Illinois contributes to EHT's capturing first-ever image of a black hole
4/10/2019 8:07:00 AM
Astronomers capture first image of a black hole —
U of I researchers contribute to paradigm-shifting observations of the gargantuan
black hole at the heart of distant galaxy Messier 87
The Event Horizon Telescope (EHT)—a planet-scale array of eight ground-based radio telescopes forged through international collaboration—was designed to capture images of a black hole. Today, in coordinated press conferences around the globe, EHT researchers revealed that they have succeeded, unveiling the first direct visual evidence of a supermassive black hole and its shadow.
The image reveals the black hole at the center of Messier 87 (M87)1, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides 55 million light-years from Earth and has a mass 6.5 billion times that of the Sun2.
The EHT links telescopes around the globe to form an Earth-sized virtual telescope with unprecedented sensitivity and resolution3. The EHT is the result of years of international collaboration and offers scientists a new way to study the most extreme objects in the universe predicted by Einstein’s general relativity, during the centennial year of the historic experiment that first confirmed the theory4.
"We have taken the first picture of a black hole," says EHT project director Sheperd S. Doeleman of the Center for Astrophysics | Harvard & Smithsonian. "This is an extraordinary scientific feat accomplished by a team of more than 200 researchers."
Black holes are extraordinary cosmic objects with enormous masses but extremely compact sizes. The presence of these objects affects their environment in extreme ways, warping spacetime and super-heating any surrounding material. This breakthrough was announced today in a series of six papers published in a special issue of Astrophysical Journal Letters. University of Illinois at Urbana-Champaign Professor of Physics and Astronomy Charles Gammie, a member of the EHT Science Council Board, co-led the theory working group and served as co-coordinator of Paper V, focused on the theoretical interpretation of the EHT data.
“If immersed in a bright region, like a disc of glowing gas, we expect a black hole to create a dark region similar to a shadow—something predicted by Einstein’s general relativity that we’ve never seen before,” explains chair of the EHT Science Council Heino Falcke of Radboud University, the Netherlands. “This shadow, caused by the gravitational bending and capture of light by the event horizon, reveals a lot about the nature of these fascinating objects and allowed us to measure the enormous mass of M87’s black hole.”
Multiple calibration and imaging methods have revealed a ring-like structure with a dark central region—the black hole’s shadow—that persisted over multiple independent EHT observations.
"Once we were sure we had imaged the shadow, we could compare our observations to extensive computer models that include the physics of warped space, superheated matter and strong magnetic fields. Many of the features of the observed image match our theoretical understanding surprisingly well,” remarks Paul T.P. Ho, EHT Board member and Director of the East Asian Observatory5. “This makes us confident about the interpretation of our observations, including our estimation of the black hole’s mass.”
The U of I research group led by Gammie made significant contributions to the collaboration’s theoretical analysis. Physics graduate students George N. Wong and Ben Prather and former graduate student Ben R. Ryan worked with Gammie to generate an extensive library of 3-dimensional time-dependent numerical models, which they compared with the 5 petabytes of EHT data. The local effort was a massive computational undertaking, and Gammie’s team developed sophisticated computer code to make running and analyzing the simulations as efficient as possible.
The U of I team’s research allowed the EHT collaboration to constrain the spin of the black hole, which is related to the asymmetry of the ring in the EHT image. The U of I researchers’ work also shed light on the physical processes underlying the large radio jet emanating from M87’s black hole.
“M87 is the nearest galaxy with a supermassive black hole that’s generating a powerful jet—a beautiful streamer made of plasma travelling at close to the speed of light,” Gammie notes. “One of the great mysteries in astronomy has been how such jets are launched. Our simulations, which are based on the motion of magnetic fields and hot gas near the black hole, showed that the jets are powered by the black hole itself. Magnetic fields act to brake the rotation of the black hole and transfer its rotational energy to the jet."
Creating the EHT was a formidable challenge that required upgrading and connecting a worldwide network of eight pre-existing telescopes deployed at a variety of challenging high-altitude sites. These locations included volcanoes in Hawaii and Mexico, mountains in Arizona and the Spanish Sierra Nevada, the Chilean Atacama Desert, and Antarctica.
The EHT observations use a technique called very-long-baseline interferometry (VLBI), which synchronizes telescope facilities around the world and exploits the rotation of our planet to form one huge, Earth-size telescope observing at a wavelength of 1.3 mm. VLBI allows the EHT to achieve an angular resolution of 20 micro-arcseconds—enough to read a newspaper in New York from a sidewalk café in Paris6.
The telescopes contributing to this result were ALMA, APEX, the IRAM 30-meter telescope, the James Clerk Maxwell Telescope, the Large Millimeter Telescope Alfonso Serrano, the Submillimeter Array, the Submillimeter Telescope, and the South Pole Telescope7. Petabytes of raw data from the telescopes were combined by highly specialized supercomputers hosted by the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory.
The construction of the EHT and the observations announced today represent the culmination of decades of observational, technical, and theoretical work. This example of global teamwork required close collaboration by researchers from around the world. Thirteen partner institutions worked together to create the EHT, using both pre-existing infrastructure and support from a variety of agencies. Key funding was provided by the US National Science Foundation (NSF), the EU's European Research Council (ERC), and funding agencies in East Asia.
“We have achieved something presumed to be impossible just a generation ago,” concludes Doeleman. “Breakthroughs in technology and the completion of new radio telescopes over the past decade enabled our team to assemble this new instrument—designed to see the unseeable.”
Research contributing to the Event Horizon Telescope done at the University of Illinois at Urbana-Champaign was funded by the National Science Foundation. The conclusions presented are those of the researchers and not necessarily those of the funding agencies.
Color-coded representation of the brightness of electromagnetic emission (at 230 GHz), generated from a simulation of M87's supermassive black hole. Color corresponds to brightness on a logarithmic scale, where red is 50 times as bright as yellow, and yellow is 50 times as bright as light blue. The viewpoint is aligned with the spin axis, looking straight down at the pole from above. The bright red circle corresponds to photon paths that are trapped in near-circular orbits due to the spacetime-warping effects of Einstein's general relativity. This circle is often called the photon ring and is a few times larger than the event horizon. The rotating wisps correspond to high temperature plasma that is falling onto the black hole from the surrounding accretion disk. The darker depression at the center of the image, the so-called black hole shadow, is an important signature of general relativity and marks the set of photons that trace back to the event horizon of the black hole itself. Credit: EHT/G. Wong, B. Prather, C. Gammie