Astronomers Capture First Image of a Black Hole
Paradigm-shifting Observations of the Gargantuan Black Hole at the Heart of Distant Galaxy Messier 87
- The first direct visual evidence of the supermassive black hole in the centre of the galaxy Messier 87, observed with the Event Horizon Telescope (EHT). Image: EHT Collaboration.
- Antennas of the Event Horizon Telescope used in April 2017 (clockwise from upper left): APEX, Pico Veleta, LMT, JCMT, ALMA, SMT (Heinrich Hertz Telescope), SMA, SPT. Images: APEX, IRAM, G. Narayanan, J. McMahon, JCMT/JAC, S. Hostler, D. Harvey, ESO/C. Malin.
The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes forged through international collaboration — was set up to capture the first images of a black hole. Today, in coordinated press conferences across the globe, EHT researchers including scientists from both, the Max-Planck-Institut für Radioastronomie (MPIfR) in Bonn, Germany, and the Institut de Radioastronomie Millimétrique (IRAM) reveal that they have succeeded, unveiling the first direct visual evidence of a black hole.
Black holes are extreme cosmic objects, containing incredible amounts of mass within a tiny region. The presence of these objects affects its surroundings in extreme ways, warping spacetime and heating any surrounding material until it glows. General relativity predicts that this superheated material will "illuminate" the strongly warped region of spacetime — leading to a dark shadow.
"The results of the EHT observations give us for the first time a direct view on a supermassive black hole and they mark an important milestone for our understanding of the fundamental processes that determine the formation and evolution of galaxies. It is remarkable that in this project we were able to take our astronomical observations and their theoretical interpretation to the success we hope for even faster than expected”, says Anton Zensus, Director at the MPIfR and Chair of the EHT Collaboration Board.
The shadow of a black hole
"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." The black hole in the center of M87 has a mass of more than 6 billion solar masses.
The observations revealed a ring-like structure with a dark central region — the black hole’s shadow. This ring appears in multiple, separate observations using different imaging methods, making the scientists involved confident that they have indeed captured the shadow.
"The confrontation of theory with observations is always a dramatic moment for a theorist. It was a relief and a source of pride to realize that the observations matched so well our predictions." remarks Luciano Rezzolla. His research group at Goethe University Frankfurt has provided fundamental contributions to all stages of the theoretical interpretation of the observations, starting from supercomputer simulations of accretion flows onto black holes and their observational appearance, over to the recognition of the best match between theory and observations.
The EHT: a network of eight telescopes
While astronomers have long studied black holes, directly measuring one required a telescope of unprecedented power and precision. Creating this telescope — the EHT — was a formidable challenge which required upgrading and connecting a worldwide network of eight pre-existing telescopes deployed at a variety of challenging sites. These locations included the summit of Maunakea, Hawai`i; the Chilean Atacama Desert; Antarctica; Mexico; Arizona; and the Spanish Sierra Nevada.
The telescopes contributing to this result were ALMA, APEX (jointly run by MPIfR, ESO and OSO in Sweden), the IRAM 30-meter telescope, the James Clerk Maxwell Telescope, the Large Millimeter Telescope, the Submillimeter Array, the Submillimeter Telescope, and the South Pole Telescope.
“The 30-m IRAM telescope is the most sensitive single-dish telescope within the EHT network”, explains Karl Schuster, director of IRAM and member of the EHT board. “Bringing together the best radio telescopes on four continents we can reach an unprecedented sensitivity and spatial resolution, allowing the scientists to tackle the very limit of observations.” The second IRAM telescope, NOEMA in the French alps, joined the EHT network in September 2018.
The telescopes work together using a technique called very-long-baseline interferometry (VLBI). This synchronises facilities around the world and exploits the rotation of our planet to form one huge, Earth-size telescope. VLBI allows the EHT to achieve a resolution of 20 micro-arcseconds — equivalent to reading a newspaper in New York from a sidewalk café in Berlin.
The data analysis to transform raw data to an image required specific computers (or correlators), hosted by the MPIfR and the MIT Haystack Observatory.
The construction of the EHT represents an effort that has spanned many years, and the observations announced today are the culmination of decades of observational and theoretical work. This is an excellent example of global teamwork requiring 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 EU's European Research Council (ERC), the US National Science Foundation (NSF), and funding agencies in East Asia.
“After decades of research where we could postulate black holes only indirectly, albeit with great precision like with the VLT-GRAVITY experiment, it was LIGO which could make the impact of merging black holes on space-time „audible”. Now we can finally „see” them in our observations. Thus we are able now to investigate these fascinating objects and the extreme warping of spacetime they are causing in a unique way”, says Michael Kramer, Director at MPIfR and Co-PI of the ERC „Black Hole Cam“ project as part of the EHT.
“In the future, Scientists far beyond our field will clearly remember a time before and after this discovery”, concludes Anton Zensus.
The Event Horizon Telescope Collaboration et al.: First M87 EHT Results I: The Shadow of the supermassive Black hole, Astrophysical Journal Letters (2019), L1.
The Event Horizon Telescope Collaboration et al.: First M87 EHT Results II: Array and Instrumentation, Astrophysical Journal Letters (2019), L2.
The Event Horizon Telescope Collaboration et al.: First M87 EHT Results III: Data Processing and Calibration, Astrophysical Journal Letters (2019), L3.
The Event Horizon Telescope Collaboration et al.: First M87 EHT Results IV: Imaging the Central Supermassive Black Hole, Astrophysical Journal Letters (2019), L4.
The Event Horizon Telescope Collaboration et al.: First M87 EHT Results V: Physical Origin of the Asymmetric ring, Astrophysical Journal Letters (2019), L5.
The Event Horizon Telescope Collaboration et al.: First M87 EHT Results VI: The Shadow and Mass of the Central Black Hole, Astrophysical Journal Letters (2019), L6.