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  • richardmitnick 5:17 pm on September 18, 2017 Permalink | Reply
    Tags: "Cosmic Lenses", , , , , , , , Polarization of the waves, , sSupport for the idea that galaxy magnetic fields are generated by a rotating dynamo effect similar to the process that produces the Sun’s magnetic field, VLA Reveals Distant Galaxy’s Magnetic Field   

    From NRAO: “VLA Reveals Distant Galaxy’s Magnetic Field” 

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    National Radio Astronomy Observatory

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    August 28, 2017

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    Artist’s conception of gravitational lens arrangement that allowed astronomers to measure galaxy’s magnetic field.
    Credit: Bill Saxton, NRAO/AUI/NSF; NASA, Hubble Heritage Team, (STScI/AURA), ESA, S. Beckwith (STScI). Additional Processing: Robert Gendler

    With the help of a gigantic cosmic lens, astronomers have measured the magnetic field of a galaxy nearly five billion light-years away. The achievement is giving them important new clues about a problem at the frontiers of cosmology — the nature and origin of the magnetic fields that play an important role in how galaxies develop over time.

    The scientists used the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) to study a star-forming galaxy that lies directly between a more-distant quasar and Earth. The galaxy’s gravity serves as a giant lens, splitting the quasar’s image into two separate images as seen from Earth. Importantly, the radio waves coming from this quasar, nearly 8 billion light-years away, are preferentially aligned, or polarized.

    “The polarization of the waves coming from the background quasar, combined with the fact that the waves producing the two lensed images traveled through different parts of the intervening galaxy, allowed us to learn some important facts about the galaxy’s magnetic field,” said Sui Ann Mao, Minerva Research Group Leader for the Max Planck Institute for Radio Astronomy in Bonn, Germany.

    Magnetic fields affect radio waves that travel through them. Analysis of the VLA images showed a significant difference between the two gravitationally-lensed images in how the waves’ polarization was changed. That means, the scientists said, that the different regions in the intervening galaxy affected the waves differently.

    “The difference tells us that this galaxy has a large-scale, coherent magnetic field, similar to those we see in nearby galaxies in the present-day universe,” Mao said. The similarity is both in the strength of the field and in its arrangement, with magnetic field lines twisted in spirals around the galaxy’s rotation axis.

    Since this galaxy is seen as it was almost five billion years ago, when the universe was about two-thirds of its current age, this discovery provides an important clue about how galactic magnetic fields are formed and evolve over time.

    “The results of our study support the idea that galaxy magnetic fields are generated by a rotating dynamo effect, similar to the process that produces the Sun’s magnetic field,” Mao said. “However, there are other processes that might be producing the magnetic fields. To determine which process is at work, we need to go still farther back in time — to more distant galaxies — and make similar measurements of their magnetic fields,” she added.

    “This measurement provided the most stringent tests to date of how dynamos operate in galaxies,” said Ellen Zweibel from the University of Wisconsin-Madison.

    Magnetic fields play a pivotal role in the physics of the tenuous gas that permeates the space between stars in a galaxy. Understanding how those fields originate and develop over time can provide astronomers with important clues about the evolution of the galaxies themselves.

    Mao and her colleagues are reporting their results in the journal Nature Astronomy.

    See the full article here .

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    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    The NRAO operates a complementary, state-of-the-art suite of radio telescope facilities for use by the scientific community, regardless of institutional or national affiliation: the Very Large Array (VLA), and the Very Long Baseline Array (VLBA)*.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    Access to ALMA observing time by the North American astronomical community will be through the North American ALMA Science Center (NAASC).

    NRAO VLBA

    NRAO VLBA

    *The Very Long Baseline Array (VLBA) comprises ten radio telescopes spanning 5,351 miles. It’s the world’s largest, sharpest, dedicated telescope array. With an eye this sharp, you could be in Los Angeles and clearly read a street sign in New York City!

    Astronomers use the continent-sized VLBA to zoom in on objects that shine brightly in radio waves, long-wavelength light that’s well below infrared on the spectrum. They observe blazars, quasars, black holes, and stars in every stage of the stellar life cycle. They plot pulsars, exoplanets, and masers, and track asteroids and planets.

    And the future Expanded Very Large Array (EVLA).

     
  • richardmitnick 10:55 pm on February 5, 2017 Permalink | Reply
    Tags: "Cosmic Lenses", Cluster Lensing And Supernova survey with Hubble (CLASH), , , Supernova Cosmology Project   

    From Hubble: “Hubble Astronomers Check the Prescription of a Cosmic Lens” From May 1, 2014 

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    NASA/ESA Hubble Telescope

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    If you need to check whether the prescription for your eye glasses or contact lenses is still accurate, you visit an ophthalmologist for an eye exam. The doctor will ask you to read an eye chart, which tests your visual acuity. Your score helps the doctor determine whether to change your prescription.

    Astronomers don’t have a giant eye chart to check the prescription for natural cosmic lenses, created by galaxy clusters. The gravity of these cosmic lenses warps space around them, magnifying and brightening the light from distant objects behind them. Without these lenses, background objects would be too dim to be detected by even NASA’s Hubble Space Telescope. But how do astronomers know whether the prescription for these zoom lenses, which tells them how much an object will be magnified, is accurate? Astronomers using the Hubble telescope have discovered the next best thing to a giant cosmic eye chart: the light from distant exploding stars behind galaxy clusters.

    Donna Weaver
    dweaver@stsci.edu
    Space Science Telescope Institute, Baltimore, Md.
    410-338-4493

    Ray Villard
    villard@stsci.edu
    Space Science Telescope Institute, Baltimore, Md.
    410-338-4514

    Photo Credit: NASA, ESA, S. Perlmutter (UC Berkeley, LBNL), A. Koekemoer (STScI), M. Postman (STScI), A. Riess (STScI/JHU), J. Nordin (LBNL, UC Berkeley), D. Rubin (Florida State University), and C. McCully (Rutgers University)

    2

    What could be more exciting than watching the fireworks of cataclysmic stellar explosions outshining entire galaxies of stars? How about watching them through the funhouse lens of a massive cluster of galaxies whose powerful gravity warps space around it?

    In fact, distant exploding stars observed by NASA’s Hubble Space Telescope are providing astronomers with a powerful tool to check the prescription of these natural “cosmic lenses,” which are used to provide a magnified view of the remote universe.

    Two teams of astronomers working independently have found three such exploding stars, called supernovae, far behind massive clusters of galaxies. Their light was amplified and brightened by the immense gravity of the foreground clusters in a phenomenon called gravitational lensing. First predicted by Albert Einstein, this effect is similar to a glass lens bending light to form an image. Astronomers use the gravitational-lensing technique to search for distant objects that might otherwise be too faint to see, even with today’s largest telescopes.

    Astronomers from the Supernova Cosmology Project and the Cluster Lensing And Supernova survey with Hubble (CLASH), are using these supernovae in a new method to check the predicted magnification, or prescription, of the gravitational lenses. Luckily, two and possibly all three of the supernovae appear to be a special type of exploding star called Type Ia supernovae, prized by astronomers because they provide a consistent level of peak brightness that makes them reliable for making distance estimates.

    “Here we have found Type Ia supernovae that can be used like an eye chart for each lensing cluster,” explained Saurabh Jha of Rutgers University in Piscataway, N.J., a member of the CLASH team. “Because we can estimate the intrinsic brightness of the Type Ia supernovae, we can independently measure the magnification of the lens, unlike for other background sources.”

    Having a precise prescription for a gravitational lens will help astronomers probe objects in the early universe and better understand a galaxy cluster’s structure and its distribution of dark matter, say researchers. Dark matter cannot be seen directly but is believed to make up most of the universe’s matter.

    How much a gravitationally lensed object is magnified depends on the amount of matter in a cluster, including dark matter, which is the source of most of a cluster’s gravity. Astronomers develop maps that estimate the location and amount of dark matter in a cluster based on theoretical models and on the observed amplification and bending of light from sources behind the cluster. The maps are the lens prescriptions that predict how distant objects behind the cluster are magnified when their light passes through it.

    “Building on our understanding of these lensing models also has implications for a wide range of key cosmological studies,” explained Supernova Cosmology Project leader Saul Perlmutter of the E.O. Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California, Berkeley. “These lens prescriptions yield measurements of the cluster masses, allowing us to probe the cosmic competition between gravity and dark energy as matter in the universe gets pulled into galaxy clusters.” Dark energy is a mysterious, invisible energy that is accelerating the universe’s expansion.

    The three supernovae in the Hubble study were each gravitationally lensed by a different cluster. The teams measured the brightnesses of the lensed supernovae and compared them to the explosions’ intrinsic brightnesses to calculate how much they were magnified due to gravitational lensing. One supernova in particular stood out, appearing to be about twice as bright as would have been expected if not for the cluster’s magnification power.

    The supernovae were discovered in the CLASH survey, a Hubble census that probed the distribution of dark matter in 25 galaxy clusters. Two of the supernovae were found in 2012, the other in 2010. The three supernovae exploded between 7 billion and 9 billion years ago, when the universe was slightly less than half its current age of 13.8 billion years old.

    To perform their analyses, both teams of astronomers used observations in visible light from Hubble’s Advanced Camera for Surveys and in infrared light from the Wide Field Camera 3. The research teams also obtained spectra from both space and ground-based telescopes that provided independent estimates of the distances to these exploding stars. In some cases the spectra allowed direct confirmation of a Type Ia pedigree. In other cases the supernova spectrum was weak or overwhelmed by the light of its parent galaxy. In those cases the astronomers also used different colored filters on Hubble to help establish the supernova type.

    Each team then compared its results with independent theoretical models of the clusters’ dark-matter content, concluding that the predictions fit the models.

    “It is encouraging that the two independent studies reach quite similar conclusions,” explained Supernova Cosmology Project team member Jakob Nordin of Berkeley Lab and the University of California, Berkeley. “These pilot studies provide very good guidelines for making future observations of lensed supernovae even more accurate.” Nordin also is the lead author on the team’s science paper describing the findings.

    Now that the researchers have proven the effectiveness of this method, they need to find more Type Ia supernovae behind behemoth lensing galaxy clusters. In fact, the astronomers estimate they need about 20 supernovae spread out behind a cluster so they can map the entire cluster field and ensure that the lens model is correct.

    They are optimistic that Hubble and future telescopes, including NASA’s James Webb Space Telescope, an infrared observatory, will nab more of these unique exploding stars.

    “Hubble is already hunting for them in the Frontier Fields, a three-year Hubble survey of the distant universe using massive galaxy clusters as gravitational lenses,” said CLASH team member Brandon Patel of Rutgers University, the lead author on the science paper announcing the CLASH team’s results. Steven Rodney of Johns Hopkins University, and co-leader of the CLASH supernova team, will direct the search for Type Ia supernovae in the Frontier Fields data.

    The CLASH team’s results will appear in the May 1 issue of The Astrophysical Journal and the Supernova Cosmology Project’s findings in the May 1 edition of the Monthly Notices of the Royal Astronomical Society.

    The CLASH survey is led by Marc Postman of the Space Telescope Science Institute in Baltimore, Md. The CLASH supernova project is co-led by Rodney and Adam Riess of the Space Telescope Science Institute and Johns Hopkins University. Aiding with the analysis on the Hubble study are Curtis McCully of Rutgers University, Or Graur of the American Museum of Natural History in New York City, and Julian Merten and Adi Zitrin of the California Institute of Technology in Pasadena.

    Other members of the Supernova Cosmology Project who worked on the supernova analysis are David Rubin of Florida State University in Tallahassee and Greg Aldering of Berkeley Lab. The project’s galaxy cluster models were created by Johan Richard of the University of Lyon in France and Jean-Paul Kneib of École Polytechnique Fédérale de Lausanne in Switzerland.

    See the full article here .

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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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