Unmasking a Monster: A ‘Stunning Confirmation’ of Black Hole Theory

The Event Horizon Telescope’s image of M87* is so good that theorists thought it was too good to be true.

This feature was originally published on April 10 by the University of Waterloo as a part of their public release about Professor Avery Broderick’s theoretical work that led to the first ever image of a black hole. Written by Ian O’Neill, edited by media relations manager Chris Wilson-Smith.

When Avery Broderick initially saw the first image from the Event Horizon Telescope (EHT), he thought it was too good to be true. After playing a critical role in the project since its inception in 2005, Broderick was staring at his ultimate quarry: a picture-perfect observation of a supermassive black hole in another galaxy. Not only was this first image sweet reward for the dedicated global effort to make the impossible possible, it was a beautiful confirmation of Broderick’s predictions and the 100-year-old theories of gravity they are based upon.

“It turns out our predictions were stunningly close; we were spot-on,” said Broderick. “I think this is a stunning confirmation that we are at least on the right track of understanding how these objects work.”

For Broderick, a professor at University of Waterloo and the Perimeter Institute for Theoretical Physics, and a key member of the international Event Horizon Telescope Collaboration, this wasn’t just an image that proved his theoretical models correct, it was the beginning of a historic journey into the unknown, with potentially revolutionary consequences that will reverberate through science and society as a whole.

Making the Impossible Possible

On April 10, the global collaboration showcased the first image of the supermassive black hole in the core of the massive elliptical galaxy M87. The image shows a ghostly bright crescent surrounding a dark disk, a feature that surrounds the most gravitationally extreme region known: a black hole’s event horizon. This first image isn’t only proof that humanity now has the ability to probe right up to the edge of an event horizon, it’s a promise that future observations will help us better understand how supermassive black holes work, how they drive the evolution of their galactic hosts and, possibly, reveal new physics by finally unmasking the true nature of gravity itself.

To Broderick, who has always been fascinated by the undiscovered, it’s mysteries like these that give him the passion to understand how the universe works – an adventure that is an important part of the human story.

“Black holes are the most extreme environments in the universe, so naturally I was hooked for as long as I can remember,” he said. “Nowhere in the universe is there a more perfect laboratory for pushing back the boundaries of our knowledge of gravity’s nature. That makes black holes irresistible.”

Few scientists would debate the reality of black holes, but the first image of M87’s supermassive black hole is definitive proof that these monsters, and their associated event horizons, exist. “These things are real, along with all the consequences for physics,” he said.

In the years preceding this announcement, Broderick and his EHT colleagues developed simulations that modeled what the Earth-spanning virtual telescope might see. And, on comparing his models with the first EHT image, Broderick was amazed.

“That first image was so good that I thought it was a test – it had to be a trial run,” said Broderick, “It’s a beautiful ring shape that’s exactly the right size. In fact, it looks very similar to the images (of theoretical models) we included in proposals for the EHT.”

The ring shape Broderick describes is the bright emissions from the hot gasses immediately surrounding the colossal maw of a supermassive black hole’s event horizon. Located inside the massive elliptical galaxy M87 in the constellation of Virgo, this gargantuan object has a mass of six-and-a-half-billion Suns and measures nearly half a light-day across. This may sound big, but because it’s located 55-million light-years away, it’s far too distant for any single telescope to photograph.

The EHT, however, is a network of many radio telescopes around the world, from the Atacama Desert to the South Pole. By working together – via a method known as very long-baseline interferometry – they create a virtual observatory as wide as our planet and, after two decades of development, the international collaboration has accomplished the impossible by resolving the event horizon around M87’s supermassive black hole.

“This is a project that has a wide breadth of collaboration, geographically – you can’t build an Earth-sized telescope without an Earth-sized collaboration! – but also in expertise, from the engineers who build these advanced telescopes, to the astronomers who work on the day-to-day and the theorists who inspire their observations,” said Broderick.

A Stunning Confirmation

The event horizon is a region surrounding a black hole where the known physics of our universe ends abruptly. Nothing, not even light, can escape a black hole’s incredible gravity, with the event horizon being the ultimate point of no return. What lies beyond the event horizon is open to debate, but one thing is for certain: if you fall inside, you’re not getting out.

Over a century ago, Albert Einstein formulated his theory of general relativity, a theoretical framework that underpins how our universe works, including how event horizons should look. Black holes are the embodiment of general relativity at its most extreme, and event horizons are a manifestation of where space-time itself caves in on itself.

“Event horizons are the end of the safe space of the universe,” said Broderick, “they should have ‘mind the gap’ or ‘mind the horizon’ signs around them!”

Physics has some key unresolved problems that may be answered by the EHT, one of which is the nature of gravity itself, added Broderick. Simply put, gravity doesn’t jibe with our current understanding of other fundamental forces and particles that underpin all matter in the universe. By stress-testing Einstein’s theories right at the edge of a black hole’s event horizon, the EHT will provide physicists with the ultimate laboratory in which to better understand gravity, the force that drives the formation of stars, planets, and the evolution of our universe.

Once we truly understand this fundamental force, the impact could be revolutionary, said Broderick. “Gravity is the key scientific problem facing physics today, and no one fully understands the ramifications of what understanding gravity fully are going to be.”

On an astronomical level, supermassive black holes are intrinsically linked with the evolution of the galaxies they inhabit, but how they form and evolve together is another outstanding mystery.

Supermassive black holes are also the purveyors of creation and doom – they have the power to kick-start star formation as well as preventing stars from forming at all – a dichotomy that astronomers hope to use the EHT to understand.

“These incredibly massive things lie at the centers of galaxies and rule their fates,” said Broderick. “Supermassive black holes are the engines behind active galactic nuclei and distant quasars, the most energetic objects known. Now we’re seeing what they look like, up close, for the first time.”

All galaxies are thought to contain a supermassive black hole, including our own galaxy, the Milky Way. Called Sagittarius A* (or Sgr A*), our supermassive black hole is 2,000 times less massive than the one in M87, but it’s 2,000 times closer – at a distance of 25,000 light-years. This means that the EHT can image both Sgr A* and M87 as they appear approximately the same size in the sky, a situation that is an incredible stroke of luck.

“If you had to choose two sources, these two would be it,” said Broderick. Whereas M87’s supermassive black hole is one of the biggest known and a “real mover and shaker,” Sgr A* is much less massive and considered to be an “everyman of black holes,” he said.

“We had to start somewhere. M87 represents the first end-to-end exercise of the entire EHT collaboration – from data taking to data interpretation,” said Broderick. “The next exercise will happen considerably faster. This is only the beginning.”

Voyage of Discovery

As the scientific benefits of observing supermassive black holes are becoming clear, Broderick pointed out that the impact on society could also be seismic.

“I would hope that an image like this will galvanize a sense of exploration; an exploration of the mind and that of the universe,” he said. “If we can excite people, inspire them to embark on a voyage of discovery in this new EHT era of observational black hole physics, I can only imagine that it will have profound consequences for humanity moving forward.

“I feel incredibly privileged to be a part of this story of exploration – the human story of understanding the universe we inhabit and using that understanding to improve our lives.”

Read more: “First image of black hole captured,” Univ. of Waterloo, by Ian O’Neill

This Is the First Image of a Black Hole

The image is the result of a global collaboration and human ingenuity — a discovery that will change our perception of the universe forever

[EHT Collaboration]

Lurking in the massive elliptical galaxy Messier 87 is a monster. It’s a supermassive black hole, 6.5 billion times the mass of our Sun, crammed inside an event horizon measuring half a light-day across. It’s very far away, over 50 million light-years, but, today, astronomers of the Event Horizon Telescope (EHT) have delivered on a promise that has been two decades in the making: They’ve recorded the first ever image of the bright ring of emissions immediately surrounding M87’s event horizon, the point at which our universe ends and only mystery lies beyond.

The magnitude of this achievement is historic. Not only does this single image prove that black holes actually exist, it is a stunning confirmation of the predictions of general relativity at its most extreme. If this theoretical framework acted somehow differently at the event horizon, the image wouldn’t look as it does. The reality is that general relativity has precisely predicted the size, shape and form of this distant object to an incredible degree of precision.

In the run-up to today’s announcement, I had the incredible fortune to write the University of Waterloo’s press release and feature about the EHT with Avery Broderick, a professor at Waterloo and the Perimeter Institute for Theoretical Physics, and a key member of the international EHT Collaboration. You can read the releases here:

Unmasking a Monster (feature)
First Image of Black Hole Captured (news)

I especially enjoyed discussing Avery’s personal excitement and passion for this project: “I would hope that an image like this will galvanize a sense of exploration; an exploration of the mind and that of the universe,” he said. “If we can excite people, inspire them to embark on a voyage of discovery in this new EHT era of observational black hole physics, I can only imagine that it will have profound consequences for humanity moving forward.”

Like the discovery of the Higgs boson and the detection of gravitational waves, the first image of a black hole will have as much of an impact on society as it will on science and, like Avery, I hope it inspires the next generation of scientists, driving our passion for exploration and understanding how our universe works.

Wow, what a morning.

Watch the NSF’s recording of today’s live feed here:

Will the EHT’s First Black Hole Image Look Like Interstellar’s “Gargantua”?

Not quite.

The supermassive black hole “Gargantua” from the movie “Interstellar.” [Paramount Pictures]

UPDATE: The EHT’s first image has been released! See: This Is the First Image of a Black Hole

Tomorrow, on April 10, the Event Horizon Telescope (EHT) will make an international announcement about a “groundbreaking result” from the global collaboration. Further details as to what this result actually is are under wraps, but as the EHT’s mission is to image a supermassive black hole for the first time, the expectation is that it will be a historic day for humanity. We may actually see what a black hole — more precisely, a black hole’s event horizon — really looks like.

But we already know what a black hole looks like, right? There have been countless science fiction imaginings of black holes over the years and, most recently, the Matthew McConaughey movie “Interstellar” depicted what is touted as the most scientifically-accurate sci-fi black hole ever.

Diving into a black hole has never been so much fun [Paramount Pictures]

Interstellar’s black hole, called “Gargantua,” is a sight to behold and many physicists and CGI experts went out of their way to base that thing on the physics that is predicted to drive these monsters. Physics heavyweight Kip Thorne even advised on how this rotating black hole — a supermassive one at that — should look and behave, based on earlier work by Jean-Pierre Luminet (ScienceAlert has a great article about this).

Back to reality, the EHT may well be presenting its own “Gargantua moment” tomorrow when the first results are presented. The EHT is a global network of radio telescopes all dedicated to probing the final frontier of general relativity. Black holes are the most extreme gravitational objects in the universe and the supermassive monsters that lurk in the cores of most galaxies are true behemoths.

The EHT currently has two targets it hopes to image, the supermassive black hole in the core of our galaxy, the Milky Way, and one inside the massive elliptical galaxy, M87. With a mass of four million Suns, our galaxy’s supermassive black hole is called Sagittarius A* (Sgr A* for short) and is located approximately 25,000 light-years away. But M87’s monster dwarfs our comparatively diminutive specimen — it’s a super-heavyweight among supermassive black holes, with a mass of a whopping 6.5 billion Suns.

In a wonderful stroke of cosmic luck, although M87 is 50 million light-years away, some 2,000 times further away than Sgr A*, it’s also approximately 2,000 times more massive. This means that both Sgr A* and M87 will appear approximately the same size in the sky to the EHT. They are also two wonderful targets to study, as both are very different in nature.

Now, back to Gargantua. As this CGI beauty is based on real physics theory, and assuming the first EHT image doesn’t throw the fidelity of general relativity into doubt, both Gargantua and the two EHT targets should, basically, look the same. Sure, there’s going to be differences based on mass, jets of material, size of accretion disks and other details, but will the EHT first image bear any resemblance to the Interstellar rendering?

Short answer: no, it should look something like this:

Screen capture from Avery Broderick’s 2015 Convergence presentation on the theoretical efforts behind the EHT. Broderick is a professor at the Perimeter Institute and University of Waterloo, and a member of the EHT collaboration. More on this here.

Long answer: It’s all about wavelength. Over to gravitational wave astrophysicist Dr. Chiara Mingarelli, of the Flatiron Center for Computational Astrophysics (CCA), who’s tweet inspired this article:

Gargantua was created with human vision in mind. Our eyes are sensitive to visual wavelengths, from 380 nanometers (violet) to 740 nanometers (red), and movies are very much based on what humans can see (I hear infrared movies are rubbish). But the EHT cares little for nanometer wavelengths — the EHT is all about seeing the universe in millimeter wavelengths, which means it can see things our eyes can’t see. It is a network of radio telescopes all working together as one planet-wide virtual telescope via a clever method known as very long baseline interferometry. By viewing a black hole target at these wavelengths, astronomers have the ability to see straight through the accretion disk, dusty torus (if it has one), jets of material and other nonsense floating around the black hole.

Here’s a few frames from the simulation Dr. Mingarelli is referring to above, wavelength increasing from nanometers to millimeters, left to right:

Frames from the black hole simulation. As the wavelength increases from left to right, features such as the black hole’s accretion disk becomes transparent, allowing the EHT to see emissions from just outside the edge of the event horizon — seen here as a small silhouetted disk (far right). [Credit: Chi-Kwan Chan]

The EHT can see right up to the innermost limit, just before nothing, not even light, can escape the gravitational grasp of the event horizon. Any hot plasma or dust that would otherwise obscure our view of the horizon are transparent at wavelengths more than one millimeter, so we can see the radiation emitted by the hot, turbulent material that is being tortured by the extreme environment right at the horizon.

Gargantua is a glorious rendering of what a supermassive black hole might look like if we could take a trip with Matthew McConaughey and co. (give or take some CGI sparkle for dramatic effect). What the EHT sees is the shadow, or the silhouette, of a black hole’s event horizon — that will likely be either perfectly circular or slightly oblate, if general relativity holds. That’s not to say that Gargantua doesn’t look like Sgr. A* or M87 in visible wavelengths as Hollywood intended, it’s just that the EHT will lack most of Gargantua’s CGI.

So, I’ll be waking up far earlier tomorrow to watch the EHT announcement and keeping my fingers crossed that we’ll finally get to see what an event horizon really looks like.

Here’s a Glimpse of the Jaw-Dropping Physics Surrounding Our Supermassive Black Hole

Simulation of Material Orbiting close to a Black Hole
Simulation of material orbiting close to a black hole (ESO/Gravity Consortium/L. Calçada)

Full disclosure: I wrote the press release for the University of Waterloo, whose researcher, Avery Broderick, developed the theory behind the accretion disk hotspots that have now been observed immediately surrounding our galaxy’s supermassive black hole. Read the full release on the UW website. Below is a long-form version of my article, including quotes from my interview with Broderick.

New observations of the center of our galaxy have, for the first time, revealed hotspots in the disk of chaotic gas orbiting our Milky Way’s supermassive black hole, Sagittarius A* (Sgr A*).

Using the tremendous resolving power of the ESO’s Very Large Telescope array in Chile, astronomers used the new GRAVITY instrument to detect the “wobble” of bright patches embedded inside the accretion disk that spins with the black hole. These bright features are clocking speeds of 30 percent the speed of light.

This is the first time any feature so close to a black hole’s event horizon has been seen and, using thirteen-year-old predictions by astrophysicists, we have a good idea about what’s causing the fireworks.

“It’s mind-boggling to actually witness material orbiting a massive black hole at 30 percent of the speed of light,” said scientist Oliver Pfuhl, of the Max Planck Institute for Extraterrestrial Physics and co-investigator of the study published in the journal Astronomy & Astrophysics. “GRAVITY’s tremendous sensitivity has allowed us to observe the accretion processes in real time in unprecedented detail.”

It is thought that the accretion disk surrounding a black hole is threaded with a powerful magnetic field that frequently becomes unstable and “reconnects.” Similar to the physics that drives the explosive flares in the Sun’s lower corona, these reconnection events rapidly accelerate the plasma in the disk, discharging vast quantities of radiation. These flaring events inside Sgr A*’s accretion disk create hotspots that get pulled in the direction of the material’s spin as it slowly gets digested by the black hole. The GRAVITY instrument was able to deduce that the accretion disk material is orbiting the black hole in a clockwise direction from our perspective and the accretion disk is almost face-on.

Artist’s impression of a hot accretion disk surrounding a black hole [NASA]
The original theory behind these hotspots was derived by Avery Broderick (University of Waterloo) and Avi Loeb (Harvard University) when they were both working at Harvard-Smithsonian Center for Astrophysics in the mid-2000s. In 2005 and 2006, the pair published papers that described theoretical computer models that simulated reconnection events in a black hole’s accretion disk, which caused intense heating and bright flares. The resulting hotspot would then continue to orbit with the speeding accretion disk material, cooling down and spreading out, before another instability and reconnection event would be triggered.

Their work was inspired by the detection of enigmatic bright flares erupting in the vicinity of Sgr A*. These flares were powerful and regular, occurring almost daily. At the time, a few theories were being explored—from supernovas detonating near the supermassive black hole, to asteroids straying too close to the black hole’s gravitational maw—but Broderick and Loeb decided to focus on the extreme region immediately surrounding the black hole’s event horizon.

“Avi and I thought: ‘well, if the flare timescales are close to orbital timescales around the black hole, wouldn’t it be interesting if they are actually bright features embedded in the accretion flow orbiting close to it?’,” Broderick told me.

Black holes are gravitational masters of their domain; anything that drifts too close will be blended into a superheated disk of plasma surrounding them. The matter trapped in the accretion disk then flows toward the event horizon—the point at which nothing, not even light, can escape—and consumed by the black hole via mechanisms that aren’t yet fully understood. The researchers knew that if their model was an accurate depiction of what is going on in the core of our galaxy, these hotspots could be used as visual probes to trace out structures in the accretion disk and in space-time itself.

This plot shows a comparison of the data with the hotspot model including various effects of General and Special Relativity. The continuous blue curve denotes a hot spot on a circular orbit with 1.17 times the innermost stable circular orbit, i.e. just outside the event horizon, of a 4 million solar mass black hole. The axis give the offset from the center in micro-arcseconds [MPE/GRAVITY collaboration]
It’s Sgr A*’s gravity of 4 million Suns that gives the flares a super-boost, however. “In our orbiting hotspot model, a key component of the brightening is actually caused by gravitational lensing,” added Broderick, referring to a consequence of Einstein’s general relativity, when the gravity of black holes warp space-time so much as to form lenses that can magnify the light from distant astronomical sources. “It’s like a black hole analog of a lighthouse.”

Now that GRAVITY has confirmed the existence of these hotspots, Broderick is overjoyed.

“I’m still absorbing it; it’s extremely exciting,” he said. “I’m bouncing around a little bit! The fact you can track these flares is completely new, but we predicted that you could do this.”

The GRAVITY study is led by Roberto Abuter of the European Southern Observatory (ESO), in Garching, Germany, and it describes the detection of three flares emanating from Sgr A* earlier this year. Although the hotspots cannot be fully resolved by the VLT, with the help of Broderick and Loeb’s predictions, Abuter’s team recognized the “wobble” of emissions from the flares as their associated hotspots orbited the supermassive black hole.

This discovery opens a brand-new understanding of the environment immediately surrounding Sgr A* and will complement observations made by the Event Horizon Telescope (EHT), an international collaboration of radio telescopes that are currently taking data to acquire the first image of a black hole, which is expected early next year.

Broderick hopes that these advances will help us to understand how black holes grow and consume matter, and if the predictions of general relativity break down at one of the most gravitationally extreme environments in the universe. But he’s most excited about how the first EHT image of a black hole will impact society as a whole: “It’s going to be a wonderful event, I think it will be an iconic image and it will make black holes real to a lot of people, including a lot of scientists,” he said.

Aside: In 2016, I had the incredible good fortune to visit the VLT at the ESO’s Paranal Observatory as part of the #MeetESO event. I interviewed several VLT and ALMA scientists, including Oliver Pfuhl, and helped produce the mini-documentary below:

Unexpectedly Large Black Holes and Dark Matter

The M87 black hole blasts relativistic plumes of gas 5000 ly from the centre of the galaxy (NASA)
The M87 black hole blasts relativistic plumes of gas 5000 ly from the centre of the galaxy (NASA)

I just spent 5 minutes trying to think up a title to this post. I knew what I wanted to say, but the subject is so “out there” I’m not sure if any title would be adequate. As it turns out, the title doesn’t really matter, so I opted for something more descriptive…

So what’s this about? Astronomers think they will be able to “see” a supermassive black hole in a galaxy 55 million light years away? Surely that isn’t possible. Actually, it might be.

When Very Long Baseline Interferometry is King

Back in June, I reported that radio astronomers may be able to use a future network of radio antennae as part of a very long baseline interferometry (VLBI) campaign. With enough observatories, we may be able to resolve the event horizon of the supermassive black hole lurking at the centre of the Milky Way, some 26,000 light years away from the Solar System.

The most exciting thing is that existing sub-millimeter observations of Sgr. A* (the radio source at the centre of our galaxy where the 4 million solar mass black hole lives) suggest there is some kind of active structure surrounding the black hole’s event horizon. If this is the case, a modest 7-antennae VLBI could observe dynamic flares as matter falls into the event horizon.

It would be a phenomenal scientific achievement to see a flare-up after a star is eaten by Sgr. A*, or to see the rotation of a possibly spinning black hole event horizon.

All of this may be a possibility, and through a combination of Sgr. A*’s mass and relatively close proximity to Earth, our galaxy’s supermassive black hole is predicted to have the largest apparent event horizon in the sky.

Or does it?

M87 Might be a Long Way Away, But…

As it turns out, there could be another challenger to Sgr. A*’s “largest apparent event horizon” crown. Sitting in the centre of the active galaxy called M87, 55 million light years away (that’s over 2,000 times further away than Sgr. A*), is a black hole behemoth.

M87’s supermassive black hole consumes vast amounts of matter, spewing jets of gas 5,000 light years from the core of the giant elliptical galaxy. And until now, astronomers have underestimated the size of this monster.

Karl Gebhardt (Univ. of Texas at Austin) and Thomas Jens (Max Planck Institute for Extraterrestrial Physics in Garching, Germany) took another look at M87 and weighed the galaxy by sifting through observational data with a supercomputer model. This new model accounted for the theorized halo of invisible dark matter surrounding M87. This analysis yielded a shocking result; the central supermassive black hole should have a mass of 6.4 billion Suns, double the mass of previous estimates.

Therefore, the M87 black hole is around 1,600 times more massive than our galaxy’s supermassive black hole.

A Measure for Dark Matter?

Now that the M87 black hole is much bigger than previously thought, there’s the tantalizing possibility of using the proposed VLBI to image M87’s black hole as well as Sgr. A*, as they should both have comparable event horizon dimensions when viewed from Earth.

Another possibility also comes to mind. Once an international VLBI is tested and proven to be an “event horizon telescope,” if we are able to measure the size of the M87 black hole, and its mass is confirmed to be in agreement with the Gebhardt-Jens model, perhaps we’ll have one of the first indirect methods to measure the mass of dark matter surrounding a galaxy…

Oh yes, this should be good.

UPDATE! How amiss of me, I forgot to include the best black hole tune ever:

Publication: The Black Hole Mass, Stellar Mass-to-Light Ratio, and Dark Matter Halo in M87, Karl Gebhardt et al 2009 ApJ 700 1690-1701, doi: 10.1088/0004-637X/700/2/1690.
Via: New Scientist