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  • richardmitnick 1:37 pm on September 28, 2016 Permalink | Reply
    Tags: , Astrophysics, , , , How Do We Classify The Stars In The Universe?   

    From Ethan Siegel: “How Do We Classify The Stars In The Universe?” 

    Ethan Siegel

    Sep 28, 2016

    The stars found in NGC 3532 show a rich variety of colors and brightnesses. Image credit: ESO/G. Beccari.

    Take a look up at a dark night sky, and you’ll find it illuminated by hundreds or even thousands of individual twinkling points of light. While they might seem, to an untrained eye, to all be the same — except for, perhaps, some appearing brighter than others — a closer look reveals a number of intrinsic differences between them. Some of them appear redder or bluer than others; some are intrinsically brighter or fainter, even if they’re the same distance away; some have larger physical sizes than others; some have greater or lesser percentages of heavy elements in them. For a long time, scientists didn’t know how stars worked or what made one type different from another. Yet at the start of the 20th century, the pieces all came together to figure out exactly how the different stars should be classified, and we owe it all to a woman you might not have heard of: Annie Jump Cannon.

    Annie Jump Cannon sitting at her desk at Harvard College Observatory, sometime in the early 20th century. Image credit: Smithsonian Institution from the United States.

    With either good enough skies and a trained observer, or with a quality telescope, a look at the stars immediately shows that they come in different colors. Because temperature and color are so closely related — heat something up and it glows red, then orange, then yellow, white and eventually blue as you turn up the temperature — it makes sense that you’d classify them based on color. But where would you make those divisions, and would those divisions encapsulate all the important physics and astrophysics going on? Without more information, there wouldn’t be a good, universal system that everyone would agree on. But the study of color in astronomy (photometry) can be augmented by breaking up the light into individual wavelengths (spectroscopy). If there are either neutral or ionized atoms in the outermost layers of the star, they’ll absorb some of the light at particular wavelengths. These absorption features can add an extra layer of information, and led to the earliest useful classification system.

    The solar spectrum shows a significant number of features, each corresponding to absorption properties of a unique element in the periodic table. Image credit: Nigel A. Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF.

    NOAO Kitt Peak National Observatory  on the Tohono O’odham reservation outside Tucson, AZ, USA
    NOAO Kitt Peak National Observatory on the Tohono O’odham reservation outside Tucson, AZ, USA

    Known as Secchi classes, for the 19th century Italian astronomer Angelo Secchi who devised them, there were originally three types:

    1. Class I: a class for the blue/white stars that exhibited strong, broad hydrogen lines.
    2. Class II: yellow stars with weaker hydrogen features, but with evidence of rich, metallic lines.
    3. Class III: red stars with complex spectra, with huge sets of absorption features.

    This system, first laid out in 1866, was the first non-arbitrary system of classification, since it relied on a combination of spectroscopic features in tandem with the photometric colors. While Secchi went on to further refine his class structure and introduce sub-classes and additional classes, this became superseded by finer spectral delineations.

    The original three Secchi classes, and the accompanying spectra that go along with them. Image credit: from a colored lithograph in a book published around 1870, retrieved from AIP.

    Researchers at Harvard College Observatory were tasked with surveying all the stars visible in the night sky down to a visual magnitude of +9, or the faintest you’d be able to see today with a very nice pair of binoculars. Except it wasn’t enough to record them in the traditional fashion; they needed to be observed and analyzed spectroscopically. Under the guidance of Edward Pickering, a group of astronomers — all women, known at the time as “Pickering’s Harem” (that was later sanitized to “Pickering’s Women” or the “Harvard Computers”) — took the data and created the Draper System, for which Pickering was given sole/full credit. The stars that had the strong hydrogen lines (Secchi Class I) were broken up into four further delineations, labeled A through D, based on how strong the hydrogen absorption features were, with A being the strongest. The stars with rich, metallic lines (and weaker hydrogen lines, Secchi Class II) were broken up into six classes, E through L, with decreasing hydrogen strength and increasing metal strength going hand-in-hand. The reddest stars, richest in absorption features (Secchi Class III) became class M. In addition, there were four other types labeled N through Q, with O being notable as having very bright, blue stars with very weak hydrogen features, but also lines not seen in any other star class.

    The seven major star classes, organized by their colors. It turns out that these colors also correspond to a star’s surface temperature, and so O-stars are the hottest, while M-stars are the coolest. Image credit: E. Siegel.

    In 1901, Annie Jump Cannon — one of the astronomers working under Pickering — synthesized the full suite of this data and consolidated the seventeen Draper System classes into just seven: A, B, F, G, K, M, and O. The big step that she took, however, was also perhaps the simplest: to reorder them by their color, from bluest to reddest. This meant the order was now O, B, A, F, G, K, and M. Star types were further broken down into ten intervals apiece, from 0 to 9, based on bluest to reddest. So a B2 star would be 20% of the way between a B0 star and an A0 star, a B5 star would be 50% of the way there, and a B9 star would be 90% of the way there. The bluest star of all would be O0, while the reddest would be M9. This system, known as the Harvard Spectral Classification System, is still in use today. There would, however, be one more great leap that would happen decades after Annie Jump Cannon’s contributions, and you can see it for yourself if you view the spectra of these different classes in descending order.

    O-stars, the hottest of all stars, actually have weaker absorption lines in many cases, because the surface temperatures are great enough that most of the atoms at its surface are at too great of an energy to display the characteristic atomic transitions that result in absorption. Image credit: NOAO/AURA/NSF, modified to illustrate the stars that demonstrate this phenomenon.

    You’ll notice that certain lines appear, get stronger and then disappear, while others simply appear and strengthen. The reason stars appear with the absorption features they do are because of their temperature, and because at certain temperatures different ionization states (and hence, different atomic transitions) are more common, and therefore, stronger. The link between temperature, color and ionization wasn’t found until 1925, with the Ph.D. dissertation of Cecilia Payne, which also enabled us to determine what the Sun (and all stars) were actually made out of! The different stellar classifications don’t just correspond to a star’s colors and absorption features, but to a star’s temperature as well.

    The (modern) Morgan–Keenan spectral classification system, with the temperature range of each star class shown above it, in kelvin. Image credit: Wikimedia Commons user LucasVB, additions by E. Siegel.

    Thanks to Payne and Cannon’s work, we learned that stars were made out of mostly hydrogen and helium, and not out of heavier elements like Earth is. Cecilia Payne’s work would have been impossible without Annie Jump Cannon’s data; Cannon herself was responsible for classifying, by hand, more stars in a lifetime than anyone else: around 350,000. She could classify a single star, fully, in approximately 20 seconds, and used a magnifying glass for the majority of the (faint) stars. Her legacy is now nearly 100 years old: on May 9, 1922, the International Astronomical Union formally adopted Annie Jump Cannon’s stellar classification system. With only minor changes having been made in the 94 years since, it is still the primary system in use today.

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

    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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    Stem Education Coalition
    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: , Astrophysics, , , 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.

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

    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 11:45 am on September 13, 2016 Permalink | Reply
    Tags: , Astrophysics, , , Impossibly bright monster pulsars   

    From EarthSky: “Impossibly bright monster pulsars” 



    September 12, 2016
    Deborah Byrd

    Astronomers in Japan used a supercomputer and a hypothetical neutron star to explain blinking, enigmatic objects known as Ultra Luminous X-ray pulsars.

    Supercomputer simulation results suggest a new lighthouse model for ULXs (Ultra Luminous X-ray sources). Red indicates stronger radiation. Arrows show the directions of photon flow. Image via NAOJ.

    Pulsars are objects in space that blink at very precise intervals. The widely accepted model to explain them is the lighthouse model, involving a rotating, very dense neutron star that emits a highly focused beam of radiation. We can only see the beam when it points toward Earth, much as we see the flash of a lighthouse beam when it’s pointed our way. There are many kinds of pulsars, with many peculiar physical manifestations, and, on September 8, 2016, a research group led by Tomohisa Kawashima at the National Astronomical Observatory of Japan announced their use of a supercomputer to add one more possibility to the list. These scientists said that the central energy source of enigmatic pulsating Ultra Luminous X-ray sources – called ULXs – could be neutron stars, not black holes as previously thought.

    Their paper is published in Publications of the Astronomical Society of Japan.

    Astronomers first noticed ULXs in the 1980s. In the intervening years, astronomers have found about one ULX per galaxy in some galaxies, but other galaxies contain many and some (like our Milky Way, so far) none at all. If you assume ULXs radiate equally in all directions, they are more consistently luminous than any known stellar process, but no one actually does assume that. Instead, the popular model to explain them has been the black hole model. It’s the classic model involving an object with strong gravity (the black hole) pulling gas from a companion star. As the gas falls towards the black hole, it collides with other gas, heating up and creating a luminous gas that astronomers actually observe when they see a ULX.

    Then, in 2014, the X-ray space telescope NuSTAR threw a wrench into the wide acceptance of the black hole model when it detected unexpected periodic pulsed emissions in a ULX named M82 X-2.


    The discovery of this ULX-pulsar has had astrophysicists scratching their heads because black holes shouldn’t be able to produce pulsed emissions.

    Kawashima’s team doesn’t use black holes in its model at all. Instead, the team’s computer simulations show that a neutron star can provide the necessary pulsed luminosity under certain conditions. The explanation involves some thorny physics, which you can read in their statement, but they also provided the two videos below to help explain.

    The first video shows an artist’s impression of the standard model of a pulsar. Photon beams are emitted from the magnetic poles of a neutron star. These photon beams twirl because of the misalignment between the magnetic poles and the rotation axis. As a result, the beams face towards an observer at regular intervals and pulsed emissions are observed coming from the neutron star.

    The second video shows the model suggested by Kawashima and colleagues’ simulations, which they called a new cosmic lighthouse model for ULXs. They said:

    “When gases (red) fall onto a neutron star, the accretion columns are heated by shock waves and shine brightly. Photons can escape from the columns through the sidewall and do not prevent additional gas from accreting. Therefore these columns continue to emit an enormous amount of photos. In this model, due to the misalignment between the accretion columns and the rotation axis, the appearance of the accretion columns changes periodically with the rotation of the neutron star. Dazzling pulsed emissions can be observed when the apparent area of the columns reaches maximum.”

    For more of the physics of this model, be sure to read the scientists’ statement at the Center for Computational Astrophysics (CfCA).

    This team said it is now planning to develop its work further by using this new lighthouse model to study the detailed observational features of the ULX-pulsar M82 X-2, and to explore other ULX-pulsar candidates.

    Bottom line: Astronomers in Japan used a supercomputer to provide an alternative model – involving a neutron star, not a black hole – to explain enigmatic pulsating Ultra Luminous X-ray sources (ULXs).

    See the full article here .

    Please help promote STEM in your local schools.

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  • richardmitnick 8:47 pm on September 12, 2016 Permalink | Reply
    Tags: , Astrophysics, , ,   

    From New Scientist: “First glimpse of a black hole being born from a star’s remains” 


    New Scientist

    12 September 2016
    Anna Nowogrodzki

    Born phoenix-like from the ashes of a dying star? Science Photo Library/Getty

    We’ve received a birth announcement from 20 million light years away, in the form of our first ever glimpse of what seems to be the birth of a black hole.

    When massive stars run out of fuel, they die in a huge explosion, shooting out high-speed jets of matter and radiation. What’s left behind collapses into a black hole, which is so dense and has such strong gravity that not even light can escape it.

    Or so the theory goes, anyway. Now, a team led by Christopher Kochanek at Ohio State University in Columbus have glimpsed something very special in data from the Hubble Space Telescope, from when it was watching the red supergiant star N6946-BH1, which is about 20 million light years from Earth.

    Fading star

    This star, first observed in 2004, was once about 25 times the mass of our sun. Kochanek and his colleagues found that for some months in 2009, the star briefly flared a million times brighter than our sun, then steadily faded away. New Hubble images show that it has disappeared in visible wavelengths, but a fainter source in the same spot is detectable in the infrared, as a warm afterglow.

    These observations mesh with what theory predicts should happen when a star that size crumples into a black hole. First, the star spews out so many neutrinos that it loses mass. With less mass, the star lacks enough gravity to hold on to a cloud of hydrogen ions loosely bound around it. As this cloud of ions floats away, it cools off, allowing the detached electrons to reattach to the hydrogen. This causes a year-long bright flare – when it fades, only the black hole remains.

    There are two other potential explanations for the star’s disappearing act: it could have merged with another star, or be hidden by dust. But they don’t fit the data: a merger would shine more brightly than the original star for much longer than a few months, and dust wouldn’t hide it for so long.

    “It’s an exciting result and long anticipated,” says Stan Woosley at Lick Observatory in California.

    “This may be the first direct clue to how the collapse of a star can lead to the formation of a black hole,” says Avi Loeb at Harvard University.

    A dark life cycle

    The find needs further confirmation, but that may not be far off. Material falling into the black hole would emit X-rays in a particular spectrum, which could be spotted by the Chandra X-ray Observatory. Kochanek says his group will be getting new data from Chandra in the next two months or so.

    If Chandra sees nothing, that doesn’t mean it’s not a black hole. In any case, the team will continue to look with Hubble – the longer the star is not there, the more likely that it’s a black hole. “Patience proves it no matter what,” says Kochanek.

    This data will help describe the beginning of the life cycle of a black hole, and will inform simulations of how black holes form and what makes a massive star form a neutron star rather than a black hole.

    Despite calling himself a “nasty pessimist”, Kochanek thinks it’s quite likely this is indeed the formation of a black hole. “I’m not quite at ‘I’d bet my life on it’ yet,” he says, “but I’m willing to go for your life.”

    See the full article here .

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

    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 .

    Please help promote STEM in your local schools.

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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 2:07 pm on August 6, 2016 Permalink | Reply
    Tags: , Astrophysics, , , Where did the Big Bang happen?   

    From Ethan Siegel: “Where did the Big Bang happen?” 

    From Ethan Siegel


    This image represents the evolution of the Universe, starting with the Big Bang. The red arrow marks the flow of time. Image credit: NASA / GSFC.

    If you’re looking for a point in space, the answer is going to shock you.

    “The world you see, nature’s greatest and most glorious creation, and the human mind which gazes and wonders at it, and is the most splendid part of it, these are our own everlasting possessions and will remain with us as long as we ourselves remain.” -Seneca

    Of all the concepts and topics that get tossed around, the Big Bang is one of the most controversial. Sure, it’s a scientific theory that’s quite old — it’s been around since the 1940s — and the evidence in favor of it has been overwhelming since the 1960s. The idea is simple: that the Universe had a beginning. That it had a birthday. That there was a day without a “yesterday,” where matter, radiation and the expanding, cooling Universe we recognize did not exist before a certain moment in time. And yet, here we are. Which brings up a slew of questions to any curious mind. Mark Trubnikov is one such curious individual, and he wants to know:

    [A]re there any theories or experiments that can find out and prove our position in space according to the Big Bang point? I think that, as far, as we have very limited observation opportunities form our planet, that would be not so easy to determine the curvature of the space here… [W]hy do we think that the Big Bang happened in a point in the 3D-space? And why do we think that the Universe is a sphere?

    These are all good questions, and they’re all common conceptions that people have of the Universe, for good reason. But are these assertions true?

    The evolution of large-scale structure in the Universe, from an early, uniform state to the clustered Universe we know today. Image credit: Angulo et al. 2008, via Durham University at http://icc.dur.ac.uk/index.php?content=Research/Topics/O6.

    We commonly think of the Big Bang as a literal “bang,” or an explosion. It’s true that the Universe was similar to a tremendous, energetic, expanding fireball in the very earliest stages. It was:

    full of particles and antiparticles of all different types, as well as radiation,
    all of which was expanding away from every other particle, antiparticle and quantum of radiation,
    all of which was cooling down and slowing down as it expanded.

    But I’ve carefully been using the word “expansion” rather than explosion when it comes to this phenomenon. An explosion is something that occurs at one location in space and whose debris emanates from that point. A supernova is an explosion; a gamma ray burst is an explosion; a bomb detonating is an explosion; a grenade igniting is an explosion.

    An artist’s impression of supernova 1993J, an exploding star in the galaxy M81. Image credit: NASA, ESA, and G. Bacon (STScI).

    But the Big Bang is not an explosion. When we talk about “the hot Big Bang,” we’re talking about the very first moment that the Universe could be described by this particle, antiparticle and radiation-filled state. Where the Universe begins expanding and cooling from this state according to the laws of General Relativity, and where we head down the path towards antimatter annihilating away, atomic nuclei and then neutral atoms forming, and finally forming stars, galaxies and the large-scale structure we see today. The key to the first question is understanding exactly what the Universe was doing at that moment: at the moment where we can first describe it in this hot Big Bang framework.

    The quark-gluon plasma of the early Universe. Image credit: Brookhaven National Laboratory.

    As far as we can tell, there was no special point. There was no “origin” to the Universe starting out this way. What all the evidence points to is a counterintuitive but no less true conclusion: that the Big Bang occurred everywhere all at once. The evidence for this is overwhelming, and comes from the Universe itself. The Universe, if we look at the large-scale structure, of how galaxies cluster, of what the leftover glow from the Big Bang looks like, of what the average density is in regions more than a few hundred million light years in size, etc., we find two important observational facts about our Universe: it appears to have the same properties everywhere, and it looks the same in all directions. In physics terms, this means the Universe is homogeneous (the same at all locations) and isotropic (the same in all directions).

    Our view of a small region of the Universe, where each pixel in the image represents a mapped galaxy. On the largest scales, the Universe is the same in all directions and at all measurable location. Image credit: SDSS III, data release 8, of the northern galactic cap.

    You don’t get a Universe with those properties from an explosion, period. The “faster moving stuff” ends up the farthest away, but it also ends up the most diffuse over time; greater distances would appear to have fewer galaxies per unit volume, but they don’t in our Universe. Wherever the explosion occurred would be a clearly identifiable point. Because of how our Universe works, that point would have to be just a few million light years offset from the Milky Way, located just outside of the local group; statistically, with more than 170 billion galaxies in the Universe, the odds are about 100 times worse than winning either the Powerball or the Mega Millions jackpot.

    The fact that the Universe is homogeneous and isotropic tells us that the Big Bang happened simultaneously, some 13.8 billion years ago, at all locations equally. But we can’t see it at all locations equally; we can only see it from where we are. Our vantage point is inherently limited. Which is why you often see illustrations like the one below: of our Universe as seen from where we are, and with us at the center.

    Artist’s logarithmic scale conception of the observable universe. Image credit: Wikipedia user Pablo Carlos Budassi.

    But this does not mean that the Universe is a sphere! In fact, if we want to know the shape of the Universe, it’s something we can actually measure, and place constraints on. If you walk outside and send two of your buddies in different directions so that you can all see each other, the three of you will form a triangle. Each one of you can measure the angle the other two appear to be at, relative to your point of view. If you then know those three angles, you can add them up: you’d expect them to be 180º, because that’s how many degrees are in the three angles of any triangle.

    Any triangle, that is, that’s in flat space.

    The angles of a triangle add up to different amounts depending on the spatial curvature present. Image credit: NASA / WMAP science team.

    As it turns out, space doesn’t need to be flat! It could be negatively curved, like the surface of a horse’s saddle, where the angles add up to less than 180º. Or it could be positively curved, like the surface of a sphere, where the angles add up to more than 180º. If you stood on the equator in South America, your friend stood on the equator in Africa and another friend stood at the North Pole, you’d discover that the difference was significant: you’d wind up with a number closer to 270º than 180º. Well, we don’t have friends who can tell us what angles they see in space, but we have something just as good: the fluctuations in the Cosmic Microwave Background, which would have very different appearances depending on what the curvature of space actually is.

    The appearance of different angular sized of fluctuations in the CMB results in different spatial curvature scenarios. Image credit: the Smoot group at Lawrence Berkeley Labs, via http://aether.lbl.gov/universe_shape.html.

    Well, we’ve made those observations, and what we’ve found is overwhelming: the Universe is flat, as far as we can tell. Really, really flat. In fact, the latest joint data from Planck and from the Sloan Digital Sky Survey tell us that if the Universe is curved — either positively or negatively — it’s on a scale that’s at least 400 times larger than the part of our Universe observable to us. And that part, the part we can see, is over 92 billion light years across.

    And that’s just the part we can see. As far as our theories indicate, there’s very likely much more Universe just like our own outside of what we can observe. Image credit: E. Siegel, based on work by Wikimedia Commons users Azcolvin 429 and Frédéric MICHEL.

    So the Big Bang happened everywhere at once, 13.8 billion years ago, and our Universe is spatially flat to the best we can measure it at present. The Big Bang did not happen at a point, and the way we can tell is through the extraordinarily high degree of isotropy and homogeneity of the Universe. (It’s so good that when we notice an inhomogeneity that’s 0.01% of the Universe’s average, we wonder if something’s wrong!) So if you want to assert that the Big Bang happened exactly where you are, and that you’re right at the center of where it all started, no one can tell you that you’re wrong. It’s just that everyone, everywhere, in the entire Universe is just as right as you are when they make that claim, too.

    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 8:21 pm on May 11, 2016 Permalink | Reply
    Tags: , Astrophysics, , , , Which Elements Will Never Be Made By Our Sun?   

    From Ethan Siegel: “Which Elements Will Never Be Made By Our Sun?” 

    Starts with a Bang

    May 11, 2016
    Ethan Siegel

    A high-resolution spectrum showing the elements in the Sun, by their visible-light absorption properties. Image credit: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF.

    Our Sun is the greatest source of heat and light in the entire Solar System, fusing hydrogen into helium in a nuclear chain reaction in its core. Because an atomic nucleus of helium is 0.7% lighter than the four hydrogen nuclei that it’s created from, that act of nuclear fusion releases a tremendously efficient amount of energy. Over the course of its 4.5 billion year lifetime (so far), the Sun had lost about the mass of Saturn due to the amount of hydrogen that’s fused into helium, through Einstein’s E = mc^2, which is the root source of all the sunlight we receive here on Earth. The Sun has a lot more going on inside of it than just fusing hydrogen (the lightest element) into helium (the second lightest), though, and is capable of making so many more elements than that. But the periodic table has a whole slew of elements the Sun can never make.

    Periodic Table 2016
    Periodic Table 2016

    We’re pretty fortunate that our Sun wasn’t among the very first stars in the Universe. Shortly after the Big Bang, the Universe was made exclusively of hydrogen and helium: 99.999999% of the Universe was composed of these two elements alone. Yet the first massive stars didn’t just fuse hydrogen into helium, but eventually fused helium into carbon, carbon into oxygen, oxygen into silicon and sulfur, and then silicon and sulfur into iron, nickel and cobalt. When the inner core reached a large enough concentration of those heavy elements, a catastrophic supernova occurred, creating a rapid burst of neutrons that were scattered into the other nuclei. Very quickly, the types of elements present in the Universe climbed up and up the periodic table, creating everything we’ve ever found in nature and many elements even heavier than that. Even the very first core-collapse supernovae created elements that are beyond the limit of what we find on Earth: elements heavier than even uranium and plutonium.

    The various layers of a supernova-bound star. During the supernova itself, many trans-uranic elements are created, through rapid neutron capture. Image credit: Nicolle Rager Fuller of the NSF.

    But our Sun won’t go supernova, and won’t ever make those elements. That rapid burst of neutrons that happens in supernova allows the creation of elements through the r-process, where elements rapidly absorb neutrons and climb the periodic table in great leaps and jumps. Instead, our Sun will burn through the hydrogen in its core, and then will contract and heat up until it can begin fusing helium in its core. This phase of life — where our Sun will become a red giant star — is something that happens to all stars that are at least 40% as massive as our own.

    Red Giant, SSL UC Berkeley

    Reaching the right temperatures and densities, simultaneously, for helium fusion, is what separates red dwarfs (which can’t get there) from all other stars (which can). Three helium atoms fuse together into carbon, and then through another hydrogen-fusion pathway — the CNO cycle — we can create nitrogen and oxygen, while we can continue to add helium to various nuclei to climb up the periodic table. Carbon and helium make oxygen; carbon and oxygen make neon; carbon and neon make magnesium. But two very particular reactions take place that will create the vast majority of elements we know:

    carbon-13 will fuse with helium-4, creating oxygen-16 and a free neutron, and
    neon-22 will fuse with helium-4, creating magnesium-25 and a free neutron.

    Image credit: screenshot from the wikipedia article on the s-process.

    Free neutrons aren’t created in great abundance, just in relatively scarce numbers, since such a small percentage of these atoms actually are carbon-13 or neon-22 at any given time. But these free neutrons can only stick around for about 15 minutes, on average, until they decay away.

    The two types (radiative and non-radiative) of neutron beta decay. Image credit: Zina Deretsky, National Science Foundation.

    Fortunately, the interior of the Sun is dense enough that 15 minutes is more than enough time for this free neutron to run into another atomic nucleus, and when it does, it inevitably gets absorbed, creating a nucleus that’s one atomic mass unit heavier than before the neutron was absorbed. There are a few nuclei this won’t work for: you can’t create a mass-5 nucleus (out of helium-4, for instance) or a mass-8 nucleus (out of lithium-7, for examples), since they’re all inherently too unstable. But everything else will either be stable on timescales of at least tens of thousands of years, or it will decay by emitting an electron (through β-decay), which causes it to move one element up the periodic table.

    Image credit: E. Siegel, based on the original from the University of Oregon’s physics department, via http://zebu.uoregon.edu/2004/a321/lec10.html.

    During any star’s red giant, helium-burning phase, this enabled you to build all the elements between carbon and iron through this process of slow neutron capture, and heavy elements from iron all the way up through lead through that very same process. This process, known as the s-process (because neutrons are produced-and-captured slowly), runs into a problem when it tries to build elements heavier than lead. The most common isotope of lead is Pb-208, with 82 protons and 126 neutrons. If you add a neutron to it, it beta decays to become bismuth-209, which can then capture a neutron and β-decay again to become polonium-210. But unlike the other isotopes, which live for years, Po-210 only lives for days before emitting an alpha particle — or a helium-4 nucleus — and returning back to lead in the form of Pb-206.

    The chain reaction that’s at the end of the line for the s-process. Image credit: E. Siegel and the English Language Wikipedia.

    This leads to a cycle: lead captures 3 neutrons, becomes bismuth, which captures one more and becomes polonium, which then decays back to lead. In our Sun and in all stars that won’t go supernova, that’s the end of the line. Combine that with the fact that there’s no good pathway to get the elements between helium and carbon (lithium, beryllium and boron are produced from cosmic rays, not inside of stars), and you’ll find that the Sun can make a total of 80 different elements: helium and then everything from carbon through polonium, but nothing heavier. For that, you need a supernova or a neutron star collision.

    Two neutron stars colliding, which is the primary source of many of the heaviest periodic table elements in the Universe. Image credit: Dana Berry, SkyWorks Digital, Inc.

    But think about that: of all the naturally occurring elements here on Earth, the Sun makes about 90% of them, all from a tiny, non-descript star of no particular cosmic significance. The ingredients for life are literally that easy to come by.

    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 11:08 am on April 29, 2016 Permalink | Reply
    Tags: Astrophysics, , , , The Globe and Mail   

    From The Globe and Mail via PI: “‘Brilliant’ physicist to hold $8-million research chair at Perimeter Institute” 

    Perimeter Institute
    Perimeter Institute


    Apr. 28, 2016

    Long before the February press conference where physicists reported the first detection of gravitational waves from space – a major scientific achievement that made headlines around the world – Asimina Arvanitaki had arrived at a way to do the same thing with a far smaller and cheaper experiment involving a microscopic disk suspended by powerful lasers.

    The 36-year-old theorist, known to friends and colleagues as Mina, has become a specialist in thinking up novel approaches to some of of the deepest problems in fundamental physics. Her work is at the forefront of an emerging area of research that is sometimes called “the precision frontier” because it involves making exacting measurements of well-understood phenomena and looking for unexpected deviations from what theory predicts.

    “Most of these ideas you can actually build on a table,” said Dr. Arvanitaki.

    Now Dr. Arvanitaki will have more scope and resources to pursue her ideas as the latest recipient of an $8-million research chair at the Perimeter Institute for Theoretical Physics in Waterloo, Ont., where she has worked as a researcher since 2014.

    The new chair is noteworthy for a few reasons. In addition to representing an area of research that thrives on working off the beaten track, Dr. Arvanitaki will become the first female chair holder at the high-profile institute and the first to be supported by a funding source from outside Canada.

    The Stavros Niarchos Foundation, a philanthropic organization headquartered in Athens and associated with a shipping industry fortune, will cover half the cost of the chair with the remaining support coming from the Perimeter Institute.

    Greek heritage is evident in the title of the new position, dubbed the Aristarchus Chair in Theoretical Physics after the ancient philosopher from the Greek island of Samos who famously suggested that the Earth revolves around the sun, some 18 centuries before Nicolaus Copernicus.

    “His thinking implied the sun is exactly like the distant stars,” said Dr. Arvanitaki, who suggested the name for the inaugural chair.

    She added that by foreseeing that our solar system many not be unique in the universe, Aristarchus was also setting the stage for a far more contentious theory in current physics, which holds that our entire universe is just one of many.

    “It’s a very controversial idea. People hate it, but I find it fascinating,” Dr. Arvanitaki said.

    Raised in a small village in southern Greece, Dr. Arvanitaki was the child of two teachers and grew up with an appetite for learning. She recalls that at a young age she correctly calculated the time it takes light to travel from Earth to the sun – about eight minutes – and was stunned to realize that “we cannot know the ‘now’ of the sun.”

    Dr. Arvanitaki came to Perimeter after earning her PhD and doing postdoctoral work at Stanford University under Savas Dimopoulus, a widely respected theorist who also hails from Greece.

    “She’s one of the most brilliant young people I’ve ever met,” Dr. Dimopoulos said of his former student and collaborator.

    He added that intelligence alone was not enough for success in physics, and that one way Dr. Arvanitaki excels is in selecting problems to work on that lead to productive results.

    “You have to have good taste,” he said. “Or in her case, even inventing new directions and new ways to see very well-motivated ideas.”

    Dr. Arvanitaki said she was looking forward to bringing on more researchers and students to accelerate her efforts to explore new domains of physics, and was pleased at the prospect of doing it at the Perimeter Institute. “There’s something about this place – you feel it when you walk in the building – it’s intoxicating.”

    The Institute was established in 1999 by BlackBerry co-founder Mike Lazaridis and has since drawn substantial government support, including a $50-million investment over five years announced in the latest federal budget.

    Black holes merging Swinburne Astronomy Productions
    Black holes merging Swinburne Astronomy Productions

    See the full article here .

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    About Perimeter

    Perimeter Institute is a leading centre for scientific research, training and educational outreach in foundational theoretical physics. Founded in 1999 in Waterloo, Ontario, Canada, its mission is to advance our understanding of the universe at the most fundamental level, stimulating the breakthroughs that could transform our future. Perimeter also trains the next generation of physicists through innovative programs, and shares the excitement and wonder of science with students, teachers and the general public.

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