Categories: AstronomyBlack HolesScience

It’s Finally here. The First Ever Image of a Black Hole

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. In coordinated press conferences across the globe, EHT researchers revealed that they succeeded, unveiling the first direct visual evidence of the supermassive black hole in the centre of Messier 87 and its shadow. The shadow of a black hole seen here 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. While this may sound large, this ring is only about 40 microarcseconds across — equivalent to measuring the length of a credit card on the surface of the Moon. 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 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. Credit: Event Horizon Telescope Collaboration

“We have taken the first picture of a black hole.”

EHT project director Sheperd S. Doeleman of the Center for Astrophysics | Harvard & Smithsonian.

What was once un-seeable can now be seen. Black holes, those difficult-to-understand singularities that may reside at the center of every galaxy, are becoming seeable. The Event Horizon Telescope (EHT) has revealed the first-ever image of a black hole, and with this image, and all the science behind it, they may help crack open one of the biggest mysteries in the Universe.

The black hole in this image resides at the center of M87, a massive galaxy that’s in the Virgo cluster of galaxies. Called M87* (M87-star), it’s a behemoth, at about 6.5 billion times the mass of the Sun. M87* is about 55 million light years from Earth. For now we only have this picture of M87*, but pictures of our very own black hole, Sagittarius A* at the center of the Milky Way, are still coming.

This may be the worst kept secret of the past couple weeks. Ever since the EHT said they would be announcing some important results, the excitement has built.

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“This is an extraordinary scientific feat accomplished by a team of more than 200 researchers.“

EHT project director Sheperd S. Doeleman of the Center for Astrophysics | Harvard & Smithsonian.

“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.“

We already knew, or were pretty sure we knew, what it would look like. Even a year ago, scientists at the EHT were pretty certain, and they released a simulated image of what this first-ever image of a black hole would look like. But with science, you don’t know until you know. That’s why this image is so important.

Simulated view of a black hole released by the EHT in April, 2017. Credit: Bronzwaer/Davelaar/Moscibrodzka/Falcke, Radboud University

The image matches with what astrophysicists theorized it would look like. This is a real feather in the cap for science, and shows the power of theory developed from evidence. It shows that even though black holes are mysterious, and that their ultimate nature is still unknowable at this moment in history, we can still nibble around the edges. Over time we can remove more and more of the mystery until we understand what remains.

“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.“

“The confrontation of theory with observations is always a dramatic moment for a theorist. It was a relief and a source of pride to realise that the observations matched our predictions so well,” elaborated EHT Board member Luciano Rezzolla of Goethe Universität, Germany.

An optical image of the M87 galaxy captured by the European Southern Observatory’s Very Large Telescope. M87* lies at the very center of that bright mass. Image Credit: ESO

Black holes are extreme objects. They are massive, almost incomprehensibly massive, yet in terms of size they are tiny. Because of their extreme nature, they affect their environment in extreme way.

As they attract matter to themselves with their massive gravitational pull, that matter begins to rotate around the hole, forming a disc. The closer it gets to the black hole, the faster the matter rotates. It heats up, and emits energy we can see. This is the source of light that can be imaged, even though the singularity at the center of M87* can not be seen.

What can be seen is the shadow that the black hole casts on this light.

This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. This thin disc of rotating material consists of the leftovers of a Sun-like star which was ripped apart by the tidal forces of the black hole. Shocks in the colliding debris as well as heat generated in accretion led to a burst of light, resembling a supernova explosion.

“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.“

This artist’s impression depicts the black hole at the heart of the enormous elliptical galaxy Messier 87 (M87). This black hole was chosen as the object of paradigm-shifting observations by the Event Horizon Telescope. The superheated material surrounding the black hole is shown, as is the relativistic jet launched by M87’s black hole.
ESO/M. Kornmesser

The EHT isn’t a single telescope. It’s more like a virtual telescope, and it’s more properly called a Very Long Baseline Interferometer. What that means is they’ve linked up radio antennae around the globe to observe the same object. This gives the telescope “high angular resolving power.” Basically, the bigger the ‘scope, the more detail we can see. And no telescope is as big as the Earth, except for the EHT. The extremely high resolving power of the EHT means it can see a credit card on the surface of the Moon.

The EHT combines the power of radio-telescope facilities in Hawaii, Mexico, high in the Chilean Atacama Desert, down in Antarctica, and other locations. The data they produce is taken to computing centers at the Max Planck Institute for radio astronomy and the MIT Haystack Observatory, where special atomic clocks are used to calibrate and combine the data, producing this image.

If one of humanity’s goals is to understand nature, then the people behind the Event Horizon Telescope are well on their way. The EHT isn’t done yet. There will be more science results coming from the over 200 researchers working on the project.

In anticipation of the first image of a black hole, Jordy Davelaar and colleagues built a virtual reality simulation of one of these fascinating astrophysical objects. Their simulation shows a black hole surrounded by luminous matter. This matter disappears into the black hole in a vortex-like way, and the extreme conditions cause it to become a glowing plasma. The light emitted is then deflected and deformed by the powerful gravity of the black hole. Image Credit:
Jordy Davelaar et al./Radboud University/BlackHoleCam

This first black hole image isn’t exactly a surprise, but the EHT may still reveal some surprising things about black holes.

The EHT is focused on two holes: M87* in Virgo, and Sagittarius A*, at the heart of our Milky Way galaxy. They represent two types of black holes. M87* emits jets of material, while Sag. A* doesn’t. We don’t why.

Images of Sag. A* are still coming, so stay tuned. Maybe the EHT will be able to answer why some black holes emit these relativistic jets, and why some don’t.

If you’re curious about black holes, and who isn’t, then the following video may contain some of the answers you’re looking for.

Evan Gough