Reidar Hahn / Fermilab

The Cryogenic Dark Matter Search experiment, or CDMS, adds new intrigue to the subatomic hunt.

Three potential signatures of exotic dark matter particles have been found hidden in the readings from an underground lab in Minnesota  — and although the results are too tentative to be classified as a discovery, scientists say they provide promising new clues to the solution of a decades-old mystery.

"People shouldn't come away from this thinking that we've found dark matter," Rupak Mahapatra, a physicist at Texas A&M University who is a principal investigator with the SuperCDMS collaboration, told NBC News. "Really, it's just the beginning. ... What we really need to do is make more detectors and run them, and be sure."

If the results are confirmed, that would point to the existence of a weakly interacting massive particle, or WIMP, that could help account for the 27 percent of the universe that is thought to consist of dark matter. Such matter seems to be invisible and is detected primarily through its gravitational effect. Another mysterious quality known as dark energy accounts for 68 percent of the universe. That leaves just 5 percent consisting of ordinary matter — the stuff that makes up everything we see around us.

Physicists have puzzled over the nature of dark matter since the 1930s, and billions of dollars have been spent building experiments to track it down. 

Finding, or fluke?
The three high-energy events were recorded in 2008 by the Cryogenic Dark Matter Search, or CDMS, an experiment that was set up a decade ago nearly a half-mile (713 meters) underground in northern Minnesota's Soudan mine. That depth helps to shield the experiment from background cosmic rays that would overwhelm the signature of dark matter interactions at the surface.

The interactions seen by the CDMS team point to the existence of WIMPs with a best-guess mass of 8.6 billion electron volts, which would be about nine times as massive as the proton. Scientists calculated that there should be, on average, 0.7 events of that type recorded during the time frame for the readings.

NASA / CXC / CfA / STScI / Magellan / Univ. of Ariz. / ESO

X-ray observations of the Bullet Cluster provide some of the best evidence for the existence of dark matter. Click on the image to learn more.

It's possible that the three events are statistical flukes — analogous to, say, rolling three 7's in a row at a Vegas craps table. In this case, the scientists say there's a 99.8 percent chance that their results reflect a real phenomenon rather than a random crap shoot. That's significant, but it's not significant enough to claim a discovery. To make such a claim, the confidence level would have to go up to 99.9999 percent, or 5-sigma in math-geek speak.

"In medicine, you can say you are curing 99.8 percent of the cases, and that's OK. When you say you've made a fundamental discovery in high-energy physics, you can't be wrong," Mahapatra explained in a Texas A&M news release. "Given the money involved — $30 million in this case — it has to be extremely precise. With a 99.8 percent chance, that means if you repeated the same experiment a few hundred times, there is one chance it can go wrong. We want one out of a million instead."

Mahapatra said it took almost five years to notice the potential dark matter events because the CDMS team began their analysis by looking at the results from a set of germanium detectors, which are sensitive to higher masses. Another set of data was collected using silicon detectors, which are sensitive to lower masses, but those readings were put aside.

In the past few years, other dark-matter experiments began pointing to a mass range that was lower than scientists expected. "When they started seeing something significant, we thought we would look at our silicon data, which we were sitting on for more than four years," Mahapatra said.

'Hot on the trail'
Caltech theoretical physicist Sean M. Carroll agreed that it was too early to declare a discovery, but said "it would not be a surprise" if the CDMS data ended up being confirmed. Other experiments, ranging from AMS to LUX to SuperCDMS to Xenon1T, will be adding to the evidence. "It is certainly a reminder that we are hot on the trail of looking for dark matter," Carroll told NBC News.

He was intrigued by the possibility that the heavier particle mass could explain why dark matter accounts for so much more of the universe than ordinary matter. "You can imagine that there is one dark matter particle for every ordinary particle," Carroll said.

Some theorists propose that ordinary matter and dark matter come into existence through a process known as cosmic cladogenesis. Mahapatra said a balance in the number of the two types of particles would fit such a hypothesis. "It's either a coincidence, or a tremendous clue," Mahapatra said.

More about dark matter:

• Dark matter hints found on space station
• How to catch dark matter
• Why dark matter matters

The report from the CDMS Collaboration, "Dark Matter Search Results Using the Silicon Detectors of CDMS II," was discussed over the weekend at the American Physical Society's April meeting in Denver and has been submitted for publication in Physical Review Letters. Mahapatra is one of 89 listed co-authors.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA file

A fish-eye view of the International Space Station from July 2011 shows the $2 billion Alpha Magnetic Spectrometer (AMS) in the foreground. A Russian Progress cargo ship and a Soyuz crew capsule are docked on the left end of the station. The structure extending to the left of the AMS is a thermal radiator. Off to the right, the shuttle Atlantis is docked to the station's Tranquility module.

Scientists say a $2 billion antimatter-hunting experiment on the International Space Station has detected its first hints of dark matter, the mysterious stuff that makes up almost a quarter of the universe.

The evidence from the Alpha Magnetic Spectrometer, revealed Wednesday at Europe's CERN particle physics lab, is based on an excess in the cosmic production of anti-electrons, also known as positrons. The AMS research team can't yet rule out other explanations for the excess, but the fresh findings provide the best clues yet as to the nature of dark matter.

"Over the coming months, AMS will be able to tell us conclusively whether these positrons are a signal for dark matter, or whether they have some other origin," Samuel Ting, an astrophysicist at the Massachusetts Institute of Technology who leads the international AMS collaboration, said in a CERN news release.

The results have been published in Physical Review Letters and were discussed during a NASA news conference.

Dark matter is so named because it hasn't been detected directly through electromagnetic emissions, but primarily through its gravitational effect. Precise measurements of the movements of galaxies and galaxy clusters, as well as studies of the big bang's afterglow, indicate that it accounts for 22.7 percent of the universe's content. Another mysterious factor known as dark energy makes up 72.8 percent, leaving just 4.5 percent for ordinary matter.

Scientists have theorized that ultra-high-energy collisions involving dark matter particles could produce more positrons than expected. The best places to detect such collisions are in huge underground experiments such as CERN's Large Hadron Collider — or in outer space, where cosmic rays can be measured more easily than they are on Earth. 

The Alpha Magnetic Spectrometer is the most sensitive cosmic-ray detector ever put into orbit. Researchers from 16 countries worked for well more than a decade to get AMS ready for the space station, but it literally took an act of Congress to get the extra money needed for the launch. The bus-sized device was brought up on the shuttle Endeavour and installed in 2011, during the shuttle fleet's second-last mission. 

Since then, readings from the AMS have been flowing in to Ting and his colleagues for analysis. CERN said the results announced on Wednesday are based on 25 billion recorded events, including 400,000 positrons with energies between 500 million electron volts and 350 billion electron volts. "This represents the largest collection of antimatter particles recorded in space," CERN said.

Researchers noticed an increase in the fraction of positrons detected in the range of 10 billion to 250 billion electron volts. They said the data showed no significant variation over time, or any preferred incoming direction. All this is consistent with the annihilation of dark matter particles in space.

CERN

This chart compares the results from AMS on positron emissions with results from other experiments. AMS measurements at different energy levels are represented by the red dots with error bars.

Other experiments have recorded similar increases in positron production, but AMS was able to chart the rise in unprecedented detail. Ting compared the resolution to seeing something with the naked eye vs. an electron microscope. "It is these fine features that are the difference between us and the rest of the experiments," he told reporters.

Further evidence is needed, however: It's possible that the bump in positrons could be created by emissions from pulsars spread across the galactic plane. The most promising hypothesis suggests that dark matter is part of a yet-to-be-detected array of "supersymmetric" particles, and if that concept is correct, researchers should see a sharp drop in the positron emissions at energies higher than 250 billion electron volts.

Ting said there's not yet enough data to render a decision about such a drop-off. "We want to know how quickly it drops off, how sharp is the drop-off," he told NBC News. "It's the way it drops off that tells you whether it's dark matter collisions, or from pulsars." 

He pointed out that the newly released findings are based on just 10 percent of the data AMS is expected to collect.

"When you take a new precision instrument into a new regime, you tend to see many new results, and we hope this this will be the first of many," Ting said. "AMS is the first experiment to measure to 1 percent accuracy in space. It is this level of precision that will allow us to tell whether our current positron observation has a dark matter or pulsar origin."

Future revelations are expected to come from AMS as well as from the Large Hadron Collider and other underground laboratories.

"The AMS result is a great example of the complementarity of experiments on Earth and in space,” CERN Director General Rolf Heuer said in Wednesday's statement. “Working in tandem, I think we can be confident of a resolution to the dark matter enigma sometime in the next few years."

Update for 4:40 p.m. ET April 3: One of the experiments that could make a direct detection of dark matter particles in the months ahead is the Large Underground Xenon Experiment. LUX is located in an old gold mine, almost a mile deep in the Black Hills of South Dakota. The project's scientists will keep watch for telltale interactions between dark matter and the xenon in their detector. In an emailed statement, LUX co-spokesperson Richard Gaitskell, a physicist at Brown University, hailed the AMS results but said that questions remain:

"Obviously it’s a fantastic new instrument. It’s considerably more sensitive than anything we’ve previously flown as far as looking for antiparticles. So it’s a tremendous step forward.

"The results themselves are consistent with a flux of antiparticles that come from dark matter. On the downside, no aspect of the data that’s been discussed so far allows one to differentiate between an explanation that these antiparticles are coming from dark matter or from another astrophysical source.

"What we see is that at the higher-energy regime that the detector, there is a significant increase in the positron flux. That’s interesting, but it’s been recorded by previous instruments. What we were hoping to see was some additional structure. We’d like to see a bump that has some upper energy threshold or edge, rather just a rise at higher energies. Right now, the new data from AMS does not provide a definitive indication of an upper edge. We’d like to see something like that as direct evidence of dark matter."

NASA Administrator Charles Bolden issued a statement that focusing on the roles played by the space agency and the International Space Station. " I am confident that this is only the first of many scientific discoveries enabled by the station that will change our understanding of the universe," Bolden said. "Multiple NASA human spaceflight centers around the country played important roles in this work, and we look forward to many more exciting results from AMS."

More about dark matter:

• How to catch a dark matter particle
• Dark matter finding thrown into question
• Why dark matter matters

To watch the full NASA news conference, click to the 48-minute mark in this Ustream recording.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

This composite image shows the distribution of dark matter, galaxies, and hot gas in the core of the merging galaxy cluster Abell 520, formed from a violent collision of massive galaxy clusters. Starlight from galaxies is indicated in orange. Green indicates hot gas, and blue indicates mass, most of which is dark matter.

Astronomers using the Hubble Space Telescope are mystified by a merging galaxy cluster known as Abell 520 in which concentrations of visible matter and dark matter have apparently come unglued.

A report on the Hubble observations, published in the Astrophysical Journal, raises more questions than answers about a cosmic pile-up that's occurring 2.4 billion light-years away.

"We were not expecting this," the study team's senior theorist, Arif Babul of the University of Victoria, said in a news release. "According to our current theory, galaxies and dark matter are expected to stay together, even through a collision. But that's not what's happening in Abell 520. Here, the dark matter appears to have pooled to form the dark core, but most of the associated galaxies seem to have moved on."

The dark core was first detected in 2007 during a survey aimed at measuring the masses of 50 galaxy clusters using data from the Canada-France-Hawaii Telescope at Mauna Kea in Hawaii.

The discovery presented the perfect opportunity to map the distribution of visible vs. dark matter in the cosmic mess. Studies have shown that we can see only about 15 percent of the matter in the universe. Most of the matter that exists around us can't be seen directly, but can be detected only by its gravitational effect. Scientists don't know what dark matter is, but they suspect it's an exotic class of subatomic particles that can interact only weakly with the kinds of matter we can see.

Dark matter is thought to provide the invisible "scaffolding" for structure in the universe, gravitationally binding galaxy clusters into a cosmic web. Those clusters get so massive that they bend the light of distant galaxies like a lens. By analyzing those subtle deflections of light, it's possible to come up with a map showing where the dark matter lies. That's what astronomers did with Abell 520 — first with the telescope in Hawaii, and then with the Hubble Space Telescope's Wide Field Planetary Camera 2.

The results contradict what scientists thought they knew about dark matter. In a previous study of the Bullet Cluster, 3 billion light-years from Earth, astronomers found that concentrations of dark matter blasted through the scene of a collision, with their associated galaxies tagging along. Meanwhile, waves of hot, X-ray-emitting gas clumped up in the middle.

In the case of Abell 520, the situation is completely different: The galaxies sailed through the collision, but the dark matter piled up in the middle, along with the hot gas.

Researchers were hoping that Hubble would resolve the mystery first posed by the detection of the dark core in 2007. No such luck.

"We know of maybe six examples of high-speed galaxy cluster collisions where the dark matter has been mapped. But the Bullet Cluster and Abell 520 are the two that show the clearest evidence of recent mergers, and they are inconsistent with each other," James Jee, an astronomer at the University of California at Davis who is the lead author of the Astrophysical Journal paper, said in a news release from the Space Telescope Science Institute. "No single theory explains the different behavior of dark matter in those two collisions. We need more examples."

Jee, Babul and their colleagues propose several possible explanations for the discrepancy. One explanation might be that the dynamics of the Abell 520 collision are more complex than the Bullet Cluster's crash. Maybe multiple collisions, involving three or four galaxy clusters, have led to the dark matter pile-up.

Another possibility is that there's actually lots of ordinary galactic material in the core, but it's just too dim to be seen, even by Hubble. That would suggest that the super-dim galaxies in the core have somehow formed far fewer stars than normal galaxies.

The most unsettling scenario proposes that there are different kinds of dark matter, and some of those kinds are "stickier" than others. Abell 520 might have a particularly sticky kind of dark matter that interacts with itself and clumps up like a wet snowball.

The astronomers behind the Abell 520 observations are now planning to run computer simulations of cluster crashes to find out whether there's an unusual set of conditions that could produce those observations and still fit current theory. "My colleagues tell me the likelihood is nil," Andisheh Mahdavi, a member of the study team from San Francisco State University, said in a news release, "but now we have the responsibility to go and do the hard work to check the simulations."

If the simulations aren't successful, the mystery might have to be left for particle physicists to mull over. Some hope that experiments such as Europe's Large Hadron Collider and the Alpha Magnetic Spectrometer, installed last year on the International Space Station, will eventually shed additional light on the dark matter mystery.

"I'm just as perplexed as I was back in 2007," Mahdavi said. "It's a pretty disturbing observation to have out there."

Update for 5:40 p.m. ET March 2: The picture of Abell 520 served as this week's "Where in the Cosmos" picture puzzle on the Cosmic Log Facebook page this morning, and it took only a few minutes for Ryan Marquis to figure out what the image was all about. "It appears the dark matter and galaxies aren't anchored as previously believed," he wrote.

I'm sending Ryan a pair of 3-D glasses as a token of my appreciation. It turns out Ryan's a fellow space blogger who posts his items on 46BLYZ. We're glad to have him as a Cosmic Log correspondent, and hope that more of you will join our Facebook community. That's where you'll find the next "Where in the Cosmos" puzzle, a week from now.

Correction for 9 p.m. ET March 5: The original version of this item had the wrong first name for SFSU's Andisheh Mahdavi. I regret the error and extend apologies to the professor.

More about dark matter:

• Crazy cosmic lens focuses on dark matter
• The darkest mystery of them all
• Dark matter mapped in 3-D detail
• Gallery: Dark matter revealed!
• Search for dark matter on msnbc.com
• ... And what about dark energy?

In addition to Jee, Mahdavi and Babul, the authors of "A Study of the Dark Core in A520 With Hubble Space Telescope: The Mystery Deepens" include H. Hoekstra, J.J. Dalanton, P. Carroll and P. Capak.

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.

How long does it take to simulate the Milky Way? The answer is about nine months, if you're using a powerful supercomputer. That's how long it took for researchers at the University of California at Santa Cruz and the Institute for Theoretical Physics in Zurich to produce the first simulation of galaxy formation that approximates the look of our own Milky Way spiral.

"Previous efforts to form a massive disk galaxy like the Milky Way had failed, because the simulated galaxies ended up with huge central bulges compared to the size of the disk," Javiera Guedes said today in a news release about the project.

Guedes worked on the project during her time at UC-Santa Cruz, and is now a postdoctoral researcher at the Swiss Federal Institute of Technology. She's the first author of a paper accepted for publication in the Astrophysical Journal that describes the simulation, known as the Eris galaxy.

For 20 years, astronomers have been trying to come up with a simulated galaxy that comes close to the look of the Milky Way and other spiral galaxies — but fell short of the mark. Guedes and her colleagues were more successful in part because of the computer firepower at their disposal: 1.4 million processor-hours on NASA's Pleiades supercomputer, plus additional supporting simulations at UC-Santa Cruz and the Swiss National Supercomputing Center.

"We took some risk spending a huge amount of supercomputer time to simulate a single galaxy with extra-high resolution," said UC-Santa Cruz astronomer Piero Madau, one of the paper's co-authors.

The effort used a software platform known as Gasoline to trace the motions of more than 60 million particles, representing galactic gas as well as dark matter, over the course of more than 13 billion years.

Madau said developing a realistic simulation of star formation was another key to Eris' success.

"Star formation in real galaxies occurs in a clustered fashion, and to reproduce that out of a cosmological simulation is hard," he said. "This is the first simulation that is able to resolve the high-density clouds of gas where star formation occurs, and the result is a Milky Way type of galaxy with a small bulge and a big disk."

The recipe for the Eris galaxy limited star formation to the high-density regions of the galactic disk, which resulted in a more realistic distribution of stars. Within the high-density regions, supernova explosions powered an outflow of gas from the inner part of the galaxy, keeping the central bulge from getting too big.

The point of the exercise wasn't merely to come up with a pretty animation. The virtual conditions for Eris' creation are consistent with the theory that galaxy-scale structures coalesced from cosmic webs that were dominated by cold dark matter. Gravity drew primordial clumps of dark matter together into bigger clumps, and the "ordinary" matter that makes up stars and galaxies fell into those dark-matter clumps — giving rise to visible galaxies embedded in halos of invisible dark matter.

Cosmologists contend that the universe consists of 4.6 percent ordinary matter, 23.3 percent dark matter and 72.1 percent dark energy. But the fact that astronomers found it difficult to produce galaxies like the Milky Way using that formula led some to question the prevailing cosmological model of the universe. The Eris galaxy simulation "shows that the cold dark matter scenario, where dark matter provides the scaffolding for galaxy formation, is able to generate realistic disk-dominated galaxies," Madau said.

The research team's effort may be a tour de force for supercomputing, but don't confuse the virtual Eris with the real-life Milky Way. Even though Eris is an incredibly high-resolution simulation, its 60 million particles of gas and dark matter pale in comparison with the Milky Way's hundreds of billions of stars.

Extra credit: Eris is named after the Greek goddess of discord, in recognition of the decades of discordant debate that have surrounded the scenarios for forming spiral galaxies, according to a description of the project on the HPC-CH weblog. Guedes' website includes a quote from the Iliad: "The soldiers fought like wolves while Eris, the Lady of Sorrow, watched with pleasure." The simulated galaxy isn't the first astronomy-related object to bear that discordant name: Eris is also the name given to the dwarf planet that caused so much trouble for Pluto. 

More about dark matter and cosmology:

• Has dark matter finally been seen?
• Dark-matter stars could solve cosmic mystery
• Gallery: Dark matter revealed!
• Dark matter mapped in 3-D detail

In addition to Madau and Guedes, co-authors of the paper include Simone Callegari and Lucio Mayer of the Institute for Theoretical Physics in Zurich. This research was funded by NASA, the U.S. National Science Foundation, the Swiss National Science Foundation and an ARCS Foundation fellowship to Guedes.

Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding me to your Google+ circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.

NASA / ESA / STScI

Light from galaxies in the cluster Abell 1689 is distorted by dark matter in this Hubble Space Telescope image. The distortions allow scientists to infer the presence of invisible dark matter.

The universe has a dark side, and an international team of astronomers is calling on scientists and computer geeks of all stripes to help them understand it better.

The call is to participate in a competition called GREAT10 (for GRavitational lEnsing Accuracy Testing) to help them analyze images of galaxies whose shape is distorted by the presence of dark matter.

Stars, galaxies, and other visible stuff in the universe only make up a tiny fraction of what's out there. The rest consists of the more mysterious dark matter and dark energy.

Scientists infer the presence of dark matter by the way it distorts the light of distant galaxies that pass through it on the way to observers. A circular galaxy, for example, may appear elliptical ... or even as curved as a fingernail clipping. The technique, called gravitational lensing, allowed scientists to infer the presence of dark matter in the giant galaxy cluster Abell 1689, as mapped in the image above.

But dark matter doesn't distort all galaxies equally. Unlike the obvious distortions in the Hubble image, the effect is often "so small that you can't really see it by the eye," challenge organizer Thomas Kitching from the University of Edinburgh told me. "So we need to do it statistically."

Astronomers want to measure this lensing effect in 52 million galaxies. An additional layer of complexity arises from the blurring of images due to other distortions from the atmosphere and the telescopes themselves.

"The challenge is to undo the blurring effect of the atmosphere and the telescopes, and get back to measuring the very slight distortion. And if algorithms and software can be developed to measure that, it then means we can directly use those algorithms to map out the dark matter," Kitching said.

The scientists ultimately hope to map out dark matter in the universe as a function of time. That would let them see how the structure of dark matter has changed as the expansion of the universe has accelerated due to an effect of another dark force -– dark energy. Astronomical observations suggest that ordinary matter accounts for just 4 percent of the universe's content, and that dark matter takes in another 25 percent or so.

"We can actually say something about dark energy, which accounts for the other 70 percent of the universe and is causing the accelerated expansion," Kitching told me.

The challenge is open to anyone, though organizers are particularly keen for citizen scientists with experience in image manipulation and software development to step up to the plate -- for instance, the kind of people behind Galaxy Zoo, another online science project.

Kitching also would love to hear from people who have an idea but are not sure how to express it mathematically or with software. "If we think it is a good idea, then we are happy to work with them and turn their idea into a method that we can test," Kitching added.

Participants who download the GREAT10 data analysis package for the "Galaxy Challenge" will have nine months to run the simulations and process imaging data. The winning teams will receive an iPod or iPad, as well as an all-expenses-paid trip to NASA's Jet Propulsion Laboratory in Pasadena, Calif., for one of the team members. JPL is where organizers will meet for a workshop on the GREAT10 project in September 2011. (Check out the project FAQ for details.)

In addition to the prizes, the winners will also get the feeling "that they helped us understand the dark matter and dark energy," Kitching added.

More about dark matter and dark energy

• Has dark matter finally been seen?
• Dark matter stars could solve cosmic mystery
• Dark matter revealed!
• Galaxies unlock new secrets of dark matter
• Are dark matter and dark energy not real?
• Dark energy in 3-D
• Dark energy mystery illuminated by cosmic lens

Learn more about the GREAT10 challenge from the Jet Propulsion Laboratory and from Lisa Grossman at Wired.com.

John Roach is a contributing writer for msnbc.com. Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on Twitter (@b0yle).

Super-Kamiokande

Technicians check the photomultiplier tubes that ring an underground cylindrical stainless steel tank known as the Super-Kamiokande detector. The detector is on watch for faint glimmers of radiation from exotic particles zipping through the earth.

Can one particle explain both dark matter and the mysterious origins of matter and antimatter? Some physicists think so. They're calling the as-yet-only-theoretical object the "X particle."

Physicists from Canada's TRIUMF particle-physics facility, the University of British Columbia and Brookhaven National Laboratory laid out their ideas on the X particle in a paper published last month by Physical Review Letters -- and since then, the ideas have been picked up by PhysicsWorld magazine as well as Discovery News. (You can read a full draft of the paper on the arxiv.org website.)

The concept addresses two of the deep mysteries in modern physics:

• Dark matter: Observations of distant galaxies and galaxy clusters suggest that the matter we can see accounts for about a fifth  of their gravitational mass. The other four-fifths is thought to exist in the form of exotic matter than can be detected only by its gravitational effect. So what is that stuff?
• Matter vs. antimatter: Theory dictates that equal amounts of matter and antimatter must have existed at the beginning of the universe -- and yet, we see lots of matter and virtually no antimatter in the universe today. What happened to the antimatter, and why did matter win out?

The physicists suggest that X particles and anti-X particles -- each with about 1,000 times as much mass as a proton -- existed in the early universe. Such particles would show a "yin-yang" pattern of decay. Theoretically, the X particles would decay into detectable neutrons, or a pair of hidden particles called Y and Φ (the Greek letter phi). The anti-X particles would decay into antineutrons, or pairs of anti-Y and anti-Φ particles. But the X's would be more likely to decay into neutrons, while the anti-X's would be more likely to produce hidden anti-Y's and anti-Φ's.

"When almost all particles with an available antiparticle annihilated one another in the early universe, these discrepancies left a chunk of visible matter and a heavier chunk of dark antimatter to form the cosmos," PhysicsWorld's Kate McAlpine wrote.

The researchers suggest that the existence of the anti-Y and anti-Φ particles could be confirmed by their interactions with protons. Such interactions "could be on the boundary of detectability" at facilities such as the Super-Kamiokande underground particle detector in Japan, said UBC's Kris Sigurdson.

This is by no means the only hypothesis that's been offered to explain the nature of dark matter and the roots of the matter-antimatter balance. One of the main experiments at Europe's Large Hadron Collider, LHCb, is designed to study the decay of B-mesons and anti-B-mesons to see if additional data can help unravel the antimatter mystery. The LHC may also identify exotic particles (neutralinos, maybe?) that account for the dark matter.

I asked SLAC particle physicist Helen Quinn, co-author of the book "The Mystery of the Missing Antimatter," to take a quick look at the X particle concept. "It's very speculative," she told me, "and this is one of the things that particle physicists do all the time."

For now, the X factor is merely one of several hypotheses that might or might not explain one or both of the great mysteries. The truth is out there, and one day physicists will figure out which hypothesis serves as the best explanation for dark matter and/or antimatter. In the meantime, Quinn told me, "there's an awful lot of space out there in which to build models."

"Time will tell," she said.

That's a saying that could be applied to lots of the things that come up in physics -- or life in general.

More on dark matter and antimatter:

• Gallery: Dark matter revealed!
• Interactive: The darkest mystery of all
• Atoms of antimatter captured at last
• Weird antimatter particles detected deep down

In addition to Sigurdson, authors of the paper in Physical Review Letters, "Unified Origin for Baryonic Visible Matter and Antibaryonic Dark Matter," include Hooman Davoudiasi, David E. Morrissey and Sean Tulin.

Connect with the Cosmic Log community by "liking" the log's Facebook page or following @b0yle on Twitter. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.