Every Time Lightning Strikes, Matter-Antimatter Annihilation Happens too

Lighting has always been a source of awe and mystery for us lowly mortals. In ancient times, people associated it with Gods like Zeus and Thor, the fathers of the Greek and Norse pantheons. With the birth of modern science and meteorology, lighting is no longer considered the province of the divine. However, this does not mean that the sense of mystery it carries has diminished one bit.

For example, scientists have found that lightning occurs in the atmospheres of other planets, like the gas giant Jupiter (appropriately!) and the hellish world of Venus. And according to a recent study from Kyoto University, gamma rays caused by lighting interact with air molecules, regularly producing radioisotopes and even positrons – the antimatter version of electrons.

The study, titled “Photonuclear Reactions Triggered by Lightning Discharge“, recently appeared in the scientific journal Nature. The study was led by Teruaki Enoto, a researcher from The Hakubi Center for Advanced Research at Kyoto University, and included members from the University of Tokyo, Hokkaido University, Nagoya University, the RIKEN Nishina Center, the MAXI Team, and the Japan Atomic Energy Agency.

For some time, physicists have been aware that small bursts of high-energy gamma rays can be produced by lightning storms – what are known as “terrestrial gamma-ray flashes”. They are believed to be the result of static electrical fields accelerating electrons, which are then slowed by the atmosphere. This phenomenon was first discovered by space-based observatories, and rays of up to 100,000 electron volts (100 MeV) have been observed.

Given the energy levels involved, the Japanese research team sought to examine how these bursts of gamma rays interact with air molecules. As Teruaki Enoto from Kyoto University, who leads the project, explained in a Kyoto University press release:

“We already knew that thunderclouds and lightning emit gamma rays, and hypothesized that they would react in some way with the nuclei of environmental elements in the atmosphere. In winter, Japan’s western coastal area is ideal for observing powerful lightning and thunderstorms. So, in 2015 we started building a series of small gamma-ray detectors, and placed them in various locations along the coast.”

Unfortunately, the team ran into funding problems along the way. As Enoto explained, they decided to reach out to the general public and established a crowdfunding campaign to fund their work. “We set up a crowdfunding campaign through the ‘academist’ site,” he said, “in which we explained our scientific method and aims for the project. Thanks to everybody’s support, we were able to make far more than our original funding goal.”

Thanks to the success of their campaign, the team built and installed particle detectors across the northwest coast of Honshu. In February of 2017, they installed four more detectors in Kashiwazaki city, which is a few hundred meters away from the neighboring town of Niigata. Immediately after the detectors were installed, a lightning strike took place in Niigata, and the team was able to study it.

What they found was something entirely new and unexpected. After analyzing the data, the team detected three distinct gamma-ray bursts of varying duration. The first was less than a millisecond long, the second was gamma ray-afterglow that took several milliseconds to decay, and the last was a prolonged emission lasting about one minute. As Enoto explained:

“We could tell that the first burst was from the lightning strike. Through our analysis and calculations, we eventually determined the origins of the second and third emissions as well.”

They determined that the second afterglow was caused by the lightning reacting with nitrogen in the atmosphere. Essentially, gamma rays are capable of causing nitrogen molecules to lose a neutron, and it was the reabsorption of these neutrons by other atmospheric particles that produced the gamma-ray afterglow. The final, prolonged emission was the result of unstable nitrogen atoms breaking down.

It was here that things really got interesting. As the unstable nitrogen broke down, it released positrons that then collided with electrons, causing matter-antimatter annihilations that released more gamma rays. As Enoto explained, this demonstrated, for the first time that antimatter is something that can occur in nature due to common mechanisms.

“We have this idea that antimatter is something that only exists in science fiction,” he said. “Who knew that it could be passing right above our heads on a stormy day? And we know all this thanks to our supporters who joined us through ‘academist’. We are truly grateful to all.”

If these results are indeed correct, than antimatter is not the extremely rare substance that we tend to think it is. In addition, the study could present new opportunities for high-energy physics and antimatter research. All of this research could also lead to the development of new or refined techniques for creating it.

Looking ahead, Enoto and his team hopes to conduct more research using the ten detectors they still have operating along the coast of Japan. They also hope to continue involving the public with their research, a process that goes far beyond crowdfunding and includes the efforts of citizen scientists to help process and interpret data.

Further Reading: University of Kyoto, Nature, NASA Goddard Media Studios

Spectrum of Antimatter Observed for First Time

Ever since the existence of antimatter was proposed in the early 20th century, scientists have sought to understand how relates to normal matter, and why there is an apparent imbalance between the two in the Universe. To do this, particle physics research in the past few decades has focused on the anti-particle of the most elementary and abundant atom in the Universe – the antihydrogen particle.

Until recently, this has been very difficult, as scientists have been able to produce antihydrogen, but unable to study it for long before it annihilated. But according to recent a study that was published in Nature, a team using the ALPHA experiment was able to obtain the first spectral information on antihydrogen. This achievement, which was 20 years in the making, could open up an entirely new era of research into antimatter.

Measuring how elements absorb or emit light – i.e. spectroscopy – is a major aspect of physics, chemistry and astronomy. Not only does it allow scientists to characterize atoms and molecules, it allows astrophysicists to determine the composition of distant stars by analyzing the spectrum of the light they emit.

Measuring the antihydrogen spectrum with high-precision offers an extraordinary new tool to test whether matter behaves differently from antimatter and thus to further test the robustness of the Standard Model (mage: Maximilien Brice/CERN)
The ALPHA experiment probes whether matter behaves differently from antimatter by measuring the antihydrogen spectrum with high-precision, further testing the robustness of the Standard Model. Credit: Maximilien Brice/CERN

In the past, many studies have been conducted into the spectrum of hydrogen, which constitutes roughly 75% of all baryonic mass in the Universe. These have played a vital role in our understanding of matter, energy, and the evolution of multiple scientific disciplines. But until recently, studying the spectrum of its anti-particle has been incredibly difficult.

For starters, it requires that the particles that constitute antihydrogen – antiprotons and positrons (anti-electrons) – be captured and cooled so that they may come together. In addition, it is then necessary to maintain these particles long enough to observe their behavior, before they inevitable make contact with normal matter and annihilate.

Luckily, technology has progressed in the past few decades to the point where research into antimatter is now possible, thus affording scientists the opportunity to deduce whether the physics behind antimatter are consistent with the Standard Model or go beyond it. As the CERN research team – which was led by Dr. Ahmadi of the Department of Physics at the University of Liverpool – indicated in their study:

“The Standard Model predicts that there should have been equal amounts of matter and antimatter in the primordial Universe after the Big Bang, but todays Universe is observed to consist almost entirely of ordinary matter. This motivates physicists to carefully study antimatter, to see if there is a small asymmetry in the laws of physics that govern the two types of matter.”
ALPHA uses a magnetic trap to hold neutral atoms of anthydrogen and then conduct spectrographic analyis. Credit: CERN
ALPHA uses a magnetic trap to hold neutral atoms of antihydrogen and then subjecting them to spectrographic analysis. Credit: CERN

Beginning in 1996, this research was conducted using the AnTiHydrogEN Apparatus (ATHENA) experiment, a part of the CERN Antiproton Decelerator facility. This experiment was responsible for capturing antiprotons and positrons, then cooling them to the point where they can combine to form anithydrogen. Since 2005, this task has become the responsibility of ATHENA’s successor, the ALPHA experiment.

Using updated instruments, ALPHA captures atoms of neutral antihydrogen and holds them for a longer period before they inevitably annihilate  During this time, research teams conduct spectrographic analysis using ALPHA’s ultraviolet laser to see if the atoms obey the same laws as hydrogen atoms. As Jeffrey Hangst, the spokesperson of the ALPHA collaboration, explained in a CERN update:

“Using a laser to observe a transition in antihydrogen and comparing it to hydrogen to see if they obey the same laws of physics has always been a key goal of antimatter research… Moving and trapping antiprotons or positrons is easy because they are charged particles. But when you combine the two you get neutral antihydrogen, which is far more difficult to trap, so we have designed a very special magnetic trap that relies on the fact that antihydrogen is a little bit magnetic.”

In so doing, the research team was able to measure the frequency of light needed to cause a positron to transition from its lowest energy level to the next. What they found was that (within experimental limits) there was no difference between the antihydrogen spectral data and that of hydrogen. These results are an experimental first, as they are the first spectral observations ever made of an antihydrogen atom.

Besides allowing for comparisons between matter and antimatter for the first time, these results show that antimatter’s behavior – vis a vis its spectrographic characteristics – are consistent with the Standard Model. Specifically, they are consistent with what is known as Charge-Parity-Time (CPT) symmetry.

This symmetry theory, which is fundamental to established physics, predicts that energy levels in matter and antimatter would be the same. As the team explained in their study:

“We have performed the first laser-spectroscopic measurement on an atom of antimatter. This has long been a sought-after achievement in low-energy antimatter physics. It marks a turning point from proof-of-principle experiments to serious metrology and precision CPT comparisons using the optical spectrum of an anti-atom. The current result… demonstrate that tests of fundamental symmetries with antimatter at the AD are maturing rapidly.”

In other words, the confirmation that matter and antimatter have similar spectral characteristics is yet another indication that the Standard Model holds up – just as the discovery of the Higgs Boson in 2012 did. It also demonstrated the effectiveness of the ALPHA experiment at trapping antimatter particles, which will have benefits other antihydrogen experiments.

Naturally, the CERN researchers were very excited by this find, and it is expected to have drastic implications. Beyond offering a new means of testing the Standard Model, it is also expected to go a long way towards helping scientists to understand why there is a matter-antimatter imbalance in the Universe. Yet another crucial step in discovering exactly how the Universe as we know it came to be.

Further Reading: CERN

Are There Antimatter Galaxies?

One of the biggest mysteries in astronomy is the question, where did all the antimatter go? Shortly after the Big Bang, there were almost equal amounts of matter and antimatter. I say almost, because there was a tiny bit more matter, really. And after the matter and antimatter crashed into each other and annihilated, we were left with all the matter we see in the Universe.

You, and everything you know is just a mathematical remainder, left over from the great division of the Universe’s first day.

We did a whole article on this mystery, so I won’t get into it too deeply.

But is it possible that the antimatter didn’t actually go anywhere? That it’s all still there in the Universe, floating in galaxies of antimatter, made up of antimatter stars, surrounded by antimatter planets, filled with antimatter aliens?

Aliens who are friendly and wonderful in every way, except if we hugged, we’d annihilate and detonate with the energy of gigatons of TNT. It’s sort of tragic, really.

If those antimatter galaxies are out there, could we detect them and communicate with those aliens?

First, a quick recap on antimatter.

Antimatter is just like matter in almost every way. Atoms have same atomic mass and the exact same properties, it’s just that all the charges are reversed. Antielectrons have a positive charge, antihydrogen is made up of an antiproton and a positron (instead of a proton and an electron).

It turns out this reversal of charge causes regular matter and antimatter to annihilate when they make contact, converting all their mass into pure energy when they come together.

We can make antimatter in the laboratory with particle accelerators, and there are natural sources of the stuff. For example, when a neutron star or black hole consumes a star, it can spew out particles of antimatter.

In fact, astronomers have detected vast clouds of antimatter in our own Milky Way, generated largely by black holes and neutron stars grinding up their binary companions.

Wyoming Milky Way set. Credit and copyright: Randy Halverson.
Wyoming Milky Way set. Credit and copyright: Randy Halverson.

But our galaxy is mostly made up of regular matter. This antimatter is detectable because it’s constantly crashing into the gas, dust, planets and stars that make up the Milky Way. This stuff can’t get very far without hitting anything and detonating.

Now, back to the original question, could you have an entire galaxy made up of antimatter? In theory, yes, it would behave just like a regular galaxy. As long as there wasn’t any matter to interact with.

And that’s the problem. If these galaxies were out there, we’d see them interacting with the regular matter surrounding them. They would be blasting out radiation from all the annihilations from all the regular matter gas, dust, stars and planets wandering into an antimatter minefield.

Astronomers don’t see this as far as they look, just the regular, quiet and calm matter out to the edge of the observable Universe.

That doesn’t make it completely impossible, though, there could be galaxies of antimatter as long as they’re completely cut off from regular matter.

But even those would be detectable by the supernova explosions within them. A normally matter supernova generates fast moving neutrinos, while an antimatter supernova would generate a different collection of particles. This would be a dead giveaway.

There’s one open question about antimatter that might make this a deeper mystery. Scientists think that antimatter, like regular matter, has regular gravity. Matter and antimatter galaxies would be attracted to each other, encouraging annihilation.

But scientists don’t actually know this definitively yet. It’s possible that antimatter has antigravity. An atom of antihydrogen might actually fall upwards, accelerating away from the center of the Earth.

The ALPHA experiment, one of five experiments that are studying antimatter at CERN Credit: Maximilien Brice/CERN

Physicists at CERN have been generating antimatter particles, and trying to detect if they’re falling downward or up.

If that was the case, then antimatter galaxies might be able to repel particles of regular matter, preventing the annihilation, and the detection.

If you were hoping there are antimatter lurking out there, hoarding all that precious future energy, I’m sorry to say, but astronomers have looked and they haven’t found it. Just like the socks in your dryer, we may never discover where it all went.

Is There a Mirror Universe?

Could there be a mirror universe, where everything is backwards – and everybody has goatees? How badly do you need to bend the laws of physics to make this happen?

One of the great mysteries in cosmology is why the Universe is mostly matter and not antimatter. If you want to learn more about that specific subject, you can click here and watch an episode all about that.

During the Big Bang, nearly equal amounts of matter and antimatter were created, and subsequently annihilated. Nearly equal. And so we’re left with a Universe made of matter.

But could there be antimatter stars out there? With antimatter planets in orbit. Could there be a backwards Universe that operates just like our regular Universe, but everything’s made of antimatter? And if it’s out there, does it have to be evil? Do they only know how to conquer? Does everyone, even the antimatter babies and ladies, have handsome goatees? How about sashes? I hear they’re big on sashes. OOH and daggers. Gold daggers with little teensy antimatter emeralds and rubies.

Antimatter, without the goatee, was theorized in 1928 by Paul Dirac, who realized that one implication of quantum physics was that you could get electrons that had a positive charge instead of a negative charge. They were discovered by Carl D. Anderson just 4 years later, which he named “positron” for positive electron.

We believe he was clearly snubbing Dirac, by not naming them the “Diracitron”, alternately they were saving that name for a giant Japanese robot.

These antiparticles are created through high energy particle collisions happening naturally in the Universe, or unnaturally inside our “laugh in the face of God and nature” particle accelerators. We can even detect the annihilation out there in the Universe where matter and antimatter crash into each other.

Physicists have discovered a range of anti-particles. Anti-protons, anti-neutrons, anti-hydrogen, anti-helium. To date, there’s been no evidence of any goatees or sashes. Naturally, they wondered what might happen if the balance of the Universe was flipped. What if we had a Universe made out of mostly antimatter? Would it still… you know, work? Could you have antimatter stars, antimatter planets, and even those antimatter people we mentioned?

The Large Hadron Collider (CERN/LHC)
The Large Hadron Collider (CERN/LHC)

When physics swap out matter for anti-matter in their equations, they call it charge conjugation. It turns out, no. If you reversed the charge of all the particles in the Universe, it wouldn’t evolve in the same way as our “plain old non-sashed” Universe.

To fix this problem, physicists considered the implications if you had an actual mirror Universe, where all the particles behaved as if they were mirror images of themselves. This sounds a little more in line with our “Through a mirror, darkly” goatee and sash every day festival universe. This is all the bits backwards. Spin, charge, velocity, the works. They called this parity inversion. So, would this work?

Again, it turns out that the answer is no. It would almost work out, but there’s a tendency for the weak nuclear force, the one the governs nuclear decay to violate this idea of parity inversion. Even in a mirror Universe, the weak nuclear force is left-handed. Dammit, weak nuclear force, get your act together, if not just for the sake of the costumes and cooler bridge lighting.

What matter and antimatter might look like annihilating one another. Credit: NASA/CXC/M. Weiss
What matter and antimatter might look like annihilating one another. Credit: NASA/CXC/M. Weiss

What if you reversed both the charge and the parity at the same time? What if you had antimatter in a mirror Universe? Physicists called this charge-parity symmetry, or CP symmetry.

In a dazzling experiment and absolute “what if” one-upmanship exercise by James Cronin and Val Fitch in 1964. They demonstrated that no, you can’t have a mirror-antimatter Universe evolve with our physical laws. This experiment won the Nobel Prize in 1980.

Physicists had one last trick up their sleeves. It turns out that if you reverse time itself as well as making everything out of antimatter and holding it up to a mirror, you get true symmetry. All the physical lays are preserved, and you’d get a Universe that would look exactly like our own.

It turns out we could live in a mirror Universe, as long as you were willing to reverse the charge of every particle and run time backwards. And if you did, it would be indistinguishable from the Universe we actually live in. Now, if you’ll excuse me, I think I need to call my tailor, I hear sashes are going to be huge this year.

So what do you think, do we live in the real Universe or the mirror Universe? Tell us in the comments below.

Could the Death Star Destroy a Planet?

In the movie Star Wars, the Darth Vader’s Death Star destroyed a planet. Could this really happen?

You’ve watched Star Wars right? Is that still a thing? With the Starring and the Warring? Anyway, there’s this classic scene where the “Death Star” sidles up to Alderaan, and it is all like “Hey Planetoid, you lookin’ fine tonight” and then it fires up the superlaser and destroys the entire orb in a single blast. “BOOM”. Shortly followed by some collective group screaming on the interstellar forceway radio.

This is generally described as “science fiction”. And when you’re making up stories, anything you like can happen in them. George Lucas’ hunger for your childhood toy money wasn’t hampered by the pesky constraints of physics in any meaningful way.

Here at the Guide to Space, we get to take our own flights of fancy and pointlessly speculate for your amusement. That’s our job. Well, that and snark. Let’s consider what it would actually take to destroy a planet with a ‘pew pew’ style laser beam, and what kinds of energy would need to be harnessed in a fully armed and operational battle station.

Let’s go back and carefully review our “evidence”. The Death Star drifts in, charges up all its lasers into a superlaser blast focused on Alderaan. The planet then detonates and chunks fly off in every direction just like the pie eating contest in “Stand By Me”.

What we saw was every part of Alderaan given enough of a kick so that it was traveling at escape velocity from every other part of the planet. If the Death Star hadn’t delivered enough explosive energy, the planet might have fluffed up for a moment, but then the collective gravity would suck it all back in together, and then the slightly re-arranged, and likely now uninhabited planet would continue orbiting its star.

You can imagine doing this the slow way. Take each continent on Alderaan, load it up into a rocket and blast that rocket off into space as though it was on escape trajectory from the planet. Sure, you’d would need an incomprehensible number of rocket launches to get that material off the planet. But hey, midichlorians, blue finger lightning and ESP.

Fortunately, as you carted away more and more of the busted up rock, it would have less mutual gravity, and so the rocket launches would require less and less energy to get the job done. Eventually, you’d just be left with one last chunk of rock that you could just force ninja kick into the neighboring star.

Death Star beam. Credit: Lucasfilm
Death Star beam. Credit: Lucasfilm

So how much energy is that going to take? Well, there’s an “easy” calculation you can make. The energy you’d need is equal to 3 times the gravitational constant (6.673 x 10^-11) times the mass of the planet squared divided by 5 times the planet’s radius. Do this math for an Earth-sized/mass world, and let’s see that’s, two and one, carry the 5… and you get 2 x 10^36 joules. That’s a two followed by 36 zeros in joules. Is that a lot? That sounds like a lot.

Well, our own Sun puts out 3 x 10^26 joules per second. So, if you poured all the energy from the Sun into the task of tearing apart the Earth, it wouldn’t have enough energy to do it. In fact, you’d need to focus the light of the Sun for a full week to get that level of planet destruction done.

According to ancient Star Warsian dork scholars, the Death Star (SOLUS MORTIS) is powered by a hyperreactor with the output of multiple main sequence stars. So there you go, problem solved. It’s the size of a small moon, but it’s more powerful than many stars. Of course it can destroy a planet.

Exploding planet. Credit: ESO
Exploding planet. Credit: ESO

The Death Star clearly destroyed Alderaan. We watched it explode. I saw it, you saw it. We heard the screams of millions of souls cry out. It happened. But what if it wasn’t a beam thingy?

Our math is good, but clearly we’re not enlightened enough to comprehend the true wisdom hidden within the Lucasian scriptures. Perhaps the Death Star’s superlaser was just a targeting laser. Directing the placement of gigantic antimatter bomb. According to Ethan Siegel, from “Starts With a Bang,” you’d only need 1.24 trillion tonnes of antimatter.

Imagine you made a bomb out of that much antimatter iron – if that’s even a thing – you’d only need a sphere about 3 km across. If the Death Star is 150 km across or so, they could carry a bunch of these. Very carefully. Like super carefully. Okay, maybe it’d be a good idea if everyone took off their boots, and make sure they only talked with their inside voices.

Obviously, Star Wars is a story, so anything, ANYTHING can happen. The future is unknown, and we might discover all kinds of weirdo physics and harness them into all kinds of powerful weapons. I’m only suggesting, that a space station capable of deploying a week’s worth of solar energy in a single second might be a stretch. And maybe, George, if you just done a little back of the napkin math, we wouldn’t be talking about this right now. Also, maybe no Ewoks. I’m just saying.

Where do you stand on the feasibility of imaginary space station weaponry? How big a planet can your imagination destroy?

Where’s All The Antimatter?

One of the biggest mysteries in the Universe is the fact there there’s matter, and not antimatter. Where did it all go?

When we look around, everything we can see is made of matter. For every type of matter from electrons, protons and quarks there is a similar type of matter known as antimatter. So why aren’t there piles of antimatter rocks, cars and chocolate bars just lying around? Why does Scotty always have a little extra kicking around in his liquor cabinet? And where do I get mine?

The primary difference between matter and antimatter is that they have opposite electric charge. Which seems pretty mundane. The negatively charged electron has an antiparticle known as the positron, which has a positive electric charge.

Anti-protons have a negative charge, and are just flat out grumpy. We’ve been able to create these particles in the lab, and have even been able to create small amounts of anti-hydrogen consisting of a positron bound to an antiproton, when examined closely there’s were shown to have a goatee and a little colorful sash or dagger.

When we create particles in accelerators such as the Large Hadron Collider, we seem to get equal amounts of matter and antimatter. This suggests that when particles were formed soon after the big bang, there should have been equal amounts of matter and antimatter.

Particle Collider
Large Hadron Collider (CERN/LHC/GridPP)

But the universe we observe is only made of matter, and… here’s the best part… we have no idea why. Why didn’t the matter and antimatter completely annihilate each other? How come we ended up with a little more matter? This delightful mystery is known as baryon asymmetry.

We do have a few ideas, and by we, I mean some giant brained crackerjacks have come up with a few plausible options. The most popular is that somehow antimatter behaves a little differently than matter. This could cause an imbalance between matter and antimatter. After particles collided in the early universe, there would still be matter left over, hence the matter we observe.

Another idea is that the observable universe just happens to be in a region dominated by matter. Other parts of the multiverse could have observable universes dominated by antimatter. Baryon asymmetry is one of the big mysteries of modern cosmology.

Zero Gravity Flight
Stephen Hawking, weightless (courtesy Zero Gravity Corporation)

There is an even crazier idea. Antimatter might have anti-gravity. In other words, an atom of anti-hydrogen would fall up instead of down. If that is the case, then matter and antimatter would repel each other, and you might have matter universes and antimatter universes that are forever separate.There have been some initial experiments to test this idea, but so far there have been no conclusive results.

What do you think? Where’s all our antimatter and how do we track it down? I’d sure love to bring some home and show my friends…

And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!

Where Have All the Pulsars Gone? The Mystery at the Center of Our Galaxy

The galactic center is a happening place, with lots of gas, dust, stars, and surprising binary stars orbiting a supermassive black hole about three million times the size of our sun. With so many stars, astronomers estimate that there should be hundreds of dead ones. But to date, scientists have found only a single young pulsar at the galactic center where there should be as many as 50.

The question thus arises: where are all those rapidly spinning, dense stellar corpses known as pulsars? Joseph Bramante of Notre Dame University and astrophysicist Tim Linden of the University of Chicago have a possible solution to this missing-pulsar problem, which they describe in a paper accepted for publication in the journal Physical Review Letters.

Maybe those pulsars are absent because dark matter, which is plentiful in the galactic center, gloms onto the pulsars, accumulating until the pulsars become so dense they collapse into a black hole. Basically, they disappeared into the fabric of space and time by becoming so massive that they punched a hole right through it.

Dark matter, as you may know, is the theoretical mass that astrophysicists believe fills roughly a quarter of our universe. Alas, it is invisible and undetectable by conventional means, making its presence known only in how its gravitational pull interacts with other stellar objects.

One of the more popular candidates for dark matter is Weakly Interacting Massive Particles, otherwise known as WIMPs. Underground detectors are currently hunting for WIMPs and debate has raged over whether gamma rays streaming from the galactic center come from WIMPs annihilating one another.

In general, any particle and its antimatter partner will annihilate each other in a flurry of energy. But WIMPs don’t have an antimatter counterpart. Instead, they’re thought to be their own antiparticles, meaning that one WIMP can annihilate another.

But over the last few years, physicists have considered another class of dark matter called asymmetric dark matter. Unlike WIMPs, this type of dark matter does have an antimatter counterpart.

Numerical simulation of the density of matter when the universe was one billion years old. Cosmic Infrared Background ExpeRIment (CIBER) Credit: Caltech/Jamie Bock
 Cosmic Infrared Background ExpeRIment (CIBER) simulation of the density of matter when the universe was one billion years old, as produced by large-scale structures from dark matter. Credit: Caltech/Jamie Bock

Asymmetric dark matter appeals to physicists because it’s intrinsically linked to the imbalance of matter and antimatter. Basically, there’s a lot more matter in the universe than antimatter – which is good considering anything less than an imbalance would lead to our annihilation. Likewise, according to the theory, there’s much more dark matter than anti-dark-matter.

Physicists think that in the beginning, the Big Bang should’ve created as much matter as antimatter, but something altered this balance. No one’s sure what this mechanism was, but it might have triggered an imbalance in dark matter as well – hence it is “asymmetric”.

Dark matter is concentrated at the galactic center, and if it’s asymmetric, then it could collect at the center of pulsars, pulled in by their extremely strong gravity. Eventually, the pulsar would accumulate so much mass from dark matter that it would collapse into a black hole.

The idea that dark matter can cause pulsars to implode isn’t new.  But the new research is the first to apply this possibility to the missing-pulsar problem.

If the hypothesis is correct, then pulsars around the galactic center could only get so old before grabbing so much dark matter that they turn into black holes. Because the density of dark matter drops the farther you go from the center, the researchers predict that the maximum age of pulsars will increase with distance from the center. Observing this distinct pattern would be strong evidence that dark matter is not only causing pulsars to implode, but also that it’s asymmetric.

“The most exciting part about this is just from looking at pulsars, you can perhaps say what dark matter is made of,” Bramante said. Measuring this pattern would also help physicists narrow down the mass of the dark matter particle.

    Artist's illustration of a pulsar that was found to be an ultraluminous X-ray source. Credit: NASA, Caltech-JPL
Artist’s illustration of a pulsar that was found to be an ultraluminous X-ray source.
Credit: NASA, Caltech-JPL

But as Bramante admits, it won’t be easy to detect this signature. Astronomers will need to collect much more data about the galactic center’s pulsars by searching for radio signals, he claims. The hope is that as astronomers explore the galactic center with a wider range of radio frequencies, they will uncover more pulsars.

But of course, the idea that dark matter is behind the missing pulsar problem is still highly speculative, and the likelihood of it is being called into question.

“I think it’s unlikely—or at least it is too early to say anything definitive,” said Zurek, who was one of the first to revive the notion of asymmetric dark matter in 2009. The tricky part is being able to know for sure that any measurable pattern in the pulsar population is due to dark-matter-induced collapse and not something else.

Even if astronomers find this pulsar signature, it’s still far from being definitive evidence for asymmetric dark matter. As Kathryn Zurek of the Lawrence Berkeley National Laboratory explained: “Realistically, when dark matter is detected, we are going to need multiple, complementary probes to begin to be convinced that we have a handle on the theory of dark matter.”

And asymmetric dark matter may not have anything to do with the missing pulsar problem at all. The problem is relatively new, so astronomers may find more plausible, conventional explanations.

“I’d say give them some time and maybe they come up with some competing explanation that’s more fleshed out,” Bramante said.

Nevertheless, the idea is worth pursuing, says Haibo Yu of the University of California, Riverside. If anything, this analysis is a good example of how scientists can understand dark matter by exploring how it may influence astrophysical objects. “This tells us there are ways to explore dark matter that we’ve never thought of before,” he said. “We should have an open mind to see all possible effects that dark matter can have.”

There’s one other way to determine if dark matter can cause pulsars to implode: To catch them in the act. No one knows what a collapsing pulsar might look like. It might even blow up.

“While the idea of an explosion is really fun to think about, what would be even cooler is if it didn’t explode when it collapsed,” Bramante said. A pulsar emits a powerful beam of radiation, and as it spins, it appears to blink like a lighthouse with a frequency as high as several hundred times per second. As it implodes into a black hole, its gravity gets stronger, increasingly warping the surrounding space and time.

Studying this scenario would be a great way to test Einstein’s theory of general relativity, Bramante says. According to theory, the pulse rate would get slower and slower until the time between pulses becomes infinitely long. At that point, the pulses would stop entirely and the pulsar would be no more.

Further Reading: APS Physics, WIRED

First Precise Measurement of Antihydrogen

The best science — the questions that capture and compel any human being — is enshrouded in mystery. Here’s an example: scientists expect that matter and antimatter were created in equal quantities shortly after the Big Bang. If this had been the case, the two types of particles would have annihilated each other, leaving a Universe permeated by energy.

As our existence attests, that did not happen. In fact, nature seems to have a one-part in 10 billion preference for matter over antimatter. It’s one of the greatest mysteries in modern physics.

But the Large Hadron Collider is working hard, literally pushing matter to the limit, to solve this captivating mystery. This week, CERN created a beam of antihydrogen atoms, allowing scientists to take precise measurements of this elusive antimatter for the first time.

Antiparticles are identical to matter particles except for the sign of their electric charge. So while hydrogen consists of a positively charged proton orbited by a negatively charged electron, antihydrogen consists of a negatively charged antiproton orbited by a positively charged anti-electron, or a positron

While primordial antimatter has never been observed in the Universe, it’s possible to create antihydrogen in a particle accelerator by mixing positrons and low energy antiprotons.

In 2010, the ALPHA team captured and held atoms of antihydrogen for the first time. Now the team has successfully created a beam of antihydrogen particles. In a paper published this week in Nature Communications, the ALPHA team reports the detection of 80 antihydrogen atoms 2.7 meters downstream from their production.

“This is the first time we have been able to study antihydrogen with some precision,” said ALPHA spokesperson Jeffrey Hangst in a press release. “We are optimistic that ALPHA’s trapping technique will yield many such insights in the future.”

One of the key challenges is keeping antihydrogen away from ordinary matter, so that the two don’t annihilate each other. To do so, most experiments use magnetic fields to trap antihydrogen atoms long enough to study them.

However, the strong magnetic fields degrade the spectroscopic properties of the antihydrogen atoms, so the ALPHA team had to develop an innovative set-up to transfer antihydrogen atoms to a region where they could be studied, far from the strong magnetic field.

To measure the charge of antihydrogen, the ALPHA team studied the trajectories of antihydrogen atoms released from the trap in the presence of an electric field. If the antihydrogen atoms had an electric charge, the field would deflect them, whereas neutral atoms would be undeflected.

The result, based on 386 recorded events, gives a value of the antihydrogen electric charge at -1.3 x 10-8. In other words, its charge is compatible with zero to eight decimal places. Although this result comes as no surprise, since hydrogen atoms are electrically neutral, it is the first time that the charge of an antiatom has been measured to such high precision.

In the future, any detectable difference between matter and antimatter could help solve one of the greatest mysteries in modern physics, opening up a window into a new realm of science.

The paper has been published in Nature Communications.

How Do You Kill a Black Hole?

Black holes want to absorb all matter and energy in the Universe. It’s just a matter of time. So what can we do to fight back? What superweapons have been devised to destroy black holes?

Black holes are the natural enemies of all spacefaring races. With their bottomless capacity to consume all light and matter, it’s just a few septillion years before all things in the Universe have found their way into the cavernous maw of a black hole, crushed into the infinitely dense singularity. If Star Trek has taught us anything, it’s that it’s mankind’s imperative to survive against all odds.

So will we take this lying down?
Heck no!

Will we strike first and destroy the black holes before they destroy us?
Heck yes!

But how? How could you kill a black hole?
This… gets a little tricky.
Continue reading “How Do You Kill a Black Hole?”