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    Here’s how cool a star can be and still achieve lasting success

    If you want to be a successful star by making the minimum possible effort, aim for a surface temperature about a quarter of the sun’s. This is the temperature that a new study says separates red dwarf stars, which shine for a long time, from failed stars known as brown dwarfs.

    It’s often hard to distinguish between red and brown dwarfs, because when young they both look the same: red and dim. But only red dwarfs are born with enough mass to sustain the same nuclear reactions that power stars like the sun. In contrast, brown dwarfs glow red primarily from the heat of their birth, but then their nuclear activity sputters out, causing them to cool and fade. Now astrophysicists Dino Hsu and Adam Burgasser at the University of California, San Diego and their colleagues have discerned the dividing line between the two types by exploiting how they move through space.

    When a star is born, it revolves around the Milky Way’s center on a fairly circular orbit. Over time, though, gravitational tugs from giant gas clouds, spiral arms and other stars toss the stars to and fro. These perturbations make the stars’ orbits around the galactic center more and more elliptical. Thus, the orbital paths of stars can reveal their approximate age.

    Most red dwarfs are fairly old; their predicted lifetimes are far longer than the current age of the universe. But because brown dwarfs cool and fade, any that are still warm are young. Thus, on average, red dwarfs should follow more elliptical orbits around the galaxy than young brown dwarfs do.

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    In the new study, Hsu’s team analyzed 172 red and brown dwarfs of different spectral types, classifications based on the objects’ spectra that correlate with their surface temperatures. The researchers found that a sharp break in stellar motions separates warmer objects, which on average have more elliptical orbits and are older, from cooler ones, which on average have more circular orbits and are younger. This break appears at a spectral type between L4 and L6, corresponding to a surface temperature of about 1200° to 1400° Celsius (1,500 to 1,700 kelvins) — a fraction of the sun’s surface temperature of about 5500°C (5,800 K) — the team reports July 5 at arXiv.org.

    Above this critical temperature, the dim suns are a mix of long-lived red dwarfs and young brown dwarfs. Below this temperature, though, “it’s all brown dwarfs,” Hsu says. These are the failed stars that are fated to fizzle out. The study will appear in a future issue of the Astrophysical Journal Supplement Series.

    This new method for detecting the temperature boundary between red and brown dwarfs is intriguing, but the result is tentative, says Trent Dupuy, an astronomer at the University of Edinburgh who was not involved in the work. “It’s right around where you would expect,” he says. Dupuy says additional red and brown dwarfs should be observed to verify the finding.

    Hsu agrees: “We need a more complete sample.” Expanding the sample will be both easy and hard. On the positive side, red dwarfs abound, outnumbering all other stellar types put together, and brown dwarfs are also common. On the negative side, though, red and brown dwarfs are faint. That makes measuring their Doppler shifts, which reveal how fast the objects move toward or away from Earth, a challenge. But knowing this motion is essential for calculating a star’s orbital path around the galaxy. More

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    Modern humans evolved not to swing our hips as much as chimpanzees

    By Michael Marshall

    Based on the average height of humans, we should have longer stridesJohnnyGreig/Getty Images
    Humans have lost their swing. Chimpanzees and other great apes swing their hips when they walk, but modern humans do not. This means our strides are shorter than those of chimpanzees, even though our legs are proportionally longer.
    “We’ve always had this idea that evolution has been acting on fossil humans to make strides longer and longer,” says Nathan Thompson at the New York Institute of Technology in the US. But in fact, he says, “humans right … More

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    Why adding a road can increase traffic and other modelling delights

    By Simon Ings

    sasilsolutions/Getty Images
    Book

    Atlas of Forecasts: Modeling and mapping desirable futures
    Katy BörnerAdvertisement
    MIT Press

    MY LEAFY, fairly affluent corner of south London has a congestion problem, and to solve it, there is a plan to close certain roads. You can imagine the furore: the trunk of every kerbside tree sports a protest sign. How can shutting off roads improve traffic flows?
    German mathematician Braess answered this question back in 1968, showing that adding a road to a network can actually increase travel times due to a boost in drivers using the same routes and therefore increasing traffic. Now a new book, Atlas of Forecasts: Modeling and mapping desirable futures by Katy Börner, uses it as a fine example of how a mathematical model predicts and can be used to resolve a real-world problem.
    This and more than 1300 other models, maps and forecasts are referenced in Börner’s latest atlas, the third to be derived from Indiana University’s travelling exhibit Places & Spaces: Mapping science.
    Her first, Atlas of Science: Visualizing what we know revealed the power of maps in science, while the second, Atlas of Knowledge: Anyone can map, focused on visualisation. In her latest foray, Börner wants to show how models, maps and forecasts inform decision-making in education, science, technology and policy-making.
    It is a well-structured, heavyweight argument, supported by descriptions of more than 300 applications. Some entries, like Bernard H. Porter’s Map of Physics of 1939, earn their place purely because of their beauty and the insights they offer. Mostly, though, Börner chooses models that were applied in practice and made a positive difference.
    Her range is impressive. We begin at equations, revealing that Newton’s law of universal gravitation has been applied to human migration patterns, and move through the centuries. We tip a wink to Jacob Bernoulli’s 1713 book The Art of Conjecturing –which introduced probability theory – and James Clerk Maxwell’s 1868 paper “On governors”, which was an early nod towards cybernetics. Finally, we arrive at our current era of massive computation and ever-more complex model building.
    It is here that interesting questions start to surface. To forecast the behaviour of complex systems, especially those that contain a human component, many current researchers reach for modelling (ABM) in which discrete autonomous agents interact with each other and with their common (digitally modelled) environment.
    But, warns Börner, “ABMs in general have very few analytical tools by which they can be studied, and often no backward sensitivity analysis can be performed because of the large number of parameters and dynamical rules involved”. In other words, an ABM model offers us an exquisitely detailed forecast, but no clear way of knowing why the model has drawn the conclusions it has – a risky state of affairs, given that its data came from foible-ridden humans.
    Her sumptuous, detailed book tackles issues of error and bias head-on, but she left me tugging at a different problem, represented by those irate protest signs smothering my neighbourhood.
    In over 50 years since Braess’s research was published, reasonably wealthy, mostly well-educated people in comfortable surroundings have remained ignorant of how traffic flows work. So what are the chances that the rest of us, busy and preoccupied as we are, will ever really understand, or trust, the other models that increasingly dictate our civic life?
    Börner argues that modelling data can counteract tribalism, misinformation, magical thinking, authoritarianism and demonisation. I can’t for the life of me see how. What happens when a model reaches such complexity that only an expert can understand it, or when even the expert can’t be sure why the forecast is saying what it is saying?
    We have enough difficulty understanding climate forecasts, let alone explaining them. To apply these technologies to the civic realm begs a host of problems that are nothing to do with the technology, and everything to do with whether anyone will listen.

    More on these topics: More

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    Don't Miss: Are viruses alive? A timely talk at the Royal Institution

    T:Stocktrek Images/Alamy
    Watch
    Are viruses alive? asks New York Times science columnist Carl Zimmer in this Royal Institution talk. Can viruses and other difficult to pin down microbes help us answer the question: what is life? Streaming live on 26 August at 7pm BST.

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    The Nature Seed by Lucy Jones and Kenneth Greenway is a handy guide to raising adventurous, nature-loving children, full of fires, potions, foraging and make-believe. Discover the awe in a humble cracked pavement or your local park.
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    Watch
    Jamming the Signal is a live conversation at FACT Liverpool on 28 August from 2pm BST that asks whether social media and instant messaging can be used to effect meaningful change in an age of digital unrest. It will also be streamed online. More

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    We need to fully explore the planet to understand our species' origins

    Nino Marcutti/Alamy
    THE tale of human origins continues to throw up surprises. For many years, the generally accepted narrative was that our species emerged on the continent of Africa, before spreading to other continents around 60,000 years ago. It is certainly true that our origins lie primarily in Africa. But in this issue, we explore the crucial role that nearby Arabia played in human evolution.
    Evidence unearthed in Stone Age Arabia points to a much richer story, in which human populations ebbed and flowed in this region over hundreds of thousands  of years as the climate shifted.
    The remarkable discoveries from … More

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    The other cradle of humanity: How Arabia shaped human evolution

    New evidence reveals that Arabia was not a mere stopover for ancestral humans leaving Africa, but a lush homeland where they flourished and evolved

    Humans

    18 August 2021

    By Michael Marshall

    Andrea Ucini
    THE Rub’ al-Khali is both desert and deserted – a landscape of reddish sand dunes that stretches as far as the eye can see. This hyper-arid region in the south-east of the Arabian peninsula is approximately the size of France. Parts of it often go an entire year without rain. Almost nobody lives there; its name means “empty quarter”.
    The rest of Arabia is less environmentally extreme, but still a very tough place to live without air conditioning and other recent technologies. However, the peninsula wasn’t always so parched. A mere 8000 years ago, it was wet enough for there to have been many lakes. The same was true at intervals throughout the past million years, when rivers criss-crossed Arabia, forming green corridors where lush vegetation and wildlife flourished amid the sand dunes. For much of recent geological time, the peninsula was at least partly green.
    Arabia’s verdant past is no mere factoid: it suggests that the region was habitable at times in the distant past. That realisation has prompted archaeologists to start looking for evidence of occupation by humans, their ancestors and their extinct relatives. In just a decade, they have found countless sites where these hominins lived, stretching hundreds of thousands of years into the past. Arabia, it seems, wasn’t a mere stopover for hominins as they moved out of Africa into the wider world. It was somewhere they settled for long stretches of time. Indeed, many researchers now think Arabia should be thought of as part of a “greater Africa”, and that the peninsula played an important role in human evolution and expansion across the world.
    For … More

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    Vera Rubin’s work on dark matter led to a paradigm shift in cosmology

    Bright Galaxies, Dark Matter, and BeyondAshley Jean YeagerMIT Press, $24.95

    Vera Rubin’s research forced cosmologists to radically reimagine the cosmos.

    In the 1960s and ’70s, Rubin’s observations of stars whirling around within galaxies revealed the gravitational tug of invisible “dark matter.” Although astronomers had detected hints of this enigmatic substance for decades, Rubin’s data helped finally convince a skeptical scientific community that dark matter exists (SN: 1/10/20).

    “Her work was pivotal to redefining the composition of our cosmos,” Ashley Yeager, Science News’ associate news editor, writes in her new book. Bright Galaxies, Dark Matter, and Beyond follows Rubin’s journey from stargazing child to preeminent astronomer and fierce advocate for women in science.

    That journey, Yeager shows, was rife with obstacles. When Rubin was a young astronomer in the 1950s and ’60s, many observatories were closed to women, and more established scientists often brushed her off. Much of her early work was met with intense skepticism, but that only made Rubin, who died in 2016 at age 88, a more dogged data collector.

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    On graphs plotting the speeds of stars swirling around galaxies, Rubin showed that stars farther from galactic centers orbited just as fast as inner stars. That is, the galaxies’ rotation curves were flat. Such speedy outer stars must be pulled along by the gravitational grip of dark matter.

    Science News staff writer Maria Temming spoke with Yeager about Rubin’s legacy and what, beyond her pioneering research, made Rubin remarkable. The following discussion has been edited for clarity and brevity.

    Temming: What inspired you to tell Rubin’s story?

    Yeager: It all started when I was working at the National Air and Space Museum in Washington, D.C., in 2007. I was walking around the “Explore the Universe” exhibit and noticed there weren’t many women featured. But then there was this picture of a woman with big glasses and cropped hair, and I thought, “Who is this?” It was Vera Rubin.

    My supervisor was a curator of oral histories. He was working on Rubin’s, so I asked him about her. He said, “I have one more oral history interview to do with her. Would you like to come?” So I got to interview her. She was charismatic, kind and curious — not a person who was all about herself, but wanted to know about you. That stuck with me.

    Temming: You spend much of the book describing evidence for dark matter besides Rubin’s research. Why?

    Yeager: I wanted to make sure I didn’t portray Rubin as this lone person who discovered dark matter, because there were a lot of different moving pieces in astronomy and physics that came together in the ’70s and early ’80s for the scientific community to say, “OK, we really have to take dark matter seriously.”

    Temming: What made Rubin’s work a linchpin for confirming dark matter?

    Yeager: She really went after nailing down that flat rotation curve in all types of galaxies. Mainly because she did get a lot of pushback, continually, that said, “Oh, that’s just a special case in that galaxy, or that’s just for those types of galaxies.” She studied hundreds of galaxies to double-check that, yes, in fact, the rotation curves are flat. People saying, “We don’t believe you,” didn’t ever really knock her down. She just came back swinging harder.

    It helped that she did the work in visible wavelengths of light. There had been a lot of radio astronomy data to suggest flat rotation curves, but because radio astronomy was very new, it was really only once you saw it with the eye that the astronomy community was convinced.

    Temming: Do you have a favorite anecdote about Rubin?

    Yeager: The one that comes to mind is how much she loved flowers. She told me about how on drives from Lowell Observatory to Kitt Peak National Observatory in Arizona, she and her colleague Kent Ford would always stop and buy wildflowers. The fact that picking these wildflowers stuck with her, I thought, was just representative of who she was. Her favorite moments weren’t necessarily these big discoveries she’d made, but stopping to pick some flowers and enjoy their beauty.

    Author Ashley Yeager (left) interviewed Vera Rubin (right) in 2007 as part of an oral history project with Smithsonian’s National Air and Space Museum.Smithsonian National Air and Space Museum (NASM 9A16674)

    Temming: Did you learn anything in your research that surprised you?

    Yeager: I didn’t initially grasp how many different types of projects she had. She did a lot with looking for larger-scale structure [in the universe] and looking at the Hubble constant [which describes how fast the universe is expanding] (SN: 4/21/21). She had a very diverse set of questions that she wanted to answer, well into her 70s.

    Temming: I was surprised by her decision to get out of the rat-race of hunting for quasars, when that area of research heated up in the 1960s.

    Yeager: She very much didn’t like to be in pressure situations where she could be wrong. She liked to go and collect so much data that no one could [dispute it]. With quasar research, it was just too fast, and she wanted to be methodical about it.

    Temming: Why is Rubin’s story important to tell now?

    Yeager: Unfortunately for women and minorities in science, it’s still very relevant, in that there are a lot of challenges to pursuing a career in STEM. Her story demonstrates that you have to surround yourself with people who are willing to help you and get away from the people who want to keep you down. Plus her story is also very encouraging: Your curiosity can keep you going and can fuel something way bigger than yourself.

    Temming: How did she advocate for women in astronomy?

    Yeager: She was very outspoken about it. At National Academy of Sciences meetings, the organizers always dreaded her standing up, because she would say, “What are we doing about women in science? We’re not doing enough.” She was constantly pushing for women to be recognized with awards. She kept tabs on the number of women who had earned Ph.D.s and who had gotten staff positions — and their salaries. She was very data-driven. She’d cull that information and use it to advocate for better representation and recognition of women in astronomy.

    Temming: How would you describe Rubin to someone who hasn’t met her?

    Yeager: She was one of the most persistent, gracious and nurturing people that I’ve ever met. You could strip away all that she did in astronomy and she would still be this incredible figure — the way she carried herself, the way she treated people. Just a beautiful human being.

    Buy Bright Galaxies, Dark Matter, and Beyond from Bookshop.org. Science News is a Bookshop.org affiliate and will earn a commission on purchases made from links in this article. More

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    Ancient dog faeces show how our canine friends became omnivores

    By James Urquhart

    Dog food often contains grains – and may have done so for thousands of yearsJaromir Chalabala / Alamy Stock Photo
    Dog diets often contain more starch than those of their carnivorous wolf ancestors, and an analysis of fossilised dog faeces helps explain how the animals made the dietary change. Long before their genomes adapted to their plant-rich chow, their gut microbiome gained a starch-digesting profile.
    Due to their close association with humans, it is thought that dogs’ diets shifted to less meat and more carbohydrates when farming began – an idea that was supported by an archaeological analysis … More