An international collaboration presents 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 across the globe, EHT researchers reveal that they have succeeded, unveiling the first direct visual evidence of a supermassive black hole and its shadow.

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 [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 Sun [2].

The EHT links telescopes around the globe to form an Earth-sized virtual telescope with unprecedented sensitivity and resolution [3]. 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 theory [4].

“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.”

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.

“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 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 Observatory [5]. “This makes us confident about the interpretation of our observations, including our estimation of the black hole’s mass.”

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 synchronises 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 Paris [6].

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 [7]. Petabytes of raw data from the telescopes were combined by highly specialised 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,” 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.”

Notes

[1] The shadow of a black hole is the closest we can come to an image of the black hole itself, a completely dark object from which light cannot escape. The black hole’s boundary — the event horizon from which the EHT takes its name — is around 2.5 times smaller than the shadow it casts and measures just under 40 billion km across.

[2] Supermassive black holes are relatively tiny astronomical objects — which has made them impossible to directly observe until now. As a black hole’s size is proportional to its mass, the more massive a black hole, the larger the shadow. Thanks to its enormous mass and relative proximity, M87’s black hole was predicted to be one of the largest viewable from Earth — making it a perfect target for the EHT.

[3] Although the telescopes 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 specialised 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.

[4] 100 years ago, two expeditions set out for the island of Príncipe off the coast of Africa and Sobra in Brazil to observe the 1919 solar eclipse, with the goal of testing general relativity by seeing if starlight would be bent around the limb of the sun, as predicted by Einstein. In an echo of those observations, the EHT has sent team members to some of the world’s highest and isolated radio facilities to once again test our understanding of gravity.

[5] The East Asian Observatory (EAO) partner on the EHT project represents the participation of many regions in Asia, including China, Japan, Korea, Taiwan, Vietnam, Thailand, Malaysia, India and Indonesia.

[6] Future EHT observations will see substantially increased sensitivity with the participation of the IRAM NOEMA Observatory, the Greenland Telescope and the Kitt Peak Telescope.

[7] ALMA is a partnership of the European Southern Observatory (ESO; Europe, representing its member states), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan, together with the National Research Council (Canada), the Ministry of Science and Technology (MOST; Taiwan), Academia Sinica Institute of Astronomy and Astrophysics (ASIAA; Taiwan), and Korea Astronomy and Space Science Institute (KASI; Republic of Korea), in cooperation with the Republic of Chile. APEX is operated by ESO, the 30-meter telescope is operated by IRAM (the IRAM Partner Organizations are MPG (Germany), CNRS (France) and IGN (Spain)), the James Clerk Maxwell Telescope is operated by the EAO, the Large Millimeter Telescope Alfonso Serrano is operated by INAOE and UMass, the Submillimeter Array is operated by SAO and ASIAA and the Submillimeter Telescope is operated by the Arizona Radio Observatory (ARO). The South Pole Telescope is operated by the University of Chicago with specialized EHT instrumentation provided by the University of Arizona.

More Information

This research was presented in a series of six papers published today in a special issue of The Astrophysical Journal Letters, along with a Focus Issue that summarizes the published studies.

Press release images in higher resolution (4000×2330 pixels) can be found here in PNG (16-bit), and JPG (8-bit) format. The highest-quality image (7416×4320 pixels, TIF, 16-bit, 180 Mb) can be obtained from repositories of our partners, NSF and ESO. A summary of latest press and media resources can be found on this page.

The EHT collaboration involves more than 200 researchers from Africa, Asia, Europe, North and South America. The international collaboration is working to capture the most detailed black hole images ever by creating a virtual Earth-sized telescope. Supported by considerable international investment, the EHT links existing telescopes using novel systems — creating a fundamentally new instrument with the highest angular resolving power that has yet been achieved.

The individual telescopes involved are; ALMA, APEX, the IRAM 30-meter Telescope, the IRAM NOEMA Observatory, the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope Alfonso Serrano (LMT), the Submillimeter Array (SMA), the Submillimeter Telescope (SMT), the South Pole Telescope (SPT), the Kitt Peak Telescope, and the Greenland Telescope (GLT).

The EHT collaboration consists of 13 stakeholder institutes; the Academia Sinica Institute of Astronomy and Astrophysics, the University of Arizona, the University of Chicago, the East Asian Observatory, Goethe-Universitaet Frankfurt, Institut de Radioastronomie Millimétrique, Large Millimeter Telescope, Max Planck Institute for Radio Astronomy, MIT Haystack Observatory, National Astronomical Observatory of Japan, Perimeter Institute for Theoretical Physics, Radboud University and the Smithsonian Astrophysical Observatory.

Including the powerful ALMA into an array of telescopes for the first time, astronomers have found that the emission from the supermassive black hole Sagittarius A* (Sgr A*) at the center of our Galaxy comes from a smaller region than previously thought. This may indicate that a radio jet from Sgr A* is pointed almost toward us. The paper, led by the Nijmegen PhD student Sara Issaoun, is published in the Astrophysical Journal.

So far, a foggy cloud of hot gas has prevented us from making sharp images of the supermassive black hole Sgr A* and causing doubt on its true nature.  Astronomers have now included for the first time the powerful ALMA telescope in northern Chile into a global network of radio telescopes to peer through this fog, but the source keeps surprising them: its emission region is so small that the source may actually have to point directly at us.

Observing at a frequency of 86 GHz with the technique of Very Long Baseline Interferometry (VLBI), which combines many telescopes to form a virtual telescope the size of the Earth, the team succeeded in mapping out the exact properties of the light scattering blocking our view of Sgr A*. The removal of most of the scattering effects has produced a first image of the surroundings of the black hole.

Top left: simulation of Sgr A* at 86 GHz. Top right: simulation with added effects of scattering. Bottom right: scattered image from the observations, this is how we see Sgr A* on the sky. Bottom left: the unscattered image, after removing the effects of scattering in our line of sight, this is how Sgr A* really looks.  Credit: S. Issaoun, M. Mościbrodzka, Radboud University/ M. D. Johnson, CfA

The high quality of the unscattered image has allowed the team to constrain theoretical models for the gas around Sgr A*. The bulk of the radio emission is coming from a mere 300 millionth of a degree, and the source has a symmetrical morphology. “This may indicate that the radio emission is produced in a disk of infalling gas rather than by a radio jet,” explains Issaoun, who has tested several computer models against the data. “However, that would make Sgr A* an exception compared to other radio emitting black holes. The alternative could be that the radio jet is pointing almost at us.”

Issaoun’s supervisor Heino Falcke, Professor of Radio Astronomy at Radboud University, calls this statement very unusual, but he also no longer rules it out. Last year, Falcke would have considered this a contrived model, but recently the GRAVITY team came to a similar conclusion using ESO’s Very Large Telescope Interferometer of optical telescopes and an independent technique. “Maybe this is true after all”, concludes Falcke, “and we are looking at this beast from a very special vantage point.”

Supermassive black holes are common in the centers of galaxies and may generate the most energetic phenomena in the known universe. It is believed that, around these black holes, matter falls in a rotating disk and part of this matter is expelled in opposite directions along two narrow beams, called jets, at speeds close to the speed of light, which typically produces a lot of radio light. Whether the radio emission we see from Sgr A* comes from the infalling gas or the outflowing jet is a matter of intense debate.

Sgr A* is the nearest supermassive black hole and ‘weighs’ about 4 million solar masses. Its apparentsize on the sky is less than a 100 millionth degree, which corresponds to the size of a tennis ball on the moon as seen from the Earth. To measure this, the technique of VLBI is required. The resolution achieved with VLBI is further increased by the observation frequency. The highest frequency to date to use VLBI is 230 GHz. “The first observations of Sgr A* at 86 GHz date from 26 years ago, with only a handful of telescopes. Over the years, the quality of the data has improved steadily as more telescopes join,” says J. Anton Zensus, director of the Max Planck Institute for Radio Astronomy.

The research of Issaoun and international colleagues describes the first observations at 86 GHz in which ALMA also participated, by far the most sensitive telescope at this frequency. ALMA became part of the Global Millimeter VLBI Array (GMVA) in April 2017. The participation of ALMA, made possible by the ALMA Phasing Project effort, has been decisive for the success of this project.

The Global Millimeter VLBI Array, joined by ALMA. Credit: S. Issaoun, Radboud University/ D. Pesce, CfA

“Sgr A* is located in the southern sky, thus the participation of ALMA is important not only because of its sensitivity but also because of its location in the southern hemisphere,” says Ciriaco Goddi, from the European ALMA Regional Center node in the Netherlands (ALLEGRO, Leiden Observatory). In addition to ALMA, twelve telescopes in North America and Europe also participated in the network. The resolution achieved was twice as large as in previous observations at this frequency and produced the first image of Sgr A* that iscompletely free of interstellar scattering (an effect caused by density irregularities in the ionized material along the line of sight between Sgr A* and the Earth).

To remove the scattering and obtain the image, the team used a technique developed by Michael Johnson of the Harvard-Smithsonian Center for Astrophysics (CfA). “Even though scattering blurs and distorts the image of Sgr A*, the incredible resolution of these observations allowed us to pin down the exact properties of the scattering,”says Johnson.“We could then remove most of the effects from scattering and begin to see what things look like near the black hole. The great news is that these observations show that scattering will not prevent the Event Horizon Telescope from seeing a black hole shadow at 230 GHz, if there’s one to be seen.”

Future studies at different wavelengths will provide complementary information and further observational constraints for this source, which holds the key to a better understanding of black holes, the most exotic objects in the known universe.

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More information? Contact:

Article:

The Size, Shape, and Scattering of Sagittarius A * at 86 GHz: First VLBI with ALMA: Issaoun, M. D. Johnson, L. Blackburn, C. D. Brinkerink, M. Mościbrodzka, A. Chael, C. Goddi, I. Martí-Vidal, J. Wagner, S. S. Doeleman, H. Falcke, T. P. Krichbaum, K. Akiyama, U. Bach, K. L. Bouman, G. C. Bower, A. Broderick, I. Cho, G. Crew, J. Dexter, V. Fish, R. Gold, J. L. Gómez, K. Hada, A. Hernández-Gómez, M. Janßen M. Kino, M. Kramer, L. Loinard, R.-S. Lu, S. Markoff, D. P. Marrone, L. D. Matthews, J. M. Moran, C. Müller, F. Roelofs, E. Ros, H. Rottmann, S. Sanchez, R. P. J. Tilanus, P. de Vicente, M. Wielgus, J. A. Zensus and G.-Y. Zhao.

Article reference: Issaoun, S., et al. 2019, ApJ, 871, 30 (https://doi.org/10.3847/1538-4357/aaf732).

Arxiv link: https://arxiv.org/abs/1901.06226

Astronomers from the BlackHoleCam team led and worked on the research.

The research team is also part of the EHT consortium, an international partnership of thirteen institutes from ten countries: Germany, the Netherlands, France & Spain (via IRAM), USA, Mexico, Japan, Taiwan, Canada and China (via EAO). http://www.eventhorizontelescope.org/

The participation of ALMA through the ALMA Phasing Project has been decisive for the success of this project. https://www.almaobservatory.org/

The data were correlated at the Max Planck Institute for Radioastronomy (MPIfR). Data analysis software was developed at the MIT Haystack Observatory and the Smithsonian Astrophysical Observatory.

This work is supported by the ERC Synergy Grant “BlackHoleCam: Imaging the Event Horizon of Black Holes”, Grant 610058. The National Science Foundation (AST-1126433, AST-1614868, AST-1716536) and the Gordon and Betty Moore Foundation (GBMF-5278) have provided financial support for this work. This work was supported in part by the Black Hole Initiative at Harvard University, which is supported by a grant from the John Templeton Foundation. The GMVA is partially supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730562 (RadioNet).

This press release was originally posted at https://www.ru.nl/astrophysics/news-agenda/news/news-ru/lifting-veil-black-hole-heart-our-galaxy/

At the centre of our own galaxy there is a black hole, called Sagittarius A*. In anticipation of the first actual photograph of a black hole, an international project  involving astronomers of BlackHoleCam, Jordy Davelaar and colleagues have built a virtual reality (VR) simulation of the phenomenon. The VR simulation was published in Computational Astrophysics and Cosmology on November 19th. We asked him two questions about this simulation.

Credits: Jordy Davelaar, Thomas Bronzwaer, Daniel Kok, Ziri Younsi, Monika Moscibrodzka and Heino Falcke. Music: Thomas Bronzwaer

What exactly are we seeing in the simulation?
‘In the simulation you move around the black hole at the centre of our galaxy. The light you see comes from matter that disappears into the black hole in a vortex-like way; due to the extreme conditions it becomes a plasma that starts to glow. This light is then deflected and deformed by the powerful gravity of the black hole. Some of the plasma is ejected away from the black hole in a jet stream at very high velocity. You can see the path that a particle could take in such a plasma flow; it moves continually inwards in a spiral trajectory until it is ejected in the jet stream.’

Why do you think Sagittarius A* looks like this?
‘The purpose of the simulation is to make the most realistic possible representation of the direct environment of Sagittarius A*. The camera calculates at every point what the environment would look like if we were able to see radio-emissions. To do this we used models that were developed in part by Nijmegen astronomers and radio telescope observations.

In our coding for the simulation, we used Einstein’s General Theory of Relativity. This enabled us to visualize all the effects you would experience when you move around a black hole, such as light deflection, the distortion of your field of view due to your speed. This provides the most realistic possible experience of what we think this environment is like. The simulation is unique and is even more realistic than the visualizations in the film “Interstellar”.’

Publication
Observing Supermassive Black Holes In Virtual Reality, Computational Astrophysics and Cosmology, Jordy Davelaar, Thomas Bronzwaer, Daniel Kok, Ziri Younsi, Monika Moscibrodzka and Heino Falcke. https://comp-astrophys-cosmol.springeropen.com/articles/10.1186/s40668-018-0023-7

The research was made possible by the ERC Synergy grant titled ‘BlackHoleCam’ given to Heino Falcke (Radboud University), M. Kramer (Max Planck Institute for Radioastronomy), L. Rezzolla (Goethe University Frankfurt).

More information? Please contact
Jordy Davelaar, j.davelaar@astro.ru.nl, +31 24 365 3206 or +31 6 10 00 39 65
Science communication Radboud University, +31 24 361 6000, media@ru.nl.
Radboud University stimulates its leading research areas. Astrophysics is one of them.

This press release was originally posted at https://www.ru.nl/english/news-agenda/news/vm/imapp/astrophysics/2018/flying-past-black-hole-simulator/

Measurement of the “Gravitational Redshift” in the Orbit of the Star S2 around the Supermassive Black Hole at the center of the Milky Way with GRAVITY

Observations made with ESO’s Very Large Telescope have for the first time revealed the effects predicted by Einstein’s general relativity on the motion of a star passing through the extreme gravitational field near the supermassive black hole in the centre of the Milky Way. This long-sought result represents the climax of a 26-year-long observation campaign using ESO’s telescopes in Chile.