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:

Neutron Star Collision Didn’t Create a Black Hole, It Birthed a Hypermassive Neutron Star Baby

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This artist’s conception portrays two neutron stars at the moment of collision [CfA/Dana Berry]

It has only been a couple of years since the first historic detection of gravitational waves, but now physicists are already dissecting a handful of signals that emanated hundreds of millions of light-years away to elucidate how some of the most violent events in our universe work.

Most of the gravitational wave signals detected so far involve the merger of black holes, but one signal, detected on Aug. 17, 2017, was special—it was caused by the smashup of two neutron stars. This merger also generated a powerful gamma-ray burst (GRB) that was detected at nearly the same time, linking GRBs with neutron star mergers and highlighting where heavy elements in our universe are forged. A new era of “multimessenger astronomy” had begun.

Now, the signal (designated GW170817) has been reanalyzed to understand what happened after the merger. Analysis that came before suggested that the collision of the two neutron stars would have tipped the mass balance to create a black hole. According to a new study, published in the journal Monthly Notices of the Royal Astronomical Society: Letters, two physicists suggest a contradictory scenario: GW170817 didn’t create a black hole, it produced a hypermassive neutron star, instead.

“We’re still very much in the pioneering era of gravitational wave astronomy. So it pays to look at data in detail,” said Maurice van Putten of Sejong University in South Korea. “For us this really paid off, and we’ve been able to confirm that two neutron stars merged to form a larger one.”

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The “chirp” of GW170817’s colliding neutron stars as seen in the LIGO dataset. New research suggests that after the two neutron stars merged, they formed one hypermassive neutron star, not a black hole [LIGO / M.H.P.M van Putten & M. Della Valle]

The secret behind this finding focuses on the datasets recorded by the US-based Laser Interferometer Gravitational-wave Observatory (LIGO) and Italian Virgo observatory. When gravitational waves are recorded during a black hole or neutron star merger event, their frequency rapidly increases (as the objects orbit one another faster and faster as they get closer and closer) and then abruptly cuts off (when they collide). When turned into an audio file, mergers sound like “chirps.” Apart from sounding like an eerie bird call coming from deep space, physicists have been able to extract surprisingly detailed information from the conditions of the merging objects, such as their mass and rates of spin.

And this is where van Putten’s work comes in.

Working with Massimo della Valle of the Osservatorio Astronomico de Capodimonte in Italy, the duo applied a new analysis technique to these data and detected a 5-second descending “chirp” (as shown by the downward arrow in the graph above). This descending chirp happened immediately after the GRB was detected coming from the same location as the gravitational wave signal’s origin. According to their analysis, the spin-down—from 1 KHz to 49 Hz—was most likely representative of a very massive neutron star and not a black hole.

If corroborated, this discovery could have profound implications for astrophysics. How hypermassive neutron stars (like the one that was created by GW170817) can exist without collapsing into a black hole will likely keep theorists busy for some time and physicists will be hopeful for another gravitational wave event like GW170817.

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.

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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.”

We’re Really Confused Why Supermassive Black Holes Exist at the Dawn of the Cosmos

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ESO

Supermassive black holes can be millions to billions of times the mass of our sun. To grow this big, you’d think these gravitational behemoths would need a lot of time to grow. But you’d be wrong.

When looking back into the dawn of our universe, astronomers can see these monsters pumping out huge quantities of radiation as they consume stellar material. Known as quasars, these objects are the centers of primordial galaxies with supermassive black holes at their hearts.

Now, using the twin W. M. Keck Observatory telescopes on Hawaii, researchers have found three quasars all with billion solar mass supermassive black holes in their cores. This is a puzzle; all three quasars have apparently been active for short periods and exist in an epoch when the universe was less than a billion years old.

Currently, astrophysical models of black hole accretion (basically models of how fast black holes consume matter — likes gas, dust, stars and anything else that might stray too close) woefully overestimate how long it takes for black holes to grow to supermassive proportions. What’s more, by studying the region surrounding these quasars, researchers at the Max Planck Institute for Astronomy (MPIA) in Germany have found that these quasars have been active for less than 100,000 years.

To put it mildly, this makes no sense.

“We don’t understand how these young quasars could have grown the supermassive black holes that power them in such a short time,” said lead author Christina Eilers, a post-doctorate student at MPIA.

Using Keck, the team could take some surprisingly precise measurements of the quasar light, thereby revealing the conditions of the environment surrounding these bright baby galaxies.

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MPIA

Models predict that after forming, quasars began funneling huge quantities of matter into the central black holes. In the early universe, there was a lot of matter in these baby galaxies, so the matter was rapidly consumed. This created superheated accretion disks that throbbed with powerful radiation. The radiation blew away a comparatively empty region surrounding the quasar called a “proximity zone.” The larger the proximity zone, the longer the quasar had been active and therefore the size of this zone can be used to gauge the age (and therefore mass) of the black hole.

But the proximity zones measured around these quasars revealed activity spanning less than 100,000 years. This is a heartbeat in cosmic time and nowhere near enough time for a black hole pack on the supermassive pounds.

“No current theoretical models can explain the existence of these objects,” said Joseph Hennawi, who led the MPIA team. “The discovery of these young objects challenges the existing theories of black hole formation and will require new models to better understand how black holes and galaxies formed.”

The researchers now hope to track down more of these ancient quasars and measure their proximity zones in case these three objects are a fluke. But this latest twist in the nature of supermassive black holes has only added to the mystery of how they grow to be so big and how they relate to their host galaxies.

Supermassive black hole with torn-apart star (artist’s impress
A supermassive black hole consumes a star in this artist’s impression (ESO)

These questions will undoubtedly reach fever-pitch later this year when the Event Horizon Telescope (EHT) releases the first radio images of the 4 million solar mass black hole lurking at the center of our galaxy. Although it’s a relative light-weight among supermassives, direct observations of Sagittarius A* may uncover some surprises as well as confirm astrophysical models.

But as for how supermassive black holes can possibly exist at the dawn of our universe, we’re obviously missing something — a fact that is as exciting as it is confounding.

Chances of the World Being Destroyed by the LHC is 50:50. Yes, Walter Wagner Is Back!

It’s one of those occasions when you’re not sure whether you should laugh… or hold back your giggling because you realise you’re witnessing some very well produced train-wreck TV.

Oh yes, it can mean only one thing, Walter Wagner is back! But this time, the media came prepared.

They made fun of him.

Yes, it was the Jon Stewart Show, and yes it was satire, but this time the joke was on the crackpot notion that the Large Hadron Collider (LHC) could actually cause harm to the world.

The subject of the LHC drove me insane last year (it also annoyed some very high profile physicists); it became almost impossible to report on the research CERN scientists were hoping to carry out, as every day Wagner (with his ‘lawsuit’ craziness) or Rossler (with his ‘infringement of human rights’ nonsense) would pop up, forcing any decent physics article into a defence of the LHC. Needless to say, this annoyed many physicists involved in the LHC, but excited media doomsday headlines into a frenzy of doomsday crackpottery.

Now, Wagner has been caught out and been made a fool of. Although I hate to see anyone in this situation, in this case, I think it is needed. Wagner only has himself to blame. He started these doomsday theories, now it’s up to mainstream comedy shows to debunk his authority on the subject.

Hold on, did he ever have an authority over physics? Oh yes, that’s right. No, he didn’t. He used the media as a tool to gain attention.

On the other hand, physicist Prof. John Ellis is an authority on physics… in fact, he’s the authority on LHC physics. I think I’d put my trust in an evil genius with a PhD and decades of experience, rather than the Caped Wagner Crusader any day.

For more on the subject, check out Ethan’s Starts With A Bang, he has more patience than me and delves into the subject a bit more »

Here’s more LHC goodness if you’re hungry for more »

Source: Gia via Twitter

Is the Universe a Holographic Projection?

Luke and Obi-Wan look at a 3D hologram of Leia projected by R2D2 (Star Wars)
Luke and Obi-Wan look at a 3D hologram of Leia projected by R2D2 (Star Wars)

Could our cosmos be a projection from the edge of the observable Universe?

Sounds like a silly question, but scientists are seriously taking on this idea. As it happens, a gravitational wave detector in Germany is turning up null results on the gravitational wave detection front (no surprises there), but it may have discovered something even more fundamental than a ripple in space-time. The spurious noise being detected at the GEO600 experiment has foxed physicists for some time. However, a particle physicist from the accelerator facility Fermilab has stepped in with his suspicion that the GEO600 “noise” may not be just annoying static, it might be the quantum structure of space-time itself
Continue reading “Is the Universe a Holographic Projection?”

I Wish Office Work Was This Interesting

Having just stumbled around the space blogs, I was enthusiastic that I would find some inspiration toward my next Astroengine.com article. Along the way, I found this rather entertaining short film on Phil Plait’s Bad Astronomy website. As Phil points out, “black holes don’t work this way.” Although, that is a shame.

There’s a strong moral to this story: don’t photocopy alone, as you never know when your Xerox machine will print out a singularity. Well, not really, perhaps the guy should have stopped at stealing a snickers bar, a lesson we could all learn from. Actually, I might have walked off with just one wad of cash… actually, maybe two… you get the picture.

Needless to say, this isn’t actually how a black hole works… it’s not even how a wormhole would work. But take the short film at face value and get some entertainment from it, I thought it was quite good fun.

Probing Variable Black Holes

Artist impression of a black hole feeding off its companion star... and a rogue Higgs particle (ESO/L. Calçada)
Artist impression of a black hole feeding off its companion star... and a rogue Higgs particle (ESO/L. Calçada/Particle Zoo)

Black holes are voracious eaters. They devour pretty much anything that strays too close. They’re not fussy; dust, gas, plasma, Higgs bosons, planets, stars, even photons are on the menu. However, for astronomers, interesting things can be observed if a star starts to be cannibalized by a neighbouring black hole. Should a star be unlucky enough to have a black hole as its binary partner, the black hole will begin to strip the stars upper layers, slowly consuming it on each agonizing orbit. Much like water spiralling down a plug hole, the tortured plasma from the star is gravitationally dragged on a spiral path toward the black hole’s event horizon. As stellar matter falls down the event horizon plug hole, it reaches relativistic velocities, blasting a huge amount of radiation into space. And now, astronomers have taken different observations from two observatories to see how the visible emissions correlate with the X-ray emissions from two known black hole sources. What they discovered came as a surprise
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No Naked Singularity After Black Hole Collision

Black holes cannot be naked... the event horizon will always be there to cover them up...
Black holes cannot be naked... the event horizon will always be there to cover them up...

You can manipulate a black hole as much as you like but you’ll never get rid of its event horizon, a new study suggests. This may sound a little odd, the event horizon is what makes the black hole, well… black. However, in the centre of a black hole, hidden deep inside the event horizon, is a singularity. A singularity is a mathematical consequence, it is also a point in space where the laws of physics do not apply. Mathematics also predicts that singularities can exist without an associated event horizon, but this means that we’d be able to physically see a black hole’s singularity. This theoretical entity is known as a “naked singularity” and physicists are at a loss to explain what one would look like.

Like any good physics experiment, an international team from the US, Germany, Portugal and Mexico have decided to simulate the most extreme situation possible in the aim of stripping a pair of black holes of their event horizons. They did this by constructing an energetic collision between two black holes travelling close to the speed of light, crashing head-on. Here’s what they discovered…
Continue reading “No Naked Singularity After Black Hole Collision”