Category: Physics

Earth’s Magnetic Field Just Hit a Phantom Speed Bump

Earth likely passed through “a fold in the heliospheric current sheet,” which induced a powerful electrical surge down here on the ground.

While science news is filled with rumbling earthquakes and rippling gravitational waves, a different kind of perturbation was felt in Norway yesterday (Jan. 6)—but its cause is a little mysterious.

“Electrical currents started flowing,” said Rob Stammes, of the Polarlightcenter geophysical observatory in Lofoten, Norway, in a report by Spaceweather.com.

A shockwave in magnetometer data and a surge in ground currents indicated that the magnetosphere had interacted with the interplanetary magnetic field (IMF) [Rob Stammes/Polarlightcenter/Spaceweather.com]

Stammes monitors the flow of electricity through the ground and compares it with the wiggles of the Earth’s magnetic field (as plotted above). These two key measurements allow space weather scientists to better understand how our planet’s magnetosphere is being affected by the magnetic field of our Sun and how it may impact our everyday lives.

While the Sun-Earth relationship is well studied, usually magnetospheric jiggles are associated with obvious (and often explosive) solar phenomena, such as coronal mass ejections (CMEs) and powerful solar wind flows. Yesterday, however, at around 1930 UT, our magnetosphere was jolted by a phantom event.

It was as if Earth orbited through an invisible magnetic speed bump.

Before we can understand what this means (and, indeed, why it’s important), let’s take a quick trip to the biggest magnetic dynamo in the Solar System.

As you can see, the Sun isn’t currently all that active [NASA/SDO]

You know it as the giant orb of superheated plasma that gives life to Earth and dazzles you during your commute home from work, but the Sun also has an invisible magnetic dominance over all the planets. Extending from the solar interior to well beyond the orbit of Pluto, the Sun’s magnetic field creates a vast magnetic bubble called the heliosphere. Carried by the solar wind, this magnetism spirals out, through interplanetary space, interacting with any other magnetic field it may come across. In the case of our planet, our global magnetic field (the magnetosphere) is generated by the constant sloshing of molten iron in Earth’s core. Our magnetosphere reaches out into interplanetary space and, like a forcefield, it deflects the highly energetic plasma (consisting mainly of protons and some highly ionized particles) sloughing from our Sun. There’s a constant magnetic battle raging over our heads; the Sun’s magnetic field washes over our protective magnetosphere, which acts like a sea wall protecting the coastline from an unrelenting stormy ocean.

Now, if the conditions are right, the Sun’s magnetic field may breach Earth’s magnetosphere, causing the two to snap and reconnect, effectively creating a temporary magnetic marriage between the Sun and Earth. When this happens, a magnetic highway for solar particles is formed, injecting the layers of our magnetosphere with solar plasma. Ultimately, this plasma can stream along our planet’s magnetic field (or get trapped and stored), creating auroras in higher latitudes and generate electrical currents through the atmosphere and surface.

The Earth’s magnetic field warps and bends, deflecting highly energetic solar particles. But sometimes, the shield is breached, often with dramatic effect. [NASA]

Usually, space weather forecasters use a plethora of instruments to predict when this might happen. For example, they may detect a CME erupt on the corona, predict its speed, and then register a flip in the interplanetary magnetic field (IMF) by a satellite between us and the Sun (such as NASA’s Advanced Composition Explorer, or ACE, which is located at the Sun-Earth L1 point, nearly a million miles “upstream” toward the Sun). But, in the case of yesterday’s mysterious event in Norway, there was no warning for the magnetic breach in our magnetosphere. No CME, no visible increase in solar wind intensity; just a magnetic blip from ACE and a shockwave sent ripping through magnetometer stations on the ground followed by a surge in electricity through our planet’s surface.

We’d been suckerpunched by the Sun’s magnetism, but there was no obvious fist. To confirm the sudden magnetic blow (called a geomagnetic storm), magnificent auroras erupted over the poles.

So, what happened? There is a theory:

Earth may have crossed through a fold in the heliospheric current sheet—a giant, wavy membrane of electrical current rippling through the solar system. Such crossings can cause these kind of effects.

Tony Phillips, Spaceweather.com

Looking like the warped disk of an old vinyl record, the heliospheric current sheet ripples throughout the solar system. As Earth rotates around the Sun, it will pass through the “surface” of this sheet, where the magnetic polarity of the IMF will rapidly change. And this is probably what happened yesterday. As the Earth orbited through a fold in the sheet, the magnetic polarity flipped 180 degrees, creating the phantom interaction with our magnetosphere. This, in turn, released solar particles that had been trapped in the layers of our magnetosphere, causing them to surge through the upper atmosphere, creating an intense—and surprise—auroral display.

Predicting when these events are going to occur is critical to space weather prediction efforts. As demonstrated by Stammes’ measurements of currents flowing through the ground, geomagnetic storms can overload national power grids, leaving entire nations (or, potentially, entire continents) in the dark.

While this Norway event didn’t cause reported damage to any infrastructure, it is a reminder that our planet’s interactions with the solar magnetic field—and subsequent impacts to our civilization—can be unpredictable and, in this case, invisible.

Is Betelgeuse About to Blow? Maybe… Maybe Not

The famous supergiant on Orion’s shoulder has rapidly dimmed, stoking excitement that a supernova may be in the offing.

Artist’s impression of the tortured, bubbling photosphere of a dying Betelgeuse. [ESO/L. Calçada]

Do you hear that ticking? Doesn’t it sound like a stellar timer is counting down to the inevitable demise of a massive star? While the excitement may be the amplified construct of social media predictions of the death of Betelgeuse, our stellar neighbor really is close to going supernova.

“Close”, however, is relative. It could be as “human close” as blowing up any minute now… to “galactic close” as blowing up in a hundred thousand years, maybe more.

So, what’s all the fuss about? In a nutshell, the brightest star in the famous constellation of Orion is bright no more. In the past few weeks, Betelgeuse has dimmed noticeably, stoking predictions that it could be about to spectacularly erupt at any time, becoming as bright as a full Moon and casting its own shadows at night.

While this may sound ominous, a Betelgeuse supernova poses no threat to life on Earth. It’s located a safe 600 light-years away, so if it did explode, we’d be treated to a historic cosmic firework display and not doomsday. Any energetic particles spewing from the explosion may reach the solar system in 100,000 years, but would have a minimal impact; the heliosphere (our Sun’s extended magnetic “bubble” that encompasses all the planets) would be more than powerful enough to deflect the tenuous gases.

The constellation of Orion, with the ruddy Betelgeuse in the upper left-hand corner on Orion’s “shoulder.” [Photo by Frank Cone from Pexels]

There has always been excitement over Betelgeuse and its explosive potential. It’s a massive star, with a mass 12-times that of our Sun, which has reached the end of its life. But with a lifespan of only eight million years or so, it may sound odd that it’s dying of old age. As a comparison, our Sun—an “average” yellow dwarf star—sounds geriatric in comparison; it’s approximately five billion years old. But the strange physics of stellar evolution dictates that the more massive the star, the shorter its lifespan. Betelgeuse is on borrowed time, whereas our Sun is only middle-aged. In other words, Betelgeuse has lived fast and it will die young.

As a star that’s about to die, Betelgeuse is experiencing the final throes of violent processes that signify the conclusion of stellar evolution—a phase that sees a massive star puff up into a red supergiant. In the case of Betelgeuse, while it is 12-times more massive than our Sun, it has expanded into a grotesque, bubbling mess of superheated plasma, puffed up to nearly 1,000-times wider than our Sun. If Betelgeuse were transplanted into the middle of our solar system, it would swallow all the planets out to Saturn. Yes, even Jupiter would be ingested.

A precision observation of Betelgeuse’s asymmetric photosphere, highlighting bright spots and a non-spherical shape, as captured by the Atacama Large Millimeter/submillimeter Array (ALMA). 

After guzzling all of its hydrogen fuel long ago, it’s now fusing heavier elements inside its tortured interior to the point where iron is being created. For any massive star, the fusion of iron is the death knell; energy is being absorbed, and soon, its immense gravity will cause the whole mess to collapse, generating an almighty shockwave that will, ultimately, rip Betelgeuse apart as a supernova.

As reported by astronomers before Christmas, the observed dimming could be interpreted as a precursor to the anticipated supernova, and for good reason. But Betelgeuse is known to regularly vary in brightness, so astronomers suspect that, while this is an unprecedented dimming event, the famous star will soon return to its “regular” brightness once more, reclaiming its rank as ninth brightest star in the sky.

In short, don’t place any serious money on Betelgeuse exploding soon. While there is a tiny chance that it might have already exploded, the light from the supernova currently galloping across the 600 light-year interstellar divide between us and Betelgeuse, it’s way more likely that it’s just Betelgeuse being Betelgeuse and keeping variable star astronomers on their toes.

That’s not to say the dimming event isn’t exciting, on the contrary. Seeing a prominent star in the night sky fade with your own eyes is something to behold, so when you get clear skies, look for Orion and ponder The Hunter’s missing shoulder.

Catching a Star’s Helium Flash

Old stellar flashers will be caught in the act in the not-so-distant future, whether they like it or not.

[Smithsonian]

While we have a pretty good idea about how stars like our Sun work, observing all the details that unfold over millions to billions of years of stellar evolution can be difficult, especially if the phenomena occur over short timescales. Take, for example, a particularly explosive and relatively short-lived period our Sun is expected to experience in roughly five billion years.

This event is predicted to happen after our nearest star has burned up all of its hydrogen fuel and starts to burn helium. This is the beginning of the end; the Sun will swell into a vast red giant, ejecting its upper layers of plasma into space via violent solar winds, brightening 1,000 times than it is today. Needless to say, this will be a terribly dramatic time for our solar system (and a definitive apocalypse for anything that remains of our planet’s biosphere), but it will be on the verge of something even more dramatic: a helium flash.

As the solar core starts using helium as fuel, the fusion process will generate carbon and as this begins, a powerful eruption of energy will detonate, as detailed by a UC Santa Barbara statement:

A star like the sun is powered by fusing hydrogen into helium at temperatures around 15 million K. Helium, however, requires a much higher temperature than hydrogen, around 100 million K, to begin fusing into carbon, so it simply accumulates in the core while a shell of hydrogen continues to burn around it. All the while, the star expands to a size comparable to the Earth’s orbit. Eventually, the star’s core reaches the perfect conditions, triggering a violent ignition of the helium: the helium core flash. The core undergoes several flashes over the next 2 million years, and then settles into a more static state where it proceeds to burn all of the helium in the core to carbon and oxygen over the course of around 100 million years.

While the helium flashes of old Sun-like stars have been predicted for 50 years, we have yet to actually observe any kicking off in our galaxy, which isn’t so surprising considering it’s only comparatively recently that we’ve developed the techniques that are capable of precisely measuring the brightness fluctuations of distant stars. This might be about to change, according to a new study published in Nature Astronomy Letters.

“The availability of very sensitive measurements from space has made it possible to observe subtle oscillations in the brightness of a very large number of stars,” said coauthor Jørgen Christensen-Dalsgaard, of the UC Santa Barbara’s Kavli Institute for Theoretical Physics (KITP).

Christensen-Dalsgaard is referring to the growing number of space-based observatories, primed to survey the sky for transiting exoplanets—such as Kepler, CoRoT and TESS—that have extremely sensitive photonics that can detect the slightest changes in stellar brightness. And by virtue of these missions’ wide field of view, taking in the light from many stars at once, the helium flashes and resulting brightness oscillations across the stars’ surfaces could be detected in the near future.

It’s thought that the flash itself should last for no more than two million years, which may sound like a long time to we puny humans, but over cosmic timescales, that’s literally a flash—we need some serious luck to detect them. But with more observatories, longer observation periods, and wider fields of view, luck may be just around the corner.

The Sun Is a Beautifully Blank Billiard Ball for Halloween

For the festive season, our nearest star is keeping its choice of costume simple.

I’m not saying the Sun isn’t being creative, it’s just not putting too much effort into this year’s stellar fancy dress party. I mean, look at it:

The Sun right now, as seen by the Helioseismic and Magnetic Imager (HMI) instrument on NASA’s Solar Dynamics Observatory (SDO) [NASA/SDO]

That flawless orange billiard ball is the photosphere of our Sun. Have you ever seen something so smooth and beautifully unremarkable?

Well, you have now, and its blank gaze is actually the reason why it’s causing a bit of a stir. According to our ever watchful solar sentry, Tony Phillips at SpaceWeather.com, the northern summer of 2019 may go down in history as “the summer without sunspots.”

From June 21st until Sept 22nd, the sun was blank more than 89% of the time. During the entire season only 6 tiny sunspots briefly appeared, often fading so quickly that readers would complain to Spaceweather.com, “you’ve labeled a sunspot that doesn’t exist!” (No, it just disappeared.) Not a single significant solar flare was detected during this period of extreme quiet.

Dr. Tony Phillips

So, what does this mean?

Sunspots are the visual cues for magnetic turmoil within our nearest star. Over cycles of approximately 11 years, the Sun’s internal magnetic field becomes stretched and twisted, driving the ebb and flow of space weather.

Starting with our solar billiard ball here, suffice to say that the solar magnetic field is pretty untwisted and, well, chilled. This is the epitome of “solar minimum” — and, as commented on by Phillips, a deep, potentially record-breaking solar minimum at that. It’s very likely that this is as minimum as solar minimum can be, so we could hazard a guess to say that things are going to start getting interesting very soon.

Differential rotation and the formation of coronal loops as demonstrated by my awesome abilities as a Microsoft Word artist [source: my PhD thesis!]

As our Sun is a massive blob of magnetized plasma, it doesn’t rotate uniformly (like the Earth does), it actually rotates a little faster at its equator than at its poles, a phenomenon known as “differential rotation.” Now, if you imagine the solar magnetic field as straight lines running from pole to pole, you can imagine that, over time, the field will start to wrap around the equator like an elastic band being stretched out of shape and wrapped around the middle. At its most extreme, so much rotational tension will be applied to the magnetic field that it becomes contorted. This contortion creates an upward pressure, forcing vast loops of magnetized plasma, known as coronal loops, to pop through the Sun’s photosphere — a.k.a. the solar “surface” — like annoyingly twisted loops of garden hosepipe (see the diagram above).

As its most extreme, in a few years time, we can expect our boring ol’ billiard ball to look something like this:

The Sun in 2014 (during the previous solar maximum), as seen by the SDO’s HMI [NASA/SDO]

About those blotches: those dark spots are sunspots and they are a direct consequence of the magnetic turmoil that rumbles inside the Sun during solar maximum. Remember those coronal loops I was talking about? Well, these huge, beautiful arcs of plasma cause the hotter outer layers of the Sun to be pushed aside, exposing the comparatively cooler (though still thousands of degrees) plasma under the surface — that’s what creates those dark blotches. And by counting sunspots, you can gauge how magnetically active the Sun is.

By viewing the Sun in different wavelengths, we can view the Sun’s atmosphere at different temperatures and, as the Sun’s atmosphere (the corona) is counter-intuitively hotter the higher above the surface you get, let’s take a look at what solar maximum looks like above these sunspots:

Yikes! The Sun’s corona in October 2014 (during the previous solar maximum), as seen by the SDO’s Atmospheric Imaging Assembly (AIA) instrument. And a damn fine effort just in time for Halloween. [NASA/SDO]

As you can see, there’s a lot of coronal loops erupting through the surface, creating huge regions of activity (called active regions, unsurprisingly). And the above observation was captured on Oct. 8, 2014, when the Sun was, apparently, in a terrifyingly festive Halloween mood! These regions can be hothouses for solar flares and coronal mass ejections; explosive phenomena that can have dramatic space weather effects on Earth.

So that was solar maximum; what does the solar corona look like now, at solar minimum?

The Sun’s corona right now, as seen by the SDO’s AIA [NASA/SDO]

Yep, as you guessed, very relaxed. In this state, we can expect very little in the way of explosive space weather events, such as flares and CMEs; there’s simply too little magnetic energy at solar minimum to create many surprises (caveat: even solar minimum can generate flares, they’re just few and far between).

While the Sun may look boring, the effects of space weather are anything but. During these times of solar minimum, the extended solar magnetic field (called the heliosphere), a magnetic bubble that reaches beyond the orbits of all the planets, contracts and weakens, allowing more cosmic rays from energetic events from the rest of the cosmos to reach Earth. Cosmic rays are ionizing particles that can boost the radiation exposure of astronauts and frequent fliers. Also, the solar wind can become a more persistent presence; streams of energized particles that are continuously streaming from the lower corona, so we still get our aurorae at high latitudes.

Recognition that the Sun is now in a deep minimum means the solar vacation is nearing an end. Astronomers have reported that of the handful of sunspots have made an appearance over the last few months with a flip in magnetic polarity, which can mean only one thing: Solar Cycle 25 is coming and the next solar maximum is only four years away.

Two Stellar Zombie Spinners Are Ripping Up Spacetime

The pair of white dwarf stars are orbiting one another every seven minutes—and future gravitational wave observatories will be able to detect them whirl.

White dwarf binaries are among some of the most fascinating star systems known, and a newly discovered compact binary, located some 8,000 light-years away in the constellation Boötes, has taken the exotic nature of these systems to new spacetime-warping extremes.

The extremely compact eclipsing binary, called ZTF J1530+5027, is one of the most extreme white dwarf systems known to exist [Caltech/IPAC]

Astronomers using Caltech’s Zwicky Transient Facility (ZTF), a precision sky survey at Palomar Observatory near San Diego in Southern California, made the discovery of ZTF J1530+5027 by detecting the dimming effect caused by one of the stars passing in front of the other. Known as an “eclipsing binary,” the cooler (and therefor dimmer) white dwarf blocks the starlight of the hotter (and brighter) star, causing the ZTF to register a periodic dimming event. This dimming occurs once every seven minutes, meaning they are zipping around each other at speeds of hundreds of miles per second! It is the second fastest white dwarf binary known and the most rapid eclipsing binary discovered in our galaxy. The fortunate alignment allows astronomers to not only precisely measure their orbital speed, they can also gauge the stars’ sizes and masses.

White dwarfs are the stellar corpses of sun-like stars that ran out of fuel long ago. Our sun will become a white dwarf in around five billion years, after it has exhausted its hydrogen fuel that maintains fusion in its core. A short period after, it will swell into a red giant (possibly expanding out as far as Earth, incinerating it) and then lose its plasma to space via powerful solar winds. All that will be left of our once glorious star will be a planetary nebula and a tiny and dense white dwarf, approximately the size of our planet, spinning in the middle. The two white dwarfs in ZTF J1530+5027 likely passed through their red giant phase at different times, but now they’re stuck, in a perpetual death spiral that spells doom for one of the objects.

To fully realize just how crazy-extreme this white dwarf binary is, they are only separated by one-fifth of the distance that the moon orbits Earth, meaning both stars would fully fit inside Saturn. They have a combined mass of our entire sun. As they orbit so snugly, it’s likely that the more massive star will start to tidally drag material from the other, cannibalizing it.

“Matter is getting ready to spill off of the bigger and lighter white dwarf onto the smaller and heavier one, which will eventually completely subsume its lighter companion,” said Kevin Burdge, Caltech graduate student and lead author of a study published in the journal Nature. “We’ve seen many examples of a type of system where one white dwarf has been mostly cannibalized by its companion, but we rarely catch these systems as they are still merging like this one.”

While impressive, the real fireworks are invisible—the stars are ripping up spacetime, generating gravitational waves that are sapping energy from the system, hastening the binary’s ultimate demise. What’s more, astronomers are anticipating that the future Laser Interferometer Space Antenna (LISA), which is scheduled for launch by the European Space Agency in 2034, will be able to detect its gravitational pulse.

“These two white dwarfs are merging because they are emitting gravitational waves,” added collaborator Tom Prince, a senior research scientist at Caltech and NASA’s Jet Propulsion Laboratory (JPL, in Pasadena, Calif. “Within a week of LISA turning on, it should pick up the gravitational waves from this system. LISA will find tens of thousands of binary systems in our galaxy like this one, but so far we only know of a few. And this binary-star system is one of the best characterized yet due to its eclipsing nature.”

This system is expected to keep blinking from our perspective for another hundred thousand years, but how will the system ultimately go kaput? Well, the researchers aren’t entirely certain. On the one hand, the more massive white dwarf may suck the other dry like a vampiric parasite, consuming all of its matter until only one, well-fed star remains. Alternatively, the act of cannibalization may cause the reverse; as mass is transferred to one star, the other may be flung outward to a wider orbit, increasing their orbital period.

“Sometimes these binary white dwarfs merge into one star, and other times the orbit widens as the lighter white dwarf is gradually shredded by the heavier one,” said co-author Jim Fuller, an assistant professor at Caltech. “We’re not sure what will happen in this case, but finding more such systems will tell us how often these stars survive their close encounters.”

One early mystery about this extreme binary is the question of X-rays, or lack thereof. The more massive star is really hot, with a temperature nine times that of the sun (50,000 Kelvin). The researchers believe that this is because it has already begun pulling material from its partner, an act that accelerates and heats the plasma that is being stolen, starting to create an accretion disk. But the accreting gas should be so hot that the system would be humming in X-rays, but it isn’t. “It’s strange that we aren’t seeing X-rays in this system. One possibility is that the accretion spots on the white dwarf—the areas the material is falling on—are bigger than what is typical, and this could result in the emission of ultraviolet light and optical light instead of X-rays,” added Burdge.

[Caltech/IPAC]

It’s exciting to think what the next generation of gravitational wave observatories (particularly LISA that will be sensitive to extremely weak spacetime ripples from systems such as these) combined with traditional (re: electromagnetic) observatories will herald for the future of astronomy. Like the emerging “multi-messenger” era for astronomy that combines observations of the electromagnetic spectrum and gravitational wave signals to confirm short gamma-ray bursts are triggered by neutron star collisions, it’s going to blow our minds when we can access more subtle gravitational wave sources such as these and directly see the gravitational energy leaking from compact binaries.

Our Supermassive Black Hole Is Slurping Down a Cool Hydrogen Smoothie

The world’s most powerful radio telescope is getting intimate with Sagittarius A*, revealing a never-before-seen component of its accretion flow

Artist impression of ring of cool, interstellar gas surrounding the supermassive black hole at the center of the Milky Way [NRAO/AUI/NSF; S. Dagnello]

As we patiently wait for the first direct image of the event horizon surrounding the supermassive black hole living in the core of our galaxy some 25,000 light-years away, the Atacama Millimeter/submillimeter Array (ALMA) has been busy checking out a previously unseen component of Sagittarius A*’s accretion flow.

Whereas the Event Horizon Telescope (EHT) will soon deliver the first image of our supermassive black hole’s event horizon, ALMA’s attention has recently been on a cool flow of gas that is orbiting just outside the event horizon, before being consumed. (The EHT delivered its first historic image on April 10, not of the supermassive black hole in our galaxy, but of the gargantuan six-billion solar mass monster in the heart of the giant elliptical galaxy, Messier 87, 50 million light-years away.)

While this may not grab the headlines like the EHT’s first image (of which ALMA played a key role), it remains a huge mystery as to how supermassive black holes pile on so much mass and how they consume the matter surrounding them. So, by zooming in on the reservoir of material that accumulates near Sagittarius A* (or Sgr A*), astronomers can glean new insights as to how supermassive black holes get so, well, massive, and how their growth relates to galactic evolution.

While Sgr A* isn’t the most active of black holes, it is feeding off limited rations of interstellar matter. It gets its sustenance from a disk of plasma, called an accretion disk, starting immediately outside its event horizon—the point at which nothing, not even light, can escape a black hole’s gravitational grasp—and ending a few tenths of a light-year beyond. The tenuous, yet extremely hot plasma (with searing temperatures of up to 10 million degrees Kelvin) close to the black hole has been well studied by astronomers as these gases generate powerful X-ray radiation that can be studied by space-based X-ray observatories, like NASA’s Chandra. However, the flow of this plasma is roughly spherical and doesn’t appear to be rotating around the black hole as an accretion disk should.

Cue a cloud of “cool” hydrogen gas: at a temperature of around 10,000K, this cloud surrounds the black hole at a distance of a few light-years. Until now, it’s been unknown how this hydrogen reservoir interacts with the black hole’s hypothetical accretion disk and accretion flow, if at all.

ALMA is sensitive to the radio wave emissions that are generated by this cooler hydrogen gas, and has now been able to see how Sgr. A* is slurping matter from this vast hydrogen reservoir and pulling the cooler gas into its accretion disk—a feature that has, until now, been elusive to our telescopes. ALMA has basically used these faint radio emissions to act as a tracer as the cool gas mingles with the accretion disk, revealing its rotation and the location of the disk itself.

“We were the first to image this elusive disk and study its rotation,” said Elena Murchikova, a member in astrophysics at the Institute for Advanced Study in Princeton, New Jersey, in a statement. “We are also probing accretion onto the black hole. This is important because this is our closest supermassive black hole. Even so, we still have no good understanding of how its accretion works. We hope these new ALMA observations will help the black hole give up some of its secrets.” Murchikova is the lead author of the study published in Nature on June 6.

ALMA image of the disk of cool hydrogen gas flowing around the supermassive black hole at the center of our galaxy. The colors represent the motion of the gas relative to Earth: the red portion is moving away, so the radio waves detected by ALMA are slightly stretched, or shifted, to the “redder” portion of the spectrum; the blue color represents gas moving toward Earth, so the radio waves are slightly scrunched, or shifted, to the “bluer” portion of the spectrum. Crosshairs indicate location of black hole [ALMA (ESO/NAOJ/NRAO), E.M. Murchikova; NRAO/AUI/NSF, S. Dagnello]

Located in the Chilean Atacama Desert, ALMA is comprised of 66 individual antennae that work as one interferometer to deliver observations of incredible precision. This is a bonus for these kinds of accretion studies, as ALMA has now probed right up to the edge of Sgr A*’s event horizon, only a hundredth of a light-year (or a few light-days) from the point of no return, providing incredible detail to the rotation of this cool disk of accreting matter. What’s more, the researchers estimate that ALMA is tracking only a minute quantity of cool gas, coming in at a total only a tenth of the mass of Jupiter.

A small quantity this may be (on galactic scales, at least), but it’s enough to allow the researchers to measure the Doppler shift of this dynamic flow, where some is blue-shifted (and therefore moving toward us) and some is red-shifted (as it moves away), allowing them to clock its orbital speed around the relentless maw of Sgr A*.

“We were able to shed new light on the accretion process around Sagittarius A*, which is a typical example of a class of black holes that have little to eat,” added Murchikova in a second statement. “The accretion behavior of these black holes is quite complex and, so far, not well understood.

“Our result is potentially important not only for our galaxy, but to any galaxy which has this type of underfed black hole in its heart. We hope that this cool disk will help us uncover more secrets of black holes and their behavior.”

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.