The image is the result of a global collaboration and human ingenuity — a discovery that will change our perception of the universe forever
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:
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:
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.
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:
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.
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.
Waiting for the Andromeda galaxy’s stars to twinkle may have extinguished hope for tiny black holes being a significant dark matter candidate
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.
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.
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
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 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.”
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.
It has only been a couple of years since the first historic detection of gravitational waves, but now physicists are already dissecting a handful of signals that emanated hundreds of millions of light-years away to elucidate how some of the most violent events in our universe work.
Most of the gravitational wave signals detected so far involve the merger of black holes, but one signal, detected on Aug. 17, 2017, was special—it was caused by the smashup of two neutron stars. This merger also generated a powerful gamma-ray burst (GRB) that was detected at nearly the same time, linking GRBs with neutron star mergers and highlighting where heavy elements in our universe are forged. A new era of “multimessenger astronomy” had begun.
Now, the signal (designated GW170817) has been reanalyzed to understand what happened after the merger. Analysis that came before suggested that the collision of the two neutron stars would have tipped the mass balance to create a black hole. According to a new study, published in the journal Monthly Notices of the Royal Astronomical Society: Letters, two physicists suggest a contradictory scenario: GW170817 didn’t create a black hole, it produced a hypermassive neutron star, instead.
“We’re still very much in the pioneering era of gravitational wave astronomy. So it pays to look at data in detail,” said Maurice van Putten of Sejong University in South Korea. “For us this really paid off, and we’ve been able to confirm that two neutron stars merged to form a larger one.”
The secret behind this finding focuses on the datasets recorded by the US-based Laser Interferometer Gravitational-wave Observatory (LIGO) and Italian Virgo observatory. When gravitational waves are recorded during a black hole or neutron star merger event, their frequency rapidly increases (as the objects orbit one another faster and faster as they get closer and closer) and then abruptly cuts off (when they collide). When turned into an audio file, mergers sound like “chirps.” Apart from sounding like an eerie bird call coming from deep space, physicists have been able to extract surprisingly detailed information from the conditions of the merging objects, such as their mass and rates of spin.
And this is where van Putten’s work comes in.
Working with Massimo della Valle of the Osservatorio Astronomico de Capodimonte in Italy, the duo applied a new analysis technique to these data and detected a 5-second descending “chirp” (as shown by the downward arrow in the graph above). This descending chirp happened immediately after the GRB was detected coming from the same location as the gravitational wave signal’s origin. According to their analysis, the spin-down—from 1 KHz to 49 Hz—was most likely representative of a very massive neutron star and not a black hole.
If corroborated, this discovery could have profound implications for astrophysics. How hypermassive neutron stars (like the one that was created by GW170817) can exist without collapsing into a black hole will likely keep theorists busy for some time and physicists will be hopeful for another gravitational wave event like GW170817.
In 2015, a stellar-mass black hole in a binary star system underwent an accretion event causing it to erupt brightly across the electromagnetic spectrum. Slurping down the plasma from its stellar partner — an unfortunate sun-like star — the eruption became a valuable observation for astronomers and, in a recent study, researchers have used the event to better understand the magnetic environment surrounding the black hole.
The binary system in question is V404 Cygni, located 7,795 light-years from Earth, and that 2015 outburst was an X-ray nova, an eruption that previously occurred in 1989. Detected by NASA’s Swift space observatory and the Japanese Monitor of All-sky X-ray Image (MAXI) on board the International Space Station, the event quickly dimmed, a sign that the black hole had consumed its stellar meal.
Combining these X-ray data with observations by radio, infrared and optical telescopes, an international team of astronomers were able to measure emissions from the plasma close to the black hole’s event horizon as it cooled.
The black hole was formed after a massive star ran out of fuel and exploded as a supernova. Much of the magnetism of the progenitor star would have been retained post-supernova, so by measuring the emissions from the highly charged plasma, astronomers have a tool to probe deep inside the black hole’s “corona.” Like the sun’s corona — which is a magnetically-dominated region where solar plasma interacts with our star’s magnetic field (producing the solar wind and solar flares, for example) — it’s predicted that there should be a powerful interplay between the accreting plasma and the black hole’s coronal magnetism.
As charged particles interact magnetic fields, they experience acceleration radially (i.e. they spin around the magnetic field lines that guide their direction of propagation) and, should the magnetism be extreme (in a solar or, indeed, black hole’s corona), this plasma can be accelerated to relativistic speeds. In this case, synchrotron radiation may be generated. By measuring the radiation across all wavelengths, astronomers can thereby probe the magnetic environment close to a black hole as this radiation is directly related to how powerful a magnetic field is generating it.
The researchers write: “Using simultaneous infrared, optical, x-ray, and radio observations of the Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its 2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the corona. This measurement is substantially lower than previous estimates for such systems, providing constraints on physical models of accretion physics in black hole and neutron star binary systems.”
Black holes are poorly understood, but with the advent of gravitational wave (and “multimessenger”) astronomy and the excitement surrounding the Event Horizon Telescope, in the next few years we’re going to get a lot more intimate with these gravitational enigmas. Why this particular black hole’s magnetic environment is weaker than what would be expected, however, suggests that our theories surrounding black hole evolution are incomplete, so there will likely be some surprises in store.
“We need to understand black holes in general,” said collaborator Chris Packham, associate professor of physics and astronomy at The University of Texas at San Antonio (UTSA), in a statement. “If we go back to the very earliest point in our universe, just after the Big Bang, there seems to have always been a strong correlation between black holes and galaxies. It seems that the birth and evolution of black holes and galaxies, our cosmic island, are intimately linked. Our results are surprising and one that we’re still trying to puzzle out.”
Imagine the early universe: The first massive stars sparked to life and rapidly consumed their supply of hydrogen. These “metal poor” stars lived hard and died fast, burning quickly and then exploding as powerful supernovas. This first population of stars seeded the universe with heavier elements (i.e. elements heavier than helium, elements known as “metals” by astronomers) and their deaths created the first stellar-mass black holes.
But say if there were black holes bumbling around the universe before the first supernovae? Where the heck did they come from?
Some models of universal evolution suggests that immediately after the Big Bang, some 13.82 billion years ago, quantum fluctuations created pockets of dense matter as the universe started to expand. As inflation occurred and the universe cooled, these density fluctuations formed the vast large-scale structure of the universe that we observe today. These cosmological models suggest the early quantum density fluctuations may have been dramatic enough to create black holes — known as primordial black holes — and these ancient Big Bang remnants may still exist to this day.
The theoretical models surrounding the genesis of primordial black holes, however, are hard to test as observing the universe immediately after the Big Bang is, needless to say, very difficult. But now we know gravitational waves exist and physicists have detected the space-time ripples generated by the collision and merger of stellar-mass black holes and neutron stars, astronomers have an observational tool at their disposal.
Simple Idea, Not-So-Simple Implementation
In a new study published in Physical Review Letters, researchers have proposed that if we have the ability to detect gravitational waves produced before the first stars died, we may be able to carry out astronomical archaeological dig of sorts to possibly find evidence of these ancient black holes.
“The idea is very simple,” said physicist Savvas Koushiappas, of Brown University, in a statement. “With future gravitational wave experiments, we’ll be able to look back to a time before the formation of the first stars. So if we see black hole merger events before stars existed, then we’ll know that those black holes are not of stellar origin.”
Primordial black holes were first theorized by Stephen Hawking and others in the 1970’s, but it’s still unknown if they exist or whether we could even distinguish the primordial ones from the garden variety of stellar-mass black holes (it’s worth noting, however, that primordial black holes would have a range of masses and not restricted to stellar masses). Now we can detect gravitational waves, however, this could change as gravitational wave detector sensitivity increases, scientists will probe more distant (and therefore more ancient) black hole mergers. And, if we can detect gravitational waves originating from black hole mergers younger than 65 million years after the Big Bang, the researchers say, those black holes wouldn’t have a stellar origin as the first stars haven’t yet died — they could have only been born from the quantum mess immediately after the birth of our universe.
Like the infamous “Crasher Squirrel” that launched one of the most prolific memes in online history, “crasher asteroids” have photobombed the Hubble Space Telescope’s otherwise uninterrupted view of the ancient universe.
While carrying out its Frontier Fields survey of a random postage stamp-sized part of the sky in the direction of the galaxy cluster Abell 370, Hubble imaged many galaxies located at different distances over different epochs in time.
Visible in the observation are elliptical galaxies and spiral galaxies. Many are bright and bluish, but the vast majority are dim and reddish. The reddest blobs are the most distant galaxies in our observable universe; their light has been stretched (red-shifted) after traveling for billions of years through an expanding cosmos. These galaxies are the most ancient galaxies that formed within a billion years after the Big Bang.
But mixed in with this Hubble view of ancient light are bright arcs and dashes — tracks carved out by the rocky junk in our own solar system that is drifting in Hubble’s field of view, located a mere 160 million miles from Earth (on average). It’s sobering to think that the light from the reddest galaxies is nearly three times older than these asteroids.*
Abel 370 is located along the solar system’s ecliptic plane, around which the planets orbit the sun and the majority of asteroids in the asteroid belt between Mars and Jupiter are located. So, like looking through a swarm of bees, Hubble has captured the trails of asteroids in the foreground.
The trails themselves are created not by the motion of the asteroids, however, but by the motion of Hubble. While fixing its gaze on distant galaxies for hours at a time as it orbits Earth, Hubble’s position changes and, through an observational effect known as parallax, the positions of those asteroids appear to trace an arc when compared with the stationary background of galaxies billions of light-years distant.
As Hubble scanned its field of view, it revealed 20 asteroid trails, seven of which are unique objects (some of the asteroid trails were repeated observations of the same object, just captured at different times in Hubble’s orbit). Only two of these asteroids were previously discovered, the other five are newly discovered objects that were too faint for other observatories to detect.
So it goes to show that photobombing asteroids are useful for science and, though Hubble was observing the most distant objects in the cosmos, it was able to see a few of the rocks in our cosmic backyard.
*NOTE: Asteroids formed around the time our solar system first started creating planets, some 4.6 billion years ago. The most ancient galaxies are located over 13 billion light-years away, meaning the ancient light from those galaxies was produced 13 billion years ago.
But the fact that I’m typing this article and you’re reading it, however, suggests that we are here, so something must be awry with our understanding of the physics the universe is governed by.
The universe is the embodiment of an epic battle between matter and antimatter that occurred immediately after the Big Bang, 13.82 billion years ago. Evidently, matter won — because there are galaxies, stars, planets, you, me, hamsters, long walks on sandy beaches and beer — but how matter won is one of the biggest mysteries hanging over physics.
It is predicted that equal amounts of matter and antimatter were produced in the primordial universe (a basic prediction by the Standard Model of physics), but if that’s the case, all matter in the universe should have been annihilated when it came into contact with its antimatter counterpart — a Big Bang followed by a big disappointment.
This physics conundrum focuses on the idea that all particles have their antimatter twin with the same quantum numbers, only the exact opposite. Protons have anti-protons, electrons have positrons, neutrinos have anti-neutrinos etc.; a beautiful example of symmetry in the quantum world. But should one of these quantum numbers be very slightly different between matter and antimatter particles, it might explain why matter became the dominant “stuff” of the universe.
So, in an attempt to measure one of the quantum states of particles, physicists of CERN’s Baryon–Antibaryon Symmetry Experiment (BASE), located near Geneva, Switzerland, have made the most precise measurement of the anti-proton’s magnetic moment. BASE is a complex piece of hardware that can precisely measure the magnetic moments of protons and anti-protons in an attempt to detect an extremely small difference between the two. Should there be a difference, this might explain why matter is more dominant than antimatter.
However, this latest measurement of the magnetic moment of anti-protons has revealed that the magnetic moments of both protons and anti-protons are exactly the same to a record-breaking level of precision. In fact, the anti-proton measurement is even more precise than our measurements of the magnetic moment of a proton — a stunning feat considering how difficult anti-protons are to study.
“It is probably the first time that physicists get a more precise measurement for antimatter than for matter, which demonstrates the extraordinary progress accomplished at CERN’s Antiproton Decelerator,” said physicist Christian Smorra in a CERN statement. The Antiproton Decelerator is a machine that can capture antiparticles (created from particle collisions that occur at CERN’s Proton Synchrotron) and funnel them to other experiments, like BASE.
Antimatter is very tricky to observe and measure. Should these antiparticles come into contact with particles, they annihilate — you can’t simply shove a bunch of anti-protons into a flask and expect them to play nice. So, to prevent antimatter from making contact with matter, physicists have to create magnetic vacuum “traps” that can quarantine anti-protons from touching matter, thereby allowing further study.
A major area of research has been to develop ever more sophisticated magnetic traps; the slightest imperfections in a trap’s magnetic field containing the antimatter can allow particles to leak. The more perfect the magnetic field, the less chance there is of leakage and the longer antimatter remains levitating away from matter. Over the years, physicists have achieved longer and longer antimatter containment records.
In this new study, published in the journal Nature on Oct. 18, researchers used a combination of two cryogenically-cooled Penning traps that held anti-protons in place for a record-breaking 405 days. In that time they were able to apply another magnetic field to the antimatter, forcing quantum jumps in the particles’ spin. By doing this, they could measure their magnetic moments to astonishing accuracy.
According to their study, anti-protons have a magnetic moment of −2.792847344142 μN (where μN is the nuclear magneton, a physical constant). The proton’s magnetic moment is 2.7928473509 μN, almost exactly the same — the slight difference is well within the experiment’s error margin. As a consequence, if there’s a difference between the magnetic moment of protons and anti-protons, it must be much smaller than the experiment can currently detect.
These tiny measurements have huge — you could say: universal — implications.
“All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist,” added Smorra. “An asymmetry must exist here somewhere but we simply do not understand where the difference is.”
Now the plan is to improve methods of capturing antimatter particles, pushing BASE to even higher precision, to see if there really is an asymmetry in magnetic moment between protons and anti-protons. If there’s not, well, physicists will need to find their asymmetry elsewhere.
One hundred and thirty million years ago in a galaxy 130 million light-years away, two neutron stars met their fate, merging as one. Trapped in a gravitational embrace, these two stellar husks spiraled closer and closer until they violently ripped into one another, causing a detonation that reverberated throughout the cosmos.
On August 17, the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and Italian Virgo gravitational wave detector felt the faint ripples in spacetime from that ancient neutron star collision washing through our planet. Until now, LIGO and Virgo have only confirmed the collisions and mergers of black holes, so the fact that a nearby (a relative term in this case) neutron star merger had been detected was already historic.
But the implications for this particular neutron star signal, which is comparatively weak in comparison with the black hole mergers that have come before it, are so profound that I’ve been finding it hard to put this grand discovery into words (though I have tried).
Why It Matters
With regards to gravitational waves, I feel I’ve described each gravitational wave discovery as “historic” and “a new era for astronomy” since their first detection on Sept. 15, 2015, but the detection of GW170817 may well trump all that have come before it, even though the signal was generated by neutron stars and not black hole heavyweights.
The thing with black holes is that when they collide and merge, they don’t necessarily produce electromagnetic radiation (i.e. visible light, X-rays or infrared radiation). They can go “bump” in the cosmic night and no intelligent being with a conventional telescope would see it happen. But in the the gravitational domain, black hole mergers echo throughout the universe; their gravitational waves travel at the speed of light, warping spacetime as they propagate. To detect these “invisible” waves, we must build instruments that can “see” the infinitesimal wobbles in the fabric of spacetime itself, and this is where laser interferometry comes in.
Very precise lasers are fired down miles-long tunnels in “L” shaped buildings in the two LIGO detectors (in Washington and Louisiana) and the Virgo detector near Pisa. When gravitational waves travel through us, these laser interferometers can measure the tiny spacetime warps. The more detectors measuring the same signal means a more precise observation and scientists can then work out where (and when) the black hole merger occurred.
There are many more details that can be gleaned from the gravitational wave signal from black hole mergers, of course — including the progenitor black holes’ masses, the merged mass, black hole spin etc. — but for the most part, black hole mergers are purely a gravitational affair.
Neutron stars, however, are a different beast and, on Aug. 17, it wasn’t only gravitational wave detectors that measured a signal from 130 million light-years away; space telescopes on the lookout for gamma-ray bursts (GRBs) also detected a powerful burst of electromagnetic radiation in the galaxy of NGC 4993, thereby pinpointing the single event that generated the gravitational waves and the GRB.
And this is the “holy shit” moment.
As Caltech’s David H. Reitze puts it: “This detection opens the window of a long-awaited ‘multi-messenger’ astronomy.”
What Reitze is referring to is that, for the first time, both gravitational waves and electromagnetic waves (across the EM spectrum) have been observed coming from the same astrophysical event. The gravitational waves arrived at Earth slightly before the GRB was detected by NASA’s Fermi and ESA’s INTEGRAL space telescopes. Both space observatories recorded a short gamma-ray burst, a type of high-energy burst that was theorized (before Aug. 17) to be produced by colliding neutron stars.
Now scientists have observational evidence that these types of GRBs are produced by colliding neutron stars as the gravitational wave fingerprint unquestionably demonstrates the in-spiraling and merger of two neutron stars. This is a perfect demonstration of multi-messenger astronomy; where an energetic event can be observed simultaneously in EM and gravitational waves to reveal untold mysteries of the universe’s most energetic events.
Another Nod to Einstein
The fact that the gravitational waves and gamma-rays arrived at approximately the same time is yet another nod to Einstein’s general relativity. The century-old theory predicts that gravitational waves should travel at the speed of light and, via this brand spanking new way of doing multi-messenger astronomy, physicists and astronomers have again bolstered relativity with observational evidence.
But why did the gravitational waves arrive slightly before the GRB? Well, NASA’s Fermi team explains: “Fermi’s [Gamma-ray Burst Monitor instrument] saw the gamma-ray burst after the [gravitational wave] detection because the merger happened before the explosion,” they said in a tweet.
In other words, when the two neutron stars collided and merged, the event immediately dissipated energy as gravitational waves that were launched through spacetime at the speed of light — that’s the source of GW170817 — but the GRB was generated shortly after.
Enter the Kilonova
As the neutron stars smashed together, huge quantities of neutron star matter were inevitably blasted into space, creating a superheated, dense volume of free neutrons. Neutrons are subatomic particles that form the building blocks of atoms and if the conditions are right, the neutron star debris will undergo rapid neutron capture process (known as “r-process”) where neutrons combine with one another faster than the newly-formed radioactive particles can decay. This mechanism is responsible for synthesizing elements heavier than iron (elements lighter than iron are formed through stellar nucleosynthesis in the cores of stars).
For decades astronomers have been searching for observational evidence of the r-process in action and now they have it. Soon after the merger, massive amounts of debris erupted in a frenzy of heavy element creation, triggering an energetic eruption known as a “kilonova” that was seen as a short GRB. The GRB was cataloged as “SSS17a.”
The Golden Ticket
Follow-up observations by the Hubble Space Telescope, Gemini Observatory and the ESO’s Very Large Telescope have all detected spectroscopic signatures in the afterglow consistent with the r-process taking place at the site of the kilonova, meaning heavy elements are being formed and, yes, it’s a goldmine. As in: there’s newly-synthesized gold there. And platinum. And all the other elements heavier than iron that aren’t quite so sexy.
And there’s lots of it. Researchers estimate that that single neutron star collision produced hundreds of Earth-masses of gold and platinum and they think that neutron star mergers could be the energetic process that seed the galaxies with heavy elements (with supernovas coming second).
So, yeah, it’s a big, big, BIG discovery that will reverberate for the decades to come.
The best thing is that we now know that our current generation of advanced gravitational wave detectors are sensitive enough to not only detect black holes merging billions of light-years away, but also detect the nearby neutron stars that are busy merging and producing gold. As more detectors are added and as the technology and techniques mature, we’ll be inundated with merging events big and small, each one teaching us something new about our universe.