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Tag: dark matter

  • Controversial New Study Points to the Most Promising Dark Matter Signal Yet

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    Astronomers have spent nearly a century searching for dark matter, the invisible scaffolding thought to hold galaxies together. While there’s abundant indirect evidence to suggest this mysterious substance exists, no one has been able to detect it directly. Now, a new study might finally signal a breakthrough.

    Using data from NASA’s Fermi Gamma-ray Space Telescope, astronomer and University of Tokyo professor Tomonori Totani is claiming to have identified gamma-ray emissions that appear to have originated from dark matter. His findings, published Tuesday in the Journal of Cosmology and Astroparticle Physics, suggest this radiation was emitted by colliding WIMPs (weakly interacting massive particles).

    “WIMPs, a leading candidate for dark matter, have long been predicted to annihilate and emit gamma rays, prompting numerous search efforts,” Totani told Gizmodo in an email. “This time, using the latest Fermi satellite data accumulated over 15 years and a new method focusing on the halo region (excluding the galactic center), I have discovered gamma-ray emissions believed to originate from dark matter.”

    It’s an intriguing finding, but experts we spoke to remain unconvinced, warning that the signal could be a case of cosmic noise mistaken for dark matter or yet another frustrating false positive.

    Totani himself emphasizes that it’s too early to definitively say these gamma rays originated from dark matter, but their characteristics suggest they could have. Based on his findings, they don’t look like those that originate from conventional astronomical sources. “At the very least, it represents the most promising candidate radiation from dark matter known to date,” he said.

    Finding a needle in a cosmological haystack

    Astronomers believe dark matter exists because no observable matter in the known universe can explain certain gravitational effects, such as the unexpectedly rapid rotation of galaxies or the fact that they’re held together more tightly than they should be.

    Dark matter is the theoretical answer to this cosmological conundrum, but if it exists, its particles clearly do not absorb, reflect, or emit light. If they did, astronomers would have detected this abundant substance long ago.

    Gamma-ray intensity map excluding components other than the halo, spanning approximately 100 degrees in the direction of the Galactic center. The horizontal gray bar in the central region corresponds to the Galactic plane area, which was excluded from the analysis to avoid strong astrophysical radiation © Tomonori Totani, The University of Tokyo

    WIMPs largely fit that description. Astronomers believe WIMPs interact through gravity, but their interactions with electromagnetic and nuclear forces are too weak to detect. When they collide with each other, however, they should theoretically annihilate and emit gamma rays.

    Researchers have hunted for these gamma-ray emissions for years, targeting regions of the Milky Way where dark matter appears to be concentrated, such as the galactic center. These searches have come up empty, so Totani decided to look elsewhere, specifically the galaxy’s halo region.

    Energy Spectrum Of The Halolike Gamma Ray Emission
    Photon energy dependence of gamma-ray intensity of the halo emission (data points). The red and blue lines represent the expected gamma-ray emission spectrum when WIMP particles annihilate, initially producing a pair of bottom quarks (b) or a pair of W bosons, and they agree well with the data © Tomonori Totani, The University of Tokyo

    This extended, roughly spherical region surrounding the Milky Way’s galactic disk contains stars, gas, and presumably a large amount of dark matter. By analyzing Fermi satellite observations of the halo, Totani identified high-energy gamma ray emissions that align with the shape expected from the dark matter halo.

    The range of gamma-ray emission intensities he observed matches what astronomers would expect to see from WIMP annihilation. Totani also estimated the frequency of WIMP annihilation from the measured gamma-ray intensity, and this also fell within the range of theoretical predictions. That raises the possibility that he may have detected a signal produced by dark matter WIMPs.

    Case closed? Not yet

    The findings are encouraging, but Totani and other experts caution that these gamma rays aren’t a smoking gun.

    “The problem is that there’s lots of ways to make gamma rays, everything from pulsars to matter inspiraling to black holes to supernovae,” a Fermilab physicist told Gizmodo. “Heck, we get gamma rays off the Sun.”

    Fermilab officials asked Gizmodo to refrain from naming the scientist who provided these quotes.

    What distinguishes the gamma rays Totani detected from most others is how energetic they are, with a photon energy of 20 gigaelectronvolts. That’s “pretty hefty,” but not totally unheard of, the Fermilab physicist explained. “There are very highly energetic things in space, and those highly energetic things can make high-energy gamma rays.”

    While the gamma emissions Totani detected appear to fit the description of those that would be produced by WIMP annihilation, there are other possible explanations that must be ruled out first, according to the Fermilab physicist. These could include high-energy phenomena such as neutron star collisions or solar wind emanating from pulsars, they explained.

    Additional studies will also need to validate Totani’s observations and calculations. “The decisive proof will be the detection of gamma rays from other regions of the sky with the same dark matter parameters,” Totani said. “I hope these results will be verified by independent analyses conducted by other researchers.”

    With that said, Dan Hooper, a professor of physics at the University of Wisconsin-Madison and director of the Wisconsin IceCube Particle Astrophysics Center, points out that many other scientists have already analyzed the Fermi satellite data Totani used, and none have detected the excess gamma ray emissions he did.

    “Now, some different choices were made, and I’m glad people are trying different things, but it doesn’t leave me very confident that this is an authentic signal of dark matter,” Hooper told Gizmodo.

    For one thing, Totani did not look for gamma rays anywhere within 10 degrees of the galactic center. Though this approach could provide some benefits, avoiding the galactic center may have swayed the findings, as this region of our galaxy is where physicists expect a big part of the dark matter signal to come from, Hooper explained.

    He also suspects that the high-energy gamma ray emissions Totani detected may actually be an artifact of the analysis. This could result from using a background model that is absorbing too much of the emission at low energies, creating the illusion of a high-energy excess.

    The bottom line is that “Dark matter is very difficult to find, it is very difficult to characterize,” the Fermilab physicist said. “Nobody should believe it without several mutually validating lines of evidence, and this is just one.”

    So, the search for dark matter continues. Whether future studies confirm or undermine Totani’s findings remains to be seen, but either way, they will help researchers refine our understanding of the invisible matter that shapes our universe.

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    Ellyn Lapointe

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  • A Newly Discovered ‘Einstein’s Cross’ Reveals the Existence of a Giant Dark Matter Halo

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    The gravitational lensing not only splits the light source, but magnifies it, allowing a detailed view of the light source behind the lens. Thanks to this, the team says that HerS-3 appears to be a bright starburst galaxy—a galaxy undergoing explosive star formation—and was formed at a time when star formation was at its peak throughout the universe. HerS-3 also has a tilted, rotating disk, from the center of which gas is gushing out at a furious rate, the team say.

    “Thanks to this natural telescope, we can zoom into regions 10 times smaller than the Milky Way, almost 12 billion light-years away, and in the process infer hidden matter in the light-of-sight,” said Hugo Mesias, a coauthor of the paper, in a statement.

    A Giant Dark Matter Halo Revealed

    At first glance, the Einstein’s cross of HerS-3 appears to have been created solely by gravitational lensing generated by the four giant galaxies located between HerS-3 and Earth. However, using a precise model of gravitational lensing, the team found that the observable mass of these four giant galaxies is insufficient to explain the arrangement of the five images of the cross: their mass is simply not great enough to produce the visual effect seen.

    “The only way to reproduce the remarkable configuration we observed was to add an invisible, massive component: a dark matter halo at the center of the galaxy group,” said lead author Pierre Cox, from the Institut d’Astrophysique de Paris.

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    Shigeyuki Hando

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  • A Physicist Wants to Turn Jupiter’s Largest Moon Into a Gigantic Dark Matter Detector

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    When searching for the unknown, classic physics wisdom holds that a bigger detector boosts the chances of discovery. A physicist is taking that advice to heart, advancing a bold plan to use none other than Ganymede—Jupiter’s largest moon—as a dark matter detector on an astronomical scale.

    Dark matter refers to the “invisible” mass that supposedly constitutes 85% of the universe. There’s considerable evidence that dark matter exists, but it’s “dark,” meaning it doesn’t respond to light and very weakly interacts with other matter. The search for dark matter has tested the limits of physicists’ creativity, but a proposal by William DeRocco, a physicist at the University of Maryland, may be the most extraordinary yet. In a preprint submitted to arXiv, Rocco suggests that Ganymede’s craters may store evidence of dark matter particles, which spacecraft like NASA’s Europa Clipper or ESA’s JUICE could observe during their respective missions.

    The paper, which has yet to be peer-reviewed, proposes that massive dark matter particles could have struck and penetrated Ganymede’s thick, icy surface, leaving deep, broad ruptures. Unlike the comparatively small-sized candidates for dark matter that ground-based detectors are searching for, these particles would be much larger. These extra-large dark matter particles would create “dark matter craters”—smaller dents on Ganymede’s surface comprised of distinctive minerals pulled to the surface from deep inside the moon’s oceans. 

    “If you used something like ground-penetrating radar, you might be able to see this column of melted ice going all the way down through the ice,” DeRocco explained in an interview with New Scientist. Studying Ganymede’s surface with this proposal in mind could uncover some unexpected insights about cosmic dark matter, according to the paper.

    In principle, the proposal sounds promising, Bradley Kavanaugh, an astrophysicist at the University of Cantabria in Spain who was not involved in the study, also told New Scientist. At the same time—like all dark matter experiments—there is still no definitive evidence that such heavy, massive dark matter particles actually exist.

    If all of this sounds bonkers, I don’t blame you. Still, it’s important to remember that, as many physicists are keen to point out, solving a physics mystery often means testing bold, unconventional ideas. And while there’s no decisive evidence that this particular proposal is correct, there isn’t any evidence to discount it, either. We’ll have to wait and see if NASA or ESA takes up DeRocco’s idea, and if they do, whether Ganymede really does have a surface dotted with dark matter craters.

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    Gayoung Lee

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  • Antimatter Could Be the Key to Solving the Universe’s Biggest Mysteries

    Antimatter Could Be the Key to Solving the Universe’s Biggest Mysteries

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    Two papers published this week showcase the perplexing origins and potential uses of antimatter, a type of matter that flips the rules governing ordinary matter onto their heads.

    One paper, published today in JCAP, found that antinuclei from cosmic rays may be an indicator of a specific kind of a dark matter. In a separate paper, published earlier this week in AIP Advances, researchers describe a method of detecting nuclear reactors’ locations and activity using antineutrinos produced by the facilities’ nuclear reactions.

    Antimatter is important because it may help to explain fundamental cosmic mysteries, like why the universe is made of matter instead of an equal mix of matter and antimatter. These studies fit into a larger effort to crack some of physics’ biggest puzzles, including the nature of dark matter, physics at the smallest scales, and possibly even the origin of the universe itself.

    Despite its name, antimatter is literally matter. It has mass. Antimatter refers to a group of particles that have opposite electrical charges to their ordinary counterparts. You’ve heard of electrons (which have a negative charge) and protons (with a positive charge); their antimatter counterparts are positrons (with a positive charge) and an antiproton (a negative charge).

    Though there are differences in the charge of the particles, antimatter isn’t entirely alien to the fundamental forces. Last year, a team of physicists found that antimatter reacts to gravity the same way as ordinary matter, a finding that affirmed both Einstein and the Standard Model of Particle Physics.

    Something more similar to the idea of “antimatter” you may have in your head is dark matter—which also has mass—but is invisible to every kind of detector humankind has so far devised. Scientists know dark matter exists because its gravitational effects are visible, even though the particle (or particles!) responsible cannot be directly observed.

    Antimatter remains a matter of confusion (sorry, awful pun) for a few reasons. As explained by Gizmodo in 2022:

    The universe rocked into being 14 billion years ago, with a Big Bang that in theory should have created equal amounts of matter and antimatter. But look around you, or at the latest Webb telescope images: We live in a universe dominated by matter. An outstanding question in physics is what happened to all the antimatter.

    Antimatter and dark matter dovetail neatly in the recent JCAP paper, which posits that the amount of antimatter detected by experiments is more than there should be—and they believe dark matter is the culprit.

    A few different particles (and other, more exotic objects) have been posited as responsible for dark matter. Among them: axions, a particle named for a laundry detergent; MAssive Compact Halo Objects, or MACHOs; dark photons, which despite their name are more like axions than some insidious version of light; and primordial black holes, which would be minuscule black holes birthed at the beginning of the universe, floating through space.

    The recent research focuses on another type—Weakly Interacting Massive Particles, or WIMPs—as the guilty party. The theory is essentially that when WIMPs collide, they sometimes annihilate—destroy one another—emitting energy and particles of matter and antimatter.

    In the aforementioned 2022 research, a team of physicists using the ALICE experiment at CERN found that antimatter could travel through our galaxy with ease instead of being snuffed out by the matter in the interstellar medium, a redeeming conclusion for antinuclei detectors like the AMS-02 experiment aboard the International Space Station.

    “Theoretical predictions suggested that, even though cosmic rays can produce antiparticles through interactions with gas in the interstellar medium, the amount of antinuclei, especially antihelium, should be extremely low,” said Pedro De la Torre Luque, a physicist at the Institute of Theoretical Physicists in Madrid and lead author of the JCAP paper, in a SISSA Medialab release.

    “We expected to detect one antihelium event every few tens of years, but the around ten antihelium events observed by AMS-02 are many orders of magnitude higher than the predictions based on standard cosmic-ray interactions,” De la Torre Luque added. “That’s why these antinuclei are a plausible clue to WIMP annihilation.”

    However, De la Torre Luque added that WIMPs could only explain the amount of antihelium-3—one antimatter isotope detected by AMS-02—and not detected amounts of the rarer, heavier antihelium-4. In other words, even if WIMPs are responsible for dark matter, they don’t tell the whole story.

    WIMPs could be responsible for the antimatter detections that space-based detectors are collecting. But regardless of the dark matter question—one that will take a long time to answer—the design of an antimatter-sniffing detector to monitor nuclear reactors on Earth shows practical applications in the here and now. Together, these findings on antimatter could offer new ways to harness the strange properties of the universe for practical use, while also helping us better understand both the cosmos and our own planet.

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    Isaac Schultz

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  • Dark Matter Will Return for More Multiverse Shenanigans

    Dark Matter Will Return for More Multiverse Shenanigans

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    Good news for fans of Apple TV’s Dark Matter: it’s coming back for a second season.

    The sci-fi drama was renewed over the weekend following the end of its debut season back in late June. Per AppleTV’s programming head Matt Cherniss, the show became “a global hit, capturing audiences’ imaginations and making it a beloved and integral part of Apple’s world class sci-fi line up. We are thrilled to continue our collaboration with Blake Crouch, our partners at Sony and the rest of the creative team and cast…on a new season that will captivate viewers with more twists and turns as we dive deeper into the mysteries of the multiverse.”

    Blake Crouch, showrunner and author of the novel the show is based on, added that over the course of season one, the creative team found “there’s so much more story to tell. We’ve only scratched the surface of these characters as they fight for survival and to find their way home through a landscape of mind-bending realities. Thanks to everyone who tuned-in for season one…you were so good to us.”

    Dark Matter stars Joel Egerton as Jason Dessen, a Chicago physicist who gets abducted by an alternate reality version of himself. While his doppelganger lives his counterpart’s life, Jason #01 goes about trying to find a way back home. Audiences have clearly taken a shine to it, and it’s another solid outing for the sci-fi part of AppleTV’s catalog; the press release name checks it alongside the upcoming seasons of Silo and Severance, plus the likes of For All Mankind and Monarch: Legacy of Monsters. Apple didn’t give a release window for season two, but hopefully it isn’t too long before we see what the Jasons are up to next.

    Want more io9 news? Check out when to expect the latest Marvel, Star Wars, and Star Trek releases, what’s next for the DC Universe on film and TV, and everything you need to know about the future of Doctor Who.

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    Justin Carter

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  • The Hunt for Ultralight Dark Matter

    The Hunt for Ultralight Dark Matter

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    If or when SLAC’s planned project, the Light Dark Matter Experiment (LDMX), receives funding—a decision from the Department of Energy is expected in the next year or so—it will scan for light dark matter. The experiment is designed to accelerate electrons toward a target made of tungsten in End Station A. In the vast majority of collisions between a speeding electron and a tungsten nucleus, nothing interesting will happen. But rarely—on the order of once every 10,000 trillion hits, if light dark matter exists—the electron will instead interact with the nucleus via the unknown dark force to produce light dark matter, significantly draining the electron’s energy.

    That 10,000 trillion is actually the worst-case scenario for light dark matter. It’s the lowest rate at which you can produce dark matter to match thermal-relic measurements. But Schuster says light dark matter might arise in upward of one in every 100 billion impacts. If so, then with the planned collision rate of the experiment, “that’s an inordinate amount of dark matter that you can produce.”

    LDMX will need to run for three to five years, Nelson said, to definitively detect or rule out thermal relic light dark matter.

    Ultralight Dark Matter

    Other dark matter hunters have their experiments tuned for a different candidate. Ultralight dark matter is axionlike but no longer obliged to solve the strong CP problem. Because of this, it can be much more lightweight than ordinary axions, as light as 10 billionths of a trillionth of the electron’s mass. That tiny mass corresponds to a wave with a vast wavelength, as long as a small galaxy. In fact, the mass can’t be any smaller because if it were, the even longer wavelengths would mean that dark matter could not be concentrated around galaxies, as astronomers observe.

    Ultralight dark matter is so incredibly minuscule that the dark-force particle needed to mediate its interactions is thought to be massive. “There’s no name given to these mediators,” Schuster said, “because it’s outside of any possible experiment. It has to be there [in the theory] for consistency, but we don’t worry about them.”

    The origin story for ultralight dark matter particles depends on the particular theoretical model, but Toro says they would have arisen after the Big Bang, so the thermal-relic argument is irrelevant. There’s a different motivation for thinking about them. The particles naturally follow from string theory, a candidate for the fundamental theory of physics. These feeble particles arise from the ways that six tiny dimensions might be curled up or “compactified” at each point in our 4D universe, according to string theory. “The existence of light axionlike particles is strongly motivated by many kinds of string compactifications,” said Jessie Shelton, a physicist at the University of Illinois, “and it’s something that we should take seriously.”

    Rather than trying to create dark matter using an accelerator, experiments looking for axions and ultralight dark matter listen for the dark matter that supposedly surrounds us. Based on its gravitational effects, dark matter seems to be distributed most densely near the Milky Way’s center, but one estimate suggests that even out here on Earth, we can expect dark matter to have a density of almost half a proton’s mass per cubic centimeter. Experiments try to detect this ever-present dark matter using powerful magnetic fields. In theory, the ethereal dark matter will occasionally absorb a photon from the strong magnetic field and convert it into a microwave photon, which an experiment can detect.

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    Lyndie Chiou

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