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  • richardmitnick 12:33 pm on September 22, 2016 Permalink | Reply
    Tags: , Cosmology, Cosmology is safe, , Scientists confirm the universe has no direction,   

    From ICL: “Scientists confirm the universe has no direction” 

    Imperial College London
    Imperial College London

    22 September 2016
    Hayley Dunning

    The universe is not spinning or stretched in any particular direction, according to the most stringent test yet.

    Looking out into the night sky, we see a clumpy universe: planets orbit stars in solar systems and stars are grouped into galaxies, which in turn form enormous galaxy clusters. But cosmologists assume this effect is only local: that if we look on sufficiently large scales, the universe is actually uniform.

    The vast majority of calculations made about our universe start with this assumption: that the universe is broadly the same, whatever your position and in whichever direction you look.

    If, however, the universe was stretching preferentially in one direction, or spinning about an axis in a similar way to the Earth rotating, this fundamental assumption, and all the calculations that hinge on it, would be wrong.

    Now, scientists from University College London and Imperial College London have put this assumption through its most stringent test yet and found only a 1 in 121,000 chance that the universe is not the same in all directions.

    Oldest light in the universe

    To do this, they used maps of the cosmic microwave background (CMB) radiation: the oldest light in the universe created shortly after the Big Bang.

    CMB per ESA/Planck
    CMB per ESA/Planck

    The maps were produced using measurements of the CMB taken between 2009 and 2013 by the European Space Agency’s Planck satellite, providing a picture of the intensity and, for the first time, polarisation (in essence, the orientation) of the CMB across the whole sky.

    Previously, scientists had looked for patterns in the CMB map that might hint at a rotating universe. The new study considered the widest possible range of universes with preferred directions or spins and determined what patterns these would create in the CMB.

    A universe spinning about an axis, for example, would create spiral patterns, whereas a universe expanding at different speeds along different axes would create elongated hot and cold spots.

    Four potential CMB patterns for universes with direction. No image credit.

    Dr Stephen Feeney, from the Department of Physics at Imperial, worked with a team led by Daniela Saadeh at University College London to search for these patterns in the observed CMB. The results, published today in the journal Physical Review Letters, show that none were a match, and that the universe is most likely directionless.

    Cosmology is safe

    Dr Feeney said: “This work is important because it tests one of the fundamental assumptions on which almost all cosmological calculations are based: that the universe is the same in every direction. If this assumption is wrong, and our universe spins or stretches in one direction more than another, we’d have to rethink our basic picture of the universe.

    “We have put this assumption to its most exacting examination yet, testing for a huge variety of spinning and stretching universes that have never been considered before. When we compare these predictions to the Planck satellite’s latest measurements, we find overwhelming evidence that the universe is the same in all directions.”

    Lead author Daniela Saadeh from University College London added: “You can never rule it out completely, but we now calculate the odds that the universe prefers one direction over another at just 1 in 121,000. We’re very glad that our work vindicates what most cosmologists assume. For now, cosmology is safe.”

    The work was kindly supported by the Perren Fund, IMPACT fund, Royal Astronomical Society, Science and Technology Facilities Council, Royal Society, European Research Council, and Engineering and Physical Sciences Research Council.

    See the full article here .

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    Imperial College London

    Imperial College London is a science-based university with an international reputation for excellence in teaching and research. Consistently rated amongst the world’s best universities, Imperial is committed to developing the next generation of researchers, scientists and academics through collaboration across disciplines. Located in the heart of London, Imperial is a multidisciplinary space for education, research, translation and commercialisation, harnessing science and innovation to tackle global challenges.

  • richardmitnick 4:04 pm on September 19, 2016 Permalink | Reply
    Tags: 2017 ESO Calendar, , , , Cosmology   

    ESO: The 2017 Calendar is now available at the ESOshop 

    ESO 50 Large

    European Southern Observatory

    The 2017 ESO Calendar is now available from the ESOshop.

    Price € 9.99

    This is a stunning calendar. There are images from La Silla, ALMA and Paranal and many images from ESO’s amazing astronomical projects.

    You might even buy some for gifts to your friends in Astronomy.

    Please help promote STEM in your local schools.
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    Visit ESO in Social Media-




    ESO Bloc Icon

    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

    ESO LaSilla


    ESO Vista Telescope


    ESO VLT Survey telescope
    VLT Survey Telescope

    ALMA Array


    Atacama Pathfinder Experiment (APEX) Telescope

  • richardmitnick 7:36 am on September 16, 2016 Permalink | Reply
    Tags: , , Cosmology, , How Certain Are We Of The Universe's 'Big Freeze' Fate?   

    From Ethan Siegel: “How Certain Are We Of The Universe’s ‘Big Freeze’ Fate?” 

    From Ethan Siegel

    Sep 15, 2016

    The four possible fates of the Universe with only matter, radiation, curvature and a cosmological constant allowed. Image credit: E. Siegel, from his book, Beyond The Galaxy.

    Ever since the expanding Universe was first discovered by Hubble himself, one of the greatest existential questions of all — what will the fate of the Universe be? — suddenly leaped from the realm of poets, philosophers and theologians into the realm of science. Rather than an unknown mystery for human mental gymnastics, it became a question that the acquisition of data and a knowledge of what existed and was observable could answer. The discovery that the Universe was full of galaxies, that it was expanding and that the expansion rate could be measured, both today and in the past, meant that we could use our best scientific theories to accurately predict how the Universe would behave in the future. And for decades, we weren’t sure what the answer would be.

    The star in the great Andromeda Nebula that changed our view of the Universe forever, as imaged first by Edwin Hubble in 1923 and then by the Hubble Space Telescope nearly 90 years later. Image credit: NASA, ESA and Z. Levay (STScI) (for the illustration); NASA, ESA and the Hubble Heritage Team (STScI/AURA) (for the image).

    A number of astronomers and physicists were detractors of cosmology (the study of the Universe), deriding it as a science, claiming that it was merely “a search for two parameters.” Those parameters were the Hubble constant, or the present rate of expansion, and the so-called deceleration parameter, which measured how the Hubble rate was changing over time. But if the physics of General Relativity was correct, those two things would be everything we needed to know to understand the Universe’s fate. The more distant you can observe an object, the farther back in time you look. And in an expanding Universe, when you see the Universe at a younger time, not only are galaxies closer together, but they’re moving apart from one another at a faster rate! In other words, the Hubble “constant” isn’t really a constant, but is decreasing over time.

    In the distant past, the Universe expanded at a much greater rate, and is now expanding more slowly than it ever has before. The best map of the CMB and the best constraints on dark energy from it. Images credit: NASA / CXC / M. Weiss.

    But how it decreases over time is dependent on all the different types of energy present in the Universe. Radiation (like photons) behave differently from neutrinos, which behave differently from matter, which behaves differently from cosmic strings, domain walls, a cosmological constant or some other form of dark energy. Normal matter is simply conserved mass, so as the volume of space increases (as the scale of the Universe, a, cubed), the matter density drops as a-3. The wavelength of radiation stretches as well, so its density drops as a-4. Neutrinos first act like radiation (a-4) and then like matter (a-3) once the Universe cools past a certain point. And cosmic strings (a-2), domain walls (a-1) and a cosmological constant (a0) all evolve according to their own physical specifications.

    How matter (top), radiation (middle), and a cosmological constant (bottom) all evolve with time in an expanding Universe. Image credit: E. Siegel, from his book, Beyond the Galaxy.

    If you know what the Universe is made up of at any given moment, however, and you know how fast it’s expanding at that moment, you can determine — thanks to physics — how the Universe will evolve in the future. And that extends, if you like, into the future arbitrarily far, limited only by the accuracy of your measurements. Given the best data from Planck (the CMB), from the Sloan Digital Sky Survey (for Baryon Acoustic Oscillations/Large-scale structure), and from type Ia supernovae (our most distant “distance indicator”), we’ve determined that our Universe is:

    68% dark energy, consistent with a cosmological constant,
    27% dark matter,
    4.9% normal matter,
    0.1% neutrinos,
    and 0.01% photons,

    for a total of 100% (within the measurement errors) and with an expansion rate today of 67 km/s/Mpc.

    The best map of the CMB and the best constraints on dark energy from it. Images credit: ESA & the Planck Collaboration (top); P. A. R. Ade et al., 2014, A&A (bottom).

    If this is 100% accurate, with no further changes, it means that the Hubble rate will continue to drop, asymptoting somewhere around a value of ~45 km/s/Mpc, but never dropping below it. The reason it never drops to zero is because of dark energy: the energy inherent to space itself. As space expands, the matter and other entities within it may get more dilute, but the energy density of dark energy remains the same. This means that an object that’s 10 Mpc away in the future will recede at 450 km/s; millions of years later, when it’s 20 Mpc away, it recedes at 900 km/s; later on it will be 100 Mpc away and receding at 4,500 km/s; by time it’s 6,666 Mpc away it recedes at 300,000 km/s (or the speed of light), and it moves away faster and faster without fail. In the end, everything that’s not already gravitationally bound to us will expand beyond our reach. In fact, 97% of the galaxies in the Universe are already gone, as even at the speed of light we’d never reach them, even if we left today.

    The observable (yellow) and reachable (magenta) portions of the Universe. Image credit: E. Siegel, based on work by Wikimedia Commons users Azcolvin 429 and Frédéric MICHEL.

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey
    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey”

    But dark energy may not be truly a constant. We might have measured that it evolves as a0 according to our best measurements, but realistically, the best we can say is that it evolves as a0±0.08, where there’s a little bit of wiggle room in the exponent. Moreover, it could change over time, where dark energy could become more positive, more negative, or could even reverse its sign. If we wanted to be honest about what dark energy can and cannot be, it’s more accurate to showcase that wiggle room as well.

    The blue “shading” represent the possible uncertainties in how the dark energy density was/will be different in the past and future. The data points to a true cosmological “constant,” but other possibilities are still allowed. Image credit: Quantum Stories.

    In the end, all we can go off of is what we’ve measured, and admit that the possibilities of what’s uncertain could go in any number of directions. Dark energy appears consistent with a cosmological constant, and there’s no reason to doubt this simplest of models in describing it. But if dark energy gets stronger over time, or if that exponent turns out to be a positive number (even if it’s a small positive number), our Universe might end in a Big Rip instead, where the fabric of space gets torn apart. It’s possible that dark energy may change over time and reverse sign, leading to a Big Crunch instead. Or it’s possible that dark energy may increase in strength and undergo a phase transition, giving rise to a Big Bang once again, and restarting our “cyclical” Universe.

    The different ways dark energy could evolve into the future. Remaining constant or increasing in strength (into a Big Rip) could potentially rejuvenate the Universe. Image credit: NASA/CXC/M.Weiss.

    The smart money is on the Big Freeze, since nothing about the data indicates otherwise. But when it comes to the Universe, remember the golden rule: anything that hasn’t been ruled out is physically possible. And we owe it to ourselves to keep our mind open to all possibilities.

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 4:57 pm on September 13, 2016 Permalink | Reply
    Tags: , , , Cosmic distance ladder, Cosmology, ,   

    From Ethan Siegel: “GAIA Satellite To Find Out If We’re Wrong About Dark Energy And The Expanding Universe” 

    From Ethan Siegel

    Sep 13, 2016

    ESA/Gaia satellite
    ESA/Gaia satellite

    How far away are the most distant objects in the Universe? How has the Universe expanded over the course of its history? And therefore, how big and how old is the Universe since the Big Bang? Through a number of ingenious developments, humanity has come up with two separate ways to answer these questions:

    To look at the minuscule fluctuations on all scales in the leftover glow from the Big Bang — the Cosmic Microwave Background — and to reconstruct the Universe’s composition and expansion history from that.
    To measure the distances to the stars, the nearby galaxies, and the more distant galaxies individually, and reconstruct the Universe’s expansion rate and history from this progressive “cosmic distance ladder.”

    The Gaia Deployable Sunshield Assembly (DSA) during deployment testing in the S1B integration building at Europe’s spaceport in Kourou, French Guiana, two months before launch. Image credit: ESA-M. Pedoussaut.

    Interestingly enough, these two methods disagree by a significant amount, and the European Space Agency’s GAIA satellite, poised for its first data release tomorrow, September 14th, intends to resolve it one way or another.

    Image credit: ESA and the Planck Collaboration, of the best-ever map of the fluctuations in the cosmic microwave background.

    The leftover glow from the Big Bang is only one data set, but it’s perhaps the most powerful data set we could have asked for nature to provide us with. It tells us the Universe expands with a Hubble constant of 67 km/s/Mpc, meaning that for every Megaparsec (about 3.26 million light years) a galaxy is apart from another, the expanding Universe pushes them apart at 67 km/s. The Cosmic Microwave Background also tells us how the Universe has expanded over its history, giving us a Universe that’s 68% dark energy, 32% dark-and-normal matter combined, and with an age of 13.81 billion years. Beginning with COBE and heavily refined later by BOOMERanG, WMAP and now Planck, this is perhaps the best data humanity has ever obtained for precision cosmology.



    The construction of the cosmic distance ladder involves going from our Solar System to the stars to nearby galaxies to distant ones. Each “step” carries along its own uncertainties. Image credit: NASA,ESA, A. Feild (STScI), and A. Riess (STScI/JHU).

    But there’s another way to measure how the Universe has expanded over its history: by constructing a cosmic distance ladder. One cannot simply look at a distant galaxy and know how far away it is from us; it took hundreds of years of astronomy just to learn that the sky’s great spirals and ellipticals weren’t even contained within the Milky Way! It took a tremendous series of steps to figure out how to measure astronomical distances accurately:

    We needed to learn how to measure Solar System distances, which took the developments of Newton and Kepler, plus the invention of the telescope.
    We needed to learn how to measure the distances to the stars, which relied on a geometric technique known as parallax, as a function of Earth’s motion in its orbit.
    We needed to learn how to classify stars and use properties that we could measure from those parallax stars in other galaxies, thereby learning our first galactic distances.
    And finally, we needed to identify other galactic properties that were measurable, such as surface brightness fluctuations, rotation speeds or supernovae within them, to measure the distances to the farthest galaxies.

    This latter method is older, more straightforward and requires far fewer assumptions. But it also disagrees with the Cosmic Microwave Background method, and has for a long time. In particular, the expansion rate looks to be about 10% faster: 74 km/s/Mpc instead of 67, meaning — if the distance ladder method is right — that the Universe is either younger and smaller than we thought, or that the amount of dark energy is different from what the other method indicates. There’s a big uncertainty there, however, and the largest component comes in the parallax measurement of the stars nearest to Earth.

    The parallax method, employed by GAIA, involves noting the apparent change in position of a nearby star relative to the more distant, background ones. Image credit: ESA/ATG medialab.

    This is where the GAIA satellite comes into play. Outstripping all previous efforts, GAIA will measure the brightnesses and positions of over one billion stars in the Milky Way, the largest survey ever undertaken of our own galaxy. It expects to do parallax measurements for millions of these to an accuracy of 20 micro-arc-seconds (µas), and for hundreds of millions more to an accuracy of 200 µas. All of the stars visible with the naked eye will do even better, with as little as 7 µas precision for everything visible to a human through a pair of binoculars.

    A map of star density in the Milky Way and surrounding sky, clearly showing the Milky Way, large and small Magellanic Clouds, and if you look more closely, NGC 104 to the left of the SMC, NGC 6205 slightly above and to the left of the galactic core, and NGC 7078 slightly below. Image credit: ESA/GAIA.

    GAIA was launched in 2013 and has been operational for nearly two full years at this point, meaning it’s collected data on all of these stars at many different points in our planet’s orbit around the Sun. Obtaining parallax measurements means we can get the full three-dimensional positions of these stars in space, and can even infer their proper motions at these accuracies, meaning we can dramatically reduce the uncertainties in the distances to the stars. What’s most spectacular is that many of these stars will be of the same types that we can measure in other star clusters and galaxies, enabling us to build a better, more robust cosmic distance ladder. When the GAIA results come out — and have been fully analyzed by the astronomical community — we’ll have our best-ever understanding of the Universe’s expansion history and of the distances to the farthest galaxies in the Universe, all because we measured what’s happening right here at home.

    Inflationary Universe. NASA/WMAP
    Inflationary Universe. NASA/WMAP

    Right now, the Cosmic Microwave Background and the cosmic distance ladder are giving us two different answers to the question of the age, expansion rate and composition of our Universe. They’re not very different, but the fact that they disagree points to one of two possible things. Either one (or both) of the measurements are in error, or there’s a fundamental tension between these two types of measurement that might mean our Universe is a funnier place than we’ve realized to date. When the results from GAIA come out tomorrow, the great hope of most astronomers is that the previous parallax measurements will be shown to have been in error, and our best understanding of the Universe will hold up and be vindicated. But nature has surprised us before, and — if you’re hoping for something new — keep in mind that it just might do so again.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 4:34 pm on September 13, 2016 Permalink | Reply
    Tags: , , , Cosmology, , Star arrangement that hid for a decade spotted at galaxy’s heart   

    From New Scientist: “Star arrangement that hid for a decade spotted at galaxy’s heart” 


    New Scientist

    13 September 2016
    Adam Mann

    Part of our galaxy’s centre, as seen in near-infrared wavelengths. ESO/S. Gillessen et al.

    There’s a party in the galactic centre. We may have found the first solid evidence of a dense conference of stars around the Milky Way’s heart, which may one day help us observe the supermassive black hole living there.

    Sag A*  NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way
    Sag A* NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    The structure is known as a stellar cusp, and it has played hide-and-seek with astronomers for more than a decade. It was first proposed in the 1970s, when models predicted that stars orbiting a supermassive black hole would jostle around every time one was devoured. Over the course of a galaxy’s lifetime, this should leave an arrangement with many stars near the black hole and exponentially fewer as you move farther away.

    But it has been hard to prove this happens. Other galaxies are too far away for us to see their centres as anything more than fuzzy blobs. Observations in the early 2000s seemed to support a cusp in the Milky Way, but better data showed that we had been tricked by obscuring dust.

    Now, Rainer Schödel at the Institute of Astrophysics of Andalusia in Granada, Spain, and his colleagues have combined images of the galactic centre to map faint old stars, which have been around long enough to settle into a cusp. They also studied the total light emitted by all stars at varying distances from our galaxy’s central black hole, and compared the results with simulations.

    Perfect probes

    These methods point to the same conclusion: the cusp exists. Around our galaxy’s central black hole, the density of stars is 10 million times that in our local area, says Schödel, who presented the work on 7 September at the LISA Symposium in Zurich, Switzerland.

    Many of those stars will eventually explode as supernovae, leaving behind black holes with masses comparable to that of our sun. If one of these merges with the black hole in the galactic centre, it will emit telltale gravitational waves that can be picked up by future observatories, like the proposed Laser Interferometer Space Antenna (LISA).


    Those waves will help figure out the mass, rotation rate and other properties of the black hole with extreme precision.

    “These stellar mass black holes would be absolutely perfect probes of spacetime around the supermassive black hole,” Schödel says.

    If the Milky Way has a cusp, then it’s likely that other galaxies do as well. That’s good news for an observatory like LISA, which may be able to pick up waves from dozens or even hundreds of interactions between stellar mass and supermassive black holes each year.

    The work is a significant advance over previous methods and seems to support the existence of a cusp, says Tuan Do at the University of California, Los Angeles. “The galactic centre is always surprising us though, so I think it would be great to take more observations to verify that there is a cusp of faint old stars,” he says.

    The next generation of enormous observatories, like the Thirty Meter Telescope and Giant Magellan Telescope, will see an order of magnitude more stars than current observatories can.

    TMT-Thirty Meter Telescope, proposed for Mauna Kea, Hawaii, USA
    TMT-Thirty Meter Telescope, proposed for Mauna Kea, Hawaii, USA

    Giant Magellan Telescope, Las Campanas Observatory, to be built  some 115 km (71 mi) north-northeast of La Serena, Chile
    Giant Magellan Telescope, Las Campanas Observatory, to be built some 115 km (71 mi) north-northeast of La Serena, Chile

    They will almost certainly observe the cusp if it’s there, Schödel says.

    See the full article here .

    Please help promote STEM in your local schools.

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  • richardmitnick 1:53 pm on September 9, 2016 Permalink | Reply
    Tags: , , , Confirming The Big Bang's Last Great Prediction, Cosmic Neutrinos Detected, Cosmology, ,   

    From Ethan Siegel: “Cosmic Neutrinos Detected, Confirming The Big Bang’s Last Great Prediction” 

    From Ethan Siegel

    Sep 9, 2016

    The Big Bang timeline of the Universe. Cosmic neutrinos affect the CMB at the time it was emitted, and physics takes care of the rest of their evolution until today. Image credit: NASA / JPL-Caltech / A. Kashlinsky (GSFC).

    The Big Bang, when it was first proposed, seemed like an outlandish story out of a child’s imagination. Sure, the expansion of the Universe, observed by Edwin Hubble, meant that the more distant a galaxy was, the faster it receded from us. As we headed into the future, the great distances between objects would continue to increase. It’s no great extrapolation, then, to imagine that going back in time would lead to a Universe that was not only denser, but thanks to the physics of radiation in an expanding Universe, hotter, too. The discovery of the cosmic microwave background [CMB] and the cosmic light-element background, both predicted by the Big Bang, led to its confirmation.

    CMB per ESA/Planck
    CMB per ESA/Planck

    But last year, a leftover glow unlike any other — of neutrinos — was finally seen. The final, elusive prediction of the Big Bang has finally been confirmed. Here’s how it all unfolded.

    An illustration of the concept of Baryonic Acoustic Oscillations, which detail how large scale structure forms from the time of the CMB onward. This is also impacted by relic neutrinos. Image credit: Chris Blake & Sam Moorfield.

    Seventy years ago, we had taken fascinating steps forward in our conception of the Universe. Rather than living in a Universe governed by absolute space and absolute time, we lived in one where space and time were relative, depending on the observer. We no longer lived in a Newtonian Universe, but rather one governed by general relativity, where matter and energy cause the fabric of spacetime itself to curve. And thanks to the observations of Hubble and others, we learned that our Universe was not static, but rather was expanding over time, with galaxies getting farther and farther apart as time went on. In 1945, George Gamow made perhaps the greatest leap of all: the great leap backwards. If the Universe were expanding today, with all the unbound objects receding from one another, then perhaps that meant that all those objects were closer together in the past. Perhaps the Universe we live in today evolved from a denser state long ago. Perhaps gravitation has clumped and clustered the Universe together over time, while it was more even and uniform in the distant past. And perhaps  — since the energy of radiation is tied to its wavelength – that radiation was more energetic in the past, and hence the Universe was hotter long ago.

    How matter and radiation dilute in an expanding Universe; note the radiation’s redshift to lower and lower energies over time. Image credit: E. Siegel.

    And if this were the case, it brought up an incredibly interesting set of events as we looked farther and farther back into the past:

    There was a time before large galaxies formed, where only small proto-galaxies and star clusters had come to be.
    Before that, there was a time before gravitational collapse had formed any stars, and all was dark: just primeval atoms and low-energy radiation.
    Prior to that, the radiation was so energetic that it could knock electrons off of the atoms themselves, creating a high-energy, ionized plasma.
    Even earlier than that, the radiation reached such levels that even atomic nuclei would be blasted apart, creating free protons and neutrons, and forbidding the existence of heavy elements.
    And finally, at even earlier times, the radiation would have so much energy that — through Einstein’s E = mc^2  —  matter-and-antimatter pairs would spontaneously be created.

    This picture is part of what’s known as the hot Big Bang, and it makes a whole slew of predictions.

    An illustration of the cosmic history/evolution of the Universe since the inception of the Big Bang. Illustration: NASA/CXC/M.Weiss.

    Each one of these predictions, like a uniformly expanding Universe whose expansion rate was faster in the past, a solid prediction for the relative abundances of the light elements hydrogen, helium-4, deuterium, helium-3 and lithium, and most famously, the structure and properties of galaxy clusters and filaments on the largest scales, and the existence of the leftover glow from the Big Bang — the cosmic microwave background — has been borne out over time. It was the discovery of this leftover glow in the mid-1960s, in fact, that led to the overwhelming acceptance of the Big Bang, and caused all other alternatives to be discarded as non-viable.

    Image credit: LIFE magazine, of Arno Penzias and Bob Wilson with the Holmdel Horn Antenna, which detected the CMB for the first time.

    But there was another prediction we haven’t talked about much, because it was thought to be untestable. You see, photons — or quanta of light — aren’t the only form of radiation in this Universe. Back when all the particles are flying around at tremendous energies, colliding into one another, creating and annihilating willy-nilly, another type of particle (and antiparticle) also gets created in great abundance: the neutrino. Hypothesized in 1930 to account for missing energies in some radioactive decays, neutrinos (and antineutrinos) were first detected in the 1950s around nuclear reactors, and later from the Sun, from supernovae and from other cosmic sources. But neutrinos are notoriously hard to detect, and they’re increasingly hard to detect the lower their energies are.

    The energy/flux spectrum of the Big Bang’s leftover glow: the cosmic microwave background. Image credit: COBE / FIRAS, George Smoot’s group at LBL.

    That’s a problem, and it’s a big problem for cosmic neutrinos in particular. You see, by time we come to the present day, the cosmic microwave background (CMB) is only at 2.725 K, less than three degrees above absolute zero. Even though this was tremendously energetic in the past, the Universe has stretched and expanded by so much over its 13.8 billion year history that this is all we have left today. For neutrinos, the problem is even worse: because they stop interacting with all the other particles in the Universe when it’s only about one second after the Big Bang, they have even less energy-per-particle than the photons do, as electron/positron pairs are still around at that time. As a result, the Big Bang makes a very explicit prediction:

    There should be a cosmic neutrino background (CNB) that is exactly (4/11)^(1/3) of the cosmic microwave background (CMB) temperature.

    That comes out to ~1.95 K for the CNB, or energies-per-particle in the ~100–200 micro-eV range. This is a tall order for our detectors, because the lowest-energy neutrino we’ve ever seen is in the mega-eV range.

    Image credit: IceCube collaboration / NSF / University of Wisconsin, via https://icecube.wisc.edu/masterclass/neutrinos. Note the huge difference between the CNB energies and all other neutrinos.

    So for a long time, it was assumed that the CNB would simply be an untestable prediction of the Big Bang: too bad for all of us. Yet with our incredible, precise observations of the fluctuations in the background of photons (the CMB), there was a chance. Thanks to the Planck satellite, we’ve measured the imperfections in the leftover glow from the Big Bang.

    Initially, these fluctuations were the same strength on all scales, but thanks to the interplay of normal matter, dark matter and the photons, there are “peaks” and “troughs” in these fluctuations. The positions and levels of these peaks and troughs tells us important information about the matter content, radiation content, dark matter density and spatial curvature of the Universe, including the dark energy density.

    The best fit of our cosmological model (red curve) to the data (blue dots) from the CMB. Image credit: Planck Collaboration: P. A. R. Ade et al., 2013, A&A, for the Planck collaboration.

    There’s also a very, very subtle effect: neutrinos, which only make up a few percent of the energy density at these early times, can subtly shift the phases of these peaks and troughs. This phase shift – if detectable — would provide not only strong evidence of the existence of the cosmic neutrino background, but would allow us to measure its temperature at the time the CMB was emitted, putting the Big Bang to the test in a brand new way.

    The fit of the number of neutrino species required to match the CMB fluctuation data. Image credit: Brent Follin, Lloyd Knox, Marius Millea, and Zhen PanPhys. Rev. Lett. 115, 091301 — Published 26 August 2015.

    Last year, a paper [Physical Review Letters] by Brent Follin, Lloyd Knox, Marius Millea and Zhen Pan came out, detecting this phase shift for the first time. From the publicly-available Planck (2013) data, they were able to not only definitively detect it, they were able to use that data to confirm that there are three types of neutrinos — the electron, muon and tau species — in the Universe: no more, no less.

    The number of neutrino species as inferred by the CMB fluctuation data. Image credit: Brent Follin, Lloyd Knox, Marius Millea, and Zhen PanPhys. Rev. Lett. 115, 091301 — Published 26 August 2015.

    What’s incredible about this is that there is a phase shift seen, and that when the Planck polarization spectra came out and become publicly available, they not only constrained the phase shift even further, but — as announced by Planck scientists in the aftermath of this year’s AAS meeting — they finally allowed us to determine what the temperature is of this Cosmic Neutrino Background today! (Or what it would be, if neutrinos were massless.) The result? 1.96 K, with an uncertainty of less than ±0.02 K. This neutrino background is definitely there; the fluctuation data tells us this must be so. It definitely has the effects we know it must have; this phase shift is a brand new find, detected for the very first time in 2015. Combined with everything else we know, we have enough to state that yes, there are three relic neutrino species left over from the Big Bang, with the kinetic energy that’s exactly in line with what the Big Bang predicts.

    Two degrees above absolute zero was never so hot.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 11:55 am on September 2, 2016 Permalink | Reply
    Tags: , , Cosmology, ,   

    From New Scientist: “Stars burning strangely make life in the multiverse more likely” 


    New Scientist

    1 September 2016
    Jacob Aron

    The answer’s in the stars. NASA, ESA, and E. Sabbi (ESA/STScI)

    Your existence depends on an improbable threesome. A delicate reaction within stars called the triple-alpha process, which creates carbon, is often used to support the idea of the multiverse. Now, two researchers argue that stars in other universes might have alternative ways of producing carbon, giving life as we know it a greater chance in multiple universes.

    The triple-alpha process gets its name from the three helium nuclei involved, which are also known as alpha particles. When the universe formed, it mostly consisted of hydrogen and helium, the simplest elements in the periodic table. Heavier elements were forged by the first stars, which fused the lighter nuclei together.

    There’s just one problem with this tidy model. Fuse two alpha particles together and you end up with a nucleus of four protons and four neutrons – namely beryllium-8, an isotope of the fourth element in the periodic table. But beryllium-8 is highly unstable and falls apart into two alpha particles within a fraction of a second. That means there isn’t much of it in our universe.

    “The natural stepping stone towards bigger elements is not present,” says Fred Adams of the University of Michigan in Ann Arbor.

    That’s no way to build a cosmos – yet puzzlingly, here we are. In the 1950s, astronomer Fred Hoyle figured out a solution. He argued that the abundance of carbon in the universe must be the result of a coincidence between the energy levels of alpha particles and carbon-12.

    Hoyle said that because the energy of three alpha particles creates carbon-12 with more energy than it needs, this extra energy must be equal to an excited state of carbon-12, allowing it to decay to its ground state and remain stable. This so-called “resonance” between the energy values makes it possible to form carbon by fusing three alpha particles together.

    Experiments later proved him right, but the resonance introduced its own problems. It occurs at a very particular value, 7.644 megaelectronvolts (MeV), and calculations show that the triple-alpha reaction is very sensitive to this value. Vary it by 0.1 MeV and the reaction will slow, producing less carbon, and a change of more than 0.3 MeV will halt carbon production altogether.

    Hoyle and others argued that this means our universe must have been fine-tuned for life. That resonance could have occurred at a range of energies, and the fact that it just happened to occur at the point we needed it to for our existence makes us astonishingly lucky.

    The odds of this happening at random are very low, and some argue that the only way to explain it is if our universe is just one of many in a multiverse. In that case, each universe could have slightly different values for the fundamental constants of physics. Life would arise only in suitable universes, meaning we shouldn’t be surprised to find ourselves in one of these.

    Another kind of universe

    But now Adams and his colleague Evan Grohs have argued that if other universes have different fundamental constants anyway, it’s possible to create a universe in which beryllium-8 is stable, thus making it easy to form carbon and the heavier elements.

    For this to happen would require a change in the binding energy of beryllium-8 of less than 0.1 MeV – something that the pair’s calculations show should be possible by slightly altering the strength of the strong force, which is responsible for holding nuclei together.

    Simulating how stars might burn in such a universe, they found that the stable beryllium-8 would produce an abundance of carbon, meaning life as we know it could potentially arise. “There are many more working universes than most people realise,” says Adams.

    These universes would arguably be more logical, he says, with stars steadily building elements along the periodic table without having to resort to the triple-alpha process. “We tend to think not only is our universe fine-tuned for us, we also think this is the best universe one could design,” says Adams. “In some sense, we’ve designed a better universe.”

    “It’s an interesting point, that there is another way of treating the physics that is no bigger than the tweaking you need to get rid of the carbon resonance,” says Martin Rees of the University of Cambridge.

    But Rees points out that we don’t really know if the multiverse exists, let alone if different universes would have different physics. “We need a measure of the relative probability of all those things to decide whether we should be surprised that we’re in the universe we are in,” he says.

    See the full article here .

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  • richardmitnick 8:50 am on September 1, 2016 Permalink | Reply
    Tags: , , Cosmology, How Much More Can We Learn About the Universe?, , ,   

    From Nautilus: “How Much More Can We Learn About the Universe?” Lawrence M. Krauss 



    September 1, 2016
    Lawrence M. Krauss

    Jackie Ferrentino

    As a cosmologist, some of the questions I hear most frequently after a lecture include: What lies beyond our universe? What is our universe expanding into? Will our universe expand forever? These are natural questions to ask. But there is an even deeper question at play here. Fundamentally what we really want to know is: Is there a boundary to our knowledge? Are there fundamental limits to science?

    The answer, of course, is that we don’t know in advance. We won’t know if there is a limit to knowledge unless we try to get past it. At the moment, we have no sign of one. We may be facing roadblocks, but those give every indication of being temporary. Some people say to me: “We will never know how the universe began.” “We can never know what happened before the Big Bang.” These statements demonstrate a remarkable conceit, by suggesting we can know in advance the locus of all those things that we cannot know. This is not only unsubstantiated, but the history of science so far has demonstrated no such limits. And in my own field, cosmology, our knowledge has increased in ways that no one foresaw even 50 years ago.

    ON A CLEAR DAY YOU CAN’T SEE FOREVER: The farthest you see, in principle, is 45.3 billion light-years. Although that represents a direct limitation on our knowledge, it doesn’t keep us from grasping the basic workings of nature. NASA / Bill Ingalls

    his is not to say that nature doesn’t impose limits on what we can observe and how we can observe it. For example, the Heisenberg uncertainty principle constrains what we can know about the motion of a particle at any time, and the speed of light restricts how far we can see or travel in a given interval. But these limits merely tell us what we cannot observe, not what we cannot eventually learn. The uncertainty principle hasn’t gotten in the way of learning the rules of quantum mechanics, understanding the behavior of atoms, or discovering that so-called virtual particles, which we can never see directly, nevertheless exist.

    The observation that the universe is expanding does imply a beginning, because if we extrapolate backward, then at some point in the distant past, everything in our observable universe was co-located at a single point. At that instant, which now goes by the name of the Big Bang, the laws of physics as we know them break down, because general relativity, which describes gravity, cannot be successfully integrated with quantum mechanics, which describes physics on microscopic length scales. But most scientists do not view this as a fundamental boundary to knowledge, because we expect that general relativity will have to be modified as part of a consistent quantum theory. String theory is one of the major ongoing efforts to do so.

    Given such a theory, we might be able to answer the question of what, if anything, came before the Big Bang. The simplest possible answer is perhaps also the least satisfying. Both special and general relativity tie together space and time into a single entity: spacetime. If space was created in the Big Bang, then perhaps time was as well. In that case, there was no “before.” It simply wouldn’t be a good question. This is not the only possible answer, though, and we will need to await a quantum theory of gravity and its experimental confirmation before we will have any confidence in our reply.

    Then there is the question of whether we can know what lies beyond our own universe, spatially. What are the boundaries of our universe? Again, we can hazard a guess. If our spacetime arose spontaneously—which, as I argued at length in my last book, A Universe from Nothing, seems the most likely possibility—then it probably has zero total energy: The energy represented by matter is exactly offset by the energy represented by gravitational fields. Put simply, something can arise from nothing if the something amounts to nothing. Right now, the only universe that we can verify has zero total energy is a closed universe. Such a universe is finite yet unbounded. Just like you can move around the surface of a sphere forever without encountering any boundaries, the same may be true of our universe. If we look far enough in one direction, we would see the back of our heads.

    In practice, we cannot do that, probably because our visible universe is only part of a much larger volume. The reason has to do with something called inflation. Most universes that arise spontaneously with microscopic size will re-collapse in a microscopic time, rather than endure for billions of years. But, in some, empty space will be endowed with energy, and that will cause the universe to expand exponentially fast, at least for a brief period. We think that such a period of inflation occurred during the earliest moments of our Big Bang expansion and prevented the universe from re-collapsing immediately. In the process, the universe puffed up in size to become so great in extent that, for all intents and purposes, it would now appear flat and infinite—like a cornfield in Kansas that looks infinite despite being located on the huge sphere we call Earth. This is why we don’t see the backs of our heads when we look up in space, even though our universe may be closed on its largest scales. In principle, though, we could see the whole thing if we waited long enough, as long as inflation hadn’t resumed in our visible universe, and is not occurring elsewhere in regions of space we cannot observe.

    As for the possibility that regions we cannot yet observe, or may never observe, may be inflating, in fact our current theories suggest that this is the most likely possibility. If we consider the phrase “our universe” to refer to that region of space with which we once could have communicated or with which we one day may communicate, then inflation generally creates other universes beyond ours. Inflation may have been brief within our volume of space, but the rest of space expands exponentially forever, with isolated regions like ours occasionally decoupling from the expansion, just as isolated ice patches can form on the surface of fast-moving water when the temperature is below freezing. Each such universe had a beginning, pegged to the time when inflation ended within its spatial volume. In this case, the beginning of our universe may not have been the beginning of time itself—further reason to doubt whether the Big Bang represents an ultimate limit to our knowledge.

    COLLIDING GALAXIES: Such cosmic commotion will one day cease to occur, and observers in the distant future may never realize how dynamic our universe once was. NASA

    Depending on the processes that cause each universe to decouple from the background space, the laws of physics might be different in each one. We have come to call this collection of possible universes a “multiverse.” The idea of a multiverse has gained traction in the scientific community not only because it is motivated by phenomena like inflation, but also because the possibility of many different universes, each with its own laws of physics, might explain various seemingly inexplicable fundamental parameters of our universe. Those parameters are simply the values that randomly arose when our universe was born.

    If other universes are out there, they are separated from ours by huge distances and recede at super-light relative velocities, so we can never detect them directly. Is the multiverse then just metaphysics? Does verifying the possible existence of a multiverse thus represent a fundamental boundary to our knowledge? The answer is: not necessarily. Although we may never see another universe directly, we can still test the theory that may have produced it empirically—for example, by observing gravitational waves that inflation would produce. This would allow us in principle to test the detailed nature of the inflationary process that resulted in our universe. These waves are similar to the gravitational waves recently discovered by LIGO, but differ in their origin. They come not from cataclysmic events such as the collisions of massive black holes in distant galaxies, but from the earliest moments of the Big Bang, during the putative period of inflation. If we can detect them directly—as we might be able to do in a variety of experiments that are now looking for the signature they would leave in the cosmic microwave background radiation left over from the Big Bang—we can probe the physics of inflation and then determine whether eternal inflation is a consequence of this physics. Thus, indirectly, we could test whether other universes must exist, even if we cannot detect them directly.

    In short, we have discovered that even the very deepest metaphysical questions—which previously we might have imagined would never be empirically addressable, including the possible existence of other universes—may in fact be accessible, if we are clever enough. No limits to what we may learn from the application of reason combined with experimental observation are yet known.

    A universe without limits is appealing and motivates us to continue searching. But can we be confident there will be no limits to our knowledge, ever? Not quite.

    Inflation does place a fundamental limit on knowledge—specifically, knowledge of the past. It essentially resets the universe, destroying potentially all the information about the dynamical processes that preceded it. The rapid expansion of space during inflation severely dilutes the contents of any region. So it may have wiped out traces of, for example, magnetic monopoles, a type of particle that theory suggests the very early universe produced in profusion. That was one of the original virtues of inflation: It reconciled the fact we have never seen such particles with predictions of their production. But in getting rid of a discrepancy, inflation erased aspects of our past.

    Worse, the erasure may not be over. We are apparently living in another period of inflation right now. Measurements of the recession of distant galaxies indicates that the expansion of our universe is currently speeding up, not slowing down, as it would be if the dominant gravitational energy resided in matter or radiation, and not in empty space. We currently have no understanding of the origin of this energy. Each of the potential explanations suggests fundamental limits to the progress of knowledge and even to our very existence.

    The energy of empty space could suddenly disappear if the universe undergoes some kind of phase transition, a cosmic version of steam condensing into liquid water. If that were to happen, the nature of fundamental forces might change, and all the structures we see in the universe, from atoms on up, might become unstable or disappear. We would disappear along with everything else.

    But even if the expansion continues, the future is still rather dismal. Within about 2 trillion years—which may seem like a long time on human scales, but is not so long on cosmic scales—the rest of the universe will disappear from our view. Any observers who evolve on planets around stars in this distant future will imagine that they live on a single galaxy surrounded by an eternal empty space, with no signs of acceleration or even any evidence of an earlier Big Bang. Just as we have lost sight of monopoles, they will be blind to the history that we readily see. (To be sure, they may have access to observable phenomenon we do not yet have access to, so we shouldn’t feel too superior.)

    Either way, we should enjoy our brief moment in the sun and learn what we can, while we can. Work harder, graduate students!

    See the full article here .

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

  • richardmitnick 3:05 pm on August 9, 2016 Permalink | Reply
    Tags: , , Cosmology, Cosmology@home   

    From BOINC project Cosmology@home: “Planck parameter sims paper out” 

    Cosmology@home new

    9 Aug 2016

    In February we started running a new application. Today the paper making use of the results that thousands of you guys calculated is out! Look here in the coming weeks for more posts detailing exactly what we found. Until then, you can see the paper here. On behalf of the C@H team and of the Planck collaboration, thanks again everyone!

    See the full article here.

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    The goal of Cosmology@home is to search for the model that best decribes our universe and to find the range of models that agree with the available astronomical and particle physics data.

    Unlike ordinary matter, dark matter does not emit or absorb light–or any other type of electromagnetic radiation. Consequently, dark matter cannot be observed directly using a telescope or any other astronomical instrument that has been developed by humans. If dark matter has these strange properties, how do we know that it exists in the first place?
    Like ordinary matter, dark matter interacts gravitationally with ordinary matter and radiation. Astronomers study the distribution of dark matter through observing its gravitational effects on ordinary matter in its vicinity and through its gravitational lensing effects on background radiation.

    Cosmology@home supporters

    Cosmology@home runs on software from BOINC at UC Berkeley. Visit BOINC, download and install the software. Then attach to this project and review all of the projects running on BOINC.


    BOINC WallPaper

  • richardmitnick 4:17 pm on June 13, 2016 Permalink | Reply
    Tags: , , Cosmology, ,   

    “From LBL: “Researchers Gear Up Galaxy-seeking Robots for a Test Run” 

    Berkeley Logo

    Berkeley Lab

    June 13, 2016
    Glenn Roberts Jr

    Parker Fagrelius of Berkeley Lab and UC Berkeley inspects ProtoDESI, a prototype system for the Dark Energy Spectroscopic Instrument. ProtoDESI will be tested at the Mayall Telescope in Arizona in August and September. (Credit: Paul Mueller/Berkeley Lab)

    A prototype system, designed as a test for a planned array of 5,000 galaxy-seeking robots, is taking shape at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).

    Dubbed ProtoDESI, the scaled-down, 10-robot system will help scientists achieve the pinpoint accuracy needed to home in on millions of galaxies, quasars and stars with the Dark Energy Spectroscopic Instrument (DESI) planned for the Mayall Telescope at Kitt Peak National Observatory near Tucson, Ariz. ProtoDESI will be installed on the Mayall Telescope this August and September.

    LBL/DESI spectroscopic instrument
    LBL/DESI spectroscopic instrument

    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA
    NOAO Mayall 4 m telescope interior
    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA

    The full DESI project, which is managed by Berkeley Lab, involves about 200 scientists and about 45 institutions from around the globe. DESI will provide the most detailed 3-D map of the universe and probe the secrets of dark energy, which is accelerating the universe’s expansion. It is also expected to improve our understanding of dark matter, the infant universe, and the structure of our own galaxy.

    Milky Way NASA/JPL-Caltech /ESO R. Hurt
    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey
    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    ProtoDESI will have 10 rodlike robots (above, left)—10 inches long and designed to point fiber-optic cables at sky objects and gather light—and 16 light-emitting devices (middle) to ensure the system is targeting correctly. The ProtoDESI setup (right, with robots and light rods shown in yellow circle) will be tested at the Mayall Telescope in Arizona from August-September.

    DESI robots (right) will poke out from 10 wedge-shaped “petals” that will be fitted together in a Focal Plate Assembly (left).

    DESI’s robots can point their fiber-optical cables (red dots, upper left) at any sky object (blue dots) within a 12-millimeter-diameter area. A rendering of the robotic array (right) with an overlay of a star field that can be reached by one robot.

    A rendering of DESI inside the Mayall Telescope (left). The robotic array is contained in a gray-shaded structure pointed toward the top of the dome.

    (Credits: Berkeley Lab, University of Michigan, DESI Collaboration, NOAO.)

    The thin, cylindrical robots that will be tested in ProtoDESI each carry a fiber-optic cable that will be precisely pointed at selected objects in the night sky in order to capture their light. A predecessor galaxy-measuring project, called BOSS, required the light-gathering cables to be routinely plugged by hand into metal plates with holes drilled to match the position of pre-selected sky objects. DESI will automate and greatly speed up this process.

    Each 10-inch-long robot has two small motors in it that allow two independent rotating motions to position a fiber anywhere within a circular area 12 millimeters in diameter. In the completed DESI array, these motions will enable the 5,000 robots to cover every point above their metal, elliptical base, which measures about 2.5 feet across.

    That requires precise, software-controlled choreography so that the tightly packed robots don’t literally bump heads as they spin into new positions several times each hour to collect light from different sets of pre-selected sky objects.

    “The main goal of ProtoDESI is to be able to fix fibers on actual objects and hold them there,” said Parker Fagrelius, who is managing the ProtoDESI project at Berkeley Lab. Fagrelius is a UC Berkeley graduate student who is also an affiliate in the Physics Division at Berkeley Lab. ProtoDESI’s robots, assembled at University of Michigan and then shipped to Berkeley Lab, are positioned far enough apart that they won’t accidentally collide during their initial test run.

    While DESI’s robots will primarily target galaxies, ProtoDESI will use mostly bright, familiar stars to tune its robotic positioning system and ensure the system is accurately tracking with the motion of objects in the sky. Mounted next to the positioners is a custom digital camera known as the GFA (for guide, focus and alignment) that will remain targeted on a “guide star”—a bright star that will aid the tracking of other objects targeted by the robot-pointed fibers. Several Spanish research institutions in Barcelona and Madrid are responsible for this GFA system.

    “We’ll choose the fields we look at quite carefully,” Fagrelius said. The robots will initially fix on isolated sky objects so that they don’t mistakenly point at the wrong objects.

    In addition to the 10-robot system, ProtoDESI is equipped with a set of 16 light-emitting rods—shaped similarly to the robots—that project small points of blue light onto a camera to calibrate the positioning system. The completed project will include 120 of these devices, called “illuminated fiducials.”

    The fibers carried by the robots each have a core that is 107 microns (millionths of a meter) wide. After repositioning, the fibers will be backlit to project points of light on a camera that can help to fine-tune their individual positions, if needed. Yale University is supplying this fiber-view camera and also the fiducials.

    A view of the ProtoDESI setup under assembly at Berkeley Lab, with the underside of the robotic fiber-positioners visible at left. (Credit: Paul Mueller/Berkeley Lab)

    Fagrelius will join a team of researchers at Kitt Peak’s 4-meter Mayall telescope in early August to run through a checklist of ProtoDESI tests. About 28 researchers from nine institutions in the DESI collaboration are working on ProtoDESI, including six Berkeley Lab researchers.

    Researchers will test the auto-positioning system by slightly shifting the pointing of the telescope and the fibers—a process known as “dithering”—to see how the components readjust to find the correct targets. A digital camera will measure light streaming in from the fibers to determine if the robots are properly targeting sky objects.

    ProtoDESI will test 10 robots like the one in this diagram. Each one can rotate in two different ways and is designed to point a fiber-optic cable at sky objects to collect their light. (Credit: MNRAS, DOI: 10.1093/mnras/stv541)

    “ProtoDESI will show us how the software and positioners are working together,” Fagrelius said. “All of the things we learn along the way from ProtoDESI will be built back into the plans for DESI’s commissioning.” Some measurements and pre-testing with ProtoDESI will be conducted at Berkeley Lab even before ProtoDESI moves to the Mayall telescope, she added.

    The full robotic array planned for DESI will be segmented in 10 pie-wedge-shaped “petals” that each contains 500 robots. The first petal will be fully assembled by October at Berkeley Lab and tested at the lab through December. The multi-petal design will allow engineers to remove and replace individual petals.

    Each robot will have an electronic circuit board and wiring, and on the final DESI project each robot’s fiber-optic cable will be spliced to a 42-meter-long fiber-optic cable that will run to a light-measuring device known as a spectrograph (ProtoDESI will not have a spectrograph).

    The completed project will feature 10 high-resolution spectrographs, that will measure the properties of objects’ light to tell us about how fast faraway galaxies are moving away from us and their distribution, and will help us trace the universe’s expansion history back 12 billion years.

    A camera test of a type of robotic fiber-optic positioner (left and center) that will be tested in ProtoDESI. (Credit: MNRAS, DOI: 10.1093/mnras/stv541)

    Joe Silber, a Berkeley Lab engineer working on DESI systems that include its robotics, said the fiber-optic cables are among the most sensitive components in DESI. “If there is too tight of a bend or you stress the fiber, it will degrade its performance,” he said, noting that there have already been tests of the repeated bends and twists to the cables caused by the movement of the robots. Over the lifetime of DESI the ends of the fiber-optic cables will be turned almost 200,000 times, he said. Installation of DESI is expected to begin in 2018.

    Fagrelius said she looks forward to the ProtoDESI run at Mayall. “September will have a lot more clear nights than August. There should be four weeks of decent time that we can get on sky,” she said, and other tests can be conducted even when viewing is obscured by weather.

    DESI is supported by the U.S. Department of Energy Office of Science; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under contract to the National Optical Astronomy Observatory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the National Council of Science and Technology of Mexico, and DESI member institutions. The DESI scientists are honored to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation.

    This video shows the rotating motions of a robotic fiber-optic positioner. ProtoDESI will test a group of 10 robotic positioners, and DESI will feature 5,000 robots. (Credit: Berkeley Lab)
    Access mp4 video here .

    A simulation of the movements of 499 DESI robots, carefully choreographed to avoid bumping into one another, as seen from above. ProtoDESI is testing 10 robots for the completed DESI project, which will have 5,000 robots. (Credit: Joe Silber/Berkeley Lab)
    Access mp4 video here .

    See the full article here .

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    A U.S. Department of Energy National Laboratory Operated by the University of California

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