Tagged: Astrophysics Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 10:39 am on January 16, 2017 Permalink | Reply
    Tags: , Astrophysics, , , There are at least two trillion galaxies in the universe ten times more than previously thought,   

    From U Nottingham: “There are at least two trillion galaxies in the universe, ten times more than previously thought” 

    1

    University of Nottingham

    13 Oct 2016 [Just turned up in a social media search]
    Lindsay Brooke
    Media Relations Manager
    lindsay.brooke@nottingham.ac.uk
    +44 (0)115 951 5751
    Location: University Park

    1
    Image of the HST GOODS-South field, one of the deepest images of the sky but covering just one millionth of its total area. The new estimate for the number of galaxies is ten times higher than the number seen in this image. Credit: NASA / ESA / The GOODS Team / M. Giavalisco (UMass., Amherst)

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    Astronomers have long sought to determine how many galaxies there are in the universe. This is a fundamental question that we have only been able to address with any certainty due to new scientific results.

    During the past 20 years very deep Hubble Space Telescope images have found a myriad of faint galaxies, and it was approximated that the observable Universe contains about 100 billion galaxies in total.

    Now, an international team, led by Christopher Conselice, Professor of Astrophysics at The University of Nottingham, has shown that the actual number is much higher than this.

    Professor Conselice and his team has shown that the number of galaxies in our universe is at least two trillion – ten times more than previously thought – the often quoted value of around 100 Billion.

    Current astronomical technology allows us to study a fraction of these galaxies– just 10%.

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

    It means that over 90% of the galaxies in our universe have yet to be discovered, and will only be seen once bigger and better telescopes are developed.

    ESO 50 Large
    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile
    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile

    LSST
    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.
    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes

    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

    NASA/ESA/CSA Webb Telescope annotated
    NASA/ESA/CSA Webb Telescope annotated

    NASA/WFIRST telescope
    NASA/WFIRST telescope

    The research – The Evolution of Galaxy number density at Z < 8 and its implications – is published today (October 13, 2016) in the Astrophysical Journal – the foremost research journal in the world dedicated to recent developments, discoveries and theories about astronomy and astrophysics.

    The results have clear implications for galaxy formation, and also help solve an ancient astronomical paradox — why is the sky dark at night?

    Professor Conselice said: “We are missing the vast majority of galaxies because they are very faint and far away. The number of galaxies in the universe is a fundamental number we would like to know, and it boggles the mind that over 90% of the galaxies in the universe have yet to be studied.

    Who knows what interesting properties we will find when we study these galaxies with the next generation of telescopes. These galaxies will likely hold the clues to many outstanding astrophysical issues.”

    Intergalactic archaeological dig

    Professor Conselice’s research is the culmination of 15 year’s work. His team converted pencil beam images of deep space from telescopes around the world, and especially from the Hubble telescope into 3D maps to calculate the volume as well as the density of galaxies of one tiny bit of space after another.

    This painstaking research enabled him to establish how many galaxies we have missed – much like an intergalactic archaeological dig.

    The results of this study are based on the measurements of the number of galaxies at different epochs – different instances in time – through the universe’s history.

    When Professor Conselice and his team at Nottingham, in collaboration with scientists from the Leiden Observatory at Leiden University in the Netherlands and the Institute for Astronomy at the University of Edinburgh, examined how many galaxies there were in a given value they found that this increased significantly at earlier times.

    In fact, it appears that there are a factor of 10 more galaxies in a given volume of space when the universe was a few billion years old compared with today. Most of these galaxies are low mass systems with masses similar to those of the satellite galaxies surrounding the Milky Way.

    Professor Conselice said: “This is very surprising as we know that over the 13.7 billion years of cosmic evolution galaxies are growing through star formation and merging with other galaxies. Thus, to find that there were in fact more galaxies in the past implies that that significant evolution in galaxies must have occurred to reduce the number of galaxies through extensive merging of systems. This also gives us a verification of the top-down formation of structure in the universe.”

    Probing cosmic history answers astronomical questions

    By probing deep into space Professor Conselice and his team have been able to go way back in time – more than 13 billion years in the past – to find out how our universe evolved and answer some vexing questions.

    The implications of this research are many, for instance; galaxies are likely to be forming by merging together. This decreases the number of systems as time progresses which provides a possible solution to Oblers’ paradox – why the sky is dark at night?

    Solutions to this in the past were based on the fact that the universe is finite in size as well as in time. However, if we consider all the undiscovered galaxies then in principle the critiera for Oblers’ paradox is met.

    However, most galaxies in the universe are very distant and their light is absorbed by gas in intergalactic space. Otherwise, we would see the night sky lit up everywhere.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    2

    “The University of Nottingham shares many of the characteristics of the world’s great universities. However, we are distinct not only in our key strengths but in how our many strengths combine: we are financially secure, campus based and comprehensive; we are research-led and recruit top students and staff from around the world; we are committed to internationalising all our core activities so our students can have a valuable and enjoyable experience that prepares them well for the rest of their intellectual, professional and personal lives.”

     
  • richardmitnick 3:07 pm on January 14, 2017 Permalink | Reply
    Tags: , Astrophysics, , , , EurekaAlert, Keck Cosmic Web Imager   

    From Caltech via EurekaAlert: “New Caltech instrument poised to image the cosmic web” 

    Caltech Logo
    Caltech

    1

    EurekaAlert

    12-Jan-2017
    Whitney Clavin
    wclavin@caltech.edu
    626-395-1856

    Keck Cosmic Web Imager ships from Caltech to Keck Observatory

    2
    Hector Rodriguez, senior mechanical technician, works on the Keck Cosmic Web Imager in a clean room at Caltech. Caltech

    An instrument designed to image the vast web of gas that connects galaxies in the universe has been shipped from Los Angeles to Hawaii, where it will be integrated into the W. M. Keck Observatory.

    Keck Observatory, Mauna Kea, Hawaii, USA
    Keck Observatory, Mauna Kea, Hawaii, USA

    The instrument, called the Keck Cosmic Web Imager, or KCWI, was designed and built by a team at Caltech led by Professor of Physics Christopher Martin. It will be one of the best instruments in the world for taking spectral images of cosmic objects–detailed images where each pixel can be viewed in all wavelengths of visible light. Such high-resolution spectral information will enable astronomers to study the compositions, velocities, and masses of many objects, such as stars and galaxies, in ways that were not possible before.

    One of KCWI’s main goals, and a passion of Martin’s for the past 30 years, is to answer the question: What is the gas around galaxies doing?

    “For decades, astronomers have demonstrated that galaxies evolve. Now we’re trying to figure out how and why,” says Martin. “We know the gas around galaxies is ultimately fueling them, but it is so faint–we still haven’t been able to get a close look at it and understand how this process works.”

    Martin and his team study what is called the cosmic web–a vast network of streams of gas between galaxies. Recently, the scientists have found evidence supporting what is called the cold flow model, in which this gas funnels into the cores of galaxies, where it condenses and forms new stars.

    3
    The forming galaxy with binary quasars as it fits into the timeline of the Universe. We’re seeing it 10 billion years ago, during the epoch of galaxy formation. Credit: Caltech Academic Media Technologies

    Researchers had predicted that the gas filaments would first flow into a large ring-like structure around the galaxy before spiraling into it–exactly what Martin and his team found using the Palomar Cosmic Web Imager, a precursor to KCWI, at Caltech’s Palomar Observatory near San Diego.

    Caltech Palomar Cosmic Web Imager
    Caltech Palomar Cosmic Web Imager

    “We measured the kinematics, or motion, of the gas around a galaxy and found a very large rotating disk connected to a gas filament,” says Martin. “It was the smoking gun for the cold flow model.”

    With KCWI, the researchers will get a closer look at the gas filaments and ring-like structures around galaxies that range from 10 to 12 billion light-years away, an era when our universe was roughly 2 to 4 billion years old. Not only can KCWI take more detailed pictures than the Palomar Cosmic Web Imager, it has other advances such as better mirror coatings. The combination of these improvements with the fact that KCWI is being installed at one of the twin 10-meter Keck telescopes–the world’s largest observatory with some of the darkest known skies on Earth–means that KCWI will have an improved performance by more than an order of magnitude over the Palomar Cosmic Web Imager.

    KCWI will map the gas flowing from the intergalactic medium–the space between galaxies–into many young galaxies, revealing, for the first time, the dominant mode of galaxy formation in the early universe. The instrument will also search for supergalactic winds from galaxies that drive gas back into the intergalactic medium. How gas flows into and out of forming galaxies is the central open question in the formation of cosmic structures.

    “We designed KCWI to study very dim and diffuse objects, our main emphasis being on the wispy cosmic web and the interactions of galaxies with their surroundings,” says Mateusz (Matt) Matuszewski, the instrument scientist for the project.

    KCWI is also designed to be more a general-purpose instrument than the Palomar’s Cosmic Web Imager, which is mainly for studies of the cosmic web. It will study everything from gas jets around young stars to the winds of dead stars and supermassive black holes and more. “The instrument is really versatile,” says Matuszewski. “Observers can configure the optics to adjust the spatial and spectral scales and resolutions to suit their interests.”

    The nuts and bolts of KCWI

    Scientists and engineers have been busy assembling the highly complex elements of the KCWI instrument at Caltech since 2012. The instrument is about the size of an ice cream truck and weighs over 4,000 kilograms. The core feature of KCWI is its ability to capture spectral information about objects, such as galaxies, across a wide image. Typically, astronomers capture spectra using instruments called spectrographs, which have narrow slit-shaped windows. The spectrograph breaks apart light from the slit into each of the colors making up the target object, just like a prism that spreads light into a rainbow. But traditional spectrographs cannot be used to capture spectral information across an entire image.

    “Traditional spectrographs use multiple small slits to capture many stars or the cores of many galaxies,” says Martin. “Now, we want to look at features that are extended across the sky, such as stellar jets and galaxies, which have complex structures, velocities, and gas flows. If you can only look through a slit, you can only see a small part of what is going on. But we want to see the whole picture. That’s why we need an imaging spectrograph, a device that gives you an image for every single wavelength across a wide view.”

    To create a spectrograph that can image more extended objects like galaxies, KCWI uses what is called an integral field design, which basically divides an image up into 24 slits, and gathers all the spectral information at once.

    “If you’re looking at something big in the sky, it’s inefficient to just have one slit and step your way across that object, so an integral field spectrograph combines a number of slit-shaped mirrors together across a continuous field of view,” says Patrick Morrissey, the project scientist for KCWI who now works at JPL. “Imagine looking into a broken mirror–the reflected image is shifted around depending on the angles of the pieces. This is how the integral field spectrograph works. A series of mirrors works together to make a square-shaped stack of slits across an image appear as a single traditional vertical slit.”

    KCWI has the highest spectral resolution of any integral field spectrograph, which means it can better break apart the rainbow of light to see more colors, or wavelengths. The first phase of the instrument, now on its way to Keck, covers the blue side of the visible spectrum, spanning wavelength ranges from 3500 to 5600 Angstroms. A second phase, extending coverage to the red side of the spectrum, out to 10400 Angstroms, will be built next.

    KCWI to Climb Mauna Kea

    After KCWI arrives in Hawaii on January 18, engineers will guide it up to the top of Mauna Kea, where Keck is perched. A series of checkout and alignment tests is planned, and will be followed in a few months by the first observations through the Keck telescope.

    “There are train tracks around the telescope where the instruments are installed,” says Morrissey. “It’s like one of those old railroad roundhouses where the train would come in and they would spin it to an available space for storage. The telescope turns around, points to the instrument that the astronomer wants to use, and then they roll that instrument on. Soon KCWI will becomes part of the telescope.”

    KCWI is funded by the National Science Foundation, through the Association of Universities for Research in Astronomy (AURA) program, and by the Heising-Simons Foundation, the W.M. Keck Foundation, the Caltech Division of Physics, Mathematics and Astronomy, and the Caltech Optical Observatories.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    Caltech campus
    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

     
  • richardmitnick 2:28 pm on January 14, 2017 Permalink | Reply
    Tags: , Astrophysics, , , , , Twinkles   

    From Symmetry: “Twinkle, twinkle, little supernova” 

    Symmetry Mag
    Symmetry

    01/12/17
    Ricarda Laasch

    1
    Phil Marshall, SLAC

    Using Twinkles, the new simulation of images of our night sky, scientists get ready for a gigantic cosmological survey unlike any before.

    Almost every worthwhile performance is preceded by a rehearsal, and scientific performances are no exception. Engineers test a car’s airbag deployment using crash test dummies before incorporating them into the newest model. Space scientists fire a rocket booster in a test environment before attaching it to a spacecraft in flight.

    One of the newest “training grounds” for astrophysicists is called Twinkles. The Twinkles dataset, which has not yet been released, consists of thousands of simulated, highly realistic images of the night sky, full of supernovae and quasars. The simulated-image database will help scientists rehearse a future giant cosmological survey called LSST.

    LSST
    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.
    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    LSST, short for the Large Synoptic Survey Telescope, is under construction in Chile and will conduct a 10-year survey of our universe, covering the entire southern sky once a year. Scientists will use LSST images to explore our galaxy to learn more about supernovae and to shine a light on the mysterious dark energy that is responsible for the expansion of our universe.

    It’s a tall order, and it needs a well prepared team. Scientists designed LSST using simulations and predictions for its scientific capabilities. But Twinkles’ thousands of images will give them an even better chance to see how accurately their LSST analysis tools can measure the changing brightness of supernovae and quasars. That’s the advantage of using simulated data. Scientists don’t know about all the objects in the sky above our heads, but they do know their simulated sky— there, they already know the answers. If the analysis tools make a calculation error, they’ll see it.

    The findings will be a critical addition to LSST’s measurements of certain cosmological parameters, where a small deviation can have a huge impact on the outcome.

    “We want to understand the whole path of the light: From other galaxies through space to our solar system and our planet, then through our atmosphere to the telescope – and from there through our data-taking system and image processing,” says Phil Marshall, a scientist at the US Department of Energy’s SLAC National Accelerator Laboratory who leads the Twinkles project. “Twinkles is our way to go all the way back and study the whole picture instead of one single aspect.”

    Scientists simulate the images as realistically as possible to figure out if some systematic errors add up or intertwine with each other. If they do, it could create unforeseen problems, and scientists of course want to deal with them before LSST starts.

    Twinkles also lets scientists practice sorting out a different kind of problem: A large collaboration spread across the whole globe that will perform numerous scientific searches simultaneously on the same massive amounts of data.

    Richard Dubois, senior scientist at SLAC and co-leader of the software infrastructure team, works with his team of computing experts to create methods and plans to deal with the data coherently across the whole collaboration and advise the scientists to choose specific tools to make their life easier.

    “Chaos is a real danger; so we need to keep it in check,” Dubois says. “So with Twinkles, we test software solutions and databases that help us to keep our heads above water.”

    The first test analysis using Twinkles images will start toward the end of the year. During the first go, scientists extract type 1a supernovae and quasars and learn how to interpret the automated LSST measurements.

    “We hid both types of objects in the Twinkles data,” Marshall says. “Now we can see whether they look the way they’re supposed to.”

    LSST will start up in 2022, and the first LSST data will be released at the end of 2023.

    “High accuracy cosmology will be hard,” Marshall says. “So we want to be ready to start learning more about our universe right away!”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 2:34 pm on January 13, 2017 Permalink | Reply
    Tags: , , Astrophysics, , , When Planets Won’t Stay Put   

    From astrobites: “When Planets Won’t Stay Put” 

    Astrobites bloc

    Astrobites

    Title: Dynamical origin of extrasolar planet eccentricity distribution
    Authors: Mario Jurić and Scott Tremaine
    First author’s institution: Department of Astrophysical Sciences, Princeton University, USA
    PrincetonUniversity
    Status: Published in ApJ (2008) [open access]

    If you fill your house with rocks and go away for a while, you may reasonably expect that the rocks will be there, in their original configuration, when you return. This is in the Constitution.

    If you instead choose to decorate with lizards (which are bound not by the Constitution, but by lizard law), you will find your house much changed when you come back. No matter how you arranged them originally, several will have escaped, and the rest will be under your furniture (whence they will need to be chased if you want to salvage your decor).

    Haters may say that planets are more like rocks than like lizards, which is true in the narrow sense that many planets are large rocks with gaseous envelopes, not reptiles with feet and external ears. But get a whole bunch of planets together, and they behave more like a house full of lizards than a house full of rocks. A system of planets placed in orbit around a star and left to its own gravitational devices doesn’t stick to its initial arrangement. Instead, the shapes of the orbits of the planets change over time. They grow more circular or more elongated as each planet feels the gravitational tug of other planets passing close by.

    Curiously, when you average over many planets in many systems with many different initial orbital shapes, this gradual, chaotic, encounter-by-encounter change tends toward a particular final arrangement of orbital shapes, just as lizards tend to congregate under your couch with obnoxious disregard for their original placement.*

    A suitcase full of planets

    The authors begin by taking a supercomputer** and dumping in a few thousand planetary systems. Each system consists of a central star and a handful of orbiting planets–sometimes as few as 3, or as many as 50. They give these planets a whole range of orbital shapes, or eccentricities: for some planets, circles, and for others, exaggerated, elongated ellipses. The orbit shape is determined by a parameter called eccentricity, or e, illustrated in Figure 1. e can range from 0 in the case of a circular orbit all the way up to very nearly 1 in the case of a long, narrow ellipse.

    1
    Figure 1: Three orbits around a star. From left to right, eccentricity e equals 0, 0.5, and 0.95. No image credit.

    They assign the eccentricities for each system according to a few slightly different rules: some systems have planets on circular orbits, while others have a mixture of shapes. (Crucially, they still love all the systems equally.)

    Next, they let their simulated planets orbit, starting from these initial eccentricities, and watch their orbital characteristics change as time goes on. Early on, the systems are a bumper-car disaster of planet-planet and planet-star collisions, with a healthy additional fraction of planets fully ejected from their systems by close encounters (much like if someone in San Diego looked up and saw a few Disneyland bumper cars flying speedily southeast overhead). After a couple dozen million years, an average of only 2-3 planets per system remain, and after a hundred million years, their average orbital properties are stable.

    A surprising convergence

    After this evolution, about half of the systems (Figure 2, bottom panel, colored bands), despite their very different rules for initial eccentricity assignment, converge to astonishingly similar shapes. These are the planetary equivalents of the under-couch lizards. Most of the remaining systems (Figure 2, middle panel, colored bands) appear to approach the same final state, but retain some imprint of their initial eccentricity distributions in the form of a low-eccentricity peak, which is like if you caught a couple of especially slow lizards in the act of moseying over to the couch from their initial perch on your shelf. Only one set of planets, which had completely circular initial orbits, is unchanged from its initial state, and this is the one that least matches a population of real exoplanets. It’s like it wasn’t even trying!

    2
    Figure 2: The final eccentricity distributions of the simulated planetary systems. Each colored band corresponds to a different rule for assigning initial eccentricities to planetary systems. One rule (that planets must start on circular orbits) yielded systems which hardly changed from the beginning of the simulation to the end (top panel); four others (bottom panel), despite their dramatically different initial conditions, converged on the same final eccentricity distribution, plotted as a smooth black line. The remaining rules (middle panel) appear to yield a mixture or superposition of the other types. The eccentricity distribution of real, observed exoplanets is plotted as a black histogram in each panel.

    Why, and what next?

    An underlying pattern emerges: the systems which converged to the same distribution in the end were tightly packed at the beginning, with little room (on average) between each planet and its nearest orbital neighbor. By the end of the hundred million years, enough of these uncomfortably close planets had collided with each other, been kicked out of their systems, or otherwise spread out that those that remained had some breathing room and no longer underwent frequent close encounters. In contrast, the few systems which maintained their initial eccentricity distribution throughout the simulation were adequately spaced out from the beginning. Our own solar system fits this bill, because the planets are adequately spaced out and all on quite circular orbits—making our solar system, yet again, a little bit different from the norm.

    So what can we do with this information? For one, now that we know that planetary systems are likely to act this way, we can make smarter assumptions to about planet populations in the future. And planet simulators can rest easier knowing that their choices of initial parameters don’t matter so much in the end, except for in systems like ours. Lizards, I suppose, can take this result as celestial validation and go about their decor-ruining business more smugly than ever.

    *Please help me, my apartment is full of uncooperative lizards. I don’t want them to leave, I just need them to listen.

    ** Supercomputer uncredited.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 3:52 pm on January 11, 2017 Permalink | Reply
    Tags: , Astrophysics, , , , Motherboard, ,   

    From PI via Motherboard: “Dark Matter Hunters Are Hoping 2017 is Their Year” 

    Perimeter Institute
    Perimeter Institute

    Motherboard

    January 3, 2017
    Kate Lunau

    It can be unsettling to realize that only five percent of the universe is made of the kind of matter we know and understand—everything from the planets and stars, to trees and animals and your dining room table.

    Roughly one-quarter is dark matter. This is thought to knit the galaxies together, and has been called the “scaffolding” of the universe, but we’ve never detected it directly. Scientists believe they can see dark matter’s traces in the way that galaxies rotate, but they still have no idea what it is. (Most of the universe, about 70 percent, is dark energy, a mysterious force that permeates space and time. It’s even less well-understood than dark matter.)

    Confirming dark matter’s existence would change humankind’s perspective on the universe. 2016 was a year of dark matter disappointments, as big searches came up empty. Most are looking for WIMPs—weakly interacting massive particles, the leading contender for a dark matter particle.

    2017 might just be the year we finally catch one. And if we don’t, well, it may be that our best theories about dark matter are wrong—that we’re looking in the wrong places, with the wrong instruments. Maybe dark matter, whatever it is, will turn out to be even weirder and more surprising than anyone has so far predicted. Maybe it’s not a WIMP, but some other bizarre kind of particle.

    Then there’s the outside possibility that dark matter doesn’t exist, that it’s an illusion. If that’s the case, we’ll have to consider whether we’ve been fundamentally misreading the universe’s clues.

    Buried deep in a mine near Sudbury in northern Ontario is SNOLAB, a vast underground laboratory where scientists are performing a range of experiments, including looking for dark matter. Often compared to the lair of a Bond villain, it’s an ultra-clean, high-tech facility. Two kilometers of solid rock overhead shield its detectors from cosmic radiation, allowing them to sift for bits of matter from dying stars and the Sun: science done here won the Nobel Prize in Physics, in 2015.

    2
    A scientist works on the deck of DEAP-3600, a dark matter search at SNOLAB. Image: SNOLAB

    I recently travelled to SNOLAB. To get there, I had to don full mining gear (including a hardhat and headlamp), drop down underground in a rattling dark cage, and hike a kilometre or so to reach the gleaming white facility, which is cleaner inside than an operating room—a startling contrast to the dirty nickel mine that surrounds it.

    After the long hike through the mine, anyone who wants to enter SNOLAB has to undress, shower (with soap and shampoo), and put on lint-free clothing and a hairnet. Any bit of dust from the mine, which is naturally radioactive, can mess up the experiments.

    There, I met research scientist Ken Clark, a congenial physicist with a sandy-coloured beard. Like me, he was wearing safety goggles and a hardhat. Clark has worked on high-profile dark matter searches like CDMS and LUX, and collaborates on the IceCube detector at the South Pole in Antarctica.

    LBL SuperCDMS
    LBL SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)
    LBL SuperCDMS, at SNOLAB (Vale Inco Mine, Sudbury, Canada)

    LUX Xenon experiment at SURF
    LUX Xenon experiment at SURF, Lead, SD, USA

    U Wisconsin ICECUBE neutrino detector at the South Pole
    IceCube neutrino detector interior
    U Wisconsin ICECUBE neutrino detector at the South Pole

    Now he’s with PICO, a dark matter search that targets the WIMP particle.

    5

    It was launched in 2013 when two other collaborations, called PICASSO and COUPP, merged.

    6
    A multi-bubble image of a neutron scattering in the PICO detector. Image: PICO Collaboration

    PICO is a bubble detector: a tank of superheated fluid kept higher than its natural boiling point. If dark matter bumps into the nucleus of another particle in the detector, it should cause a tiny bubble to form. Dark matter courses through the Earth and right through our bodies, so it will reach the detector underground, even through all that rock overhead. But that’s also part of the challenge—dark matter is thought to only rarely interact with normal matter, if at all, so it’s really tricky to catch.

    Clark believes we might just find dark matter in the next year or two. “It’s exciting times,” he said.

    Other searches are due to turn on soon, he explained, and those that are already up-and-working are getting increasingly sensitive. In 2017, Clark said it’s possible we’ll see new results from PICO, DEAP (a different detector, also at SNOLAB), as well as China’s ambitious PandaX project, and another in Italy called XENON1T. Even more searches will turn on in 2018.

    “Provided the models are correct, we should see something soon,” Clark told me.

    7
    A scientist works on the steel vessel of DEAP-3600. Image: DEAP Collaboration

    Still, there’s no guarantee, and WIMP searches keep turning up empty-handed. For example, in the summer, the highly sensitive LUX—which uses liquid xenon in a South Dakota mine as its detector—announced it had seen zero WIMPs, after looking for more than a year.

    I phoned Lisa Randall, a prominent theoretical physicist and professor at Harvard University, to ask whether she thinks there’s a chance we’ll find dark matter in the next year or two.

    “I would say kind of the opposite,” said Randall, author of Dark Matter and the Dinosaurs. While she agrees that if dark matter is indeed a WIMP, these searches could find it soon, “that’s just one possibility,” she said.

    The WIMP is “lowest-hanging fruit,” Randall continued: this theoretical particle fits snugly within what’s already known about the Standard Model of physics, which explains how the building blocks of the universe interact. And scientists can imagine ways to actually look for WIMPs, unlike some of the more far-out theories, which are much harder to test in experiments.

    “What if it’s not a WIMP?” Randall said. “Could we still learn something about what dark matter is?”

    Other scientists have different strategies for solving the dark matter puzzle.

    Leslie Rosenberg, a professor of physics at the University of Washington in Seattle, is project scientist on the Axion Dark Matter Experiment, or ADMX, which is looking for a theoretical particle called the axion, which is thought to be much lighter than a WIMP.

    ADMX Axion Dark Matter Experiment
    U Washington ADMX
    U Washington ADMX

    It’s being targeted by other searches under development around the world, Rosenberg told me. ADMX, though, is “the only high-sensitivity axion search now,” he said.

    Maybe we’re being fooled into thinking that dark matter is there.

    ADMX, which uses a resonant microwave cavity nested inside a huge superconducting magnet, started out of a collaboration that began in the mid-nineties. It’s been at full sensitivity for about a year now, Rosenberg told me, and will only get better as the team continues to tweak it. He’s hoping they turn up something soon: their next update should come in the summer of 2017.

    “Axions are bound up in our galaxy,” Rosenberg said. “There [should be] an awful lot of them, and we depend on that as the source of our signal.”

    Axions are a mainstream dark matter candidate. Other ideas get weirder.

    “Personally, I’m interested in the idea that dark matter might have nothing to do with the Standard Model,” Randall told me. “One of the possibilities is that it could be some other type of particle. Maybe it interacts [with itself] via its own light, a dark photon.”

    7
    ESA/Gaia’s first sky map of the Milky Way, based on data collected from July 2014 to Sept. 2015. Image: ESA/Gaia/DPAC

    Randall thinks that one of the best ways to learn about dark matter may be to study the structure of galaxies, and watching the universe at work, to understand how it interacts with itself. The European Space Agency’s Gaia mission, which is making a three-dimensional map of over a thousand million stars, could give insight into some of this, Randall said.

    Asimina Arvanitaki, a theoretical physicist at the Perimeter Institute for Theoretical Physics, suggested to me in a Skype call that dark matter might be detectable through resonant-mass detectors, which are used to hunt for gravitational waves. These ripples in spacetime were detected for the first time in 2016, a hundred years after Albert Einstein predicted their existence.

    Dark matter could also be behaving like a wave, “trapped by gravity and oscillat[ing] at a frequency set by the mass,” she said.

    “The funny thing is you could perhaps even hear dark matter,” Arvanitaki said, “depending on the frequency.”

    Over millions of years, humans have come up with ingenious ways to probe the world around us, from Copernicus and Kepler, through the thousands of scientists involved in the search for the Higgs boson particle at the Large Hadron Collider, and those who are now shaking out the endless diversity of exoplanets that populate our galaxy.

    Because of them, our perspective has changed. When we look up at the night sky today, we understand that just about every star we see hosts at least one planet. The first confirmed exoplanet was announced just over two decades ago.

    Nature can still surprise us.

    7
    The Bullet cluster, formed by the collision of two large galaxy clusters, provides some of the best evidence yet for dark matter. Image: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

    “There’s a chance that dark matter isn’t necessarily a particle at all,” Clark told me. “Some [theorists] say there’s no dark matter. It’s just that we don’t understand how gravity works at large scales,” he continued. “If that’s the case, we’re being fooled into thinking that dark matter is there.”

    Clark and the other dark matter hunters continue their search. If it’s real, “we’re not even made of what most of the universe is made of,” Rosenberg told me. In the grand scheme of things, then, it isn’t dark matter that’s really so exotic and strange—it’s us.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About Perimeter

    Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement.

     
  • richardmitnick 12:30 pm on January 11, 2017 Permalink | Reply
    Tags: , Astrophysics, , , , Galaxy clusters prove dark matter’s existence   

    From Ethan Siegel: “Galaxy clusters prove dark matter’s existence” 

    Ethan Siegel
    1.10.17

    1
    A Hubble image of galaxy cluster MACS J0717, which contains a huge amount of information about the cluster itself thanks to the light from background galaxies. Image credit: ESA/Hubble, NASA and

    You don’t have to detect a particle to know that dark matter is real.

    “You may hate gravity, but gravity doesn’t care.” –Clayton Christensen

    In the 1970s, Vera Rubin’s observations showed galactic rotation was too quick at the outskirts for normal matter alone to explain.

    2
    Vera Rubin in 2009

    3
    Traceable stars, neutral gas, and (even farther out) globular clusters all point to the existence of dark matter, which has mass but exists in a large, diffuse halo well beyond the normal matter’s location. Image credit: Wikimedia Commons user Stefania.deluca.

    But 40 years prior, Fritz Zwicky observed the motions of individual galaxies within clusters, and found the same effect.

    4
    Fritz Zwicky

    5
    The Coma cluster of galaxies, whose galaxies move far too quickly to be accounted for by gravitation given the mass observed alone. Image credit: KuriousG of Wikimedia Commons, under a c.c.a.-s.a.-4.0 license.

    Even as we’ve learned to observe gas, dust, plasma, failed stars and planets, normal matter only explains 15% of the gravitational signal we see.

    6
    This image illustrates a gravitational lensing effect due to the distortion of space by mass. Image credit: NASA, ESA, and Johan Richard (Caltech, USA); Acknowledgements: Davide de Martin & James Long (ESA/Hubble).

    The key to understanding gravitational observations arises from gravitational lensing, where mass bends the background starlight.

    7
    Six examples of the strong gravitational lenses the Hubble Space Telescope discovered and imaged. Image credit: NASA, ESA, C. Faure (Zentrum für Astronomie, University of Heidelberg) and J.P. Kneib (Laboratoire d’Astrophysique de Marseille).

    Under serendipitous configurations, background galaxies are deformed into arcs and multiple, distorted images.

    8
    The galaxy cluster Abell 68, and its many lensed and distorted background galaxies. Image credit: NASA & ESA. Acknowledgement: N. Rose.

    9
    Any configuration of background points of light — stars, galaxies or clusters — will be distorted due to the effects of foreground mass via weak gravitational lensing. Even with random shape noise, the signature is unmistakeable. Image credit: Wikimedia Commons user TallJimbo.

    Even without optimal configurations, weak gravitational lensing causes a well-defined distortion in the shape of background galaxies.

    10
    The galaxy cluster SDSS J1004+4112 severely distorts the light from background galaxies, allowing us to measure its mass. Image credit: ESA, NASA, K. Sharon (Tel Aviv University) and E. Ofek (Caltech).

    With numerous enough galaxy counts — obtainable anywhere with deep telescope observations — the total mass of any galaxy cluster can be reconstructed.

    11
    The overlay in the lower left hand corner represents the distortion of background images due to gravitational lensing expected from the dark matter “haloes” of the foreground galaxies, indicated by red ellipses. The blue polarization “sticks” indicate the distortion. Image credit: Mike Hudson, of shear and weak lensing in the Hubble Deep field. His research page is at http://mhvm.uwaterloo.ca/.

    Consistently, about five times too much mass is needed compared to the existing normal matter.

    12
    Four colliding galaxy clusters, showing the separation between X-rays (pink) and gravitation (blue), indicative of dark matter. Images credit: X-ray: NASA/CXC/UVic./A.Mahdavi et al. Optical/Lensing: CFHT/UVic./A. Mahdavi et al. (top left); X-ray: NASA/CXC/UCDavis/W.Dawson et al.; Optical: NASA/ STScI/UCDavis/ W.Dawson et al. (top right); ESA/XMM-Newton/F. Gastaldello (INAF/ IASF, Milano, Italy)/CFHTLS (bottom left); X-ray: NASA, ESA, CXC, M. Bradac (University of California, Santa Barbara), and S. Allen (Stanford University) (bottom right).

    No alternative gravity theory explains all this. We need dark matter.

    13
    On the largest scales, the way galaxies cluster together observationally (blue and purple) cannot be matched by simulations (red) unless dark matter is included. Image credit: Gerard Lemson & the Virgo Consortium, with data from SDSS, 2dFGRS and the Millennium Simulation, via http://www.mpa-garching.mpg.de/millennium/.

    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 12:09 pm on January 11, 2017 Permalink | Reply
    Tags: , Astrophysics, , , , ,   

    From Ethan Siegel: “The James Webb Space Telescope Will Truly Do What Hubble Only Dreamed Of” 

    Ethan Siegel
    Jan 10, 2017

    NASA/ESA/CSA Webb Telescope annotated
    NASA/ESA/CSA Webb Telescope annotated

    In 1990, NASA launched the Hubble Space Telescope. This observatory would come to revolutionize not only our scientific understanding of the Universe, but would reveal to humanity, for the first time, what our Universe actually looked like. We could peer inside the densest, most gas-and-dust-rich star forming nebulae, and see exactly how and were stars were beginning to form.

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    2
    The pillars of creation, as taken for Hubble’s 25th anniversary. Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

    We could look out at dying stars, reaching the end of their lives, and see exactly what their final moments in the Universe looked like.

    3
    Four individual planetary nebulae — He 2-47, NGC 5315, IC 4593, and NGC 5307 — were imaged by Hubble in February of 2007. Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA).

    We could look out at distant galaxies, and reveal their shapes, ages, stellar populations and histories with simply a glimpse.

    4
    The irregular, interacting galaxy pair Arp 230. Image credit: ESA/Hubble & NASA. Acknowledgement: Flickr user Det58.

    We could look out at the largest gravitationally bound structures in the Universe, and see how mass bent starlight, giving us a firsthand, visual look at the stunning phenomenon of gravitational lensing.

    5
    Gravitational lensing in galaxy cluster Abell S1063, showcasing the bending of starlight by the presence of matter and energy. Image credit: NASA, ESA, and J. Lotz (STScI).

    And perhaps most importantly of all, we were able to look into the vast abyss of nothingness, photographing what lies beyond our visual reach for hours, days or even weeks at a time. What we wound up seeing changed our view of everything.

    6
    The full UV-visible-IR composite of the Hubble eXtreme Deep Field; the greatest image ever released of the distant Universe. Image credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI).

    Thanks to Hubble, we now know how stars are born, live and die. We know how galaxies form and grow in the Universe. We know what the ultimate fate of our Universe will be, and where we’re headed in the future. But even without any of this scientific knowledge, Hubble taught us something absolutely incredible: it showed us that this is what our Universe looks like.

    7
    The James Webb Space Telescope vs. Hubble in size (main) and vs. an array of other telescopes (inset) in terms of wavelength and sensitivity. Image credit: NASA / JWST team.

    By the same token, the James Webb Space Telescope will teach us an incredible amount about the Universe, including further details about how stars form, what the earliest stellar populations look like, will show us gas giants and rogue planets in unprecedented detail and will tell us what made up the Universe at any given time in the past. It will show us a whole slew of things that Hubble cannot, by virtue of it reaching to much longer wavelengths of light than Hubble could ever hope to see. And with its huge, large-aperture primary mirror, it will be able to collect more light in a single day than Hubble could in a week. The most exciting things, of course, will be the unexpected: the things we’ll discover that we don’t even know to look for yet.

    8
    An artist’s conception of what the Universe might look like as it forms stars for the first time. Image credit: NASA/JPL-Caltech/R. Hurt (SSC).

    But even if you don’t learn about any of the science that James Webb will bring to us, there’s one thing it will deliver that everyone can enjoy: the James Webb Space Telescope will show us how the Universe grew up.

    9
    An illustration of CR7, the first galaxy detected that’s thought to house Population III stars: the first stars ever formed in the Universe. JWST will reveal actual images of this galaxy and others like it. Image credit: ESO/M. Kornmesser.

    It will show us how the Universe went from the hot Big Bang and a state with no stars, no planets and no galaxies into the Universe we have today. It will reveal the very first populations of stars, which were created out of the pristine elements — hydrogen and helium alone — which provided the first light in the Universe.

    10
    On the left, the infrared light from the end of the Universe’s dark ages is shown, with the (foreground) stars subtracted out. JWST will be able to probe all the way back to the very first stars of all. Image credit: NASA/JPL-Caltech/A. Kashlinsky (GSFC).

    It will reveal how these first stars grew into star clusters, dwarf galaxies and eventually massive behemoths like our own. It will show us how the neutral atoms became ionized, and transparent to visible light. It will show us when and where the Universe became filled with oxygen, carbon and nitrogen: the elements essential to life. In short, it will tell us how the Universe went from being an inhospitable, smooth complex of pristine gas to the rich, diverse set of planets, stars, galaxies, clusters and great cosmic voids we enjoy today.

    11
    The biggest ‘big idea’ that JWST has is to reveal to us the very first luminous objects in the Universe, including stars, supernovae, star clusters, galaxies, and luminous black holes. Image credit: Karen Teramura, UHIfA / NASA.

    Hubble showed us what the Universe looks like; James Webb will show us how the Universe came to be the way it is today. Don’t ever say that James Webb is the “next Hubble,” it isn’t and it should never be. Instead, it’s the first James Webb, and when it starts returning images of the Universe, you may never look at your place in the Cosmos the same way 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 10:57 am on January 11, 2017 Permalink | Reply
    Tags: , Astrophysics, , , , Farthest Stars in Milky Way Might Be Ripped from Another Galaxy,   

    From CfA: “Farthest Stars in Milky Way Might Be Ripped from Another Galaxy” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    January 11, 2017
    Christine Pulliam
    Media Relations Manager
    Harvard-Smithsonian Center for Astrophysics
    617-495-7463
    cpulliam@cfa.harvard.edu

    1
    In this computer-generated image, a red oval marks the disk of our Milky Way galaxy and a red dot shows the location of the Sagittarius dwarf galaxy. The yellow circles represent stars that have been ripped from the Sagittarius dwarf and flung far across space. Five of the 11 farthest known stars in our galaxy were probably stolen this way. Marion Dierickx / CfA

    The 11 farthest known stars in our galaxy are located about 300,000 light-years from Earth, well outside the Milky Way’s spiral disk. New research by Harvard astronomers shows that half of those stars might have been ripped from another galaxy: the Sagittarius dwarf. Moreover, they are members of a lengthy stream of stars extending one million light-years across space, or 10 times the width of our galaxy.

    “The star streams that have been mapped so far are like creeks compared to the giant river of stars we predict will be observed eventually,” says lead author Marion Dierickx of the Harvard-Smithsonian Center for Astrophysics (CfA).

    The Sagittarius dwarf is one of dozens of mini-galaxies that surround the Milky Way.

    1
    Stars from the Sagittarius dwarf galaxy are being spread all around the Milky Way, contributing to the lumpiness of the distribution of stars found in SDSS. In this illustration, the Milky Way is shown in yellow and the sun is a green star. The white dots show the expected positions of the stars from a simulation done by Rensselaer graduate student Ben Willett. The blue dots show the positions of actual stars extracted from the SDSS database by graduate student Nate Cole. The red dashed line shows the general direction all of the stars are going as they orbit around the center of the Milky Way. http://www.rpi.edu/about/inside/issue/v2n19/galaxy.html

    Over the age of the universe it made several loops around our galaxy. On each passage, the Milky Way’s gravitational tides tugged on the smaller galaxy, pulling it apart like taffy.

    Dierickx and her PhD advisor, Harvard theorist Avi Loeb, used computer models to simulate the movements of the Sagittarius dwarf over the past 8 billion years. They varied its initial velocity and angle of approach to the Milky Way to determine what best matched current observations.

    “The starting speed and approach angle have a big effect on the orbit, just like the speed and angle of a missile launch affects its trajectory,” explains Loeb.

    At the beginning of the simulation, the Sagittarius dwarf weighed about 10 billion times the mass of our Sun, or about one percent of the Milky Way’s mass. Dierickx’s calculations showed that over time, the hapless dwarf lost about a third of its stars and a full nine-tenths of its dark matter. This resulted in three distinct streams of stars that reach as far as one million light-years from the Milky Way’s center. They stretch all the way out to the edge of the Milky Way halo and display one of the largest structures observable on the sky.

    Moreover, five of the 11 most distant stars in our galaxy have positions and velocities that match what you would expect of stars stripped from the Sagittarius dwarf. The other six do not appear to be from Sagittarius, but might have been removed from a different dwarf galaxy.

    Mapping projects like the Sloan Digital Sky Survey have charted one of the three streams predicted by these simulations, but not to the full extent that the models suggest.

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

    Future instruments like the Large Synoptic Survey Telescope, which will detect much fainter stars across the sky, should be able to identify the other streams.

    LSST
    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    “More interlopers from Sagittarius are out there just waiting to be found,” says Dierickx.

    These findings have been accepted for publication in The Astrophysical Journal and are available online.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 3:41 pm on January 10, 2017 Permalink | Reply
    Tags: , , Astrophysics, , ,   

    From astrobites: “A Too-Hot Pulsar Speeding Through the Galaxy” 

    Astrobites bloc

    Astrobites

    Jan 10, 2017
    Thankful Cromartie

    Title: Hubble Space Telescope detection of the millisecond pulsar J2124-3358 and its far-ultraviolet bow shock nebula
    Authors: B. Rangelov, G. G. Pavlov, O. Kargaltsev, A. Reisenegger, S. Guillot, M. van Kerkwijk & C. Reyes
    First Author’s Institution: Department of Physics, The George Washington University, Washington, DC
    1
    Status: Accepted to ApJ [open access]

    1
    Pulsars Are Spinning Neutron Stars
    CREDIT: Bill Saxton, NRAO/AUI/NSF

    Pulsars – the rapidly rotating, highly magnetized neutron stars that beam radiation from their magnetic axes — are as mysterious as they are exotic. They’re most often observed at radio frequencies using single-dish telescopes, and are sometimes glimpsed in X-ray and gamma-ray bands. Far rarer are pulsar observations at “in-between” frequencies, such as ultraviolet (UV), optical, and infrared (IR) (collectively, UVOIR); in fact, only about a dozen pulsars have been detected this way. However, their study in this frequency range has proved enlightening, as we will see in today’s post.
    A pulsar too hot to handle

    While one would expect a neutron star to cool with age if an internal heating mechanism does not operate throughout its lifetime, observations of the millisecond pulsar J0437–4715 (an interesting object in its own right) yielded surprising results. In a 2016 study, far-UV observations revealed the 7-billion-year-old pulsar to have a surface temperature of about 2 × 105 K — about 35 times the temperature of the Sun’s photosphere. This finding inspired Rangelov et al. to observe another millisecond pulsar, J2124-3358 (a 3.8-billion-year-old pulsar with a spin period of 4.93 ms), in the far-UV and optical bands using the Hubble Space Telescope (HST).

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    Because so few pulsars have been studied in these frequency ranges, their spectral energy distributions (SEDs) in this regime are poorly understood. Generally speaking, the spectra of normal, rotation-powered pulsars reveal a nonthermal (not dependent on temperature) component in optical and X-rays caused by electrons and positrons in the pulsar magnetosphere. In the far-UV, some pulsars show a thermal (blackbody) component in their spectra, thought to come from the surface of the cooling object. Analysis of the team’s HST images revealed an SED that is best modeled by a combined nonthermal and thermal spectral fit, with nonthermal emission dominating at optical wavelengths and thermal emission appearing in the far-UV (see Figure 1). If their interpretation is correct, this implies a surface temperature for J2124-3358 that is between 0.5 × 105 and 2.1 × 105 K, which is very much in line with the temperature of J0437-4715. If this proves to be the case, these two measurements will strongly suggest the presence of a heating mechanism in millisecond pulsars. However, various fits using only nonthermal components in the far-UV are still valid, so it is impossible to make an absolute determination of the correct fit.

    There are quite a few heating mechanisms that could be invoked to explain these objects’ high temperatures, ranging from the release of stored strain energy from the pulsar’s crust to dark matter annihilation in the pulsar’s interior. More spectral coverage of J2124-3358 is necessary to both check the validity of the nonthermal and thermal combined fit and to get closer to determining more specifically the heating mechanism in play.

    2
    Figure 1: Thermal (red dashed) and nonthermal (blue dashed) combined spectral fit to HST far-UV/optical data for J2124-3358. The black line signifies the sum of both components. Because there is uncertainty about the nature of the nonthermal component, two possible spectral slopes are shown. Figure 7 in the paper.

    A (bow) shocking find in the far-UV

    Images of J2124-3358 also show the presence of a bow shock, which is an arc-shaped shock that occurs when an object is moving faster than the interstellar medium (ISM) sound speed. J2124-3358 was known before this study to be accompanied by such a shock in H-alpha (Hydrogen transition from n=3 to n=2) filters, for which plenty of neutral hydrogen is required. As a result of the HST observations, J2124-3358 was found to have an (albeit fainter) far-UV shock coincident with the H-alpha shock (see Figure 2). This is only the second such object (after J0437-4715) to show a far-UV bow shock. It is absolutely possible that many pulsars cause bow shocks that don’t emit in H-alpha, but do in other wavelength regimes. Studying these more carefully will yield information about the nature of the ISM.

    In order to learn more about the heating mechanisms operating in these objects as well as the bow shocks that sometimes accompany them, many more pulsars will need to be studied using various optical, UV, and IR filters. Studies in the far-UV are only possible with Hubble, so it will be a long time before a sufficient number of objects will be studied at these frequencies in order to make solid conclusions about the nature of such interesting phenomena.

    3
    Figure 2: New observations of J2124-3358 from this study using the HST at three different wavelengths are shown in the top (left and right) and bottom left images. The shock is clearly visible in the far-UV using the F125LP filter. The bottom right image shows a previous H-alpha observation of the same pulsar. Figure 1 in the paper.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 2:24 pm on January 10, 2017 Permalink | Reply
    Tags: , Astrophysics, , , ,   

    From EarthSky: “Hubble peers along Voyagers’ future paths” 

    1

    EarthSky

    January 8, 2017
    Deborah Byrd

    1
    Artist’s concept of the paths of the Voyager 1 and 2 spacecraft on their journey through our solar system and out into interstellar space. The Hubble Space Telescope is gazing at 2 sight lines (the twin cone-shaped features) along each spacecraft’s star-bound route. Each sight line stretches several light-years to nearby stars. Image via NASA, ESA, and Z. Levay (STScI).

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    NASA launched the twin Voyager 1 and 2 spacecraft in 1977. Both explored the outer planets Jupiter and Saturn, and Voyager 2 went on to visit Uranus and Neptune. Now both Voyagers are heading beyond our solar system, into the space between the stars. Voyager 1 officially became the first earthly craft to leave the solar system in 2013. Last week (January 6, 2017), at the 229th meeting of the American Astronomical Society in Grapevine, Texas, astronomers spoke of using the Hubble Space Telescope to provide what they called a road map for the Voyagers. A NASA statement said:

    “Even after the Voyagers run out of electrical power and are unable to send back new data, which may happen in about a decade, astronomers can use Hubble observations to characterize the environment of through which these silent ambassadors will glide.”

    This is a great opportunity to compare data from in situ measurements of the space environment by the Voyager spacecraft and telescopic measurements by Hubble. The Voyagers are sampling tiny regions as they plow through space at roughly 38 thousand miles per hour [61 thousand km/hr]. But we have no idea if these small areas are typical or rare.

    The Hubble observations give us a broader view because the telescope is looking along a longer and wider path. So Hubble gives context to what each Voyager is passing through.

    2
    Artist’s concept of Voyager 1. Circles represent the orbits of the major outer planets: Jupiter, Saturn, Uranus, and Neptune. Image via NASA, ESA, and G. Bacon (STScI).

    Voyager 1 is now 13 billion miles (21 billion km) from Earth, making it the farthest and fastest-moving human-made object ever built. It’s now zooming through interstellar space, the region between the stars filled with gas, dust and material recycled from dying stars. In about 40,000 years, long after both spacecraft are no longer operational, Voyager 1 will pass within 1.6 light-years of the star Gliese 445, in the constellation Camelopardalis.

    Meanwhile, Voyager 2 is about 10.5 billion miles (17 billion km) from Earth. Voyager 2 will pass 1.7 light-years from the star Ross 248 in about 40,000 years. NASA said:

    ” For the next 10 years, the Voyagers will be making measurements of interstellar material, magnetic fields and cosmic rays along their trajectories. Hubble complements the Voyagers’ observations by gazing at two sight lines along each spacecraft’s path to map interstellar structure along their star-bound
    routes. Each sight line stretched several light-years to nearby stars. Sampling the light from those stars, Hubble’s Space Telescope Imaging Spectrograph measures how interstellar material absorbs some of the starlight, leaving telltale spectral fingerprints.

    Hubble found that Voyager 2 will move out of the interstellar cloud that surrounds our solar system in a couple thousand years. The astronomers, based on Hubble data, predict that the spacecraft will spend 90,000 years in a second cloud and pass into a third interstellar cloud.

    An inventory of the clouds’ composition reveals slight variations in the abundances of the chemical elements contained in the structures.”

    These variations could mean the clouds formed in different ways, or from different areas, and then came together. NASA also said:

    “An initial look at the Hubble data also suggests that the sun is passing through clumpier material in nearby space, which may affect the heliosphere, the large bubble containing our solar system that is produced by our sun’s powerful solar wind. At its boundary, called the heliopause, the solar wind pushes outward against the interstellar medium. Hubble and Voyager 1 made measurements of the interstellar environment beyond this boundary, where the wind comes from stars other than our sun.”

    3
    This picture of a crescent-shaped Earth and moon – 1st of its kind ever taken by a spacecraft – was recorded September 18, 1977, by Voyager 1 at a distance of 7.25 million miles (11.66 million km) from Earth. The moon is at the top of the picture and beyond the Earth as viewed by Voyager. Image via NASA.

    Bottom line: The Hubble Space Telescope is gazing along the future trajectories of the 2 Voyager spacecraft.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: