From The University of Arizona: “Making sense of the nonsensical-Black holes and the simulation library”

From The University of Arizona


Media contact(s)
Mikayla Mace Kelley
Science Writer, University Communications

Researcher contact(s)
Chi-Kwan Chan
Steward Observatory

The international Event Horizon Telescope collaboration has snapped a second image of a black hole – this time at the center of our own Milky Way galaxy. But to give the image meaning, the collaboration had to compare it with black hole simulations.

A view between two rows of Frontera servers in the Texas Advanced Computing Center data center, where UArizona’s Chi-Kwan “C.K.” Chan is the principal investigator.

Texas Advanced Computing Center

After mobilizing more than 300 scientists and engineers to establish a network of synchronized telescopes that form an Earth-sized virtual telescope, the international Event Horizon Telescope Collaboration snapped the first-ever images of supermassive black holes. The first image, of the black hole at the center of the Messier 87 galaxy, was released in 2019.

The latest image, released Thursday, shows the black hole at the center of our own Milky Way galaxy, called Sagittarius A*.

Sagittarius A* from the EHT.

But what happens after these images are captured?

“Snapping an image is just the beginning. To really understand the object we’re observing, we had to compare it to simulations,” said Chi-Kwan “CK” Chan, a University of Arizona associate research professor in the College of Science’s Steward Observatory. Chan serves as the secretary of the EHT Science Council and is a senior investigator for the international Black Hole PIRE Project, which works to develop the infrastructure to usher astronomical projects like EHT into the era of big data science.

Chan is also a leader of the EHT collaboration’s theoretical modeling and interpretation efforts for Sagittarius A*, the subject of the latest photograph and a round scientific papers published by the EHT Collaboration in The Astrophysical Journal Letters [All papers with links included]. He coordinated the fifth paper, which focuses on creating black hole simulations and turning them into synthetic images that can be compared with real observations to teach us something new about the black hole.

As a result of this process, EHT scientists determined that Sagittarius A* is likely spinning and has a magnetic field slightly stronger than a refrigerator magnet, which is enough to push away nearby gas. The gas falling into the black hole forms a disk that, from Earth, appears to be face-on rather than from the edge. This diffuse glowing disk is made up of super-heated gas, or plasma, and charged particles. The electrons are 100 times cooler than the ions in the plasma, and the disk rotates in the same direction the black hole spins. Also, only some of this material falls into the black hole. If Sagittarius A* was a person, it would consume a single grain of rice every million years.

Finding meaning

UArizona, together with The University of Illinois and Harvard University, led the effort to create the biggest collection of simulations to date, which EHT calls the simulation library. This library is made up thousands of data sets – containing information about how the plasma interacts with magnetic fields around black holes – and millions of simulated images. Each simulation assumes something different about the properties and characteristics of the black hole and its surrounding environment.

EHT scientists can compare each simulated image with the actual black hole image to find a match. The simulation that creates the snapshot with the closest match can teach us something about the actual black hole, including its plasma temperature and the strength of its magnetic field.

The simulation process involves using supercomputers to solve what’s called general relativistic magnetohydrodynamic – or GRMHD – equations, which reveal the movement of material and energy around black holes within dramatically warped space and time. GRMHD simulations are similar to simulations used to understand how air flows around aircrafts, Chan said, but GRMHD simulations also factor in extreme forces of gravity as described by Einstein’s theory of general relativity and the interaction between magnetic fields and plasma.

Unlike simpler equations, which can be solved with pencil, paper and time, GRMHD equations are much more complex, as they account for the constant feedback between magnetic fields and plasma, resulting in an ever-changing equation.

To create the simulation library, the EHT Collaboration needed 80 million CPU hours, or processing time, which is the equivalent of running 2,000 laptops at full speed for a full year. The collaboration ran the calculations to create the library with the National Science Foundation-funded Frontera supercomputer at the Texas Advanced Computing Center, where Chan is principal investigator of the Frontera Large-Scale Community Partnerships allocation. With this resource, the team was able to finish the full library of simulations in two months.

“To compare simulations like this with EHT observations, we need to run additional calculations to translate the GRMHD data into images, too,” Chan said. “Those kinds of calculations are called general relativistic ray tracing.”

The EHT was designed to detect a specific wavelength – 1.3 millimeters – of radio wave from the galactic center of a black hole. To simulate these radio waves and create images, scientists trace the path that light traveled back to the black hole, again using supercomputers.

Chan led much of the ray tracing calculation efforts for Sagittarius A* through CyVerse, a national cyberinfrastructure based at UArizona, and the NSF-funded Open Science Grid, a consortium for the computation of large amounts of data. The UArizona team not only spearheaded the effort to acquire the computational resources to run these simulations, but they also created the software that facilitated the calculations.

The final product is many simulated movies and simulated images of a black hole produced by different assumptions about the underlying physics. The team then compares those movies and images with real black holes.

More to learn

UArizona students played an important role in making the comparison possible. Yuan Jea Hew, a recent graduate who studied astronomy, and Anthony Hsu, a sophomore studying computer science and applied mathematics, developed data analysis algorithms to make comparison possible.

The collaboration relied on 11 different tests that the black hole simulations had to pass in order to sufficiently match the real black hole.

“It is remarkable that we understand Sagittarius A* so well that we have some models pass 10 out of the 11 tests,” Chan said.

The tests considered variables such as brightness of certain wavelengths, image size, and the size and width of the glowing ring surrounding the black hole.

“However, no single model passed all 11 tests,” Chan said. The test that was hardest for the models to beat was the variability, which measures how much the black hole changes from moment to moment. The simulations are more variable than the real Sagittarius A*.

“No matter how long we run the simulations to let them settle down, most of the simulations still failed that test,” Chan said. “They don’t quite match the reality, but I think this is more exciting than if everything simply worked out. Now, we can learn some new physics and understand our own black hole better.”

The UArizona faculty members working to understand black holes have been tackling this challenge for decades and were part of the research groups that identified the black hole at the center of the Milky Way and the one at the center of Messier 87 galaxy as ideal targets of study. The university also contributed two of the eight telescopes in the EHT array used to create these images – the Sub-Millimeter Telescope on Mount Graham in Arizona and the South Pole Telescope in Antarctica. In 2019, UArizona also added the 12-meter telescope on Kitt Peak in Arizona to the array.

In all, 36 UArizona researchers, graduate students and undergraduate students are involved in the EHT Collaboration, including professors of astronomy Dimitrios Psaltis, Feryal Özel, Dan Marrone and research professor and astronomer Remo Tilanus. Astronomy department head Buell Jannuzi serves on the EHT board.

The EHT Collaboration created a flurry of possible images of Sagittarius A* using ray tracing, a technique that predicts who black holes would look like based on Einstein’s Theory of General Relativity. The images shown here were created by UArizona’s Chi-kwan Chan on CyVerse and Open Science Grid and visualized by University of Illinois’ Ben Prather, as part of a larger simulation library assembled by EHT’s Theory Working Group. EHT Collaboration

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As of 2019, the The University of Arizona enrolled 45,918 students in 19 separate colleges/schools, including The University of Arizona College of Medicine in Tucson and Phoenix and the James E. Rogers College of Law, and is affiliated with two academic medical centers (Banner – University Medical Center Tucson and Banner – University Medical Center Phoenix). The University of Arizona is one of three universities governed by the Arizona Board of Regents. The university is part of the Association of American Universities and is the only member from Arizona, and also part of the Universities Research Association . The university is classified among “R1: Doctoral Universities – Very High Research Activity”.

Known as the Arizona Wildcats (often shortened to “Cats”), The University of Arizona’s intercollegiate athletic teams are members of the Pac-12 Conference of the NCAA. The University of Arizona athletes have won national titles in several sports, most notably men’s basketball, baseball, and softball. The official colors of the university and its athletic teams are cardinal red and navy blue.

After the passage of the Morrill Land-Grant Act of 1862, the push for a university in Arizona grew. The Arizona Territory’s “Thieving Thirteenth” Legislature approved The University of Arizona in 1885 and selected the city of Tucson to receive the appropriation to build the university. Tucson hoped to receive the appropriation for the territory’s mental hospital, which carried a $100,000 allocation instead of the $25,000 allotted to the territory’s only university Arizona State University was also chartered in 1885, but it was created as Arizona’s normal school, and not a university). Flooding on the Salt River delayed Tucson’s legislators, and by the time they reached Prescott, back-room deals allocating the most desirable territorial institutions had been made. Tucson was largely disappointed with receiving what was viewed as an inferior prize.

With no parties willing to provide land for the new institution, the citizens of Tucson prepared to return the money to the Territorial Legislature until two gamblers and a saloon keeper decided to donate the land to build the school. Construction of Old Main, the first building on campus, began on October 27, 1887, and classes met for the first time in 1891 with 32 students in Old Main, which is still in use today. Because there were no high schools in Arizona Territory, the university maintained separate preparatory classes for the first 23 years of operation.


The University of Arizona is classified among “R1: Doctoral Universities – Very high research activity”. UArizona is the fourth most awarded public university by National Aeronautics and Space Administration for research. The University of Arizona was awarded over $325 million for its Lunar and Planetary Laboratory (LPL) to lead NASA’s 2007–08 mission to Mars to explore the Martian Arctic, and $800 million for its OSIRIS-REx mission, the first in U.S. history to sample an asteroid.

National Aeronautics Space Agency OSIRIS-REx Spacecraft.

The LPL’s work in the Cassini spacecraft orbit around Saturn is larger than any other university globally.

National Aeronautics and Space Administration/European Space Agency [La Agencia Espacial Europea][Agence spatiale européenne][Europäische Weltraumorganisation](EU)/ASI Italian Space Agency [Agenzia Spaziale Italiana](IT) Cassini Spacecraft.

The University of Arizona laboratory designed and operated the atmospheric radiation investigations and imaging on the probe. The University of Arizona operates the HiRISE camera, a part of the Mars Reconnaissance Orbiter.

U Arizona NASA Mars Reconnaisance HiRISE Camera.

NASA Mars Reconnaissance Orbiter.

While using the HiRISE camera in 2011, University of Arizona alumnus Lujendra Ojha and his team discovered proof of liquid water on the surface of Mars—a discovery confirmed by NASA in 2015. The University of Arizona receives more NASA grants annually than the next nine top NASA/JPL-Caltech-funded universities combined. As of March 2016, The University of Arizona’s Lunar and Planetary Laboratory is actively involved in ten spacecraft missions: Cassini VIMS; Grail; the HiRISE camera orbiting Mars; the Juno mission orbiting Jupiter; Lunar Reconnaissance Orbiter (LRO); Maven, which will explore Mars’ upper atmosphere and interactions with the sun; Solar Probe Plus, a historic mission into the Sun’s atmosphere for the first time; Rosetta’s VIRTIS; WISE; and OSIRIS-REx, the first U.S. sample-return mission to a near-earth asteroid, which launched on September 8, 2016.

NASA – GRAIL Flying in Formation (Artist’s Concept). Credit: NASA.
National Aeronautics Space Agency Juno at Jupiter.

NASA/Lunar Reconnaissance Orbiter.


NASA Parker Solar Probe Plus named to honor Pioneering Physicist Eugene Parker. The Johns Hopkins University Applied Physics Lab.
National Aeronautics and Space Administration Wise/NEOWISE Telescope.

The University of Arizona students have been selected as Truman, Rhodes, Goldwater, and Fulbright Scholars. According to The Chronicle of Higher Education, UArizona is among the top 25 producers of Fulbright awards in the U.S.

The University of Arizona is a member of the Association of Universities for Research in Astronomy , a consortium of institutions pursuing research in astronomy. The association operates observatories and telescopes, notably Kitt Peak National Observatory just outside Tucson.

National Science Foundation NOIRLab National Optical Astronomy Observatory Kitt Peak National Observatory on Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers (55 mi) west-southwest of Tucson, Arizona, Altitude 2,096 m (6,877 ft). annotated.

Led by Roger Angel, researchers in the Steward Observatory Mirror Lab at The University of Arizona are working in concert to build the world’s most advanced telescope. Known as the Giant Magellan Telescope (CL), it will produce images 10 times sharper than those from the Earth-orbiting Hubble Telescope.

GMT Giant Magellan Telescope(CL) 21 meters, to be at the Carnegie Institution for Science’s NOIRLab NOAO Las Campanas Observatory(CL), some 115 km (71 mi) north-northeast of La Serena, Chile, over 2,500 m (8,200 ft) high.

The telescope is set to be completed in 2021. GMT will ultimately cost $1 billion. Researchers from at least nine institutions are working to secure the funding for the project. The telescope will include seven 18-ton mirrors capable of providing clear images of volcanoes and riverbeds on Mars and mountains on the moon at a rate 40 times faster than the world’s current large telescopes. The mirrors of the Giant Magellan Telescope will be built at The University of Arizona and transported to a permanent mountaintop site in the Chilean Andes where the telescope will be constructed.

Reaching Mars in March 2006, the Mars Reconnaissance Orbiter contained the HiRISE camera, with Principal Investigator Alfred McEwen as the lead on the project. This National Aeronautics and Space Agency mission to Mars carrying the UArizona-designed camera is capturing the highest-resolution images of the planet ever seen. The journey of the orbiter was 300 million miles. In August 2007, The University of Arizona, under the charge of Scientist Peter Smith, led the Phoenix Mars Mission, the first mission completely controlled by a university. Reaching the planet’s surface in May 2008, the mission’s purpose was to improve knowledge of the Martian Arctic. The Arizona Radio Observatory , a part of The University of Arizona Department of Astronomy Steward Observatory , operates the Submillimeter Telescope on Mount Graham.

University of Arizona Radio Observatory at NOAO Kitt Peak National Observatory, AZ USA, U Arizona Department of Astronomy and Steward Observatory at altitude 2,096 m (6,877 ft).

Kitt Peak National Observatory in the Arizona-Sonoran Desert 88 kilometers 55 mi west-southwest of Tucson, Arizona in the Quinlan Mountains of the Tohono O’odham Nation, altitude 2,096 m (6,877 ft)

The National Science Foundation funded the iPlant Collaborative in 2008 with a $50 million grant. In 2013, iPlant Collaborative received a $50 million renewal grant. Rebranded in late 2015 as “CyVerse”, the collaborative cloud-based data management platform is moving beyond life sciences to provide cloud-computing access across all scientific disciplines.

In June 2011, the university announced it would assume full ownership of the Biosphere 2 scientific research facility in Oracle, Arizona, north of Tucson, effective July 1. Biosphere 2 was constructed by private developers (funded mainly by Texas businessman and philanthropist Ed Bass) with its first closed system experiment commencing in 1991. The university had been the official management partner of the facility for research purposes since 2007.

U Arizona mirror lab-Where else in the world can you find an astronomical observatory mirror lab under a football stadium?

University of Arizona’s Biosphere 2, located in the Sonoran desert. An entire ecosystem under a glass dome? Visit our campus, just once, and you’ll quickly understand why The University of Arizona is a university unlike any other.

University of Arizona Landscape Evolution Observatory at Biosphere 2.