrophysicists Earth. These include the UA's Arizona Radio will have to get by with gaming on steroids—or going Observatory as well as the South Pole Telescope, to the movies. outfitted with new receivers built by a group led by UA assistant professor of astronomy Daniel More information: "GRay: a Massively Parallel Marrone. GPU-Based Code for Ray Tracing in Relativistic Spacetimes." arXiv:1303.5057 [astro-ph.IM]. "We wouldn't be able to observe a black hole arxiv.org/abs/1303.5057 against a black sky," Ozel said. "Therefore, we look for other telltale signatures telling us about the "The Power of Imaging: Constraining the Plasma presence of a black hole." Properties of GRMHD Simulations using EHT Observations of Sgr A*." arXiv:1410.3492 [astro- The gravitational field around a black hole is so ph.HE]. arxiv.org/abs/1410.3492 immense that it swallows everything in its reach. Not even light can escape its grip. For that reason, black holes are just that: They emit no light whatsoever, and their "nothingness" blends into the Provided by University of Arizona black void of the universe.

As matter comes under the black hole's spell of extreme gravity, a cosmic traffic jam ensues, in which gas swirls around it like water circling a drain. As matter compresses, the resulting friction turns it into plasma heated to a billion degrees or more, causing it to "glow"—and radiate energy that astronomers can detect here on Earth.

"Our visualizations show there is a place where photons linger and form a ring outlining the shadow of the black hole," Psaltis said. "That ring of light

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