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  • richardmitnick 9:59 am on November 20, 2020 Permalink | Reply
    Tags: , , , , , Does all the gold in the universe come from stars?, From UCSC "All the Gold in the Unverse"   

    From Astronomy Magazine: “Does all the gold in the universe come from stars?” 

    From Astronomy Magazine

    November 10, 2020
    Raymond Shubinski

    Humanity’s fascination with this precious metal is increased by knowing it comes from the stars.

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    Two neutron stars collide somewhere in the depths of space in this artist’s concept. In addition to generating gravitational waves, such an event can produce many heavy elements, including gold. Credit: Iconic image from Mark Garlick/University of Warwick.

    In a remote galaxy, two neutron stars circled one another in a ballet of ultimate destruction and inevitable creation. Both objects were the remnants of massive stars, probably from a binary system, that had become supernovae long before. Each was incredibly massive, with neutrons so closely packed that their cores became diamond. The dance, alas, could not go on forever and the stars collided, releasing unimaginable energy and sending gravitational waves speeding through the fabric of space-time.

    In 2017, 1.3 billion years later, astronomers detected those waves with the Laser Interferometer Gravitational-wave Observatory.

    MIT /Caltech Advanced aLigo .

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    Albert Einstein’s prediction that the universe should be filled with such faint ripples caused by gravity from massive objects included sources such as neutron star mergers. Yet finding a disturbance in the fabric of space-time from this kind of event had proven elusive until then. When news of the detection of gravitational waves broke, the media wanted to know what else happens when neutron stars collide. Astronomers explained that, beyond the destruction of the stars and the ripples in space, such events also create all the heavy elements we know in the blink of an eye. But what did the media key into? That gold comes from outer space.

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    The mask of the Egyptian pharaoh Tutankhamun is one of the most famous ancient artifacts on Earth. Made mostly of gold decorated with semiprecious stones, it weighs 22.6 pounds (10.23 kg). Credit: Roland Unger/Wikimedia Commons.

    Gold-plated history

    It’s not surprising that of the many elements formed in the cataclysmic destruction of massive stars, gold should be the one that captures our imaginations the most.

    Elements necessary for life, such as carbon, oxygen, potassium, and sulfur, should rank higher on a list of favorites. But we have an emotional connection with gold.

    Thousands of years ago, someone may have seen a shiny object in a stream and picked up a piece of gold. It must have looked intriguing — though, because the metal is so soft, it’s not very useful. Archaeologists have found a 6,500-year-old gold bead in Bulgaria and recovered a nearly 3,000-year-old gold coin from the Black Sea. The oldest known gold artifacts in England were found buried at Stonehenge, part of the grave goods belonging to a mysterious individual from Europe.

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    This gold coin from the First Persian Empire was struck around 420 b.c. It honors King Darius II. Credit: Deflim/Wikimedia Commons.

    The ancient Egyptians had vast gold mines far south of their capital of Thebes, allowing them to encase the mummy of Tutankhamun in the precious metal. Few other ancient civilizations had such wealth. When the mummy was unwrapped, archaeologists found two daggers. One was made of what is now known to be meteoritic iron, and the other was made of pure gold.

    Gold was treasured, though useful only as decoration or for trade, and not much else. But its scarcity made it desirable, and its unchanging nature made it alluring: Unlike silver, which turns black, copper that goes green, or iron that rusts, gold never changes. It seems to be immortal — a gift from the gods.

    It took 20th-century science to unravel this mystery. Iron, silver, and copper rust or turn colors due to reactions with oxygen. Oxygen is always hungry for electrons. Iron will give up two or three electrons to oxygen and will oxidize (rust) as a result. Other elements also fall victim to oxygen. But not gold. It’s the most nonreactive of all metals because it refuses to share electrons with oxygen.

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    The 1933 Saint-Gaudens double eagle is one of the rarest U.S. coins. Most of the more than 445,000 minted were melted into gold bars. Only 13 specimens remain. Credit: National Numismatic Collection, National Museum of American History.

    Elemental facts

    Like all the heavy elements on the periodic table, there just isn’t much gold to be found.

    Periodic Table from
    International Union of Pure and Applied Chemistry 2019

    If all the gold mined in human history were formed into one solid cube, it would measure about 70 feet (21.3 meters) on a side. That would be around 183,000 tons of gold. Sounds like a lot, but if melted, it would fill only three and a half Olympic-size swimming pools. In 2018, Barrick Gold Corporation’s mines in Nevada processed millions of tons of ore to recover just 4 million ounces (125 tons) of gold.

    Because it is so dense and heavy, most of Earth’s gold sank to the core of our planet. Australian geologist Bernard Wood estimates that 99 percent of the world’s gold is buried thousands of miles below our feet. He also estimates that 1.6 quadrillion tons of gold lie within the core. Wood calculates that all this gold, if brought to the surface, would form a layer of the shimmering metal just 16 inches (40.6 centimeters) thick. Compared to Earth’s total size, that’s not much gold. There is actually six times more platinum in our planet’s core, which contains about 1 part per million of gold. Gold is, in fact, quite rare.

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    The original Golden Spike, driven in by Leland Stanford, connected the Union Pacific and Central Pacific railways in 1869 near Ogden, Utah. It is on display at the Cantor Arts Center at Stanford University. Credit: Wjenning/Wikimedia Commons.

    Our golden Sun

    Working one night in 1859, chemists Robert Bunsen and Gustav Kirchhoff saw a fire raging in the town of Mannheim, Germany, about 10 miles (16 km) from their Heidelberg University laboratory. They rolled their newly improved spectroscope (a device they invented that breaks light into its component wavelengths, which allows chemical elements to be identified) to the window and quickly detected the elements barium and strontium within the bright glow given off by the flames. Bunsen wrote that the “same mode of analysis must be applicable to the atmospheres of the Sun and the bright stars.” The second half of the 19th century saw an explosion of discoveries using this powerful tool.

    During the total solar eclipse on August 18, 1868, several astronomers using spectroscopy detected a new element — and, it turned out, the universe’s second most abundant one — in the Sun: helium. Carbon, nitrogen, iron, and all the heavier elements of the periodic table — including gold — were eventually identified in a gaseous state in the Sun’s atmosphere.

    In the late 18th and early 19th centuries, rock and mineral collecting became the science of geology. Men and women such as Charles Lyell, James Hutton, and the great fossil collector Mary Anning, discoverer of the first Ichthyosaurus skeleton, clearly demonstrated that Earth was far older than the 6,000 years suggested by many contemporary theologians. Lyell and Hutton said Earth must be millions or even billions of years old. If this was true, what could keep the Sun and stars shining for such an incredibly long time?

    German physicist Julius Robert Mayer strongly favored the meteoric theory of solar heat. He had calculated that, lacking an external source of energy, the Sun could shine for only 5,000 years. In 1848, he suggested the Sun was fueled by billions of meteorites raining down on it, which provided its energy. This material also, supposedly, would have brought heavy elements to our star.

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    During the total solar eclipse July 29, 1878, Cleveland Abbe, America’s first U.S. Weather Bureau meteorologist, suggested that the solar corona was a swarm of meteorites that provided the energy for the Sun to shine. Credit: Michael E. Bakich library.

    During the 1878 total solar eclipse, Cleveland Abbe, America’s first U.S. Weather Bureau meteorologist, suggested that the Sun’s corona, visible at totality, was in fact this swarm of meteors plunging into the Sun. But scientists soon proved that the corona was made of ultra-thin gas and demonstrated that meteors would be an insufficient source of solar energy.

    Eventually, scientists calculated that the Sun contains almost 2.5 trillion tons of gold, enough to fill Earth’s oceans and more. Still, that’s just eight atoms of gold for every trillion atoms of hydrogen — a tiny amount when compared to the mass of the Sun. But how did gold come to be in the Sun and Earth?

    Science is golden

    For more than a millennium, alchemists struggled to transmute one element into another. They were in search of the philosopher’s stone, which could turn base metals like lead and mercury into gold. Even the great Isaac Newton was fascinated by the idea of transmutation. Indeed, some historians refer to him as “the last great alchemist.” But the tremendous forces of nature that create the elements were beyond the grasp of these early experimenters.

    The origins of heavy elements started to come into focus with the publication of Einstein’s special theory of relativity in 1905. It was in this seminal work that the equation E=mc2 first appeared. It wasn’t obvious at first just how important this equation was to our understanding of the universe, but its application to the problem of the Sun’s immense energy output would have far-reaching implications. Not only did it explain why the Sun and other stars could shine for billions of years, but it also helped show how elements heavier than hydrogen form.

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    The spectrum of gold shows the element’s unique fingerprints, which are used to identify its presence. Credit: MCZUSATZ/WIKIMEDIA COMMONS.

    Most of us think of the first atomic bomb and splitting atoms — the process of nuclear fission — when E=mc2 comes to mind. In 1920, however, Sir Arthur Eddington, then at Cavendish Laboratory in Cambridge, England, thought that the fusing of hydrogen into helium could be the powerhouse of the Sun. Einstein’s famous equation showed that incredible energy would be released in such a process.

    Almost two decades after Eddington and others began to explore fusion, German-American physicist Hans Bethe described the now famous proton-proton chain reaction that explains how hydrogen fuses into helium. Deep within the Sun is a vast “soup” of hydrogen atoms consisting of one proton and one electron each, which are in constant, rapid motion. Most of the time, the electromagnetic force repels any collisions. Trying to stick similar poles of two magnets together gives a feel for such repulsion. But collisions happen, and protons fuse together. When four protons eventually fuse, helium–4 forms, releasing energy and making the Sun shine.

    Our Sun contains enough hydrogen to continue this fusion process for another 5 billion years. Eventually, helium will begin to fuse, forming the final products of carbon, nitrogen, and oxygen (element No. 8). Within more massive stars, whose stronger gravity creates more pressure and heat, elements beyond oxygen can fuse. But this process can continue only until iron (element No. 26) forms at the center of giant stars, and that’s when fusion shuts down. Finally, the star’s core will collapse and then rebound in a supernova explosion.

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    The proton-proton cycle is the chain reaction by which hydrogen fuses into helium in the Sun’s core. The tiny bits of mass that are converted to energy satisfy Albert Einstein’s famous equation, E=mc2. Credit: ASTRONOMY: ROEN KELLY.

    As the outer layers of the star are blasted into space, one of two neutron capture reactions takes place. In both, free neutrons penetrate the nuclei of nearby atoms and are “captured” by elements released in the explosion. Slow neutron capture (called “slow” because radioactive decay into other elements can occur before other neutrons are captured) creates about half of the elements heavier than iron. But that still leaves a lot of heavyweights on the periodic table. To make the rest, you need massive colliding stars that produce rapid neutron capture.

    Once astronomers had pinpointed the source of the 2017 gravitational waves, researchers at the Max Planck Institute for Astronomy were able to detect strontium in the maelstrom of matter expanding into space at nearly 30 percent the speed of light. This element and others were formed by the rapid neutron capture reaction. The merger of these stars sent 1022 free neutrons flying through just 1 cubic centimeter of space every second.

    Such a high density of neutrons creates conditions that allow existing elements to quickly capture free neutrons. Strontium, thorium, uranium, and even gold form in a literal flash. And off they go into the depths of space. During the nearly 14-billion-year life span of our universe, this has happened enough times to seed the nebulae that eventually collapse to form solar systems such as ours with gold — and all the other heavy elements, too.

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    This illustration shows the spectroscope that Joseph Norman Lockyer used to discover helium in the Sun’s atmosphere in 1868.
    Credit: WELLCOME IMAGES.

    Gold standard

    Gold pervades our lives. The element is in every cellphone and computer. We coat sunglasses and astronaut visors with it. Gold thread is used in electronics and in clothing. Nations pay their debts with gold. We make precious objects out of it, from jewelry to religious artifacts. We put gold in our teeth and even make toilets with it. Doctors inject patients with gold to help relieve rheumatoid arthritis. You can even eat chocolate covered in gold.

    Carl Sagan famously said we are made from the stuff of stars. So is the world around us. The next time you glance at the gold ring on your finger or feel the gold chain around your neck, remember that they are indeed a gift from the stars.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Astronomy is a magazine about the science and hobby of astronomy. Based near Milwaukee in Waukesha, Wisconsin, it is produced by Kalmbach Publishing. Astronomy’s readers include those interested in astronomy and those who want to know about sky events, observing techniques, astrophotography, and amateur astronomy in general.

    Astronomy was founded in 1973 by Stephen A. Walther, a graduate of the University of Wisconsin–Stevens Point and amateur astronomer. The first issue, August 1973, consisted of 48 pages with five feature articles and information about what to see in the sky that month. Issues contained astrophotos and illustrations created by astronomical artists. Walther had worked part time as a planetarium lecturer at the University of Wisconsin–Milwaukee and developed an interest in photographing constellations at an early age. Although even in childhood he was interested to obsession in Astronomy, he did so poorly in mathematics that his mother despaired that he would ever be able to earn a living. However he graduated in Journalism from the University of Wisconsin Stevens Point, and as a senior class project he created a business plan for a magazine for amateur astronomers. With the help of his brother David, he was able to bring the magazine to fruition. He died in 1977.

     
  • richardmitnick 9:45 am on July 6, 2019 Permalink | Reply
    Tags: , , , , , From UCSC "All the Gold in the Unverse", , Neutron star collisions   

    From COSMOS Magazine: “We are stardust. And Big Bang dust.” 

    Cosmos Magazine bloc

    From COSMOS Magazine

    06 July 2019
    Katie Mack

    Neutron star collisions appear to be essential to our chemical origin story.

    1
    Artist’s now iconic conception shows two merging black holes similar to those detected by LIGO in 2017.
    LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)

    When, in 2017, the LIGO experiment detected gravitational waves from two neutron stars colliding, it sent electromagnetic and gravitational ripples through the universe and the astronomical community.

    This remarkable event, hotly anticipated but never before seen in this way, did more than give us a few new data points about the deaths of stars – it fundamentally changed our understanding of where we and our constituent atoms come from.

    You may have heard before that “we are stardust”. This isn’t wrong. But it’s not the whole story, either.

    A star is, fundamentally, an alchemy machine. It starts as a giant ball of mostly hydrogen gas, slowly crushing its central regions with the pressure of its own gravity. The core of a star eventually gets so hot and dense that it becomes a nuclear reactor, fusing hydrogen into helium.

    In the core of our own sun, this process is converting hundreds of millions of tons of hydrogen into helium every second; what we receive as sunlight is essentially just the waste heat from the reaction.

    This is how the vast majority of stars spend their lives: steadily burning themselves up, turning hydrogen into helium for billions of years. In their final death throes, as they become red giants ready to expel their outer layers, the fusion flares up in bursts, making lithium, carbon and nitrogen, and a smattering of heavier elements.

    To fill in the rest of the periodic table, though, we need stars much more massive than our own. A star more than about eight times as massive as the sun contains at its centre a nuclear furnace that’s burning unimaginably hot.

    After it tears through its supply of hydrogen in the core, it climbs up the list of elements, burning helium, carbon, neon, oxygen and silicon, until after only a few million years the centre of the star is iron and the fusion radiation that had been puffing the star up finally runs out.

    At that point, nothing can stop the star from collapsing on itself, resulting in a spectacular supernova explosion. In the end, at the centre of the debris field will be either a super-dense neutron star or a black hole.

    It’s this final explosion itself, rather than the interior burning, that creates the star’s ultimate chemical legacy. For a brief moment, a shock wave explodes through the layers of the star, creating heat and pressure so intense that a blast front of nuclear fusion carries a radioactive shell of new elements out into interstellar space.

    The universe is seeded with stardust, ready to coalesce into new stars, new planets, new life. For years, it was thought that these stellar deaths were the main mechanisms by which the universe was enriched with metals and other heavy elements.

    But evidence has been mounting that for heavy metals like gold, platinum and uranium, the supernova is just the beginning. It’s the tiny, dense, neutron star that carries within it the potential to explode across the rest of the periodic table.

    Which brings us back to the LIGO detection. When the signal was first seen, astronomers around the world trained their telescopes on the same part of the sky. The resulting observations showed a clear sign in the brief flash that the stars had created enough gold to outweigh the Earth several times over.

    2

    https://reports.news.ucsc.edu/neutron-star-merger/
    Please access this huge project on the 2017 find
    Credits

    Writing:
    Tim Stephens
    Video:
    Nick Gonzales
    Photos:
    Carolyn Lagattuta
    Header image:
    Illustration by Robin Dienel courtesy of the Carnegie Institution for Science
    Design and development:
    Rob Knight
    Project managers:
    Sherry Main, Scott Hernandez-Jason, Tim Stephens

    Neutron star collisions appear to be essential to our chemical origin story. We are born of unimaginable violence in the stellar generations that came before our own. But there’s more to the story.

    Most of the atoms in our bodies didn’t come from stars at all. They are, in fact, much more ancient. If you count up all the atoms in your body, more than 60% will be hydrogen, and the majority of the hydrogen in the universe has never been in a star at all.

    Hydrogen, or, specifically, the protons that would later join with electrons to make neutral hydrogen atoms, was created in the primordial fire of the Big Bang itself.

    In the first moments of the universe, every part of space was filled with a kind of prenuclear plasma hotter and denser than the centre of even the most massive star.

    As this fire expanded and cooled, protons and neutrons, the building blocks of atomic nuclei, first came into being.

    Hydrogen appeared in the form of solitary protons, along with small amounts of helium and lithium. These nuclei have persisted for the 13.8 billion years since those first moments, coming together in stars and, eventually, us.

    So, yes, you are stardust. But you are also the ashes of the Big Bang: ancient atomic alchemy brought together by the inexorable flow of gravity and time.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

     
  • richardmitnick 1:27 pm on October 17, 2018 Permalink | Reply
    Tags: , , , , , from Euclid to LIGO, From UCSC "All the Gold in the Unverse", , The Australian International Gravitational Research Centre   

    From The Australian International Gravitational Research Centre via COSMOS: “A short [?] history of spacetime from Euclid to LIGO” 

    From The Australian International Gravitational Research Centre

    via

    COSMOS

    17 October 2018
    David Blair

    A year ago today, the world learned that a huge team of scientists around the world had confirmed the existence of gravitational waves, the long history of discovery that led to breakthrough.

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    The discovery of gravitational waves marked an important step on a never-ending journey of discovery regarding the nature of the universe.
    sakkmesterke/Getty Images

    In 2015 we first heard the whooping sound made by a pair of colliding black holes. Two years later it was the unique chirp made by a pair of colliding neutron stars. Our newfound ability to eavesdrop on cataclysmic events at the far reaches of the universe is thanks to a new generation of gravitational wave detectors. The gravitational sound show is just beginning, and it promises to reveal the nature of spacetime as never before.

    The quest to understand space

    What is space? We know thinkers have pondered that question at least for as long as there are recorded texts. The clay tablets left by Ancient Babylonians show they were toying with the nature of triangles.

    But, 2300 years ago, the Greek mathematician Euclid revolutionised the science of geometry with systematic thinking that captured the descriptive work of the past and elevated it to the level of universal truths or axioms.

    His 13-volume treatise Elements uncovered the perfection of lines and shapes and put it all together in the most influential science book of all time, in print for 2000 years and published in 1000 editions. It is still taught in schools today.

    But are Euclid’s axioms truly universal?

    In the early 1800s, German mathematician and physicist Carl Gauss was the first to challenge Euclid’s laws of geometry, especially his fifth axiom, which states that parallel lines can never meet.

    Gauss observed that on curved surfaces, parallel lines – such as longitude lines at the earth’s equator – intersect at the poles. He also realised that space could have shape, and his Egregium Theorem showed that you could measure its shape if you measured distances and angles.

    Imagine you’re an ant living on a balloon; your world would seem flat. But an ant familiar with the Egregium Theorem would stretch strings and draw triangles. If the angles of the triangle added up to more than 180 degrees, the ant would know it’s living on curved space.

    Egregium, by the way, is Latin for “exceptional”.

    Gauss’ determination to put Euclid’s theorems to the test set the scene for Einstein.

    By 1905, he had already come up with his theory of Special Relativity. This was the theory that gave us E=Mc2, which means that energy has mass and mass has energy.

    In 1907 Einstein had another revelation that he later described as “the happiest thought of my life”. He realised that gravity is indistinguishable from acceleration. If you’re riding an elevator with your bathroom scales, you’ll find you’re lighter as the elevator accelerates down and heavier when it decelerates. So, Einstein realised, gravity is the force you feel when you prevent free fall.

    It took eight more years and help from his friends for him to combine this happy thought with Gauss’s thinking about the shape of space, to create his final theory of gravity: General Relativity. Published in 1915, it was based on the revolutionary idea that mass and energy deform space and time, and that deformed spacetime itself has energy. In a certain sense spacetime is an elastic material: immensely stiff but deformable – like a trampoline.

    Einstein’s publication gave rise to a succession of remarkable discoveries.

    Within months, while serving in the German army, physicist and astronomer Karl Schwarzschild solved Einstein’s equations to reveal how the curvature of space and the warping of time depends on distance from a central mass. The closer the distance and the larger the mass, the more warping there is, and at a certain distance from a central point mass space and time actually come to an end.

    He was of course imagining a ‘black hole’, but it would take 50 years before the term was coined.

    A few months later, in 1916, Einstein found a solution to his own equations. It predicted the existence of gravitational waves, ripples in spacetime that would travel at the speed of light.

    And in the following years, discoveries provided support for the notion that space was a deformable elastic medium – one that could propagate gravitational waves.

    In 1919, English physicist Sir Arthur Eddington’s observation of an eclipse from the island of Principe near West Africa proved that space is curved by the Sun. In 1922 Russian scientist Alexander Friedmann showed that Einstein’s equations predicted a dynamic universe in which space itself must either expand or contract. And in 1929 American astronomer Edwin Hubble discovered that the universe was in fact expanding.

    When Einstein predicted gravitational waves in 1916 he realised that they could be generated by pair of stars circling each other. He came up with a formula that describes how gravitational wave power depends on their masses, the speeds and the spacing – all measurable numbers.

    But there was a catch: in his formula, the wave power was divided by an enormous number, a crazy number, that I call Einstein’s number. Algebraically, Einstein’s number is c5/G – the speed of light multiplied by itself five times, divided by G, the tiny number that tells us the weakness of gravity.

    Put together, c5/G is more than 1054. If you divide anything by a number this vast, you get next to nothing. Einstein realised this. Nothing he could conceive of could possibly produce measurable gravitational waves. The waves were of academic interest only, he concluded.

    What Einstein hadn’t been aware of was that Schwarzschild, who died of an auto-immune disease in 1916, had left him a hidden treasure. The trouble was that Schwarzschild’s solution, which described a singularity where space and time cease to exist, was viewed by Einstein and others as a mathematical oddity, not a description of anything that could possibly be real.

    But 50 years on, black holes – as these singularities were later dubbed – were the best hypothesis to explain a strange x-ray emitting star called Cygnus X-1.

    A tiny object with vast gravity was needed to explain this powerful erratic x-ray emission. People began to think that black holes might be real.

    Then someone took Einstein’s 1916 equation for wave power, and substituted in Schwarzschild’s black hole formula. A school kid could have done it. The result was miraculous!

    With Schwarzschild’s formula, the division by Einstein’s number that made gravitational waves merely academic is transformed into a multiplication by the same number. Suddenly the wave power for a pair of black holes circling each other up-close becomes almost as big as Einstein’s number itself.

    This is roughly the power of all the stars in the visible universe! The catch is it lasts for only an instant. This was Schwarzschild’s hidden treasure.

    Schwarzschild’s work tells us that when black holes collide they create a pure gravitational explosion, more powerful than a supernova or a gamma ray burst. Nothing beats it except the Big Bang itself.

    However, as an explosion of rippling space, it would pass freely through you. Even if it happened as nearby to Earth as the Sun, you would feel no more than a tiniest shudder. Yet each such gravitational explosion would in principle be detectable across the entire universe.

    Harnessing inertia to build a gravitational wave detector

    I was inspired to join the quest to detect colliding black holes by the eccentric pioneer of gravitational wave astronomy, American physicist Joseph Weber. Back then, we reasoned that explosions so vast must be detectable. We thought that if we worked hard at inventing a gravitational detector, we might pick up a signal by Christmas! That was in 1973.

    Our ability to detect gravitational waves relies on the concept of inertia – the tendency of matter to continue in its state of motion unless acted on by an external force.

    Scientists have been relying on inertia to detect relative motion for nearly 2000 years. In 132 AD, Chinese scientist Zhang Heng harnessed inertia to build the first seismometer.

    Inside a big bronze urn he suspended a mass so that it could swing freely in the horizontal plane. If the ground moved, so would the urn, but the mass, anchored to space by the law of inertia, would stay in place.

    Inside, the movement dislodged a ball from the mouth of one of eight dragons that marked the cardinal directions. The ball rolled out and was caught in the mouth of a bronze toad. This way he detected an earthquake hundreds of kilometres away.

    Heng’s seismometer allowed him to detect the motion of the earth against unchanging space. But what if space suddenly stretches? You won’t feel a thing, and nor will a seismometer, just as you do not feel the universe expanding. But, you might notice that a distant object has just moved away from you. It did this because inertia caused it to follow expanding space.

    Modern day gravitational wave detectors like the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US detect the stretching and shrinking of space caused by a passing wave by suspending two 40 kilogram masses four kilometres apart.

    These masses are coated with near-perfect mirrors, so changes in the distance between them can be measured by using a beam of laser light as a ruler. The catch is the minuscule size of the change. Like ripples in a pond, gravitational waves diminish as they expand away from the source.

    Even though LIGO was aiming to measure the space distortion created by colliding black holes – the biggest dynamic distortion possible – the ripples they create reduce to half every time you double the distance.

    By the time the wave reaches the Earth from a black hole collision a billion light years away, the stretching and shrinking of space in a LIGO detector has reduced to a hundredth of a billionth of a billionth of a metre – much smaller than the size of a proton.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    A dream fulfilled

    It took more than 40 years and several generations of detectors, before, finally, the pair of advanced LIGO detectors were ready to begin listening for the sounds of gravitational waves. The new detectors were three times more sensitive than previous ones, but still three times below their ultimate design specification. We were hopeful but not optimistic.

    On September 14, 2015, a few days before the official start date, the first signal came in. Was it a hoax? Was it accidental? A short rapidly rising pitch, from two octaves below to middle-C made a brief whoop sound. It was heard in two detectors 3000 kilometres apart and had a time delay just right for a wave travelling at the speed of light. After months of investigation there was no doubt that it was real.

    All our dreams were finally fulfilled on February 11, 2016, when gravitational wave astronomers announced in a Washington press conference, that they had indeed detected a pair of black holes spiralling together and merging into a single black hole.

    And since that first detection, more whoops from other colliding black holes have followed.

    You might think that detecting the collision of a pair black holes would be a hard act to follow. Yet a year and a half after that announcement, the world was again thrilling to the news of another type of cosmic cataclysm.

    We had not been optimistic about detecting colliding black holes because we had very little idea how many pairs of black holes might exist. Instead we had placed our hopes on something we knew much more about: neutron stars.

    Neutron stars are one step away from becoming a black hole. Many exist as pulsars: rapidly spinning remnants of supernova explosions that emit powerful flickering beams of radio waves. They have a dimeter of about 20 kilometres, are composed of neutrons, and are denser than an atomic nucleus.

    Thousands of them are known in the Milky Way, and the predictions were that out in the distant universe we might be able to detect one or two of them merging every year.

    Little did we know that we were already detecting those events.

    During the 1980s astronomers were puzzling over vast bursts of gamma rays being detected by orbiting gamma ray telescopes, on average one every day.

    In 1989 a paper published in Nature by Hebrew University physicist Tsvi Piran proposed these bursts were created by merging neutron stars, spiralling together at 10% of light speed, and flinging some of their nearly pure neutron matter out into space. Here it would go off like an enormous nuclear fission bomb, giving off bursts of gamma rays. The process would also be a forge for heavy elements in the universe like platinum and gold.

    Since the advanced LIGO detectors started working in 2015, our 1000-strong team comprising researchers based at more than 80 universities around the world were hoping for all of this: a long slow chirp of gravitational waves as a pair of neutron stars spiralled together, a burst of gamma rays produced when they collided, and an atomic explosion where we might see the signature of gold production.

    Most of us thought the chances of all of this was very small. The gamma ray beam might miss the earth. The explosion, called a macronova or kilonova, is much weaker than a supernova and would be hard to detect.

    However, more than 100 telescopes around the world had already signed up to receive alerts from the LIGO detectors on either side of the US, and the European Virgo detector in Pisa, Italy, in the event of a gravitational wave signal.

    On August 17, 2017, all of our Christmases came at once.

    It was exactly what we had dreamed of. The gravitational wave signal was loud and clear in the two LIGO detectors in the US, but very weak in the European Virgo detector because of its orientation.

    The non-detection by Virgo told us roughly where to look in the sky. The Fermi gamma ray observatory out in space detected a burst of gamma rays 1.7 seconds later, coming from the same region of sky. A few hours later the Swope telescope in Chile detected the fading glow of a vast explosion, in that same region, at the edge of a known galaxy, 130 million light years away.

    Before long 100 telescopes across the southern hemisphere were watching it. The colours in the light indicated the presence of heavy elements like gold and platinum.

    The future

    We called this the birth of multi-messenger astronomy: the gravity wave messenger and the electromagnetic messenger worked in unison. This discovery was a stupendous example of scientific prediction. It confirmed Einstein’s 102 year-old prediction that gravity waves travel at the speed of light, and Piran’s 28 year-old prediction that gamma ray bursts were the signature of colliding neutron stars, and that gold and platinum were formed in this explosion.

    Think about this: that gold on your finger is a fossil from the collision of two neutron stars.

    From these recent discoveries we can predict what lies ahead. As sensitivity improves, we’ll exponentially increase our reach into the universe. Increase the sensitivity by two and you’re reaching into a volume 23 times larger, which means eight times as many signals.

    In the next few years the world’s existing three detectors, plus two more under construction in Japan and India, should be tuning in to the sounds of hundreds of black hole and neutron stars collisions every year.

    More detectors will help to pinpoint the source of the signals, but the biggest pay-off comes from increasing sensitivity. Just a four-fold increase in sensitivity would expand our horizon to more than half of the visible universe. A 10-fold improvement would give us the whole universe! Detectors with this capability have been suggested for Australia, China, Europe and the USA.

    The legacy of Einstein, the recent Nobel Prize winners and the huge international LIGO and Virgo team, will be the ability to listen to the symphony of the universe. It will be in a minor key because the truth is that our universe is winding down as black holes form, grow and gobble up each other.

    But I can’t end on a melancholy note. Rather I want to sing in celebration of gravitational waves as humanity’s new set of ears. We are no longer deaf to the sounds of space. And we can be pretty certain that our cosmic ears will give us deeper understanding of the nature of space.

    We are still groping to understand its microstructure and its reason for being. Is it a quantum foam inhabited by strings, or is it something else?

    Stay tuned for surprises, unforeseen revelations, and an avalanche of discoveries as our remarkable new technology develops.

    An extra treat https://sciencesprings.wordpress.com/2017/10/20/from-ucsc-neutron-stars-gravitational-waves-and-all-the-gold-in-the-universe/

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Australian International Gravitational Observatory (AIGO) Located at Gingin

    Welcome to the Australian International Gravitational Research Centre. The Australian International Gravitational Research Centre is based in the School of physics of the University of Western Australia (UWA) and is part of the Australian Consortium for Interferometric Gravitational Astronomy (ACIGA). It was established in 1990 to enable a cooperative research centre providing a national focus in a major frontier in physics: the detection of gravitational waves and the development of gravitational astronomy. Through strong national and international participation, the research centre concentrates on the development of advanced technologies driven by the goal of the next generation large scale gravitational observatory construction.

     
  • richardmitnick 6:19 am on August 24, 2018 Permalink | Reply
    Tags: , , From UCSC "All the Gold in the Unverse", , ,   

    From The Conversation: “We’re going to get a better detector: time for upgrades in the search for gravitational waves” 

    Conversation
    From The Conversation

    August 16, 2018
    Robert Ward

    It’s been a year since ripples in space-time from a colliding pair of dead stars tickled the gravitational wave detectors of the Advanced LIGO and Advanced Virgo facilities.


    Soon after, astronomers around the world began a campaign to observe the afterglow of the collision of a binary neutron star merger in radio waves, microwaves, visible light, x-rays and more.

    See https://sciencesprings.wordpress.com/2017/10/16/from-ucsc-a-uc-santa-cruz-special-report-neutron-stars-gravitational-waves-and-all-the-gold-in-the-universe/

    This was the dawn of multi-messenger astronomy: a new era in astronomy, where events in the universe are observed with more than just a single type of radiation. In this case, the messengers were gravitational waves and electromagnetic radiation.

    What we’ve learned (so far)

    From this single event, we learned an incredible amount. Last October, on the day the detection was made public, 84 scientific papers were published (or the preprints made available).

    We learned that gravity and light travel at the same speed, neutron star mergers are a source of short gamma-ray bursts, and that kilonovae – the explosion from a neutron star merger – are where our gold comes from.

    This rich science came from the fact that we were able to combine our observatories to witness this single event from multiple astronomical “windows”. The gravitational waves arrived first, followed 1.7 seconds later by gamma-rays. That is a pretty small delay, considering the waves had been travelling for 130 million years.

    Over the next few weeks, visible light and radio waves began to be observed and then slowly faded.

    It seemed like the news about gravitational waves was coming fast and furious, with the first detection announced in 2016, a Nobel prize in 2017, and the announcement of the binary neutron star merger just weeks after the Nobel prize.

    Time for upgrades

    On this first anniversary of the neutron star merger, the gravitational wave detectors are offline for upgrades. They actually went offline shortly after the detection and will come back online some time early in 2019.

    The work of making gravitational wave detectors function requires extraordinary patience and dedication. These are exquisite experiments – it took more than 40 years of technological development by a community of more than a thousand scientists to get to the point of detecting the first signal.

    Naturally, improving on this work is not easy. So what does it actually take?

    We really do listen to gravitational waves, and our detectors act more like microphones than telescopes or cameras.

    Quiet please!

    To detect gravitational waves, we need to do more than just turn off the dishwasher. We need to build the quietest, best-isolated thing on Earth.

    Unfortunately, the laws of quantum mechanics and thermodynamics both prevent us from eliminating the noise entirely. Nonetheless, we strive to do the best that these fundamental limits permit. This involves, among many other extraordinary things, hanging our mirrors on glass threads .

    2
    Before sealing up the chamber and pumping the vacuum system down, a LIGO optics technician inspects one of LIGO’s core optics (mirrors) by illuminating its surface with light at a glancing angle. Matt Heintze/Caltech/MIT/LIGO Lab

    Our mirrors weight 40kg each and are suspended from four of these glass threads, which are less than a half-millimetre in diameter and exquisitely crafted.

    The threads are under enormous stress, and the slightest imperfection (or the slightest touch) can cause them to explode.

    Just such an explosion happened earlier this year while installing a new mirror. Fortunately, the precious mirror fell into a cradle designed for just such a possibility, and was not damaged.

    Nonetheless, the delicate, intricate work of creating the glass threads, attaching them to the mirror, hanging the mirror and then installing it all needed to be redone.

    Improvements to the detector

    This was a heartbreaking setback for the team, but the added delay was not entirely in vain. In parallel with remaking the glass threads and rehanging the new mirror, we made some other improvements to the detector, for which we otherwise would not have had enough time.

    One of the goals of this upgrade period is to install something called a quantum squeezed light source into the gravitational wave detectors.

    As mentioned earlier, quantum mechanics mandates a certain minimum amount of noise in any measurement. We can’t arbitrarily reduce this quantum noise, but we can move it around and change its shape by squeezing it.

    This is a bit like sweeping dust under the rug. It’s not really gone, but it might not bother you so much anymore. The quantum squeezed light source does just this.

    3
    Australian National University scientists Nutsinee Kijbunchoo and Terry McCrae build components for a quantum squeezed light source at LIGO Hanford Observatory in Washington, US. Nutsinee Kijbunchoo

    A gravitational wave detector is already a very complex system, and a squeezed light source is another complex system, so putting them together can be a challenge.

    Despite the complexity of this challenge, when the squeezed light source was activated for the first time at the LIGO detector in Livingston, Louisiana, US, in February this year there was an immediate improvement in the quantum noise: the gravitational wave detector output got just a bit quieter.

    ESA/NASA eLISA space based, the future of gravitational wave research

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Conversation US launched as a pilot project in October 2014. It is an independent source of news and views from the academic and research community, delivered direct to the public.
    Our team of professional editors work with university and research institute experts to unlock their knowledge for use by the wider public.
    Access to independent, high quality, authenticated, explanatory journalism underpins a functioning democracy. Our aim is to promote better understanding of current affairs and complex issues. And hopefully allow for a better quality of public discourse and conversation.

     
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