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.

Primordial Black Holes Probably Don’t Pack a Dark Matter Punch

Waiting for the Andromeda galaxy’s stars to twinkle may have extinguished hope for tiny black holes being a significant dark matter candidate

Should a black hole drift in front of a star, it could trigger a microlensing event, so astronomers set out to estimate the number of primordial black holes in Andromeda [Kavli IPMU]

Using the Andromeda galaxy as a huge detector, astronomers have taken a stab at seeing the unseeable — possibly disproving a hypothesis first put forward by the late Stephen Hawking 45 years ago.

According to Hawking’s work, the universe should be filled with black holes that were formed at the beginning of time, when the universe was a chaotic soup of energy just after the Big Bang. Known as “primordial” black holes, these ancient objects are hypothesized to invisibly occupy modern galaxies, including our own, boosting their dark matter mass.

These black holes aren’t the supermassive monsters that lurk in the centers of most galaxies; they’re not even stellar-mass black holes, formed after massive stars go supernova. Primordial black holes are much smaller than that, having leaked most of their mass via Hawking radiation since their formation 13.8 billion years ago. They should, however, still have powerful gravitational effects on the space surrounding them and, in new research published last week in the journal Nature Astronomy, an international team of researchers have leveraged these hypothetical black holes’ space-time-warping powers to reveal their presence.

Or not, as it turns out.

Central to this study is the effect of microlensing. This astronomical method relies on an object passing between us and a distant star. It has been used to great effect when detecting distant exoplanets, or rogue brown dwarfs wandering through interstellar space. Should one of these objects drift directly in front of a star, its gravitational field can create a magnification effect that briefly brightens the star’s light. The gravitational field creates a natural “lens” out of space-time itself, a prediction that arises from Einstein’s general relativity.

The effect of gravitational microlensing on a star in the Andromeda galaxy should a primordial black hole drift in front [Kavli IPMU]

It stands to reason that even though primordial black holes don’t generate any light themselves, if you stare at at entire galaxy for long enough, you should see a lot of twinkling stars, or microlensing events caused by the hypothetical swarm of primordial black holes the galaxy should contain. Count the number of events, and you can take a statistical stab the total number of primordial black holes in a galaxy like Andromeda, thereby providing an estimate as to how much of the universe’s missing dark matter mass is made up from these objects.

Using the power of the Subaru telescope in Hawaii, the researchers put this to the test, capturing 190 consecutive images of Andromeda over seven hours during one night with the observatory’s Hyper Suprime-Cam digital camera. If Hawking’s theory held, the telescope should have recorded approximately 1,000 microlensing events caused by primordial black holes with a mass of less than our moon drifting in front of Andromeda’s stars. Alas, only one microlensing event was detected that night. From this observation campaign alone, the researchers estimate that primordial black holes make up no more than 0.1 percent of the total dark matter mass in our universe.

Although this elegant study doesn’t necessarily disprove the existence of primordial black holes — one single event is interesting, but not compelling — it does put a wrench in the idea that they dominate the mass holed up in dark matter. So, the quest to understand the nature of dark matter grinds on and, with the help of this study, astronomers have now narrowed down the search by removing primordial black holes from the dark matter equation.

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:

Black Hole’s Personality Not as Magnetic as Expected

V404Cyg_XRT_halo_fullsize
This 2015 NASA Swift observation of V404 Cygni shows the X-ray echoes bouncing off rings of dust surrounding the binary system after the X-ray nova (Andrew Beardmore/Univ. of Leicester/NASA/Swift)

In 2015, a stellar-mass black hole in a binary star system underwent an accretion event causing it to erupt brightly across the electromagnetic spectrum. Slurping down the plasma from its stellar partner — an unfortunate sun-like star — the eruption became a valuable observation for astronomers and, in a recent study, researchers have used the event to better understand the magnetic environment surrounding the black hole.

The binary system in question is V404 Cygni, located 7,795 light-years from Earth, and that 2015 outburst was an X-ray nova, an eruption that previously occurred in 1989. Detected by NASA’s Swift space observatory and the Japanese Monitor of All-sky X-ray Image (MAXI) on board the International Space Station, the event quickly dimmed, a sign that the black hole had consumed its stellar meal.

Combining these X-ray data with observations by radio, infrared and optical telescopes, an international team of astronomers were able to measure emissions from the plasma close to the black hole’s event horizon as it cooled.

The black hole was formed after a massive star ran out of fuel and exploded as a supernova. Much of the magnetism of the progenitor star would have been retained post-supernova, so by measuring the emissions from the highly charged plasma, astronomers have a tool to probe deep inside the black hole’s “corona.” Like the sun’s corona — which is a magnetically-dominated region where solar plasma interacts with our star’s magnetic field (producing the solar wind and solar flares, for example) — it’s predicted that there should be a powerful interplay between the accreting plasma and the black hole’s coronal magnetism.

As charged particles interact magnetic fields, they experience acceleration radially (i.e. they spin around the magnetic field lines that guide their direction of propagation) and, should the magnetism be extreme (in a solar or, indeed, black hole’s corona), this plasma can be accelerated to relativistic speeds. In this case, synchrotron radiation may be generated. By measuring the radiation across all wavelengths, astronomers can thereby probe the magnetic environment close to a black hole as this radiation is directly related to how powerful a magnetic field is generating it.

black-hole
A black hole with a magnetic field threading through an accretion disk (ESO)

According to the study, published in the journal Science on Dec. 8, V404 Cygni’s hungry black hole has a much weaker magnetic field than theory would suggest. And that’s a bit of a problem.

The researchers write: “Using simultaneous infrared, optical, x-ray, and radio observations of the Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its 2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the corona. This measurement is substantially lower than previous estimates for such systems, providing constraints on physical models of accretion physics in black hole and neutron star binary systems.”

Black holes are poorly understood, but with the advent of gravitational wave (and “multimessenger”) astronomy and the excitement surrounding the Event Horizon Telescope, in the next few years we’re going to get a lot more intimate with these gravitational enigmas. Why this particular black hole’s magnetic environment is weaker than what would be expected, however, suggests that our theories surrounding black hole evolution are incomplete, so there will likely be some surprises in store.

“We need to understand black holes in general,” said collaborator Chris Packham, associate professor of physics and astronomy at The University of Texas at San Antonio (UTSA), in a statement. “If we go back to the very earliest point in our universe, just after the Big Bang, there seems to have always been a strong correlation between black holes and galaxies. It seems that the birth and evolution of black holes and galaxies, our cosmic island, are intimately linked. Our results are surprising and one that we’re still trying to puzzle out.”

Gravitational Waves Might Reveal Primordial Black Hole Mergers Just After the Big Bang

Web_C0288811-Black_hole_merger_and_gravitational_waves-SPL
RUSSELL KIGHTLEY/SCIENCE PHOTO LIBRARY

Imagine the early universe: The first massive stars sparked to life and rapidly consumed their supply of hydrogen. These “metal poor” stars lived hard and died fast, burning quickly and then exploding as powerful supernovas. This first population of stars seeded the universe with heavier elements (i.e. elements heavier than helium, elements known as “metals” by astronomers) and their deaths created the first stellar-mass black holes.

But say if there were black holes bumbling around the universe before the first supernovae? Where the heck did they come from?

Quantum Fluctuations

Some models of universal evolution suggests that immediately after the Big Bang, some 13.82 billion years ago, quantum fluctuations created pockets of dense matter as the universe started to expand. As inflation occurred and the universe cooled, these density fluctuations formed the vast large-scale structure of the universe that we observe today. These cosmological models suggest the early quantum density fluctuations may have been dramatic enough to create black holes — known as primordial black holes — and these ancient Big Bang remnants may still exist to this day.

The theoretical models surrounding the genesis of primordial black holes, however, are hard to test as observing the universe immediately after the Big Bang is, needless to say, very difficult. But now we know gravitational waves exist and physicists have detected the space-time ripples generated by the collision and merger of stellar-mass black holes and neutron stars, astronomers have an observational tool at their disposal.

Simple Idea, Not-So-Simple Implementation

In a new study published in Physical Review Letters, researchers have proposed that if we have the ability to detect gravitational waves produced before the first stars died, we may be able to carry out astronomical archaeological dig of sorts to possibly find evidence of these ancient black holes.

“The idea is very simple,” said physicist Savvas Koushiappas, of Brown University, in a statement. “With future gravitational wave experiments, we’ll be able to look back to a time before the formation of the first stars. So if we see black hole merger events before stars existed, then we’ll know that those black holes are not of stellar origin.”

Primordial black holes were first theorized by Stephen Hawking and others in the 1970’s, but it’s still unknown if they exist or whether we could even distinguish the primordial ones from the garden variety of stellar-mass black holes (it’s worth noting, however, that primordial black holes would have a range of masses and not restricted to stellar masses). Now we can detect gravitational waves, however, this could change as gravitational wave detector sensitivity increases, scientists will probe more distant (and therefore more ancient) black hole mergers. And, if we can detect gravitational waves originating from black hole mergers younger than 65 million years after the Big Bang, the researchers say, those black holes wouldn’t have a stellar origin as the first stars haven’t yet died — they could have only been born from the quantum mess immediately after the birth of our universe.

Read more about this fascinating line of investigation in the Brown University press release.

How Gravitational Waves Led Us to Neutron Star Gold

grav-neutron-stars
Artist impression of a violent neutron star collision (Dana Berry, SkyWorks Digital, Inc.)

One hundred and thirty million years ago in a galaxy 130 million light-years away, two neutron stars met their fate, merging as one. Trapped in a gravitational embrace, these two stellar husks spiraled closer and closer until they violently ripped into one another, causing a detonation that reverberated throughout the cosmos.

On August 17, the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and Italian Virgo gravitational wave detector felt the faint ripples in spacetime from that ancient neutron star collision washing through our planet. Until now, LIGO and Virgo have only confirmed the collisions and mergers of black holes, so the fact that a nearby (a relative term in this case) neutron star merger had been detected was already historic.

But the implications for this particular neutron star signal, which is comparatively weak in comparison with the black hole mergers that have come before it, are so profound that I’ve been finding it hard to put this grand discovery into words (though I have tried).

Why It Matters

With regards to gravitational waves, I feel I’ve described each gravitational wave discovery as “historic” and “a new era for astronomy” since their first detection on Sept. 15, 2015, but the detection of GW170817 may well trump all that have come before it, even though the signal was generated by neutron stars and not black hole heavyweights.

The thing with black holes is that when they collide and merge, they don’t necessarily produce electromagnetic radiation (i.e. visible light, X-rays or infrared radiation). They can go “bump” in the cosmic night and no intelligent being with a conventional telescope would see it happen. But in the the gravitational domain, black hole mergers echo throughout the universe; their gravitational waves travel at the speed of light, warping spacetime as they propagate. To detect these “invisible” waves, we must build instruments that can “see” the infinitesimal wobbles in the fabric of spacetime itself, and this is where laser interferometry comes in.

Very precise lasers are fired down miles-long tunnels in “L” shaped buildings in the two LIGO detectors (in Washington and Louisiana) and the Virgo detector near Pisa. When gravitational waves travel through us, these laser interferometers can measure the tiny spacetime warps. The more detectors measuring the same signal means a more precise observation and scientists can then work out where (and when) the black hole merger occurred.

There are many more details that can be gleaned from the gravitational wave signal from black hole mergers, of course — including the progenitor black holes’ masses, the merged mass, black hole spin etc. — but for the most part, black hole mergers are purely a gravitational affair.

Neutron stars, however, are a different beast and, on Aug. 17, it wasn’t only gravitational wave detectors that measured a signal from 130 million light-years away; space telescopes on the lookout for gamma-ray bursts (GRBs) also detected a powerful burst of electromagnetic radiation in the galaxy of NGC 4993, thereby pinpointing the single event that generated the gravitational waves and the GRB.

And this is the “holy shit” moment.

As Caltech’s David H. Reitze puts it: “This detection opens the window of a long-awaited ‘multi-messenger’ astronomy.”

What Reitze is referring to is that, for the first time, both gravitational waves and electromagnetic waves (across the EM spectrum) have been observed coming from the same astrophysical event. The gravitational waves arrived at Earth slightly before the GRB was detected by NASA’s Fermi and ESA’s INTEGRAL space telescopes. Both space observatories recorded a short gamma-ray burst, a type of high-energy burst that was theorized (before Aug. 17) to be produced by colliding neutron stars.

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The growing family of merging black holes and neutron stars observed with gravitational waves (LIGO-Virgo/Frank Elavsky/Northwestern University)

Now scientists have observational evidence that these types of GRBs are produced by colliding neutron stars as the gravitational wave fingerprint unquestionably demonstrates the in-spiraling and merger of two neutron stars. This is a perfect demonstration of multi-messenger astronomy; where an energetic event can be observed simultaneously in EM and gravitational waves to reveal untold mysteries of the universe’s most energetic events.

Another Nod to Einstein

The fact that the gravitational waves and gamma-rays arrived at approximately the same time is yet another nod to Einstein’s general relativity. The century-old theory predicts that gravitational waves should travel at the speed of light and, via this brand spanking new way of doing multi-messenger astronomy, physicists and astronomers have again bolstered relativity with observational evidence.

But why did the gravitational waves arrive slightly before the GRB? Well, NASA’s Fermi team explains: “Fermi’s [Gamma-ray Burst Monitor instrument] saw the gamma-ray burst after the [gravitational wave] detection because the merger happened before the explosion,” they said in a tweet.

In other words, when the two neutron stars collided and merged, the event immediately dissipated energy as gravitational waves that were launched through spacetime at the speed of light — that’s the source of GW170817 — but the GRB was generated shortly after.

Enter the Kilonova

As the neutron stars smashed together, huge quantities of neutron star matter were inevitably blasted into space, creating a superheated, dense volume of free neutrons. Neutrons are subatomic particles that form the building blocks of atoms and if the conditions are right, the neutron star debris will undergo rapid neutron capture process (known as “r-process”) where neutrons combine with one another faster than the newly-formed radioactive particles can decay. This mechanism is responsible for synthesizing elements heavier than iron (elements lighter than iron are formed through stellar nucleosynthesis in the cores of stars).

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Artist impression of colliding neutron stars generating gravitational waves and a “kilonova” (NSF/LIGO/Sonoma State University/A. Simonnet)

For decades astronomers have been searching for observational evidence of the r-process in action and now they have it. Soon after the merger, massive amounts of debris erupted in a frenzy of heavy element creation, triggering an energetic eruption known as a “kilonova” that was seen as a short GRB. The GRB was cataloged as “SSS17a.”

The Golden Ticket

Follow-up observations by the Hubble Space Telescope, Gemini Observatory and the ESO’s Very Large Telescope have all detected spectroscopic signatures in the afterglow consistent with the r-process taking place at the site of the kilonova, meaning heavy elements are being formed and, yes, it’s a goldmine. As in: there’s newly-synthesized gold there. And platinum. And all the other elements heavier than iron that aren’t quite so sexy.

And there’s lots of it. Researchers estimate that that single neutron star collision produced hundreds of Earth-masses of gold and platinum and they think that neutron star mergers could be the energetic process that seed the galaxies with heavy elements (with supernovas coming second).

So, yeah, it’s a big, big, BIG discovery that will reverberate for the decades to come.

The best thing is that we now know that our current generation of advanced gravitational wave detectors are sensitive enough to not only detect black holes merging billions of light-years away, but also detect the nearby neutron stars that are busy merging and producing gold. As more detectors are added and as the technology and techniques mature, we’ll be inundated with merging events big and small, each one teaching us something new about our universe.

Gravity and the Dark Side of the Cosmos: LIVE Perimeter Institute Lecture

Streaming LIVE here, today, at 4 p.m. PDT/7 p.m. EDT/11 p.m. GMT

The Perimeter Institute’s public lecture series is back! At 7 p.m. EDT (4 p.m. PDT) today, Erik Verlinde of the University of Amsterdam will ask: Are we standing on the brink of a new scientific revolution that will radically change our views on space, time, and gravity? Specifically, Verlinde will discuss the possibility that gravity may be an emergent phenomena and not a fundamental force of nature. Ohh, interesting.

The Perimeter Institute for Theoretical Physics (in Ontario, Canada) always puts on a superb production and you can watch Dr Verlinde’s talk via the live feed above. You can also participate via social media using the hashtag #piLIVE and follow @perimeter and @erikverlinde on Twitter.

Watch the preview:

Primordial Black Holes Might be Cosmic Gold Diggers

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Neutron stars might have black hole parasites in their cores (NASA’s Goddard Space Flight Center)

When the universe’s first black holes appeared is one of the biggest mysteries in astrophysics. Were they born immediately after the Big Bang 13.8 billion years ago? Or did they pop into existence after the first population of massive stars exploded as supernovas millions of years later?

The origin of primordial black holes isn’t a trivial matter. In our modern universe, the majority of galaxies have supermassive black holes in their cores and we’re having a hard time explaining how they came to be the monsters they are today. For them to grow so big, there must have been a lot of primordial black holes formed early in the universe’s history clumping together to form progressively more massive black holes.

Now, in a new study published in Physical Review Letters, Alexander Kusenko and Eric Cotner, who both work at the University of California, Los Angeles (UCLA), have arrived at an elegant theory as to how the early universe birthed black holes.

Primordial beginnings

Immediately after the Big Bang, the researchers suggest that a uniform energy field pervaded our baby universe. In all the superheated chaos, long before stars started to form, this energy field condensed as “Q balls” and clumped together. These clumps of quasi-matter collapsed under gravity and the first black holes came to be.

These primordial black holes have been singled out as possible dark matter candidates (classed as massive astrophysical compact halo objects, or “MACHOs”) and they may have coalesced to quickly seed the supermassive black holes. In short: if these things exist, they could explain a few universal mysteries.

But in a second Physical Review Letters study, Kusenko teamed up with Volodymyr Takhistov (also from UCLA) and George Fuller, at UC San Diego, to investigate how these primordial black holes may have triggered the formation of heavy elements such as gold, platinum and uranium — through a process known as r-process (a.k.a. rapid neutron capture process) nucleosynthesis.

It is thought that energetic events in the universe are responsible for the creation for approximately half of elements heavier than iron. Elements lighter than iron (except for hydrogen, helium and lithium) were formed by nuclear fusion inside the cores of stars. But the heavier elements formed via r-process nucleosynthesis are thought to have been sourced via supernova explosions and neutron star collisions. Basically, the neutron-rich debris left behind by these energetic events seeded regions where neutrons could readily fuse, creating heavy elements.

These mechanisms for heavy element production are far from being proven, however.

“Scientists know that these heavy elements exist, but they’re not sure where these elements are being formed,” Kusenko said in a statement. “This has been really embarrassing.”

A cosmic goldmine

So what have primordial black holes got to do with nucleosynthesis?

If we assume the universe is still populated with these ancient black holes, they may collide with spinning neutron stars. When this happens, the researchers suggest that the black holes will drop into the cores of the neutron stars.

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Alexander Kusenko/UCLA

Like a parasite eating its host from the inside, material from the neutron star will be consumed by the black hole in its core, causing the neutron star to shrink. As it loses mass, the neutron star will spin faster, causing neutron-rich debris to fling off into space, facilitating (you guessed it) r-process nucleosynthesis, creating the heavy elements we know and love — like gold. The whole process is expected to take about 10,000 years before the neutron star is no more.

So, where are they?

There’s little evidence that primordial black holes exist, so the researchers suggest further astronomical work to study the light of distant stars that may flicker by the passage of invisible foreground black holes. The black holes’ gravitational fields will warp spacetime, causing the starlight to dim and brighten.

It’s certainly a neat theory to think that ancient black holes are diving inside neutron stars to spin them up and create gold in the process, but now astronomers need to prove that primordial black holes are out there, possibly contributing to the dark matter budget of our universe.