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.

Psychedelic Simulation Showcases the Ferocious Power of a Solar Flare

Scientists are closing in on a better understanding about how these magnetic eruptions evolve

[Mark Cheung, Lockheed Martin, and Matthias Rempel, NCAR]

For the first time, scientists have created a computer model that can simulate the evolution of a solar flare, from thousands of miles below the photosphere to the eruption itself in the lower corona — the sun’s multimillion degree atmosphere. And the results are not only scientifically impressive, the visualization is gorgeous.

I’ve always had a fascination with the sun — from how our nearest star generates its energy via fusion reactions in its core, to how the tumultuous streams of energetic plasma slams into our planet’s magnetosphere, igniting spectacular aurorae. Much of my interest, however, has focused on the lower corona; a region where the intense magnetic field emerges from the solar interior and reaches into space. With these magnetic fields comes a huge release of hot plasma that is channeled by the magnetism to form beautiful coronal loops. Intense regions of magnetism can accumulate in violently-churning “active regions,” creating sunspots and explosive events — triggered by large-scale magnetic reconnection — such as flares and coronal mass ejections (or CMEs). This is truly a mysterious place and solar physicists have tried to understand its underlying dynamics for decades.

The eruption of an X-class solar flare in the sun’s multimillion degree corona [NASA/SDO]

Now, with increasingly-sophisticated solar observatories (such as NASA’s Solar Dynamics Observatory), we are getting an ever more detailed look at what’s going on inside the sun’s deep atmosphere and, with improvements of theoretical models and increases in computer processing power, simulations of the corona are looking more and more like the real thing. And this simulation, detailed in the journal Nature Astronomyis truly astonishing.

In the research, led by researchers at the National Center for Atmospheric Research (NCAR) and the Lockheed Martin Solar and Astrophysics Laboratory, the evolution of a solar flare has been modeled. This simulation goes beyond previous efforts as it is more realistic and creates a more complete picture of the range of emissions that can be generated when a solar flare is unleashed.

One of the biggest questions hanging over solar (and indeed, stellar) physics is how the sun (and other stars) heat the corona. As we all know, the sun is very hot but its corona is too hot; the photosphere is a few thousand degrees, whereas, only just above it, the coronal plasma skyrockets to millions of degrees, generating powerful radiation beyond what the human eye can see, such as extreme-ultraviolet and X-rays. Basic thermodynamics says that this shouldn’t be possible — this situation is analogous to finding the air surrounding a light bulb is hotter than the bulb’s glass. But what our sun has that a light bulb does not is a powerful magnetic field that dictates the size, shape, temperature and dynamics of the plasma our sun is blasting into space. (If you want some light reading on the subject, you can read my PhD thesis on the topic.)

“This work allows us to provide an explanation for why flares look like the way they do, not just at a single wavelength, but in visible wavelengths, in ultraviolet and extreme ultraviolet wavelengths, and in X-rays. We are explaining the many colors of solar flares.”

Mark Cheung, staff physicist at Lockheed Martin Solar and Astrophysics Laboratory.

The basis of this new simulation, however, investigates another mystery: How and why do solar flares erupt and evolve? It looks like the research team might be on the right track.

When high-energy particles from the sun impact our atmosphere, vast light shows called auroras can be generated during the geomagnetic storm, as shown in this view from the International Space Station [NASA]

Inspired by a powerful flare that was observed in the corona in March 2014, the researchers provided their magnetohydrodynamic model with an approximation of the conditions that were observed at the time. The magnetic conditions surrounding the active region were primed to generate a powerful X-class flare (the most powerful type of solar flare) and several less powerful (but no less significant) M-class flares. So, rather than forcing their simulation to generate flares, they re-enacted the conditions of the sun that were observed and just let their simulation run to create its own flares.

“Our model was able to capture the entire process, from the buildup of energy to emergence at the surface to rising into the corona, energizing the corona, and then getting to the point when the energy is released in a solar flare,” said NCAR scientist Matthias Rempel in a statement. “This was a stand-alone simulation that was inspired by observed data.

“The next step is to directly input observed data into the model and let it drive what’s happening. It’s an important way to validate the model, and the model can also help us better understand what it is we’re observing on the sun.”

Solar flares, CMEs and even the solar wind can have huge impacts on our technological society. The X-rays blasting from the sun’s atmosphere millions of miles away can have dramatic impacts on the Earth’s ionosphere (impacting communications) and can irradiate unprotected astronauts in space, for example. CMEs can be launched from the corona and arrive at Earth orbit in a matter of hours or days, triggering geomagnetic storms that can impact entire power grids. We’re not just talking a few glitches on your cellphone here; satellites can be knocked out, power supplies neutralized and global communications networks interrupted. It’s simulations like these, which aim to get to the bottom of how these solar storms are initiated, that can help us better prepare for our sun’s next big temper tantrum.

For more on this research, watch this video:

This Weird Star System Is Flipping Awesome

The binary system observed by ALMA isn’t wonky, it’s the first example of a polar protoplanetary disk

Artwork of the system HD 98000. This is a binary star comprising two sun-like components, surrounded by a thick disk of material. What’s different about this system is that the plane of the stars’ orbits is inclined at almost 90 degrees to the plane of the disk. Here is a view from the surface of an imagined planet orbiting in the inner edge of the disk [University of Warwick/Mark Garlick].

Some star systems simply don’t like conforming to cosmic norms. Take HD 98000, for example: It’s a binary system consisting of two sun-like stars and it also sports a beautiful protoplanetary disk of gas and dust. So far, so good; sounds pretty “normal” to me. But that’s only part of the story.

When a star is born, it will form a disk of dust and gas — basically the leftovers of the molecular cloud the star itself formed in — creating an environment in which planets can accrete and evolve. Around a single star (like our solar system) the protoplanetary disk is fairly well behaved and will create a relatively flat disk around the star’s spin axis. For the solar system, this flat disk would have formed close to the plane of the ecliptic, an imaginary flat surface that projects out from the sun’s equator where all the planets, more or less, occupy. There are “wonky” exceptions to this rule (as, let’s face it, cosmic rules are there to be broken), but the textbook descriptions of a star system in its infancy will usually include a single star and a flat, boring disk of swirling material primed to build planets.

Cue HD 98000, a star system that has flipped this textbook description on its head, literally. As a binary, this is very different to what we’re used to with our single, lonely star. Binary stars are very common throughout the galaxy, but HD 98000 has a little something extra that made astronomers take special note. As observed by the Atacama Large Millimeter/sub-millimeter Array (ALMA), its protoplanetary disk doesn’t occupy the same plane as the binary orbit; it’s been flipped by 90 degrees over the orbital plane of the binary pair. Although such systems have been long believed to be theoretically possible, this is the first example that has been found.

“Discs rich in gas and dust are seen around nearly all young stars, and we know that at least a third of the ones orbiting single stars form planets,” said Grant M. Kennedy, of the University of Warwick and lead author of the study published today in the journal Nature Astronomy, in a statement. “Some of these planets end up being misaligned with the spin of the star, so we’ve been wondering whether a similar thing might be possible for circumbinary planets. A quirk of the dynamics means that a so-called polar misalignment should be possible, but until now we had no evidence of misaligned discs in which these planets might form.”

Artwork of the system HD 98000. This is a binary star comprising two sun-like components, surrounded by a thick disc of material [University of Warwick/Mark Garlick]

This star system makes for some rather interesting visuals, as shown in the artist’s impression at the top of the page. Should there be a planetary body orbiting the stars on the inner edge of the disk, an observer would be met with a dramatic pillar of gas and dust towering into space with the two stars either side of it in the distance. As they orbit one another, the planetary observer would see them switch positions to either side of the pillar. It goes without saying that any planet orbiting two stars would have very different seasons than Earth. It will even have two different shadows cast across the surface.

“We used to think other solar systems would form just like ours, with the planets all orbiting in the same direction around a single sun,” added co-author Daniel Price of Monash University. “But with the new images we see a swirling disc of gas and dust orbiting around two stars. It was quite surprising to also find that that disc orbits at right angles to the orbit of the two stars.”

Interestingly, the researchers note that there are another two stars orbiting beyond the disk, meaning that our hypothetical observer would have four suns of different brightnesses in the sky.

The most exciting thing to come out of this study, however, is that ALMA has detected signatures that hint at dust growth in the disk, meaning that material is in the process of clumping together. Planetary formation theories suggest that accreting dust will go on to form small asteroids and planetoids, creating a fertile enviornment in which planets can evolve.

“We take this to mean planet formation can at least get started in these polar circumbinary discs,” said Kennedy. “If the rest of the planet formation process can happen, there might be a whole population of misaligned circumbinary planets that we have yet to discover, and things like weird seasonal variations to consider.”

What was that I was saying about “cosmic norms”? When it comes to star system formation, there doesn’t appear to be any.

Reference: https://warwick.ac.uk/newsandevents/pressreleases/double_star_system
Paper:
https://www.nature.com/articles/s41550-018-0667-x

How Is Stardust Created? #TRIUMFology

I worked on TRIUMF’s Five-Year Plan (2020-2025) last year, so Astroengine is featuring a few physicsy articles that were included in the document to tell the center’s story

When (neutron) stars collide… [NASA/CXC/M.WEISS]

Last year, I had the honor to help write TRIUMF’s Five-Year Plan for 2020-2025. TRIUMF is Canada’s particle accelerator center, located next to the University of British Columbia’s campus in Vancouver, and it tackles some of the biggest problems facing physics today.

Every five years, research facilities in Canada prepare comprehensive documents outlining their strategies for the next five. In this case, TRIUMF asked me to join their writer team and I was specifically tasked with collaborating with TRIUMF’s management to develop and write the Implementation Plan (PDF) — basically an expanded version of the Strategic Plan (PDF) — detailing the key initiatives the center will carry out between 2020 and 2025.

As the location of the world’s largest and oldest operational cyclotron, the center is a multi-faceted physics lab with hundreds of scientists and engineers working on everything from understanding the origins of matter to developing radiopharmaceuticals to treat late-stage cancers. I only had a vague understanding about the scope of TRIUMF’s work before last year, but, as the months progressed after visiting the center in April 2018, I was treated to an unparalleled learning experience that was as dizzying as it was rewarding.

As a science communicator, I wanted to understand what makes TRIUMF “tick,” so I decided to speak to as many TRIUMF scientists, engineers, collaborators, and managers as possible. During my interviews, I was excited and humbled to hear stories of science breakthroughs, personal achievements and mind-bending physics concepts, so I included a series of miniature articles to complement the Implementation Plan’s text. As the Five-Year Plan is a public document (you can download the whole Plan here, in English and French), I’ve been given permission by TRIUMF to re-publish these articles on Astroengine.

“Beyond Multimessenger Astronomy”

Background: To kick off the series, we’ll begin with nuclear science. Specifically, how astrophysical processes create heavy elements and how TRIUMF studies the formation of radioisotopes in the wake of neutron star collisions.

After the 2017 LIGO detection of gravitational waves caused by the collision of two neutron stars (get the details here), and the near-simultaneous detection of a gamma-ray burst from the same location, scientists heralded a new era for astronomy — nicknamed “multimessenger astronomy,” where gravitational wave and electromagnetic signals measured at the same time from the same event can create a new understanding of astrophysical processes. In this case, as it was confirmed to be a neutron star merger — an event that is theorized to generate r-process elements — spectroscopic analysis of the GRB’s afterglow confirmed that, yes, neutron star collisions do indeed create the neutron-rich breeding ground for heavy elements (like gold and platinum). Although multimessenger astronomy may be a new thing, TRIUMF has been testing these theories in the laboratory environment for years, using rare isotope beams colliding into targets that mimic the nuclear processes that produce the heavy elements in our universe. This process is known as nucleogenesis, and it’s how our cosmos forges the elements that underpin stardust, the stuff that makes the planets, stars, and the building blocks of life.

For this mini-article, I had a fascinating chat with Dr. Iris Dillmann, a nuclear physics research scientist at TRIUMF. I’ve lightly edited the text for context and clarity. The original article can be found on page 22 of the Implementation Plan (PDF).

The GRIFFIN experiment is part of the ISAC facility that uses rare-isotope beams to carry out physics experiments [TRIUMF]

The article: TRIUMF’s investigations into neutron-rich isotopes were well-established before the advent of multi-messenger astronomy. “It was a cherry on top of the cake to get this confirmation, but the experimental program was already going on,” said Dillmann.

“What we do is multi-messenger nuclear physics; we are not looking directly into stars. TRIUMF is doing experiments here on Earth.”

Whereas the combination of gravitational waves and electromagnetic radiation from astrophysical events gives rise to a new era of multi-messenger astronomy, TRIUMF’s Isotope Separator and Accelerator (ISAC) facilitates the investigation of heavy isotopes through an array of nuclear physics experiments all under one roof that can illuminate the characteristics of isotopes that have been identified in neutron star mergers.

“For example, astronomers can identify one interesting isotope and realize that they need more experimental information on that one isotope,” she said. “We then have the capability to go through the different setups and, say, measure the mass of the isotope with the TRIUMF Ion Trap for Atomic and Nuclear Science (TITAN) experiment’s Penning trap.”

From there, Dillmann added, the Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei (GRIFFIN) experiment can use decay spectroscopy to investigate the half-lives of rare isotope beams and their underlying nuclear structure. Other nuclear properties such as moments and charge radii can be measured using laser spectroscopy. TRIUMF scientists can also directly measure the reaction cross-sections of explosive hydrogen and helium burning in star explosions with the Detector of Recoils And Gammas Of Nuclear reactions experiment (DRAGON) and the TRIUMF UK Detector Array (TUDA).

With ISAC, all these measurements are carried out in one place, where teams from each experiment work side by side to solve problems quickly and collaborate effectively. “We have the setups in the hall to investigate an isotope from different perspectives to try to get a complete picture just from one department — the nuclear physics department,” said Dillmann.

*****

Why “TRIUMFology”?

…because I have a “PhD” in TRIUMFology! Not sure if I can include it in my resume, but I love the honor all the same. Thanks Team TRIUMF!

Wonky Star Systems May Be Born That Way

A nearby baby star has been discovered with a warped protoplanetary disk — a feature that may reveal the true nature of the solar system’s planetary misalignments

[RIKEN]

Textbook descriptions of our solar system often give the impression that all the planets orbit the sun in well-behaved near-circular orbits. Sure, there’s a few anomalies, but, in general, we’re led to believe that everything in our interplanetary neighborhood travels around the sun around a flat orbital plane. This, however, isn’t exactly accurate.

Pluto, for example, has an orbit around the sun that is tilted by over 17 degrees out of the plane of the ecliptic (an imaginary flat plane around which the Earth orbits the sun). Mercury has an inclination of seven degrees. Even Venus likes to misbehave and has an orbital inclination of over three degrees. If all the material that built the planets originated from the same protoplanetary disk that was — as all the artist’s impressions would have us believe — flat, what knocked all the planet’s out of alignment with the ecliptic?

Until now, it was assumed that, during the early epoch of our solar system’s planet-forming days, dynamic chaos ruled. Planets jostled for gravitational dominance, Jupiter bullied smaller worlds into other orbits (possibly chucking one or two unfortunates into deep space), and gravitational instabilities threw the rest into disorderly orbital paths. Other star systems also exhibit this orbital disorder, so perhaps it’s just an orbital consequence of a star system’s growing pains.

But there might be another contribution to the chaos: perhaps wonky star systems were just born that way.

Cue a recent observation campaign of the nearby baby star L1527. Located 450 light-years away in the direction of the Taurus Molecular Cloud, L1527 is a protostar embedded in a thick protoplanetry disk. Using the Atacama Large Millimeter/submillimeter Array (ALMA), in Chile, astronomers of the RIKEN Cluster for Pioneering Research (CPR) and Chiba University in Japan discovered that the L1527 disk is actually two disks morphed into one — both of which are out of alignment with one another. Imagine a vinyl record that has been left on a heater and you wouldn’t be far off visualizing what this baby star system looks like.

The RIKEN study, published on Jan. 1 in Nature, suggests that this warping may have been caused by jets of material emanating from the star’s birth, kicking planet-forming material into this warped configuration and, should this configuration remain stable, could result in planets with orbital planes that are significantly out of alignment.

“This observation shows that it is conceivable that the misalignment of planetary orbits can be caused by a warp structure formed in the earliest stages of planetary formation,” said team leader Nami Sakai in a RIKEN press release. “We will have to investigate more systems to find out if this is a common phenomenon or not.”

It’s interesting to think that if this protoplanetary disk warping is due to the mechanics behind the formation of the star itself, we might be able to look at mature star systems to see the ancient fingerprint of a star’s earliest outbursts or, possibly, its initial magnetic environment.

It’s possible “that irregularities in the flow of gas and dust in the protostellar cloud are still preserved and manifest themselves as the warped disk,” added Sakai. “A second possibility is that the magnetic field of the protostar is in a different plane from the rotational plane of the disk, and that the inner disk is being pulled into a different plane from the rest of the disk by the magnetic field.”

Though orbital chaos undoubtedly contributed to how our solar system looks today, with help of this research, we may be also getting a glimpse of how warped our sun’s protoplanetry disk may have been before the planets even formed.