Philippa Kaur

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    The Milky Way may have grown up faster than astronomers suspected

    The Milky Way as we know it today was shaped by a collision with a dwarf galaxy about 10 billion years ago. But most of the modern galaxy was already in place even at that early date, new research shows.

    Ages of stars left behind by the galactic interloper are a bit younger or on par with stars in the Milky Way’s main disk, researchers report May 17 in Nature Astronomy. And that could mean that the Milky Way grew up faster than astronomers expected, says study author Ted Mackereth, an astrophysicist at the University of Toronto.

    “The Milky Way had already built up a lot of itself before this big merger happened,” he says.

    Our galaxy’s history is one of violent conquest. Like other giant spiral galaxies in the universe, the Milky Way probably built up its bulk by colliding and merging with smaller galaxies over time. Stars from the unfortunate devoured galaxies got mixed into the Milky Way like cream into coffee, making it difficult to figure out what the galaxies were like before they merged.

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    In 2018, astronomers realized that they could identify stars from the last major merger using detailed maps of several million stars from the European Space Agency’s Gaia spacecraft (SN: 5/9/18). Streams of stars orbit the galactic center at an angle to the main disk of stars. Those stars’ motions and chemistries suggest they once belonged to a separate galaxy that plunged into the Milky Way about 10 billion years ago (SN: 11/1/2018).

    “Those stars are left there like fossil remnants of the galaxy,” Mackereth says.

    Two groups discovered evidence of the ancient galaxy at around the same time. One called the galaxy Gaia-Enceladus; the other group called it the Sausage. The name that stuck was Gaia-Enceladus/Sausage.

    Mackereth and his colleagues wondered if they could figure out how well developed the Milky Way was when Gaia-Enceladus/Sausage came crashing in. If the oldest stars in the Milky Way’s disk formed after this merger, then they probably formed as a result of this collision, suggesting that Gaia-Enceladus/Sausage met a proto–Milky Way that still had a lot of growing up to do. On the other hand, if the oldest stars are about the same age or older than the stars from the galactic interloper, then our galaxy was probably pretty well developed at the time of the run-in. 

    Previous researchers had made estimates. But Mackereth and his colleagues used a precise tool called asteroseismology to figure out the ages of individual stars from both the Milky Way and from Gaia-Enceladus/Sausage (SN: 8/2/19). Just like seismologists on Earth use earthquakes to probe the interior of our planet, asteroseismologists use variations in brightness caused by starquakes and other oscillations to probe the innards of stars.

    “Asteroseismology is the only way we have to access the internal part of the stars,” says physicist and study coauthor Josefina Montalbán of the University of Birmingham in England. From intel on the star’s interior structures, researchers can deduce the stars’ ages.

    The team selected about 95 stars that had been observed by NASA’s exoplanet-hunting Kepler space telescope, which ended its mission in 2018 (SN: 10/30/18). Six of those stars were from Gaia-Enceladus/Sausage, and the rest were from the Milky Way’s thick disk. By measuring how the brightnesses of those stars fluttered over time, Mackereth and colleagues deduced ages with about 11 percent precision.

    The Gaia-Enceladus/Sausage stars are slightly younger than the Milky Way stars, but all were pretty close to 10 billion years old, the team found. That suggests that a large chunk of the Milky Way’s disk was already in place when Gaia-Enceladus/Sausage came crashing through. It’s still possible that the incoming galaxy sparked the formation of some new stars, though, Mackereth says. To tell how much, they’ll need to get ages of a lot more stars.

    Measuring ages for individual stars represents a step forward for galactic astronomy, says astrophysicist Tomás Ruiz-Lara of the University of Groningen, the Netherlands, who studies galactic evolution but was not involved in the new work.

    “If you cannot tell the difference between a kid and a teenager and an adult, then we cannot say anything” about a population of people, Ruiz-Lara says. “But if I can distinguish between someone in his 40s or her 50s, you have a better graph of society. With the stars, it’s the same. If we are able to distinguish the age properly, then we can distinguish individual events in the history of the galaxy. In the end, that’s the goal.” More

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    A study of Earth’s crust hints that supernovas aren’t gold mines

    A smattering of plutonium atoms embedded in Earth’s crust are helping to resolve the origins of nature’s heaviest elements.

    Scientists had long suspected that elements such as gold, silver and plutonium are born during supernovas, when stars explode. But typical supernovas can’t explain the quantity of heavy elements in our cosmic neighborhood, a new study suggests. That means other cataclysmic events must have been major contributors, physicist Anton Wallner and colleagues report in the May 14 Science.

    The result bolsters a recent change of heart among astrophysicists. Standard supernovas have fallen out of favor. Instead, researchers think that heavy elements are more likely forged in collisions of two dense, dead stars called neutron stars, or in certain rare types of supernovas, such as those that form from fast-spinning stars (SN: 5/8/19).

    Heavy elements can be produced via a series of reactions in which atomic nuclei swell larger and larger as they rapidly gobble up neutrons. This series of reactions is known as the r-process, where “r” stands for rapid. But, says Wallner, of Australian National University in Canberra, “we do not know for sure where the site for the r-process is.” It’s like having the invite list for a gathering, but not its location, so you know who’s there without knowing where the party’s at.

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    Scientists thought they had their answer after a neutron star collision was caught producing heavy elements in 2017 (SN: 10/16/17). But heavy elements show up in very old stars, which formed too early for neutron stars to have had time to collide. “We know that there has to be something else,” says theoretical astrophysicist Almudena Arcones of the Technical University of Darmstadt, Germany, who was not involved with the new study.

    If an r-process event had recently happened nearby, ­some of the elements created could have landed on Earth, leaving fingerprints in Earth’s crust. Starting with a 410-gram sample of Pacific Ocean crust, Wallner and colleagues used a particle accelerator to separate and count atoms. Within one piece of the sample, the scientists searched for a variety of plutonium called plutonium-244, which is produced by the r-process. Since heavy elements are always produced together in particular proportions in the r-process, plutonium-244 can serve as a proxy for other heavy elements. The team found about 180 plutonium-244 atoms, deposited into the crust within the last 9 million years.

    Scientists analyzed a sample of Earth’s deep-sea crust (shown) to search for atoms of plutonium and iron with cosmic origins.Norikazu Kinoshita

    Researchers compared the plutonium count to atoms that had a known source. Iron-60 is released by supernovas, but it is formed by fusion reactions in the star, not as part of the r-process. In another, smaller piece of the sample, the team detected about 415 atoms of iron-60.

    Plutonium-244 is radioactive, decaying with a half-life of 80.6 million years. And iron-60 has an even shorter half-life of 2.6 million years. So the elements could not have been present when the Earth formed, 4.5 billion years ago. That suggests their source is a relatively recent event. When the iron-60 atoms were counted up according to their depth in the crust, and therefore how long ago they’d been deposited, the scientists saw two peaks at about 2.5 million years ago and at about 6.5 million years ago, suggesting two or more supernovas had occurred in the recent past.

    The scientists can’t say if the plutonium they detected also came from those supernovas. But if it did, the amount of plutonium produced in those supernovas would be too small to explain the abundance of heavy elements in our cosmic vicinity, the researchers calculated. That suggests regular supernovas can’t be the main source of heavy elements, at least nearby.  

    That means other sources for the r-process are still needed, says astrophysicist Anna Frebel of MIT, who was not involved with the research. “The supernovae are just not cutting it.”

    The measurement gives a snapshot of the r-process in our corner of the universe, says astrophysicist Alexander Ji of Carnegie Observatories in Pasadena, Calif. “It’s actually the first detection of something like this, so that’s really, really neat.” More

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    Isotope study hints ancient Greeks used foreign fighters in key battle

    By Krista Charles

    The Temple of Victory at Himera, Sicily, constructed after the first Battle of Himera in 480 BCKatherine Reinberger
    The ancient Greeks relied on help from non-Greek mercenaries when it came to fighting their enemies, suggests an analysis of bodies in 2500-year-old mass graves.
    The western Mediterranean witnessed several conflicts between about 2600 and 2300 years ago as a number of Greek-led city-states – including Syracuse on the island of Sicily – fought against the Carthaginians, whose base of power lay in what is now Tunisia. The Sicilian wars were documented by contemporary writers, including Herodotus in his book The Histories. But given that Herodotus was Greek, it is possible that his accounts of the conflicts may have been biased to paint the Greek fighters in a favourable light.

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    In particular, Herodotus suggests that in 480 BC, during the first Battle of Himera, local soldiers received aid from other Greek allies and successfully defeated the Carthaginians. But during a second battle in 409 BC, the local soldiers went unaided and the city of Himera fell to the Carthaginians.
    Following the recent discovery of eight mass graves associated with the Battles of Himera, it is now possible to explore whether Herodotus’s account was faithful or not.
    Katherine Reinberger at the University of Georgia and her colleagues analysed strontium and oxygen isotopes from the tooth enamel of 62 individuals from the mass graves, which can reveal whether someone was born and raised locally or not.

    The team’s analysis revealed that some historical claims could be validated – there were two battles, about two thirds of the Himeran forces in the first conflict weren’t local while only a quarter in the second battle weren’t from there, and Greek soldiers from outside of the city did fight alongside local Himerans. But the contemporary accounts weren’t entirely accurate: the isotope evidence suggests that many of the non-local soldiers weren’t actually Greek, but came from across the Mediterranean.
    “Finding evidence of people who were foreign and maybe not even Greek is unusual and interesting and sort of indicates that maybe ancient communities, and definitely ancient armies, could have been more diverse than we originally thought,” says Reinberger. These foreign soldiers might have been hired mercenaries, she says.
    “Isotopic studies suggest that these could have been people hired all the way from the Catalan coast, from the Iberian peninsula, or from mainland Greece or even from the Black Sea coast,” says Mario Novak at the Institute for Anthropological Research in Croatia.
    “So, this could have been either Greeks but also some Indigenous people that classical sources considered barbarians. Obviously, these ‘barbarians’ were much more incorporated into the everyday lives of the “proper” Greeks than previously thought,” he says.
    The team theorises that historical accounts downplayed the involvement of foreign mercenaries in order to create a more Greek-centric narrative and align the victory of the first battle with Greek successes against other forces they were facing at the time, including the Persians under Xerxes the Great.
    Journal reference: PLoS One, DOI: 10.1371/journal.pone.0248803
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    Don't Miss: A Nobel prize-winner on thinking green

    Read
    The Spirit of Green is Nobel prize-winning economist William D. Nordhaus’s account of how green thinking can help overcome today’s challenges, from climate change to corporate wrongdoing, without sacrificing prosperity.
    Claudia Marcelloni, CERN
    Visit
    Halo, at Brighton Festival in the UK, is an intricate multisensory installation that lets you experience conditions shortly after the big bang. Created by artist duo Semiconductor, it is driven by data collected at the CERN particle physics lab. From 19 May to 4 June.
    Toni Marinov/Alamy
    Listen
    Princeton University Press Ideas Podcast interviews Lucas Bessire in an episode called “The water crisis on the High Plains”. Bessire talks about his new book, Running Out, and the imminent depletion of a vital aquifer. More

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    Rubber slabs washed up in Brazil traced to second world war shipwreck

    By Karina Shah

    Bales of rubber like this one washed up on Brazilian shores during 2018Carlos Teixeira at Federal University of Ceará
    Unidentified packages that appeared along the Brazilian coast in 2018 have been confirmed as bales of natural rubber coming from a German shipwreck from the second world war.
    Throughout 2018, around 200 square packages washed up along 1600 kilometres of the Brazilian coastline from the states of Maranhão to Sergipe. Each weighed up to 200 kilograms and they ranged in size from 0.06 to 3.4 cubic metres. They caused considerable public concern as people were unsure what they were made … More

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    Cerne Abbas Giant may have been carved into hill over 1000 years ago

    By Michael Marshall

    The Cerne Abbas GiantNational Trust Images/Mike Calnan/James Dobson
    A mysterious chalk carving of a huge, naked man on an English hillside was made in the 10th century, according to the first attempt to archaeologically date the giant. The finding is unexpected because the earliest mentions of the Cerne Abbas Giant are from just over 300 years ago, suggesting it was forgotten for centuries.
    Historians and archaeologists had many ideas about when the giant was constructed, says team member Mike Allen, an independent geoarchaeologist at Allen Environmental Archaeology in Codford, UK. “Everyone was wrong.”

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    The giant is carved into a hillside overlooking the village of Cerne Abbas in southern England. It is a figure of a man with a large, erect penis, holding a club. It was made by digging trenches into the hillside, then filling them with white chalk.
    The earliest known reference to the giant is from 1694, from the records of the church in Cerne Abbas. The giant is absent from earlier records, notably a 1617 survey of the area by John Norden, who was famously thorough.
    Historians have argued for decades over when the giant was created and what it represents. Some believe it was made in the 1600s, in line with the historical records, while others think it dates to Roman times.

    Allen is part of a team that carried out excavations on the giant in 2020, with the support of its owner, the National Trust. The researchers dug in the soles of both its feet and the crooks of its elbows.
    The team looked for grains of quartz in the chalk and in the soil next to the trenches. A method called optically stimulated luminescence dating could then be used to determine when the quartz was last exposed to sunlight.
    Using the technique, the researchers dated the oldest chalk to between AD 650 and 1310. The giant was probably created sometime between these dates, with the year AD 980 falling in the middle of that window. In theory, the giant might be older, because the chalking has been replaced several times. But the soil data suggests not. The oldest date for the soil is AD 700 to 1100. “[The giant] cannot be older than that,” says Allen.
    Intriguingly, a Benedictine monastery was founded in Cerne Abbas in the late 10th century. Allen speculates that the giant might represent a response to that.
    “It would almost seem to be an act of resistance by local people to create this fantastically rude pagan image on the hillside,” says Alison Sheridan, a freelance archaeological consultant based in Edinburgh, UK. “It’s like a big two fingers to the abbey.”
    It isn’t clear why there are no mentions of the giant for centuries. Allen says other findings from the excavation hint there was a time when the site was covered with long grass, suggesting the giant became overgrown and invisible.
    However, Timothy Darvill at Bournemouth University, UK, says prehistoric monuments were often ignored. “Even sites like Stonehenge don’t get that much mention,” he says.
    The giant is one of only three surviving “ancient” hill figures in England. The others are the Long Man at Wilmington and the Uffington White Horse. Only the horse can safely be said to be prehistoric, however.
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    Did you know? Some people can taste music

    By Alexander McNamara
    and Matt Hambly

    Anna Bizon / Alamy
    Forget feeling the music, some of us can actually taste it. Around one in 20 of us have synaesthesia, a condition that creates a strange connection between our senses. For these people, words may take on certain colours and music may have a particular taste or texture.
    Although we aren’t certain of the causes of this unusual condition, studies have given us some idea of what is happening. As infants, our brains’ cells have millions of connections that are pruned away as we get older. Some studies suggest that people with synaesthesia have genetic variations that prevent this pruning from happening normally in certain brain regions, giving them unusual connections between sensory areas.
    Being stronger reduces your risk of death
    Javier Sanchez Mingorance / Alam

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    Here’s the motivation you need for your next trip to the gym: having stronger muscles reduces the risk of dying of any cause, and is especially important in preventing type-2 diabetes, cardiovascular disease and cancer. Broadly speaking, exercise of any kind is good for you, but unlike aerobic fitness regimes, strength training also helps to build bone, which can decrease your risk of osteoporosis. It can even help to prevent cognitive decline and memory loss in old age. Maintaining and improving your strength throughout life has become such an important, yet forgotten, aspect of general fitness that the UK government recently placed it above aerobic exercise in its new guidelines.
    We have 19 different smiles but only one is ‘genuine’
    Superb Images/Getty Images
    The 42 facial muscles it takes to break out into a grin are capable of producing 19 different types of smile, but, according to French anatomist Duchenne de Boulogne, only one is ‘genuine’. In 1862 Duchenne identified that the difference between a genuine smile and a fake one lay in the eyes — the orbicularis oculi — to be precise. All smiling involves contraction of the zygomatic major muscles, which lifts the corners of the mouth. But a Duchenne smile is characterised by the additional contraction of the orbicularis oculi, crumpling the skin around the eyes into crows’ feet. Largely overlooked at the time, the Duchenne smile’s reputation has grown. In the 1950s a study found that Duchenne smilers had a 70 per cent chance of living until age 80 compared with 50 per cent for non-smilers. However, more recent findings have suggested that smiles don’t necessarily indicate that we are happy, but instead signal collaboration or bonding.
    The hydrogen in your body was formed in the Big Bang
    Worldspec/NASA/ Alamy
    You may have heard that we are all stardust, but that isn’t strictly true. There are about 20 different elements in the human body, most of which were made inside ancient stars. There’s oxygen, which makes up about half of your body’s mass but only a quarter of its atoms, and then carbon, accounting for another 12 per cent. And just after that, there’s hydrogen, the only element in your body that wasn’t made inside a star long ago and flung into space by a supernova explosion. The hydrogen atoms in your body, accounting for a little over 10 per cent of you, were formed much earlier during the Big Bang, some 13.8 billion years ago.
    The smallest insect on Earth is a wasp
    The Mymaridae, commonly known as fairyflies or fairy wasps.Scenics & Science / Alamy
    There are more than 110,000 known species of wasp, and while we tend to think of them as the black-and-yellow-striped nuisances, wasps come in a huge variety of shapes and sizes. Only one third of species have stings, for instance, and while some live in colonies, the vast majority of wasp species are solitary. There’s even a wasp that can lay claim to the title of smallest insect on the planet. The Mymaridae or fairy wasp has a body length of just 0.139mm, shorter than that of an amoeba.
    The first space walker became trapped outside his ship
    Over the Black Sea. Museum: Memorial Museum of Cosmonautics, Moscow. Author: Leonov, Alexei Arkhipovich.Album / Alamy
    Alexei Leonov became the first person to walk in space when, on 18 March 1965, he left the Voskhod 3KD spacecraft for 12 minutes. Although he spent such a short time alone in the vacuum of space, the walk was not without incident. Free from the atmospheric pressures of the spacecraft, his space suit ballooned, preventing him from getting back inside the airlock. Leonov had to bleed his suit of air until it was flexible enough for him to get back inside the ship. Despite the rapid decompression resulting in Leonov developing the bends, he made it back inside safely and returned to Earth shortly afterwards.

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    Planet-forming disks around stars may come preloaded with ingredients for life

    The chemistry leading to life may start before stars are even born.

    In the planet-forming disk of gas and dust around a young star, astronomers have detected methanol. The disk is too warm for the methanol to have formed there, so this complex organic molecule probably originated in the interstellar cloud that collapsed to form the star and its disk, researchers report online May 10 in Nature Astronomy. This finding offers evidence that at least some organic matter from interstellar space can seed the disks around newborn stars to provide potential ingredients for life on new planets.

    “That’s pretty exciting, because it means that, in principle, all planets forming around any kind of star could have this material,” says Viviana Guzmán, an astrochemist at the Pontifical Catholic University of Chile in Santiago not involved in the work.

    Complex organic molecules have been observed in interstellar clouds of gas and dust (SN: 3/22/21), as well as in planet-forming disks around young stars (SN: 2/18/08). But astronomers didn’t know whether organic material from interstellar space could survive the formation of a protoplanetary disk, or whether organic chemistry had to start from scratch around new stars.

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    “When you form a star and its disk, it’s not a very easy, breezy process,” says Alice Booth, an astronomer at Leiden University in the Netherlands. Radiation from the new star and shock waves in the imploding material, she says, “could destroy a lot of the molecules that were originally in your initial cloud.”

    Using the ALMA radio telescope array in Chile, Booth and colleagues observed the disk around a bright, young star named HD 100546, about 360 light-years away. There, the team spotted methanol, which is thought to be a building block for life’s molecules, such as amino acids and proteins.

    Methanol could not have originated in the disk, because this molecule forms when hydrogen interacts with carbon monoxide ice, which freezes below temperatures of about –253° Celsius. The disk around HD 100546 is much warmer than that, heated by a star whose surface is roughly 9,700° C — some 4,000 degrees hotter than the sun. So the disk must have inherited its methanol from the interstellar cloud that forged its central star, the researchers conclude.

    “This is the first evidence that the really interesting chemistry we see early on [in star formation] actually survives incorporation into the planet-forming disk,” says Karin Öberg, an astrochemist at Harvard University who was not involved in the work. Astronomers should next search the disks around other young stars for methanol or other organic molecules, she says, to “explore whether this is a one-time, get lucky kind of thing, or whether we can safely assume that planet-forming disks always inherit these kinds of molecules.” More