ESO, ALMA, and APEX contribute to paradigm-shifting observations of the gargantuan black hole at the heart of the galaxy Messier 87

This breakthrough was announced today in a series of six papers published in a special issue of The Astrophysical Journal Letters. The image reveals the black hole at the center of Messier 87, 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 Sun.

The EHT links telescopes around the globe to form an unprecedented Earth-sized virtual telescope. The EHT offers scientists a new way to study the most extreme objects in the Universe predicted by Einstein's general relativity during the centenary year of the historic experiment that first confirmed the theory.

"We have taken the first picture of a black hole," said 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."

A team of hundreds of scientists pointed the networked telescopes towards Messier 87 and scanned its heart over a period of 10 days. The data they gathered was too big to be sent across the internet. Instead, the data was stored on hundreds of hard drives that were flown to supercomputing centers in Boston and Bonn, Germany, to assemble the information. Prof Doeleman described the achievement as "an extraordinary scientific feat." {module In-article} 

Although the telescopes making up the EHT are not physically connected, they are able to synchronize their recorded data with atomic clocks -- hydrogen masers -- which precisely time their observations. These observations were collected at a wavelength of 1.3 mm during a 2017 global campaign. Each telescope of the EHT produced enormous amounts of data - roughly 350 terabytes per day - which was stored on high-performance helium-filled hard drives. These data were flown to highly specialized supercomputers -- known as correlators -- at the Max Planck Institute for Radio Astronomy and MIT Haystack Observatory to be combined. They were then painstakingly converted into an image using novel computational tools developed by the collaboration.

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 superheating any surrounding material.

"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," explained 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 has allowed us to measure the enormous mass of M87's black hole."

Multiple calibrations 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 supercomputer 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 Observatory. "This makes us confident about the interpretation of our observations, including our estimation of the black hole's mass."

"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 our predictions so well," elaborated EHT Board member Luciano Rezzolla of Goethe Universität, Germany.

Creating 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 high-altitude sites. These locations included volcanoes in Hawai`i 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 1.3mm. VLBI allows the EHT to achieve an angular resolution of 20 micro-arcseconds -- enough to read a newspaper in New York from a café in Paris.

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 Telescope. 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.

European facilities and funding played a crucial role in this worldwide effort, with the participation of advanced European telescopes and the support from the European Research Council -- particularly a €14 million grant for the BlackHoleCam project. Support from ESO, IRAM and the Max Planck Society was also key. "This result builds on decades of European expertise in millimeter astronomy", commented Karl Schuster, Director of IRAM and member of the EHT Board.

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 [8].

"ESO is delighted to have significantly contributed to this result through its European leadership and pivotal role in two of the EHT's component telescopes, located in Chile -- ALMA and APEX," commented ESO Director General Xavier Barcons. "ALMA is the most sensitive facility in the EHT, and its 66 high-precision antennas were critical in making the EHT a success."

"We have achieved something presumed to be impossible just a generation ago," concluded Doeleman. "Breakthroughs in technology, connections between the world's best radio observatories, and innovative algorithms all came together to open an entirely new window on black holes and the event horizon."