Space & Astronomy

Subterms

    More stories

    • 150 Shares189 Views

      in Space & Astronomy

      Fossil mimics may be more common in ancient rocks than actual fossils

      by

      When it comes to finding fossils of very ancient microbial life — whether on Earth or on other worlds, such as Mars — the odds are just not in our favor.
      Actual microbial life-forms are much less likely to become safely fossilized in rocks compared with nonbiological structures that happen to mimic their shapes, new research finds. The finding suggests that Earth’s earliest rocks may contain abundant tiny fakers — minuscule objects masquerading as fossilized evidence of early life — researchers report online January 28 in Geology.
      The finding is “at the very least a cautionary tale,” says study author Julie Cosmidis, a geomicrobiologist at the University of Oxford.
      Tiny, often enigmatic structures found in some of Earth’s oldest rocks, dating back to more than 2.5 billion years, can offer tantalizing hints of the planet’s earliest life. And the hunt for ever-more-ancient signs of life on Earth has sparked intense debate — in part because the farther back in time you go, the harder it is to interpret tiny squiggles, filaments and spheres in the rock (SN: 1/3/20). One reason is that the movements of Earth’s tectonic plates over time can squeeze and cook the rocks, deforming and chemically altering tiny fossils, perhaps beyond recognition.

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      But an even more pernicious and contentious problem is that such tiny filaments or spheres may not be biological in origin at all. Increasingly, scientists have found that nonbiological chemical processes can create similar shapes, suggesting the possibility of “false positives” in the biological record.
      One such discovery led to the new study, Cosmidis says. A few years ago, she and others were trying to grow bacteria and make them produce sulfur. “We were mixing sulfides with organic matter, and we started forming these objects,” she says. “We thought they were formed by the bacteria, because they looked so biological. But then we realized they were forming in laboratory tubes that happened to have no bacteria in them at all.”
      That led her to wonder about such processes happening in the rocks themselves. So she and others decided to examine what would happen if they tried to re-create the early formation stages of chert, a kind of compact, silica-rich rock common on the early Earth. “Microfossils are often found in chert formations,” says study coauthor Christine Nims, a geobiologist now at the University of Michigan in Ann Arbor. “Anything hosted in [chert] will be well-preserved.”
      Chert forms out of silica-rich water; the silica precipitates out of the water and accumulates, eventually hardening into rock. Cosmidis, Nims and colleagues added sulfur-containing bacteria called Thiothrix to solidifying chert to see what might happen during actual fossilization. To other chert samples, they added sulfur-containing “biomorphs,” spheres and filaments made of tiny crystals but shaped like bacteria.
      At first, nanoparticles of silica encrusted the bacteria and the biomorphs, Nims says. But after a week or so, the bacteria started to deform, their cells deflating from cylinders into flattened, unrecognizable ribbons as the sulfur inside the cells diffused out and reacted with the silica outside the cells, forming new minerals.
      The biomorphs, on the other hand, “had this impressive resiliency,” she says. Although they, too, lost sulfur to the surrounding solution, they kept their silica crust. As a result, “they kept their shape and showed very little change over time.” That endurance suggests that enigmatic structures found in the early rock record have a better chance of being pseudofossils, rather than actual fossils, the team says.
      In a new study, researchers produced twisted filament-shaped biomorphs (top) from the reactions of sulfide with prebiotic organic compounds. The biomorphs resemble possible microbial fossils (bottom, filaments indicated by red arrows) found in rocks dating to 3.5 billion years ago.From top: C. Nims; R.J. Baumgartner et al/Geology 2019
      The idea that once-living creatures are harder to preserve makes sense, says Sean McMahon, an astrobiologist at the University of Edinburgh who was not involved in the new study. “It’s not totally surprising,” he says. “We know that biomass does tend to break down quite quickly.”
      In fact, scientists have known for centuries that certain chemical reactions can act as “gardens” that “grow” strange-shaped mineral objects, twisting into tubes or sprouting branches or otherwise mimicking the weirdness of life. “There’s a complacency about it, a misconception that we kind of know all this and it’s already been dealt with,” McMahon says.
      Strategies to deal with this conundrum have included looking for particular structures — such as mound-shaped stromatolites — or chemical compounds in a potential fossil that are thought to be uniquely formed or modified by the presence of life (SN: 10/17/18). Those criteria are the product of decades of field studies, through which scientists have amassed a vast reference dataset of fossil structures, against which researchers can compare and evaluate any new discoveries.
      “Anything we find, we can look at through that lens,” McMahon says. But what’s lacking is a similarly rich dataset for how such structures might form in the absence of life. This study, he says, highlights that attempts “to define criteria for recognizing true fossils in very ancient rocks are premature, because we don’t yet know enough about how nonbiological processes mimic true fossils.”
      It’s an increasingly urgent problem with rising stakes, as NASA’s Perseverance rover is about to set down on Mars to begin a new search for traces of life in ancient rocks (SN: 7/28/20), he adds. “Paleontologists and Mars exploration scientists should take [this study] very seriously.” More

    • 125 Shares199 Views

      in Space & Astronomy

      Two exoplanet families redefine what planetary systems can look like

      by

      Two tightly packed families of exoplanets are pushing the boundaries of what a planetary system can look like. New studies of the makeup of worlds orbiting two different stars show a wide range of planetary possibilities, all of them different from our solar system.
      “When we study multiplanet systems, there’s simply more information kept in these systems” than any single planet by itself, says geophysicist Caroline Dorn of the University of Zurich. Studying the planets together “tells us about the diversity within a system that we can’t get from looking at individual planets.”
      Dorn and colleagues studied an old favorite planetary system called TRAPPIST-1, which hosts seven Earth-sized planets orbiting a small dim star about 40 light-years away. Another team studied a recently identified system called TOI-178, which has at least six planets — three already known and three newly found — circling a bright, hot star roughly 200 light-years away.
      Both systems offer planetary scientists an advantage over the more than 3,000 other exoplanet families spotted to date: All seven planets in TRAPPIST-1 and all six in TOI-178 have well-known masses and radii. That means planetary scientists can figure out their densities, a clue to the planets’ composition (SN: 5/11/18).

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      The two systems also offer another advantage: The planets are packed in so close to their stars that most are engaged in a delicate orbital dance called a resonance chain. Every time an outer planet completes an orbit around its star, some of its closer-in sibling planets complete multiple orbits.
      Resonance chains are fragile arrangements, and knocking a planet even slightly out of its orbit can destroy them. That means the TRAPPIST-1 and TOI-178 systems must have formed slowly and gently, says astronomer Adrien Leleu of the University of Geneva.
      [embedded content]
      TOI-178’s planets are engaged in a delicate orbital dance called a resonance chain that suggests the system formed gently. This video illustrates this rhythmic dance: as an outer planet completes one full orbit, the inner planets complete multiple orbits. Each full and half orbit is assigned a musical note. When planets align, the notes harmonize.
      “We don’t think there could have been giant impacts, or strong interactions where one planet ejected another planet,” Leleu says. That gentle evolution gives astronomers a unique opportunity to use TRAPPIST-1 and TOI-178 as testbeds for planetary theory.
      In a pair of papers, two teams describe these systems in unprecedented detail. Both buck the trend astronomers expected from theories of how planetary systems form.
      In the TOI-178 system, the planets’ densities are all jumbled up, Leleu and colleagues report January 25 in Astronomy & Astrophysics.
      “In the most vanilla scenario, we expect that planets farther from the star…would have larger components of hydrogen and helium gas than the planets closer in,” says astrophysicist Leslie Rogers of the University of Chicago, who was not involved in either study. The closer to the star, the denser a planet should be. That’s because farther-out planets probably formed where it’s cold, and there was more low-density material like frozen water, rather than rock, to begin with. Plus, starlight can strip atmospheres from close-in planets more easily than far-out ones, leaving the inner planets with thinner atmospheres — or no atmospheres at all (SN: 7/1/20).
      TOI-178 flouts that trend entirely. The innermost planets seem to be rocky, with densities similar to Earth’s. The third one is “very fluffy,” Leleu says, with a density like Jupiter’s, but in a much smaller planet. The next planet out has a density like Neptune’s, about one-third Earth’s density. Then, there’s one with about 60 percent Earth’s density, still fluffy enough to float if you could put it in a tub of water, and the final planet is Jupiter-like.
      “The orbits seem to point out that there was no strong evolution from [the system’s] formation,” Leleu says. “But the compositions are not what we would have expected from a gentle formation in the disk.”
      TRAPPIST-1’s planet septet, on the other hand, has an eerie self-similarity. Each world is roughly the same size as Earth, between 0.76 and 1.13 times Earth’s radius, astrophysicist Eric Agol of the University of Washington in Seattle and colleagues reported in 2017 (SN: 2/22/17). Plus, at least three of them appear to be in the star’s habitable zone, the region where temperatures might be right for liquid water.
      Now, Agol, Dorn and colleagues have made the most precise measurements of the TRAPPIST-1 masses yet. All seven worlds are almost identical to each other but slightly less dense than Earth, the team reports in the February Planetary Science Journal. That means the planets could be rocky yet have a lower proportion of heavy elements such as iron compared with Earth. Or it could mean they have more oxygen bound to the iron in their rocks, “basically rusting it,” Agol says.
      TRAPPIST-1’s seven planets seem to have similar compositions to each other, but different from Earth. They could have an Earthlike makeup but with a smaller iron-rich core (center), or have no core at all (left). They could also have deep oceans (right), but the inner three planets are probably too hot for that much water to last.JPL-Caltech/NASA
      TRAPPIST-1’s seven planets seem to have similar compositions to each other, but different from Earth. They could have an Earthlike makeup but with a smaller iron-rich core (center), or have no core at all (left). They could also have deep oceans (right), but the inner three planets are probably too hot for that much water to last.JPL-Caltech/NASA
      Oxidized iron wouldn’t form a planetary core, which could be bad news for life, Rogers says. No core might mean no magnetic field to protect the planets from the star’s damaging flares (SN: 3/5/18).
      However, it’s not clear how to form coreless planets. “There are propositions for how to form such planets, but we don’t actually have one candidate in the solar system where we see this,” Dorn says. The analogs in the solar system are all asteroid-sized bodies much less massive than Earth.
      Astronomers may soon get a better handle on the compositions of TRAPPIST-1’s planets. The James Webb Space Telescope, set to launch in October, will probe the planets’ atmospheres (if they have any) for signs of chemical elements that would reveal in more detail what they’re made of.
      The TRAPPIST-1 planets’ similarities to each other are not as surprising as the differences among TOI-178’s planets, Rogers says. But they’re still unexpected. If all the planets have identical compositions, then any formation model needs to explain that, she says.
      While these systems challenge astronomers’ views of what sorts of planets are possible, Dorn says, it will take discovering more multiplanet systems to tell how weird they truly are. More

    • 138 Shares109 Views

      in Space & Astronomy

      Einstein’s theory of general relativity unveiled a dynamic and bizarre cosmos

      by

      Albert Einstein’s mind reinvented space and time, foretelling a universe so bizarre and grand that it has challenged the limits of human imagination. An idea born in a Swiss patent office that evolved into a mature theory in Berlin set forth a radical new picture of the cosmos, rooted in a new, deeper understanding of gravity.
      Out was Newton’s idea, which had reigned for nearly two centuries, of masses that appeared to tug on one another. Instead, Einstein presented space and time as a unified fabric distorted by mass and energy. Objects warp the fabric of spacetime like a weight resting on a trampoline, and the fabric’s curvature guides their movements. With this insight, gravity was explained.
      Einstein presented his general theory of relativity at the end of 1915 in a series of lectures in Berlin. But it wasn’t until a solar eclipse in 1919 that everyone took notice. His theory predicted that a massive object — say, the sun — could distort spacetime nearby enough to bend light from its straight-line course. Distant stars would thus appear not exactly where expected. Photographs taken during the eclipse verified that the position shift matched Einstein’s prediction. “Lights all askew in the heavens; men of science more or less agog,” declared a New York Times headline.
      Even a decade later, a story in Science News Letter, the predecessor of Science News, wrote of “Riots to understand Einstein theory” (SN: 2/1/30, p. 79). Apparently extra police had to be called in to control a crowd of 4,500 who “broke down iron gates and mauled each other” at the American Museum of Natural History in New York City to hear an explanation of general relativity.

      By 1931, physicist Albert A. Michelson, the first American to win a Nobel Prize in the sciences, called the theory “a revolution in scientific thought unprecedented in the history of science.”
      But for all the powers of divination we credit to Einstein today, he was a reluctant soothsayer. We now know that general relativity offered much more than Einstein was willing or able to see. “It was a profoundly different way of looking at the universe,” says astrophysicist David Spergel of the Simons Foundation’s Flatiron Institute in New York City, “and it had some wild implications that Einstein himself didn’t want to accept.” What’s more, says Spergel (a member of the Honorary Board of the Society for Science, publisher of Science News), “the wildest aspects of general relativity have all turned out to be true.”
      What had been masquerading as a quiet, static, finite place is instead a dynamic, ever-expanding arena filled with its own riot of space-bending beasts. Galaxies congregate in superclusters on scales vastly greater than anything experts had considered before the 20th century. Within those galaxies reside not only stars and planets, but also a zoo of exotic objects illustrating general relativity’s propensity for weirdness, including neutron stars, which pack a fat star’s worth of mass into the size of a city, and black holes, which pervert spacetime so strongly that no light can escape. And when these behemoths collide, they shake spacetime, blasting out ginormous amounts of energy. Our cosmos is violent, evolving and filled with science fiction–like possibilities that actually come straight out of general relativity.
      “General relativity opened up a huge stage of stuff for us to look at and try out and play with,” says astrophysicist Saul Perlmutter of the University of California, Berkeley. He points to the idea that the universe changes dramatically over its lifetime — “the idea of a lifetime of a universe at all is a bizarre concept” — and the idea that the cosmos is expanding, plus the thought that it could collapse and come to an end, and even that there might be other universes. “You get to realize that the world could be much more interesting even than we already ever imagined it could possibly be.”

      General relativity has become the foundation for today’s understanding of the cosmos. But the current picture is far from complete. Plenty of questions remain about mysterious matter and forces, about the beginnings and the end of the universe, about how the science of the big meshes with quantum mechanics, the science of the very small. Some astronomers believe a promising route to answering some of those unknowns is another of general relativity’s initially underappreciated features — the power of bent light to magnify features of the cosmos.
      Today’s scientists continue to poke and prod at general relativity to find clues to what they might be missing. General relativity is now being tested to a level of precision previously impossible, says astrophysicist Priyamvada Natarajan of Yale ​University. “General relativity expanded our cosmic view, then gave us sharper focus on the cosmos, and then turned the tables on it and said, ‘now we can test it much more strongly.’ ” It’s this testing that will perhaps uncover problems with the theory that might point the way to a fuller picture.
      And so, more than a century after general relativity debuted, there’s plenty left to foretell. The universe may turn out to be even wilder yet.
      Ravenous beasts
      Just over a century after Einstein unveiled general relativity, scientists obtained visual confirmation of one of its most impressive beasts. In 2019, a global network of telescopes revealed a mass warping spacetime with such fervor that nothing, not even light, could escape its snare. The Event Horizon Telescope released the first image of a black hole, at the center of galaxy M87 (SN: 4/27/19, p. 6).
      In 2019, the Event Horizon Telescope Collaboration released this first-ever image of a black hole, at the heart of galaxy M87. The image shows the shadow of the monster surrounded by a bright disk of gas.Event Horizon Telescope Collaboration
      “The power of an image is strong,” says Kazunori Akiyama, an astrophysicist at the MIT Haystack Observatory in Westford, Mass., who led one of the teams that created the image. “I somewhat expected that we might see something exotic,” Akiyama says. But after looking at the first image, “Oh my God,” he recalls thinking, “it’s just perfectly matching with our expectation of general relativity.”
      For a long time, black holes were mere mathematical curiosities. Evidence that they actually reside out in space didn’t start coming in until the second half of the 20th century. It’s a common story in the annals of physics. An oddity in some theorist’s equation points to a previously unknown phenomenon, which kicks off a search for evidence. Once the data are attainable, and if physicists get a little lucky, the search gives way to discovery.
      In the case of black holes, German physicist Karl Schwarzschild came up with a solution to Einstein’s equations near a single spherical mass, such as a planet or a star, in 1916, shortly after Einstein proposed general relativity. Schwarzschild’s math revealed how the curvature of spacetime would differ around stars of the same mass but increasingly smaller sizes — in other words, stars that were more and more compact. Out of the math came a limit to how small a mass could be squeezed. Then in the 1930s, J. Robert Oppenheimer and Hartland Snyder described what would happen if a massive star collapsing under the weight of its own gravity shrank past that critical size — today known as the “Schwarzschild radius” — reaching a point from which its light could never reach us. Still, Einstein — and most others — doubted that what we now call black holes were plausible in reality.
      The term “black hole” first appeared in print in Science News Letter. It was in a 1964 story by Ann Ewing, who was covering a meeting in Cleveland of the American Association for the Advancement of Science (SN: 1/18/64, p. 39). That’s also about the time that hints in favor of the reality of black holes started coming in.
      Just a few months later, Ewing reported the discovery of quasars — describing them in Science News Letter as “the most distant, brightest, most violent, heaviest and most puzzling sources of light and radio waves” (SN: 8/15/64, p. 106). Though not linked to black holes at the time, quasars hinted at some cosmic powerhouses needed to provide such energy. The use of X-ray astronomy in the 1960s revealed new features of the cosmos, including bright beacons that could come from a black hole scarfing down a companion star. And the motions of stars and gas clouds near the centers of galaxies pointed to something exceedingly dense lurking within.  
      Quasars (one illustrated) are so bright that they can outshine their home galaxies. Though baffling when first discovered, these outbursts are powered by massive, feeding black holes.Mark Garlick/Science Source
      Black holes stand out among other cosmic beasts for how extreme they are. The largest are many billion times the mass of the sun, and when they rip a star apart, they can spit out particles with 200 trillion electron volts of energy. That’s some 30 times the energy of the protons that race around the world’s largest and most powerful particle accelerator, the Large Hadron Collider.
      As evidence built into the 1990s and up to today, scientists realized these great beasts not only exist, but also help shape the cosmos. “These objects that general relativity predicted, that were mathematical curiosities, became real, then they were marginal. Now they’ve become central,” says Natarajan.
      We now know supermassive black holes reside at the centers of most if not all galaxies, where they generate outflows of energy that affect how and where stars form. “At the center of the galaxy, they define everything,” she says.
      Though visual confirmation is recent, it feels as though black holes have long been familiar. They are a go-to metaphor for any unknowable space, any deep abyss, any endeavor that consumes all our efforts while giving little in return.
      Real black holes, of course, have given plenty back: answers about our cosmos plus new questions to ponder, wonder and entertainment for space fanatics, a lost album from Weezer, numerous episodes of Doctor Who, the Hollywood blockbuster Interstellar.
      For physicist Nicolas Yunes of the University of Illinois at Urbana-Champaign, black holes and other cosmic behemoths continue to amaze. “Just thinking about the dimensions of these objects, how large they are, how heavy they are, how dense they are,” he says, “it’s really breathtaking.”
      [embedded content]
      In 2019, scientists gave us the first real picture of the supermassive black hole at the center of galaxy M87. How? We explain.
      Spacetime waves
      When general relativity’s behemoths collide, they disrupt the cosmic fabric. Ripples in spacetime called gravitational waves emanate outward, a calling card of a tumultuous and most energetic tango.
      Einstein’s math predicted such waves could be created, not only by gigantic collisions but also by explosions and other accelerating bodies. But for a long time, spotting any kind of spacetime ripple was a dream beyond measure. Only the most dramatic cosmic doings would create signals that were large enough for direct detection. Einstein, who called the waves gravitationswellen, was unaware that any such big events existed in the cosmos.
      Gravitational waves ripple away from two black holes that orbit each other before merging (shown in this simulation). The merging black holes created a new black hole that’s much larger than those found in previous collisions.Deborah Ferguson, Karan Jani, Deirdre Shoemaker and Pablo Laguna/Georgia Tech, Maya Collaboration
      Beginning in the 1950s, when others were still arguing whether gravitational waves existed in reality, physicist Joseph Weber sunk his career into trying to detect them. After a decade-plus effort, he claimed detection in 1969, identifying an apparent signal perhaps from a supernova or from a newly discovered type of rapidly spinning star called a pulsar. In the few years after reporting the initial find, Science News published more than a dozen stories on what it began calling the “Weber problem” (SN: 6/21/69, p. 593). Study after study could not confirm the results. What’s more, no sources of the waves could be found. A 1973 headline read, “The deepening doubt about Weber’s waves” (SN: 5/26/73, p. 338).
      Weber stuck by his claim until his death in 2000, but his waves were never verified. Nonetheless, scientists increasingly believed gravitational waves would be found. In 1974, radio astronomers Russell Hulse and Joseph Taylor spotted a neutron star orbiting a dense companion. Over the following years, the neutron star and its companion appeared to be getting closer together by the distance that would be expected if they were losing energy to gravitational waves. Scientists soon spoke not of the Weber problem, but of what equipment could possibly pick up the waves. “Now, although they have not yet seen, physicists believe,” Dietrick E. Thomsen wrote in Science News in 1984 (SN: 8/4/84, p. 76).
      It was a different detection strategy, decades in the making, that would provide the needed sensitivity. The Advanced Laser Interferometry Gravitational-wave Observatory, or LIGO, which reported the first confirmed gravitational waves in 2016, relies on two detectors, one in Hanford, Wash., and one in Livingston, La. Each detector splits the beam of a powerful laser in two, with each beam traveling down one of the detector’s two arms. In the absence of gravitational waves, the two beams recombine and cancel each other out. But if gravitational waves stretch one arm of the detector while squeezing the other, the laser light no longer matches up.

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      The machines are an incredible feat of engineering. Even spacetime ripples detected from colliding black holes might stretch an arm of the LIGO detector by as little as one ten-thousandth of the width of a proton.
      When the first detection, from two colliding black holes, was announced, the discovery was heralded as the beginning of a new era in astronomy. It was Science News’ story of the year in 2016, and such a big hit that the pioneers of the LIGO detector won the Nobel Prize in physics the following year.
      Scientists with LIGO and another gravitational wave detector, Virgo, based in Italy, have by now logged dozens more detections (SN: 1/30/21, p. 30). Most of the waves have emanated from mergers of black holes, though a few events have featured neutron stars. Smashups so far have revealed the previously unknown birthplaces of some heavy elements and pointed to a bright jet of charged subatomic particles that could offer clues to mysterious flashes of high-energy light known as gamma-ray bursts. The waves also have revealed that midsize black holes, between 100 and 100,000 times the sun’s mass, do in fact exist — along with reconfirming that Einstein was right, at least so far.
      Researchers at two gravitational wave observatories, LIGO in the United States and Virgo in Italy (shown), have reported dozens of detections of black hole smashups, as well as neutron star mergers, in the last five years.The Virgo Collaboration
      Just five years in, some scientists are already eager for something even more exotic. In a Science News article about detecting black holes orbiting wormholes via gravitational waves, physicist Vítor Cardoso of Instituto Superior Técnico in Lisbon, Portugal, suggested a coming shift to more unusual phenomena: “We need to look for strange but exciting signals,” he said (SN: 8/29/20, p. 12).
      Gravitational wave astronomy is truly only at its beginnings. Improved sensitivity at existing Earth-based detectors will turn up the volume on gravitational waves, allowing detections from less energetic and more distant sources. Future detectors, including the space-based LISA, planned for launch in the 2030s, will get around the troublesome noise that interferes when Earth’s surface shakes.
      “Perhaps the most exciting thing would be to observe a small black hole falling into a big black hole, an extreme mass ratio inspiraling,” Yunes says. In such an event, the small black hole would zoom back and forth, back and forth, swirling in different directions as it followed wildly eccentric orbits, perhaps for years. That could offer the ultimate test of Einstein’s equations, revealing whether we truly understand how spacetime is warped in the extreme. More

    • 163 Shares109 Views

      in Space & Astronomy

      The Milky Way’s newfound high-energy glow hints at the secrets of cosmic rays

      by

      The Milky Way glows with a gamma ray haze, with energies vastly exceeding anything physicists can produce on Earth, according to a new paper. Gamma rays detected in the study, to be published in Physical Review Letters, came from throughout the galaxy’s disk, and reached nearly a quadrillion (1015) electron volts, known as a petaelectron volt or PeV.
      These diffuse gamma rays hint at the existence of powerful cosmic particle accelerators within the Milky Way. Physicists believe such accelerators are the source of mysterious, highly energetic cosmic rays, charged particles that careen through the galaxy, sometimes crash-landing on Earth. When cosmic rays — which mainly consist of protons — slam into interstellar debris, they can produce gamma rays, a form of high-energy light.  
      Certain galactic environments could rev up cosmic ray particles to more than a PeV, scientists suspect. In comparison, the Large Hadron Collider, the premier particle accelerator crafted by humans, accelerates protons to 6.5 trillion electron volts. But physicists haven’t definitively identified any natural cosmic accelerators capable of reaching a PeV, known as PeVatrons. One possibility is that supernova remnants, the remains of exploded stars, host shock waves that can accelerate cosmic rays to such energies (SN: 11/12/20).
      If PeVatrons exist, the cosmic rays they emit would permeate the galaxy, producing a diffuse glow of gamma rays of extreme energies. That’s just what researchers with the Tibet AS-gamma experiment have found. “It’s nice to see things fitting together,” says physicist David Hanna of McGill University in Montreal, who was not involved with the study.

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      After cosmic rays are spewed out from their birthplaces, scientists believe, they roam the galaxy, twisted about by its magnetic fields. “We live in a bubble of cosmic rays,” says astrophysicist Paolo Lipari of the National Institute for Nuclear Physics in Rome, who was not involved with the research. Because they are not deflected by magnetic fields, gamma rays point back to their sources, revealing the whereabouts of the itinerant cosmic rays. The new study “gives you information about how these particles fill the galaxy.”
      Lower-energy gamma rays also permeate the galaxy. But it takes higher-energy gamma rays to understand the highest-energy cosmic rays. “In general, the higher the energy of the gamma rays, the higher the energy of the cosmic rays,” says astrophysicist Elena Orlando of Stanford University, who was not involved with the research. “Hence, the detection … tells us that PeV cosmic rays originate and propagate in the galactic disk.”
      Scientists with the Tibet AS-gamma experiment in China observed gamma rays with energies between about 100 trillion and a quadrillion electron volts coming from the region of the sky covered by the disk of the Milky Way. A search for possible sources of the 38 highest-energy gamma rays, above 398 trillion electron volts, came up empty, supporting the idea that the gamma rays came from cosmic rays that had wandered about the galaxy. The highest-energy gamma ray carried about 957 trillion electron volts.
      Tibet AS-gamma researchers declined to comment on the study.
      Scientists have previously seen extremely energetic gamma rays from individual sources within the Milky Way, such as the Crab Nebula, a supernova remnant (SN: 6/24/19). Those gamma rays are probably produced in a different manner, by electrons radiating gamma rays while circulating within the cosmic accelerator. More

    • 113 Shares179 Views

      in Space & Astronomy

      Crushed space rocks hint at exoplanets’ early atmospheric makeup

      by

      Burning bits of ground-up meteorites may tell scientists what exoplanets’ early atmospheres are made of.
      A set of experiments baking the pulverized space rocks suggests that rocky planets had early atmospheres full of water, astrophysicist Maggie Thompson of the University of California, Santa Cruz reported January 15 at the virtual meeting of the American Astronomical Society. The air could also have had carbon monoxide and carbon dioxide, with smaller amounts of hydrogen gas and hydrogen sulfide.
      Astronomers have discovered thousands of planets orbiting other stars. Like the terrestrial planets in the solar system, many could have rocky surfaces beneath thin atmospheres. Existing and future space telescopes can peek at starlight filtering through those exoplanets’ atmospheres to figure out what chemicals they contain, and if any are hospitable to life (SN: 4/19/16).
      Thompson and her colleagues are taking a different approach, working from the ground up. Instead of looking at the atmospheres themselves, she’s examining the rocky building blocks of planets to see what kind of atmospheres they can create (SN: 5/11/18).

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      The researchers collected small samples, about three milligrams per experiment, of three different carbonaceous chondrite meteorites (SN: 8/27/20). These rocks are the first solids that condensed out of the disk of dust and gas that surrounded the young sun and ultimately formed the planets, scientists say. The meteorites form “a record of the original components that formed planetesimals and planets in our solar system,” Thompson said in a talk at the AAS meeting. Exoplanets probably formed from similar stuff.
      The researchers ground the meteorites to powder, then heated the powder in a special furnace hooked up to a mass spectrometer that can detect trace amounts of different gases. As the powder warmed, the researchers could measure how much of each gas escaped.
      That setup is analogous to how rocky planets formed their initial atmospheres after they solidified billions of years ago. Planets heated their original rocks with the decay of radioactive elements, collisions with asteroids or other planets, and with the leftover heat of their own formation. The warmed rocks let off gas. “Measuring the outgassing composition from meteorites can provide a range of atmospheric compositions for rocky exoplanets,” Thompson said.
      All three meteorites mostly let off water vapor, which accounted for 62 percent of the gas emitted on average. The next most common gases were carbon monoxide and carbon dioxide, followed by hydrogen, hydrogen sulfide and some more complex gases that this early version of the experiment didn’t identify. Thompson says she hopes to identify those gases in future experimental runs.
      The results indicate astronomers should expect water-rich steam atmospheres around young rocky exoplanets, at least as a first approximation. “In reality, the situation will be far more complicated,” Thompson said. Planets can be made of other kinds of rocks that would contribute other gases to their atmospheres, and geologic activity changes a planet’s atmosphere over time. After all, Earth’s breathable atmosphere is very different from Mars’ thin, carbon dioxide-rich air or Venus’s thick, hot, sulfurous soup (SN: 9/14/20).
      Still, “this experimental framework takes an important step forward to connect rocky planet interiors and their early atmospheres,” she said.
      This sort of basic research is useful because it “has put a quantitative compositional framework on what those planets might have looked like as they evolved,” says planetary scientist Kat Gardner-Vandy of Oklahoma State University in Stillwater, who was not involved in this new work. She studies meteorites too and is often asked whether experiments that crush the ancient, rare rocks are worth it.
      “People inevitably will ask me, ‘Why would you take a piece of a meteorite and then ruin it?’” she says. “New knowledge from the study of meteorites is just as priceless as the meteorite itself.” More

    • 113 Shares189 Views

      in Space & Astronomy

      Astronomers spotted a rare galaxy shutting down star formation

      by

      A distant galaxy has been caught in the act of shutting down.
      The galaxy, called CQ 4479, is still forming plenty of new stars. But it also has an actively feeding supermassive black hole at its center that will bring star formation to a halt within a few hundred million years, astronomers reported January 11 at the virtual meeting of the American Astronomical Society. Studying this galaxy and others like it will help astronomers figure out exactly how such shutdowns happen.
      “How galaxies precisely die is an open question,” says astrophysicist Allison Kirkpatrick of the University of Kansas in Lawrence. “This could give us a lot of insight into that process.”
      Astronomers think galaxies typically start out making new stars with a passion. The stars form from pockets of cold gas that contract under their own gravity and ignite thermonuclear fusion in their centers. But at some point, something disrupts the cold star-forming fuel and sends it toward the supermassive black hole at the galaxy’s core. That black hole gobbles the gas, heating it white-hot. An actively feeding black hole can be seen from billions of light-years away and is known as a quasar. Radiation from the hot gas pumps extra energy into the rest of the galaxy, blowing away or heating up the remaining gas until the star-forming factory closes for good (SN: 3/5/14).

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      That picture fits with the types of galaxies astronomers typically see in the universe: “blue and new” star formers, and “red and dead” dormant galaxies. But while examining data from large surveys of the sky, Kirkpatrick and colleagues noticed another type. The team found about two dozen galaxies that emit energetic X-rays characteristic of an actively gobbling black hole, but also shine in low-energy infrared light, revealing that there is still cold gas somewhere in the galaxies. Kirkpatrick and colleagues dubbed these galaxies “cold quasars” in a paper in the Sept. 1 Astrophysical Journal.
      “When you see a black hole actively accreting material, you expect that star formation has already shut down,” says coauthor and astrophysicist Kevin Cooke, also of the University of Kansas, who presented the research at the meeting. “But cold quasars are in a weird time when the black hole in the center has just begun to feed.”
      To investigate individual cold quasars in more detail, Kirkpatrick and Cooke used SOFIA, an airplane outfitted with a telescope that can see in a range of infrared wavelengths that the original cold quasar observations didn’t cover. SOFIA looked at CQ 4479, a cold quasar about 5.25 billion light-years away, in September 2019.
      The observations showed that CQ 4479 has about 20 billion times the mass of the sun in stars, and it’s adding about 95 suns per year. (That’s a furious rate compared with the Milky Way; our home galaxy builds two or three solar masses of new stars per year.) CQ 4479’s central black hole is 24 million times as massive as the sun, and it’s growing at about 0.3 solar masses per year. In terms of percentage of their total mass, the stars and the black hole are growing at the same rate, Kirkpatrick says.
      The cold quasar CQ 4479, the blue fuzzy dot at the center of this image, showed up in images taken by the Sloan Digital Sky Survey. The red dot nearby might be another galaxy interacting with CQ 4479, or it could be unrelated.K.C. Cooke et al/arxiv.org 2020, Sloan Digital Sky Survey
      That sort of “lockstep evolution” runs counter to theories of how galaxies wax and wane. “You should have all your stars finish growing first, and then your black hole grows,” Kirkpatrick says. “This [galaxy] shows there’s a period that they actually do grow together.”
      Cooke and colleagues estimated that in half a billion years, the galaxy will host 100 billion solar masses of stars, but its black hole will be passive and quiet. All the cold star-forming gas will have heated up or blown away.
      The observations of CQ 4479 support the broad ideas of how galaxies die, says astronomer Alexandra Pope of the University of Massachusetts Amherst, who was not involved in the new work. Given that galaxies eventually switch off their star formation, it makes sense that there should be a period of transition. The findings are a “confirmation of this important phase in the evolution of galaxies,” she says. Taking a closer look at more cold quasars will help astronomers figure out just how quickly galaxies die. More

    • 113 Shares189 Views

      in Space & Astronomy

      The most ancient supermassive black hole is bafflingly big

      by

      The most ancient black hole ever discovered is so big it defies explanation.
      This active supermassive black hole, or quasar, boasts a mass of 1.6 billion suns and lies at the heart of a galaxy more than 13 billion light-years from Earth. The quasar, dubbed J0313-1806, dates back to when the universe was just 670 million years old, or about 5 percent of the universe’s current age. That makes J0313-1806 two times heavier and 20 million years older than the last record-holder for earliest known black hole (SN: 12/6/17).
      Finding such a huge supermassive black hole so early in the universe’s history challenges astronomers’ understanding of how these cosmic beasts first formed, researchers reported January 12 at a virtual meeting of the American Astronomical Society and in a paper posted at arXiv.org on January 8.
      Supermassive black holes are thought to grow from smaller seed black holes that gobble up matter. But astronomer Feige Wang of the University of Arizona and colleagues calculated that even if J0313-1806’s seed formed right after the first stars in the universe and grew as fast as possible, it would have needed a starting mass of at least 10,000 suns. The normal way seed black holes form — through the collapse of massive stars — can only make black holes up to a few thousand times as massive as the sun.
      A gargantuan seed black hole may have formed through the direct collapse of vast amounts of primordial hydrogen gas, says study coauthor Xiaohui Fan, also an astronomer at the University of Arizona in Tucson. Or perhaps J0313-1806’s seed started out small, forming through stellar collapse, and black holes can grow a lot faster than scientists think. “Both possibilities exist, but neither is proven,” Fan says. “We have to look much earlier [in the universe] and look for much less massive black holes to see how these things grow.” More