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    The James Webb telescope may have spotted stars powered by dark matter

    The James Webb Space Telescope has spotted objects in the early universe that might be a new kind of star — one powered by dark matter.

    These “dark stars” are still hypothetical. Their identification in JWST images is far from certain. But if any of the three candidates — reported in the July 25 Proceedings of the National Academy of Sciences — turn out to be this new type of star, they could offer a glimpse of star formation in the early universe, hint at the nature of dark matter and possibly explain the origins of supermassive black holes.

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    First proposed in 2007 by cosmologist Katherine Freese and colleagues, dark stars might have been some of the first types of stars to form in the universe (SN: 1/1/08). Though dark stars have yet to be observed, they’re thought to be powered by heat from dark matter interactions rather than by nuclear fusion reactions like in the sun.

    Dark stars “would be very weird looking,” says Freese, of the University of Texas at Austin. The hypothetical stars would have formed from clouds of hydrogen and helium that drew in locally abundant dark matter as they coalesced. Though the true nature of dark matter isn’t known — its presence is inferred largely via its effect on how stars move within galaxies — it’s possible that dark matter particles can interact with themselves, annihilating each other when they collide and producing vast amounts of light and heat (SN: 7/7/22). That heat would keep the cloud of hydrogen and helium from condensing into a dense, hot core like the stars that exist today.

    Because the heat from dark matter annihilations would keep the gas cloud from condensing, dark stars could grow to gargantuan size. Theoretically, dark stars could be 10 times as wide as Earth’s orbit around the sun. They could also be millions of times as massive as the sun and shine billions of times brighter — bright enough, potentially, to be spotted by JWST.

    To see if any dark stars are lurking in data from the orbiting observatory, Freese and colleagues pored over images from a JWST survey of early galaxies. In such images, JWST has so far discovered over 700 objects that may have originated in the first few hundred million years of the universe — the epoch when dark stars would have emerged (SN: 12/16/22). Light from these remote objects is stretched, or redshifted, as the universe expands. So Freese and colleagues zeroed in on four objects already confirmed to be highly redshifted, making them some of the oldest objects seen to date.

    Those objects are currently thought to be small galaxies from the universe’s relative infancy. But because they’re so far away, JWST can’t resolve them well enough to determine whether they’re actually galaxies or large, ultrabright stars, the researchers say.

    Three dark star candidates were identified from data collected by the JWST Advanced Deep Extragalactic Survey. One of the candidates, JADES-GS-z13-0, is shown here (arrow).NASA, ESA, CSA, JADES Collaboration

    The team ran computer simulations of how much light a hypothetical dark star might produce at various wavelengths. They compared those spectra to light from images collected by JWST at different wavelengths for each of the four objects. JWST data from three of those objects are consistent with the simulated dark star patterns, Freese and colleagues report.

    Some scientists are skeptical. Known types of stars could also create the observed light from the three candidates, says Sandro Tacchella, an astrophysicist at the University of Cambridge. And identifying any of the objects as a dark star would require that the simulated patterns fit well to more detailed spectra, says Brant Robertson, a theoretical astrophysicist at the University of California, Santa Cruz.

    If dark stars were to be found, though, “that would be revolutionary,” says study coauthor Cosmin Ilie, an astrophysicist at Colgate University in Hamilton, N.Y.

    Detecting dark stars would confirm the existence of a dark matter particle and hint at how it works (SN: 7/7/22). “Just having the information that [dark matter] is something that could annihilate would be really, really powerful,” says Tracy Slatyer, a theoretical physicist at MIT who was not involved in the study. That knowledge could help scientists look for dark matter elsewhere in the universe, she says.

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    Dark stars could also help explain the formation of supermassive black holes (SN: 3/16/18). Once the dark matter inside the star has annihilated itself, the remaining hydrogen and helium — millions of times the mass of the sun in a relatively compact space — would collapse in on itself and form a black hole. Those black holes could merge over time into black holes like the ones at the centers of most galaxies, millions or billions of times as massive as the sun.

    Future experiments, like looking for brighter or dimmer light at certain wavelengths, could help confirm whether any of the three objects are dark stars. Freese also expects to find more dark star candidates in future JWST data, she says. But for now, whether dark stars truly exist remains a mystery. More

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    NASA’s DART mission lofted a swarm of boulders into space

    When a probe smashed into a small asteroid last year, the collision did more than change the asteroid’s orbit — it blasted a few dozen hefty boulders into space too.

    Last September, NASA steered the DART spacecraft into Dimorphos, a moonlet of the larger asteroid Didymos, to test a strategy for knocking any future Earth-bound asteroids off course (SN: 10/11/22). About three months after the impact, the Hubble Space Telescope spied a halo of 37 previously unseen objects accompanying the space rock duo in their orbit around the sun, researchers report in the July 21 Astrophysical Journal Letters.

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    The boulders probably aren’t bits that were pulverized from larger rocks during the impact. Instead, simulations suggest they were likely intact when they were blasted off Dimorphos and could have been launched off the moonlet’s rubble-covered surface by the energy of either the collision or the seismic waves bouncing around inside it in the wake of the impact.

    Still, “there’s a lot of uncertainty in such simulations,” planetary astronomer David Jewitt of the University of California, Los Angeles.

    The last complete image from NASA’s DART spacecraft shows Dimorphos’ rubble-strewn surface just two seconds before the probe smashed into the asteroid.NASA, APL

    Based on the brightness of the new objects, some of the dimmest ever spied by Hubble in our solar system, Jewitt and colleagues estimate that these boulders may be as wide as 7 meters. At least 15 are larger than 4 meters across. Together, the researchers calculate, the boulders probably weigh just over 5 million kilograms — roughly the weight of 300 dump truck loads of gravel.

    Repeated observations by Hubble reveal that, on average, the boulders are drifting away from Dimorphos and Didymos at about 1 kilometer per hour — a little faster than the escape velocity for the double asteroid system. So, Jewitt says, the boulders, as well as a presumed multitude of rocks too small and dim for Hubble to see, will eventually break away from the asteroid system’s orbit and circle the sun on their own. More

  • in

    Granite likely lurks beneath the moon’s surface

    Watch out Yosemite — the moon has its own impressive rock display.

    An enormous chunk of granite, measuring roughly 50 kilometers wide, may be buried beneath the lunar surface, researchers reported July 5 in Nature. Finding such a behemoth, by far the largest granite structure spotted beyond Earth, is a surprise given that forming this type of rock typically requires plate tectonics or abundant water.

    When Apollo astronauts landed on the moon in the 1960s and 1970s, they encountered vistas dominated by basalt. The igneous rock is run-of-the-mill stuff on both the moon and our planet, says Matthew Siegler, a planetary scientist at the Planetary Science Institute in Tucson. “Everything starts as basalt.”

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    But over time, with enough heat and pressure, basalt can melt and morph into more durable granite. Plate tectonics and water, both mainstays on Earth, often help facilitate that transformation: Tectonic forces can help drag rocks down deep, where it’s hotter, and water, acting like a salt, helps rocks melt at lower temperatures (SN: 1/13/21).

    Because the moon has no plate tectonics and very little water, finding copious amounts of granite there would be unexpected, Siegler says. Indeed, out of the roughly 380 kilograms of moon rocks (about the heft of a large bear) brought back to Earth by Apollo astronauts, just a handful of millimeter-sized pieces are granite (SN: 7/15/19). “That’s our whole inventory,” Siegler says.

    But Siegler and his colleagues now have strong evidence that a massive piece of granite might be lurking under the moon’s surface. The team analyzed microwave data collected from the farside of the moon by China’s Chang’e-1 and Chang’e-2 lunar orbiters and discovered a geothermal hotspot roughly 9 degrees Celsius warmer than expected. Elevated temperatures are often an indicator of granite, Siegler says, because uranium and thorium — radioactive elements that decay over time and release heat — tend to aggregate within the rock.  

    To estimate how large a piece of granite could be lying beneath the region, known as the Compton-Belkovich Volcanic Complex, the researchers ran computer simulations of different sizes of granite buried at different depths. The team concluded that an ellipsoidal hunk of granite roughly 50 kilometers wide and 25 kilometers tall capped by a smaller ellipsoid of granite, all buried four kilometers below the lunar surface, best explained the Chang’e-1 and Chang’e-2 observations.

    The big question is how such an edifice formed. One idea that Siegler and his colleagues propose is that a mantle plume — a column of molten rock — once persisted under the Compton-Belkovich Volcanic Complex. That plume would have turned some of the region’s basalt into granite.

    On Earth, mantle plumes famously combine with tectonic plate movement to create island chains like Hawaii, Siegler says (SN: 9/19/11). But on the moon, where there is no plate tectonics, a mantle plume would just continuously heat one region, he says. “You get a single spot of the crust that keeps getting roasted.”

    This is an intriguing discovery that should be followed up with a lunar mission, says Brad Jolliff, a planetary scientist at Washington University in St. Louis who was not involved with the new study. “It’s ripe for a robotic mission that has a small rover that can test some of these properties up close.”

    In the next few years, scientists plan to do just that. NASA’s Lunar Vulkan Imaging and Spectroscopy Explorer mission, or Lunar-VISE, which is slated to launch by 2027, will land on the summit of one of the Gruithuisen domes. Located on the moon’s nearside, these volcanic features are believed to also contain granite. Lunar-VISE will be able to take a closeup look at the region’s chemical composition, says the mission’s principal investigator Kerri Donaldson Hanna, a planetary geologist at the University of Central Florida in Orlando.

    That’s important because it’s often difficult to capture small details from orbit. Landers like Lunar-VISE can shed light on the moon’s geology, says Donaldson Hanna. “We need new observations.” More

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    A rain of electrons causes Mercury’s X-ray auroras

    Mercury’s auroras are perfectly in character. While temperate Earth gets heavenly light shows over its poles, hellish Mercury gets invisible ribbons of X-ray radiation that cling to its sun-blasted surface.

    But as alien as they may appear, Mercury’s X-ray auroras have a lot in common with Earth’s polar lights, and with auroras throughout the solar system.

    Scientists have now directly shown that fluctuations in Mercury’s magnetic field can fling electrons toward the planet, where they eventually rain down and cause auroras of X-ray light. This process, called electron precipitation, now appears to be practically universal in the solar system: It causes auroras on every planet with a global magnetic field except Neptune, researchers report July 18 in Nature Communications. Even Mars, which has only localized magnetic fields, has auroras caused by raining electrons (SN: 3/19/15).

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    For Mercury, “this is really the first time to detect these electrons directly,” says space plasma physicist Sae Aizawa of the University of Pisa in Italy.

    Electron precipitation usually happens because of interactions between planets’ magnetic fields and the solar wind — a stream of charged particles spewed from the sun’s upper atmosphere.

    Buffeted by the solar wind, the sun-facing side of a planet’s magnetic field gets squished while the night side is swept out into a long “magnetotail” that extends behind the planet. Eventually, the magnetotail stretches so much that its formerly mostly-parallel magnetic field lines snap and reconnect, sending some field lines flying off behind the planet and others back toward it.

    Part of Mercury’s northern hemisphere comes into view in this picture taken by the BepiColombo probe (parts of which are visible in the foreground) during its first flyby of Mercury in 2021.BepiColombo/MTM/ESA, CC BY-SA 3.0 IGO

    “The magnetic field lines sort of break and form new ones,” says space physicist Ryan Dewey of the University of Michigan in Ann Arbor, who was not involved in the study. “And in that process, a lot of energy is released.”

    All that energy sends packets of electrons flying planetward, spiraling in corkscrew-like trajectories along magnetic field lines. When these electrons hit the planet or its atmosphere, they release energy as light.

    The light’s wavelength depends on what the electrons encounter as they rain down. Earth’s auroras shine in visible wavelengths because incoming electrons excite molecules of uncharged gases in the atmosphere like oxygen and nitrogen, which release visible light when they relax back to their normal states. Mercury’s auroras shine in X-ray wavelengths because electrons decelerate as they smack the planet’s rocky surface. The lost energy is released as X-rays.

    Researchers first spotted Mercurian X-ray auroras in data beamed back from the MESSENGER probe, which orbited Mercury from 2011 to 2015 (SN: 4/30/15). But while scientists reasoned that electrons must rain down on Mercury to cause its X-ray glow, MESSENGER didn’t have the right instruments to measure the precipitating particles.

    The European Space Agency’s BepiColombo spacecraft does. Analyzing data from the probe’s first flyby of Mercury in 2021, Aizawa and her colleagues spotted telltale signs of the process.

    One clue was that as BepiColombo flew through Mercury’s magnetosphere, it observed surges of fast-moving, high-speed electrons followed by several subsequent waves of progressively slower, lower-energy electrons. “This is exactly what we’d describe as a precipitating signature,” says Aizawa, who did the work while at the Institute of Research in Astrophysics and Planetology in Toulouse, France.

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    To Dewey, the new discovery is a tantalizing sneak peek at the discoveries waiting to be made at Mercury once BepiColombo enters orbit in 2025. By then, it will have been a decade since scientists last had a probe continuously orbiting Mercury.

    “To me, it’s very exciting to see just how much we can learn from even just a short pass through the magnetosphere,” he says. “It’s a glimpse.” More

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    Ryugu asteroid samples are sprinkled with stardust older than the solar system

    Samples of the asteroid Ryugu contain bits of stardust that predate the birth of our solar system.

    Slivers of Ryugu material, snagged by the Japanese Hayabusa2 spacecraft, appear to come from the solar system’s frozen fringes, rather than from the asteroid itself, scientists report July 14 in Science Advances. These foreign fragments could illuminate details of the solar system’s history.

    Finding these fragments “is really unique,” says cosmochemist Ann Nguyen of NASA’s Johnson Space Center in Houston. “It’s showing us a new type of material, but also telling us about the dynamics of material from the outer solar system.”

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    The Hayabusa2 spacecraft visited the asteroid in 2018 and 2019, then returned to Earth with 5.4 grams of the space rock in 2020 (SN: 12/7/20). Scientists examined those samples in the lab in ways that can’t be done with telescopes or even spacecraft, like getting detailed measurements of chemical composition.

    So far, those examinations have shown that Ryugu is rich in carbon, that it’s made of the same material as some of the rarest meteorites found on Earth, and that it was altered by water at some point in its past (SN: 6/9/22). Scientists think that Ryugu formed from the debris of a larger asteroid, which broke up in a collision and re-formed into a loose pile of rubble (SN: 3/20/19).

    Nguyen, however, was searching for something different. “My focus of research is presolar grains,” tiny specks of material that formed from the ashes of dying stars, she says (SN: 1/13/20). “I was on the hunt for them.” These delicate grains contain different isotopes — atoms of an element that have different numbers of neutrons — than those formed by the sun, giving away their alien origins.

    Nguyen and her colleagues examined two samples of Ryugu, each less than a millimeter in size. They then picked out tiny slivers of rock, 50 to 200 micrometers wide, called clasts, that stood out from the rest of the Ryugu sample.

    Using scanning electron microscopes and other imaging techniques, Nguyen and colleagues found that two of the clasts are chemically different from the rest of Ryugu, with lower oxygen, magnesium and silicon contents, and greater amounts of iron and sulfur.

    Electron microscope images of a sliver of solar system material (outlined in white) in a sample of the asteroid Ryugu show that the material is different from the rest of the asteroid. The different colors highlight different elements in the sample: oxygen (magenta), magnesium (green), silicon (light blue), iron (dark blue) and sulfur (yellow). The slivers also contain grains of silicates (white arrows) that come from outside the solar system.A. Nguyen et al/Science Advances 2023

    The clasts also have much higher concentrations of presolar grains than the rest of the Ryugu material. The grains contain silicon carbide, which is easily destroyed by water, plus an extra abundance of organic matter.

    That means the grains could not have been part of Ryugu’s parent body, which was extensively altered by water. The researchers think the grains were bits of a comet that formed in the outer solar system’s Kuiper belt, where the conditions were cool and dry. Then the grains sprinkled onto the rubble that formed Ryugu sometime between the original asteroid’s destruction and the rubble pile’s formation.

    “Between these events, it kind of collected some other friends that came from other bodies, from different parts of the solar system,” Nguyen says. It’s not yet clear how material from the outer solar system found its way to Ryugu. Perhaps the asteroid formed farther from the sun — and hence, closer to the Kuiper belt — than it is today. “It’s interesting to visualize how this asteroid came about and what it gathered along the way.”

    The discovery is “very exciting,” says cosmochemist Philipp Heck of the Field Museum of Natural History in Chicago, who was not involved in the new work. “These clasts that got incorporated into Ryugu after it formed, they’re really valuable. I think they’re even more valuable than the Ryugu sample itself.”

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    The clasts can reveal what the unaltered ingredients that formed the solar system were made of. Think of the disk that formed the planets as bread dough, Heck says. Once the dough is well-mixed, it’s hard to tell what went into it. Clasts like the ones in the Ryugu sample are like bits of unmixed flour that survived intact in the final loaf, he says — not delicious, but very informative.

    “If we want to understand the ingredients from which the solar system formed, the original ingredients, we need to find these very rare, unaltered clasts,” Heck says. “This is one of them.” More

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    Coronal rain has been seen splashing on the sun

    Plasma rain in the sun’s atmosphere makes a splash when it lands. New observations from the European Space Agency’s Solar Orbiter have revealed previously unseen details of how this coronal rain falls, including bright fireball effects and sudden upward surges in plasma.

    “These are the highest resolution images we have ever obtained from the solar corona,” says solar physicist Patrick Antolin of Northumbria University in Newcastle upon Tyne, England. He presented the results at the National Astronomy Meeting in Cardiff, Wales, the week of July 3 and in a paper to be published in Astronomy & Astrophysics.

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    The corona is the sun’s wispy upper atmosphere, the sizzling tangle of plasma and magnetism that is visible during a total eclipse (SN: 6/30/19). When clumps of scorching-hot plasma in the corona suddenly cool, they condense and fall toward the solar surface, just like water droplets in Earth’s atmosphere. This coronal rain has been observed before, but details of its formation and falling were fuzzy (SN: 5/24/18).

    The 2020 launch of Solar Orbiter promised to change that (SN: 2/9/20). The probe is making passes over the sun’s unexplored polar regions, carrying high resolution cameras and other instruments to investigate solar mysteries. In late March 2022, Solar Orbiter made its closest approach to the sun to date, swooping within 49 million kilometers of our star — about a third of the distance between the sun and Earth.

    In images from the spacecraft taken during that close encounter, Antolin and colleagues discovered a new feature in the coronal rain. As the plasma raindrops fell, the region immediately below them brightened. The researchers think the brightening came from other plasma below the falling rain getting compressed and heated, similar to the way meteors in Earth’s atmosphere can create fireballs just ahead of the falling rocks (SN: 2/15/13).

    “This is the first time we’ve seen that kind of compression from the rain falling this clearly,” says Emily Mason, a solar physicist at Predictive Science, a research company based in San Diego, who was not involved in the study. “The resolution just wasn’t there before.”

    Antolin and colleagues also saw a rebound and upward flow of material after coronal raindrops smacked onto the chromosphere, the thin layer of plasma that lies between the sun’s visible surface and the corona.

    “This rain is as dense as the chromosphere,” Antolin says. “It can fall to the chromosphere and then make a splash.” This sort of splash was predicted in computer simulations but had never been observed on the actual sun before.

    On their own, the observations won’t directly solve the biggest solar mysteries, like why the diffuse corona sizzles at millions of degrees Celsius higher than the surface of the sun (SN: 8/20/17). But more observations of the same phenomena can help figure out details of the coronal environment, like how easily its gas compresses, or what its chemical composition is.

    “We are not able to send a probe to the inner part of the corona because it’s so hot,” Antolin says. “So we can use these observations as indirect probes of the local environment.”

    The observations are “an important litmus test for Solar Orbiter itself,” Mason says. “It’s good to see what Solar Orbiter is capable of.” More

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    A newfound gravitational wave ‘hum’ may be from the universe’s biggest black holes

    Citations
    G. Agazie et al. The NANOGrav 15-Year data set: Detector characterization and noise budget. Astrophysical Journal Letters. Published online June 28, 2023. doi: 10.3847/2041-8213/acda88.G. Agazie et al. The NANOGrav 15-year data set: Evidence for a gravitational-wave background. Astrophysical Journal Letters. Published online June 28, 2023. doi: 10.3847/2041-8213/acdac6.G. Agazie et al. The NANOGrav 15-year data set: Observations and timing of 68 millisecond pulsars. Astrophysical Journal Letters. Published online June 28, 2023. doi: 10.3847/2041-8213/acda9a.A. Afzal et al. The NANOGrav 15-year data set: Search for signals from new physics. Astrophysical Journal Letters. Published online June 28, 2023. doi: 10.3847/2041-8213/acdc91G. Agazie et al. The NANOGrav 15-year data set: An astrophysical interpretation of a gravitational wave background from supermassive black hole binaries. Astrophysical Journal Letters. In press, 2023.J. Antoniadis et al. The second data release from the European Pulsar Timing Array I. The dataset and timing analysis. Astronomy & Astrophysics. Published online June 28, 2023.J. Antoniadis et al. The second data release from the European Pulsar Timing Array II. Customised pulsar noise models for spatially correlated gravitational waves. Astronomy & Astrophysics. Published online June 28, 2023.J. Antoniadis et al. The second data release from the European Pulsar Timing Array. III. Search for gravitational wave signals. Astronomy & Astrophysics. Published online June 28, 2023.A. Zic et al. The Parkes Pulsar Timing Array Third Data Release. Publications of the Astronomical Society of Australia. Published online June 28, 2023.D.J. Reardon et al. Search for an isotropic gravitational-wave background with the Parkes Pulsar Timing Array. Astrophysical Journal Letters. Published online June 28, 2023. D.J. Reardon et al. The gravitational-wave background null hypothesis: Characterizing noise in millisecond pulsar observations with the Parkes Pulsar Timing Array. Astrophysical Journal Letters. Published online June 28, 2023.H. Xu et al. Searching for the Nano-Hertz Stochastic Gravitational Wave Background with the Chinese Pulsar Timing Array Data Release I. Research in Astronomy and Astrophysics. Vol. 23, July 2023, p. 075024. doi: 10.1088/1674-4527/acdfa5. More

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    Julian Muñoz has a ‘ruler’ that could size up the early universe

    Julian Muñoz has come up with a ruler to measure the early universe.

    A theoretical physicist, Muñoz studies the distant, dim period in the universe’s history known as cosmic dawn. That’s when stars first began flickering on, a few hundred million years after the Big Bang, infusing the universe with initial glimmers of starlight and forming the first galaxies.

    Before the first stars, the universe was cold and dark — as Muñoz describes it, “boring.” Then, starlight began to reshape the universe. “It is a very dramatic epoch,” says Muñoz, of the University of Texas at Austin.

    That epoch is also poorly understood. Cosmic dawn is so unexplored that Muñoz compares it to an uncharted area on early maps of Earth. There, Muñoz says, “there could be dragons.” By studying this era, he hopes to reveal the behavior of one dragon of the cosmos, dark matter, the inscrutable substance whose mass binds galaxies.

    But to understand the cosmos, scientists have to be able to measure it. Looking far into space means looking deep into the past. The trouble is our 2-D view of the sky doesn’t readily reveal how far away things are. “When we look at the night sky, we’ve got no depth perception,” says cosmologist Adrian Liu of McGill University in Montreal.

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    Scientists have devised a variety of methods to get a handle on distances, including standard candles and standard rulers — objects of known brightness or length. If you know how bright an object is (compared with how bright it appears) or you know how long a particular feature is on the sky (compared with its apparent length), you can tell how far away it is. A ruler looks smaller from 20 meters away than from 10 meters away, and a 20-watt lightbulb looks dimmer the farther away it is. The same applies over cosmic distances.

    Scientists use certain types of exploding stars, for example, to estimate distances, because the blasts put out a predictable light show (SN: 5/8/12). Standard rulers or standard candles can be used to trace out how far away other objects of interest are and reveal how rapidly the universe has expanded over its history.

    But none of the known standard objects reach back to the cosmic dawn era. That’s where Muñoz’s ruler comes in. “This ability to reach that far back,” Liu says, “that’s the really valuable thing.”

    Sizing up cosmic dawn

    No one has ever seen a conclusive signature of cosmic dawn — the very first galaxies are too distant to observe directly. But there’s another way to spot cosmic dawn’s effects, one that’s been a long-sought target for astronomers. As the first stars formed, their light heated the surrounding hydrogen gas, causing it to absorb light with a wavelength of 21 centimeters, a number that results from the separation between energy levels in hydrogen atoms. Observing that 21-centimeter absorption signal is the aim of the Hydrogen Epoch of Reionization Array, or HERA, collaboration, an effort that Muñoz and Liu both work on, using a radio telescope in South Africa.

    If it can be detected, this absorption signal should have subtle, ring-shaped patterns imprinted in it, Muñoz reported in 2019 in Physical Review Letters.

    Secrets of the universe’s cosmic dawn era are revealed in patterns of the absorption of light with a 21-centimeter wavelength, shown in a computer simulation. Regions with more absorption (red) correspond to denser pockets of stars, compared with sparsely populated regions with less absorption (blue). Sparse areas tend to be separated by distances of about half a billion light-years (arrow indicates one example); the same goes for dense areas.J.B. Muñoz

    Those patterns, the basis of his ruler, result from the differing behavior of dark matter and normal matter during an even earlier period, less than 400,000 years after the Big Bang. Sound waves careening through the plasma at that time would have pushed normal matter to high speeds while leaving dark matter at a standstill.

    This mismatch in velocities affected where galaxies formed during the later cosmic dawn era. To create a galaxy, dark matter must gravitationally reel in normal matter. But where the velocities differed, the normal matter zipped right on by. The early universe was left with sparsely populated regions of the sky, arranged in ring-shaped patterns with a predictable distance scale. The rings, which are too subtle to pick out by eye from the data but show up in statistical analyses, have radii of half a billion light-years – that’s one long measuring stick.

    The new standard ruler could reveal how fast the universe was expanding back then. That information can tell scientists what that youthful universe was made of, revealing the amount of dark matter, normal matter and dark energy, another hidden piece of the cosmic puzzle.

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    A new expansion measurement could also add fuel to one of the fiercest debates in cosmology. Currently, different measurements of the universe’s expansion rate clash with one another, leaving scientists pondering whether there are flaws in our understanding of the cosmos.

    Seeking to understand the unknown, including these shadowy cosmic realms, is “an integral component of human nature — like art and poetry,” Muñoz says. “You could live without it, but I really hope you don’t have to.”

    Looking into dark corners

    Muñoz’s interest in dark matter drew him to the cosmic dawn. The first galaxies grew off a scaffold of dark matter. So information about how and when those galaxies formed can reveal dark matter’s properties. In a report published in 2018 in Nature, for example, Muñoz and colleagues suggested that, if some of the universe’s dark matter had a tiny electric charge, a millionth of an electron’s, that could alter the expected cosmic dawn signal.

    He has also developed important computational tools, like a new technique that allows for lightning-fast simulations of the cosmic dawn, reported in May in Monthly Notices of the Royal Astronomical Society. The time it takes to perform these simulations has previously limited what scientists can study.

    “He’s got an eye for interesting ideas,” says theoretical physicist Marc Kamionkowski of Johns Hopkins University, Muñoz’s Ph.D. adviser. But the cosmic ruler, “that’s probably the most singular idea that he’s had.”

    Becoming a physicist, in itself, was uncharted territory for Muñoz. As a child, he liked science. He recalls being amazed by fossilized shark teeth that were millions of years old — perhaps his first experience grappling with such grand timescales.

    But Muñoz didn’t have a scientific role model; his parents didn’t finish high school. He focused his attention on video games and coding until a high school physics teacher encouraged his scientific streak. He turned to physics, he says, where “it was possible to channel all this nerdy energy for knowledge.” That’s what drives Muñoz to explore the questions that swirl around dark corners of the cosmos. “I do it because I think the answers enrich the human experience.”

    Julian Muñoz is one of this year’s SN 10: Scientists to Watch, our list of 10 early and mid-career scientists who are making extraordinary contributions to their field. We’ll be rolling out the full list throughout 2023.

    Want to nominate someone for the SN 10? Send their name, affiliation and a few sentences about them and their work to sn10@sciencenews.org. More