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  • richardmitnick 3:33 pm on December 6, 2017 Permalink | Reply
    Tags: , , , , , , Dark matter provides the pull of gravity that causes the Universe to collapse into structures, Gravitational Lensing, Massive Primordial Galaxies Found Swimming in Vast Ocean of Dark Matter, , , SPT0311-58, With these exquisite ALMA observations astronomers are seeing the most massive galaxy known in the first billion years of the Universe in the process of assembling itself   

    From ALMA: “Massive Primordial Galaxies Found Swimming in Vast Ocean of Dark Matter” Revised to add contacts 

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

    ALMA

    5 December, 2017

    Nicolás Lira
    Education and Public Outreach Coordinator
    Joint ALMA Observatory, Santiago – Chile
    Phone: +56 2 2467 6519
    Cell phone: +56 9 9445 7726
    Email: nicolas.lira@alma.cl

    Charles E. Blue
    Public Information Officer
    National Radio Astronomy Observatory Charlottesville, Virginia – USA
    Phone: +1 434 296 0314
    Cell phone: +1 202 236 6324
    Email: cblue@nrao.edu

    Richard Hook
    Public Information Officer, ESO
    Garching bei München, Germany
    Phone: +49 89 3200 6655
    Cell phone: +49 151 1537 3591
    Email: rhook@eso.org

    Masaaki Hiramatsu
    Education and Public Outreach Officer, NAOJ Chile
    Observatory
, Tokyo – Japan
    Phone: +81 422 34 3630
    Email: hiramatsu.masaaki@nao.ac.jp

    1
    Artist impression of a pair of galaxies from the very early Universe. Credit: NRAO/AUI/NSF; D. Berry

    Astronomers expect that the first galaxies, those that formed just a few hundred million years after the Big Bang, would share many similarities with some of the dwarf galaxies we see in the nearby Universe today. These early agglomerations of a few billion stars would then become the building blocks of the larger galaxies that came to dominate the Universe after the first few billion years.

    Ongoing observations with the Atacama Large Millimeter/submillimeter Array (ALMA), however, have discovered surprising examples of massive, star-filled galaxies seen when the Cosmos was less than a billion years old. This suggests that smaller galactic building blocks were able to assemble into large galaxies quite quickly.

    The latest ALMA observations push back this epoch of massive-galaxy formation even further by identifying two giant galaxies seen when the Universe was only 780 million years old, or about 5 percent its current age. ALMA also revealed that these uncommonly large galaxies are nestled inside an even-more-massive cosmic structure, a halo of dark matter with as much mass as several trillion suns.

    2
    To correct for the effects of gravitational lensing in these galaxies, the ALMA data (left panel) is compared to a lensing-distorted model image (second panel). The difference is shown in the third panel from the left. The structure of the galaxy, after removing the lensing effect, is shown at right. This image loops through the different velocity ranges within the galaxy, which appear at different frequencies to ALMA due to the Doppler effect. Credit: ALMA (ESO/NAOJ/NRAO); D. Marrone et al.

    The two galaxies are in such close proximity — less than the distance from the Earth to the center of our galaxy — that they will shortly merge to form the largest galaxy ever observed at that period in cosmic history. This discovery provides new details about the emergence of large galaxies and the role that dark matter plays in assembling the most massive structures in the Universe.

    The researchers report their findings in the journal Nature.

    “With these exquisite ALMA observations, astronomers are seeing the most massive galaxy known in the first billion years of the Universe in the process of assembling itself,” said Dan Marrone, associate professor of astronomy at the University of Arizona in Tucson and lead author on the paper.

    Astronomers are seeing these galaxies during a period of cosmic history known as the Epoch of Reionization when most of the intergalactic space was suffused with an obscuring fog of cold hydrogen gas.

    Reionization era and first stars, Caltech

    As more stars and galaxies formed, their energy eventually ionized the hydrogen between the galaxies, revealing the Universe as we see it today.

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

    “We usually view that as the time of little galaxies working hard to chew away at the neutral intergalactic medium,” said Marrone. “Mounting observational evidence with ALMA, however, has helped to reshape that story and continues to push back the time at which truly massive galaxies first emerged in the Universe.”

    The galaxies that Marrone and his team studied, collectively known as SPT0311-58, were originally identified as a single source by the National Science Foundation’s South Pole Telescope.

    South Pole Telescope SPTPOL. The SPT collaboration is made up of over a dozen (mostly North American) institutions, including the University of Chicago, the University of California, Berkeley, Case Western Reserve University, Harvard/Smithsonian Astrophysical Observatory, the University of Colorado Boulder, McGill University, The University of Illinois at Urbana-Champaign, University of California, Davis, Ludwig Maximilian University of Munich, Argonne National Laboratory, and the National Institute for Standards and Technology. It is funded by the National Science Foundation.

    These first observations indicated that this object was very distant and glowing brightly in infrared light, meaning that it was extremely dusty and likely going through a burst of star formation. Subsequent observations with ALMA revealed the distance and dual nature of the object, clearly resolving the pair of interacting galaxies.

    To make this observation, ALMA had some help from a gravitational lens, which provided an observing boost to the telescope.

    Gravitational Lensing NASA/ESA

    Gravitational lenses form when an intervening massive object, like a galaxy or galaxy cluster, bends the light from more distant galaxies. They do, however, distort the appearance of the object being studied, requiring sophisticated computer models to reconstruct the image as it would appear in its unaltered state.

    This “deconvolution” process provided intriguing details about the galaxies, showing that the larger of the two is forming stars at a rate of 2,900 solar masses per year. It also contains about 270 billion times the mass of our Sun in gas and nearly 3 billion times the mass of our Sun in dust. “That’s a whopping large quantity of dust, considering the young age of the system,” noted Justin Spilker, a recent graduate of the University of Arizona and now a postdoctoral fellow at the University of Texas at Austin.

    The astronomers determined that this galaxy’s rapid star formation was likely triggered by a close encounter with its slightly smaller companion, which already hosts about 35 billion solar masses of stars and is increasing its rate of starburst at the breakneck pace of 540 solar masses per year.

    The researchers note that galaxies of this era are messier than the ones we see in the nearby Universe. Their more jumbled shapes would be due to the vast stores of gas raining down on them and their ongoing interactions and mergers with their neighbors.

    The new observations also allowed the researchers to infer the presence of a truly massive dark matter halo surrounding both galaxies. Dark matter provides the pull of gravity that causes the Universe to collapse into structures (galaxies, groups, and clusters of galaxies, etc.).

    “If you want to see if a galaxy makes sense in our current understanding of cosmology, you want to look at the dark matter halo — the collapsed dark matter structure — in which it resides,” said Chris Hayward, an associate research scientist at the Center for Computational Astrophysics at the Flatiron Institute in New York City.

    Dark matter halo Image credit: Virgo consortium / A. Amblard / ESA

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    “Fortunately, we know very well the ratio between dark matter and normal matter in the Universe, so we can estimate what the dark matter halo mass must be.”

    By comparing their calculations with current cosmological predictions, the researchers found that this halo is one of the most massive that should exist at that time.

    “There are more galaxies discovered with the South Pole Telescope that we’re following up, and there is a lot more survey data that we are just starting to analyze. Our hope is to find more objects like this, possibly even more distant ones, to better understand this population of extreme dusty galaxies and especially their relation to the bulk population of galaxies at this epoch,” said Joaquin Vieira of the University of Illinois at Urbana-Campaign.

    “In any case, our next round of ALMA observations should help us understand how quickly these galaxies came together and improve our understanding of massive galaxy formation during reionization,” added Marrone.

    Additional Information

    The research team was composed by D. P. Marrone[1], J. S. Spilker[1], C. C. Hayward[2,3], J. D. Vieira[4], M. Aravena[5], M. L. N. Ashby[3], M. B. Bayliss[6], M. Be ́thermin[7], M. Brodwin[8], M. S. Bothwell[9,10], J. E. Carlstrom[11,12,13,14], S. C. Chapman[15], Chian-Chou Chen[16], T. M. Crawford[11,14], D. J. M. Cunningham[15,17], C. De Breuck[16], C. D. Fassnacht[18], A. H. Gonzalez[19], T. R. Greve[20], Y. D. Hezaveh[21,28], K. Lacaille[22], K. C. Litke[1], S. Lower[4], J. Ma[19], M. Malkan[23], T. B. Miller[15], W. R. Morningstar[21], E. J. Murphy[24], D. Narayanan[19], K. A. Phadke[4], K. M. Rotermund[15], J. Sreevani[4], B. Stalder[25], A. A. Stark[3], M. L. Strandet[26,27], M. Tang[1], & A. Weiß[26].

    [1] Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA

    [2] Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA

    [3] Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

    [4] Department of Astronomy, University of Illinois, 1002 West Green St., Urbana, IL 61801

    [5] Nucleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile

    [6] Kavli Institute for Astrophysics & Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA

    [7] Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France

    [8] Department of Physics and Astronomy, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110, USA

    [9] Cavendish Laboratory, University of Cambridge, 19 J.J. Thomson Avenue, Cambridge, CB3 0HE, UK

    [10] Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

    [11] Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

    [12] Department of Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

    [13] Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

    [14] Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

    [15] Dalhousie University, Halifax, Nova Scotia, Canada

    [16] European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany

    [17] Department of Astronomy and Physics, Saint Mary’s University, Halifax, Nova Scotia, Canada

    [18] Department of Physics, University of California, One Shields Avenue, Davis, CA 95616, USA

    [19] Department of Astronomy, University of Florida, Bryant Space Sciences Center, Gainesville, FL 32611 USA

    [20] Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

    [21] Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305, USA

    [22] Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 Canada

    [23] Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA

    [24] National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA

    [25] Large Synoptic Survey Telescope, 950 North Cherry Avenue, Tucson, AZ 85719, USA

    [26] Max-Planck-Institut fu ̈r Radioastronomie, Auf dem Hu ̈gel 69 D-53121 Bonn, Germany

    [27] International Max Planck Research School (IMPRS) for Astronomy and Astrophysics, Universities of Bonn and Cologne

    [28] Hubble Fellow

    See the full article here .

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    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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  • richardmitnick 3:29 pm on December 1, 2017 Permalink | Reply
    Tags: André Maeder, , , , , Gravitational Lensing, Katie Mack, , The strongest evidence for dark matter comes not from the motions of stars and galaxies “but from the behavior of matter on cosmological scales as measured by signatures in the cosmic microwave back   

    From COSMOS: “Radical dark matter theory prompts robust rebuttals” 

    Cosmos Magazine bloc

    COSMOS Magazine

    01 December 2017
    Richard A Lovett

    1
    Most cosmologists invoke dark energy to explain the accelerating expansion of the universe. A few are not so certain. Mina De La O / Getty
    Images

    In 1887, physicists Alfred Michelson and Edward Morley set up an array of prisms and mirrors in an elegant attempt to measure the passage of the Earth through what was then known as “luminiferous ether” – a mysterious substance through which light waves were believed to propagate, like sound waves through air.

    The experiment should have worked, but in one of the most famous results of Nineteenth Century physics no ether movement was detected. That was a head-scratcher until 1905, when Albert Einstein took the results at face value and used them as a cornerstone in developing his theory of relativity.

    Today, physicists are hunting for two equally mysterious commodities: dark matter and dark energy. And maybe, suggests a recent line of research from astrophysicist André Maeder at the University of Geneva, Switzerland, they too don’t exist, and scientists need to again revise their theories, this time to look for ways to explain the universe without the need for either of them.

    Dark matter was first proposed all the way back in 1933, when astrophysicists realised there wasn’t enough visible matter to explain the motions of stars and galaxies. Instead, there appeared to be a hidden component contributing to the gravitational forces affecting their motion. It is now believed that even though we still have not successfully observed it, dark matter is five times more prevalent in the universe than normal matter.

    Dark energy came into the picture more recently, when astrophysicists realised that the expansion of the universe could not be explained without the existence of some kind of energy that provides a repulsive force that steadily accelerates the rate at which galaxies are flying away from each other. Dark energy is believed to be even more prevalent than dark matter, comprising a full 70% of the universe’s total mass-energy.

    Maeder’s argument, published in a series of papers this year in The Astrophysical Journal is that maybe we don’t need dark matter and dark energy to explain these effects. Maybe it’s our concept of Einsteinian space-time that’s wrong.

    His argument begins with the conventional cosmological understanding that the universe started with a Big Bang, about 13.8 billion years ago, followed by continual expansion. But in this mode, there is a possibility that hasn’t been taken into account, he says: “By that I mean the scale invariance of empty space; in other words the empty space and its properties do not change following a dilation or contraction.”

    If so, that would affect our entire understanding of gravity and the evolution of the universe.

    Based on this hypothesis, Maeder found that with the right parameters he could explain the expansion of the universe without dark energy. He could also explain the motion of stars and galaxies without the need for dark matter.

    To say that Maeder’s ideas are controversial is an understatement. Katie Mack, an astrophysicist at the University of Melbourne on Australia, calls them “massively overhyped.” And physicist and blogger Sabine Hossenfelder of the Frankfurt Institute for Advanced Studies, Germany, wrote that while Maeder “clearly knows his stuff,” he does not yet have “a consistent theory.”

    Specifically, Mack notes that the strongest evidence for dark matter comes not from the motions of stars and galaxies, “but from the behavior of matter on cosmological scales, as measured by signatures in the cosmic microwave background [CMB] and the distribution of galaxies.” Gravitational lensing of distant objects by nearer galaxies also reveals the existence of dark matter, she says.

    CMB per ESA/Planck

    ESA/Planck

    Gravitational Lensing NASA/ESA

    Also, she notes that while there are a “whole heap” of ways to modify Einstein’s theories, these are “nothing new and not especially interesting.”

    The challenge, she says, is to reproduce everything, including “dark matter and dark energy’s biggest successes.” Until a new theory can produce “precise agreement” with measurements of a wide range of cosmic variables, she says, there’s no reason “at all” to throw out the existing theory.

    Dark matter researcher Benjamin Roberts, at the University of Reno, Nevada, US, agrees. “The evidence for dark matter is very substantial and comes from a large number of sources,” he says. “Until a single theory can explain all of these observations, there is no reason to doubt the existence of dark matter.”

    That said, this doesn’t mean that “new physics” theories such as Maeder’s should be ignored. “They should be, and are, taken seriously,” he says.

    Or as Maeder puts it, “Nothing can ever be taken for granted.”

    See the full article here .

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  • richardmitnick 6:23 am on October 24, 2017 Permalink | Reply
    Tags: , , , , , Gravitational Lensing,   

    From phys.org: “Artificial intelligence finds 56 new gravitational lens candidates” 

    physdotorg
    phys.org

    October 23, 2017

    1
    This picture shows a sample of the handmade photos of gravitational lenses that the astronomers used to train their neural network. Credit: Enrico Petrillo, University of Groningen

    A group of astronomers from the universities of Groningen, Naples and Bonn has developed a method that finds gravitational lenses in enormous piles of observations. The method is based on the same artificial intelligence algorithm that Google, Facebook and Tesla have been using in the last years. The researchers published their method and 56 new gravitational lens candidates in the November issue of Monthly Notices of the Royal Astronomical Society.

    When a galaxy is hidden behind another galaxy, we can sometimes see the hidden one around the front system. This phenomenon is called a gravitational lens, because it emerges from Einstein’s general relativity theory which says that mass can bend light. Astronomers search for gravitational lenses because they help in the research of dark matter.

    The hunt for gravitational lenses is painstaking. Astronomers have to sort thousands of images. They are assisted by enthusiastic volunteers around the world. So far, the search was more or less in line with the availability of new images. But thanks to new observations with special telescopes that reflect large sections of the sky, millions of images are added. Humans cannot keep up with that pace.

    Google, Facebook, Tesla

    To tackle the growing amount of images, the astronomers have used so-called ‘convolutional neural networks’. Google employed such neural networks to win a match of Go against the world champion. Facebook uses them to recognize what is in the images of your timeline. And Tesla has been developing self-driving cars thanks to neural networks.

    The astronomers trained the neural network using millions of homemade images of gravitational lenses. Then they confronted the network with millions of images from a small patch of the sky. That patch had a surface area of 255 square degrees. That’s just over half a percent of the sky.

    Gravitational lens candidates

    Initially, the neural network found 761 gravitational lens candidates. After a visual inspection by the astronomers the sample was downsized to 56. The 56 new lenses still need to be confirmed by telescopes as the Hubble space telescope.

    In addition, the neural network rediscovered two known lenses. Unfortunately, it did not see a third known lens. That is a small lens and the neural network was not trained for that size yet.

    In the future, the researchers want to train their neural network even better so that it notices smaller lenses and rejects false ones. The final goal is to completely remove any visual inspection.

    Kilo-Degree Survey

    Carlo Enrico Petrillo (University of Groningen, The Netherlands), first author of the scientific publication: “This is the first time a convolutional neural network has been used to find peculiar objects in an astronomical survey. I think it will become the norm since future astronomical surveys will produce an enormous quantity of data which will be necessary to inspect. We don’t have enough astronomers to cope with this.”

    The data that the neuronal network processed, came from the Kilo-Degree Survey. The project uses the VLT Survey Telescope of the European Southern Observatory (ESO) on Mount Paranal (Chile). The accompanying panoramic camera, OmegaCAM, was developed under Dutch leadership.


    ESO/Vista Telescope at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    ESO Omegacam on VST at ESO’s Cerro Paranal observatory,with an elevation of 2,635 metres (8,645 ft) above sea level

    See the full article here .

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 5:17 pm on September 18, 2017 Permalink | Reply
    Tags: , , , , , Gravitational Lensing, , , 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

    1
    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 12:44 pm on August 21, 2017 Permalink | Reply
    Tags: , , , , , Gravitational Lensing   

    From astrobites: “Sneaky pete baryons in gravitational lensing” 

    Astrobites bloc

    Astrobites

    Aug 21, 2017
    Suk Sien Tie

    Title: Flux-ratio anomalies from discs and other baryonic structures in the Illustris simulation
    Authors: Jen-Wei Hsueh, Giulia Despali, Simona Vegetti et al.
    First Author’s Institution: University of California, Davis

    Status: Submitted to MNRAS, open access

    When a photon perilously escapes being engulfed by gases in its galaxy, it embarks on a long journey to reach our telescopes. Along the way, the combined gravitational field of nearby galaxies and galaxy clusters lures the photon away from sticking to a straight path. Occasionally, its path gets very bent when it passes very close to a galaxy, so much so that when the photon reaches our telescope, we see multiple images of the galaxy where the photon originates. This phenomenon of light bending due to the gravity of matter is known as gravitational lensing.

    Gravitational Lensing NASA/ESA

    As you gaze at the Sun later today during the solar eclipse, remember Albert Einstein, Sir Arthur Eddington, and gravitational lensing. Nearly a century ago on May 29, 1919 when the Sun was completely eclipsed by the Moon, on the west coast of Africa and Brazil, Sir Arthur Eddington and his team proved Einstein’s theory of general relativity. On the day of the eclipse, the Sun was destined to pass by the Hyades cluster, and the darkness that ensued cause the stars to be visible. Eddington and his team measured the stars to have shifted in positions due to the Sun’s gravitational field by the amounts predicted by Einstein. This was also the first observation of gravitational lensing.

    In the context of today’s paper, gravitational lensing is a tool to detect dark matter substructures in the halo of the lensing galaxy. Dark matter is that mysterious stuff that makes up nearly 85% of the Universe mass, does not emit light, and interacts only through gravity. The ratio of fluxes between any pair of lensed images is sensitive to the underlying mass distribution of the lens galaxy. In the absence of dark matter substructures, the flux ratios of the images are well predicted using a smooth lens model. But it does not work as well if dark matter substructures are present, resulting in anomalous flux ratios. Hence, flux ratio anomaly is a telltale sign of dark matter.

    Or is it?

    See the full article here .

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    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 4:20 pm on July 27, 2017 Permalink | Reply
    Tags: , , , , , , Gravitational Lensing   

    From CfA: “Mapping Dark Matter” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    July 21, 2017 [Not making it into social media, but I need the work.]

    1
    Abell 2744, a cluster of galaxies whose dark matter halo has imaged more distant galaxies as seen in this Hubble Space Telescope image. Astronomers have compared the image to simulations of dark matter lensing and found excellent agreement, indicating that that current models of dark matter behavior on the large scale are quite good. NASA/ESA/Hubble.

    About eighty-five percent of the matter in the universe is in the form of dark matter, whose nature remains a mystery. The rest of the matter in the universe is of the kind found in atoms. Astronomers studying the evolution of galaxies in the universe find that dark matter exhibits gravity and, because it is so abundant, it dominates the formation of large-scale structures in the universe like clusters of galaxies. Dark matter is hard to observe directly, needless to say, and it shows no evidence of interacting with itself or other matter other than via gravity, but fortunately it can be traced by modeling sensitive observations of the distributions of galaxies across a range of scales.

    Galaxies generally reside at the centers of vast clumps of dark matter called haloes because they surround the clusters of galaxies.

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    Dark matter halo Image credit: Virgo consortium / A. Amblard / ESA

    Gravitational lensing of more distant galaxies by dark matter haloes offers a particularly unique and powerful probe of the detailed distribution of dark matter.

    So-called strong gravitational lensing creates highly distorted, magnified and occasionally multiple images of a single source; so-called weak lensing results in modestly yet systematically deformed shapes of background galaxies that can also provide robust constraints on the distribution of dark matter within the clusters.

    Gravitational Lensing NASA/ESA

    Weak gravitational lensing HST

    CfA astronomers Annalisa Pillepich and Lars Hernquist and their colleagues compared gravitationally distorted Hubble images of the galaxy cluster Abell 2744 and two other clusters with the results of computer simulations of dark matter haloes. They found, in agreement with key predictions in the conventional dark matter picture, that the detailed galaxy substructures depend on the dark matter halo distribution, and that the total mass and the light trace each other. They also found a few discrepancies: the radial distribution of the dark matter is different from that predicted by the simulations, and the effects of tidal stripping and friction in galaxies are smaller than expected, but they suggest these issues might be resolved with more precise simulations. Overall, however, the standard model of dark matter does an excellent and reassuring job of describing galaxy clustering.

    Science paper:
    Mapping Substructure in the HST Frontier Fields Cluster Lenses and in Cosmological Simulations MNRAS

    See the full article here .

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    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 2:52 pm on July 16, 2017 Permalink | Reply
    Tags: , , , Gravitational Lensing, How to Weigh a Star,   

    From Optics & Photonics: “How to Weigh a Star” 

    Optics & Photonics

    08 June 2017
    Stewart Wills

    1
    Astronomers used the superior angular resolution of the Hubble Space Telescope’s Wide Field Camera 3 to assess the gravitational bending of light from a background star (small object in picture), about 5,000 light years away, by the much closer and brighter white-dwarf star Stein 2051B (larger object), 17 light years away. [Image: NASA, ESA, and K. Sahu (STScI)]

    NASA/ESA Hubble Telescope

    NASA/ESA Hubble WFC3

    With excitement continuing to build over the next year’s planned launch of the James Webb Space Telescope, it’s easy to forget that its predecessor—the Hubble Space Telescope (HST), originally put into Earth orbit more than 27 years ago—still has some great science left to do.

    NASA/ESA/CSA Webb Telescope annotated

    The latest evidence: researchers have used the superior angular resolution of the HST’s Wide Field Camera 3 to directly determine, through the gravitational bending of light, the mass of a white-dwarf star 17 light years away (http://science.sciencemag.org/content/early/2017/06/06/science.aal2879).

    Radio galaxies gravitationally lensed by a very large foreground galaxy cluster Hubble

    Stellar lenses and “Einstein rings”

    What is now called “gravitational microlensing” was one of the most famous predictions of Einstein’s general theory of relativity. Under that theory of gravity, massive bodies such as stars actually deform the space around them; as a result, the theory predicts that the spatial warping could deflect light from distant stars around such a body. That prediction, made in 1915, was borne out four years later in a celebrated experiment by the British astronomer Arthur Eddington, who measured the deflection of a background star’s light by the sun’s gravity during a total solar eclipse.

    In a 1936 gloss [Science]on his original theory in the journal Science, Einstein noted “the results of a little calculation which I had made” on the lens-like effects of stars. If two stars were lined up precisely, he suggested, the observer would in principle perceive, because of the bending of the light from the far star by the nearer one, a “luminius [sic] circle” of a predictable angular radius around the closer star—a phenomenon that came to be called an “Einstein ring.”

    Einstein himself blithely noted that “of course, there is no hope of observing this phenomenon directly,” given that the chances of such alignment are remote in themselves, and because the angular deflection of light by a star outside of our solar system “will defy the resolving power of our instruments.” The most one could hope to observe, he wrote, would be an increase in the apparent brightness of the closer of the two stars.

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    The gravity of a white dwarf star warps space and bends the light of a distant star behind it. [Image: NASA, ESA, and A. Feild (STScI)]

    Subtle signal

    Some eighty years later, scientists did have an instrument with potentially sufficient resolving power, the HST. But they still needed to find a pair of stars with the right alignment at the right time.

    To do so, researchers in the United States, Canada, and the United Kingdom—led by Kailash Sahu of the Space Telescope Science Institute (STScI) in Baltimore, Md., USA—computationally scoured a catalog of more than 5,000 nearby stars. They looked for candidates that had particularly rapid apparent motions in the sky, and that thus might have a better shot at lining up in the right way with a more distant star. They settled on the white-dwarf star called Stein 2051B, around 17 light years from earth. They then observed Stein 2051B (using the HST’s Wide Field Camera 3) seven times over the course of two years to assess its gravitational effect on light from a specific, much more distant background star around 5,000 light years away.

    Even with the HST’s superior resolving power, that effect was tough to see; Stein 2015B appears about 400 times brighter to an Earth observer than the background star, and the lensing effect was expected to be around three orders of magnitude smaller than the one observed by Eddington during the 1919 eclipse. Nonetheless, the team did indeed manage to tease out the gravitational lensing of the distant star’s light by the closer one—the first measurement of such a deflection by a star other than the sun.

    Weighing a star with light

    The STScI-led team went further, however, using the angular deflection they observed from the light of the background star to get at the mass of the closer Stein 2015B. Under Einstein’s equations, the radius of an Einstein ring relates directly to the square root of the mass of the closer (lensing) object. While, even with the HST’s sensitive instruments, the research team did not directly observe an Einstein ring, they were able to infer the ring’s radius over the series of measurements through the slightly asymmetric apparent offsets of the distant star and their impacts on the closer star’s brightness.

    As a result, the researchers were able to put the mass of Stein 2015B at 0.675±0.051 solar masses—right in line with the theoretical expectations for a white dwarf of its radius. That observation was interesting in itself, since Stein 2015B in particular has attracted some controversy, with suggestions that it might represent an exotic “iron-core” white dwarf with an anomalously large mass. The new observations suggest that the star actually lies right in the white-dwarf mainstream.

    More broadly, the “astrometric lensing” technique that the new research lays out offers a nice additional arrow in the quiver of astronomers seeking to suss out stellar masses across the sky. And the catalog of stars open for such analysis could expand significantly in coming years as new instruments come online, conducting even more massive sky surveys. (The Large Synoptic Survey Telescope, for example, slated to go online in 2023, will undertake a 10-year sky-survey campaign that’s expected to produce a 200-petabyte data set.)

    LSST


    LSST Camera, built at SLAC



    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.

    “This microlensing method is a very independent and direct way to determine the mass of a star,” team leader Sahu said in a press release. “It’s like placing the star on a scale.”

    See the full article here .

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    Optics & Photonics News (OPN) is The Optical Society’s monthly news magazine. It provides in-depth coverage of recent developments in the field of optics and offers busy professionals the tools they need to succeed in the optics industry, as well as informative pieces on a variety of topics such as science and society, education, technology and business. OPN strives to make the various facets of this diverse field accessible to researchers, engineers, businesspeople and students. Contributors include scientists and journalists who specialize in the field of optics. We welcome your submissions.

     
  • richardmitnick 7:40 am on July 11, 2017 Permalink | Reply
    Tags: , , , , Gravitational Lensing, GTC-Gran Telescopio Canarias, ,   

    From IAC via Manu Garcia: “A lens galaxy” 


    Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.

    IAC

    Instituto de Astrofísica de Canarias – IAC

    1
    Lensing galaxy. IAC.

    Thanks to the amplified image produced by a gravitational lens and the Gran Telescopio Canarias (GTC), a scientific team from the Polytechnic University of Cartagena and the Institute of Astrophysics of the Canary Islands (IAC) discovers one of the brightest galaxies to date when the Universe was 20% of its current age.

    Gravitational Lensing NASA/ESA

    According to the theory of General Relativity Einstein, when a ray of light passes near a massive object, the severity of that object attracts photons and deviates from its initial course. This phenomenon, called gravitational lens is the same producing lenses on light rays and acts as a magnifying glass, increasing the size of the object.

    Using this effect, a scientific team from the Institute of Astrophysics of the Canary Islands (IAC), led by researcher Anastasio Diaz-Sanchez, of the Polytechnic University of Cartagena (UPCT) has discovered a distant galaxy, about 10 billion years light and about 1,000 times brighter than the Milky Way. It is the brightest known submillimeter galaxies called strong emission present in the far infrared. In his characterization he has participated the Gran Telescopio Canarias (GTC) located at the Observatorio del Roque de los Muchachos (Garafía, La Palma).

    “Thanks to the gravitational lens -said Anastasio Diaz Sánchez, researcher UPCT and first author of the study consists of a cluster of galaxies, which acts like a telescope, the galaxy is 11 times bigger and brighter than which it is actually and produce different images of the same on an arc centered on the mass of the cluster, known as “Einstein ring”. The advantage of this type of amplification is not distorted the spectral properties of light can be studied very distant objects as if they were closer. ”

    To find this galaxy, whose discovery was recently published in an article in Astrophysical Journal Letters, a search was realized across the sky combining databases of WISE (NASA) and Planck (ESA) satellites to identify brightest submillimeter galaxies.

    NASA/WISE Telescope

    ESA/Planck

    This light, amplified by a cluster of nearby galaxies that acts as a lens, gives an even greater apparent brightness of it actually has, and because of this effect might characterize their nature and properties spectroscopy using the GTC.

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    Roque de los Muchachos Observatory, Garafía, La Palma, Canary I slands, Spain.

    Forming stars at high speed.

    This galaxy stands out as having a high rate of star formation, ie, is generating stars whose total mass is about 1,000 times the mass of the sun. By way of comparison, the Milky Way form each year stars with a total mass of twice the Sun. In this regard, Susana Iglesias-Groth, astrophysics IAC and co-author, adds: “These types of objects are home to the most powerful star-forming regions known in the universe and the next step will be to study their molecular wealth”.

    The fact that the galaxy is so bright, is amplified and has multiple images will delve into its gut, something impossible to carry out otherwise in such remote galaxies.

    “In the future, we can do more detailed studies of stellar formation using interferometers as the Northern Extended Millimeter Array (NOEMA / IRAM) in France and the Atacama Large Millimeter Array (ALMA) in Chile,” says Helmut Dannerbahuer, researcher IAC has also contributed to this discovery.

    IRAM NOEMA interferometer, Located in the French Alpes on the wide and isolated Plateau de Bure at an elevation of 2550 meters

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

    Science paper: Discovery of a very bright submillimeter galaxy at z = 2.0439 by Anastasio Diaz Sanchez, Susana Iglesias Groth, Rafael Rebolo and Helmut Dannerbauer, 2017, ApJ Letter.

    See the full article here.

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    Stem Education Coalition
    The Instituto de Astrofísica de Canarias(IAC) is an international research centre in Spain which comprises:

    The Instituto de Astrofísica, the headquarters, which is in La Laguna (Tenerife).
    The Centro de Astrofísica en La Palma (CALP)
    The Observatorio del Teide (OT), in Izaña (Tenerife).
    The Observatorio del Roque de los Muchachos (ORM), in Garafía (La Palma).

    These centres, with all the facilities they bring together, make up the European Northern Observatory(ENO).

    The IAC is constituted administratively as a Public Consortium, created by statute in 1982, with involvement from the Spanish Government, the Government of the Canary Islands, the University of La Laguna and Spain’s Science Research Council (CSIC).

    The International Scientific Committee (CCI) manages participation in the observatories by institutions from other countries. A Time Allocation Committee (CAT) allocates the observing time reserved for Spain at the telescopes in the IAC’s observatories.

    The exceptional quality of the sky over the Canaries for astronomical observations is protected by law. The IAC’s Sky Quality Protection Office (OTPC) regulates the application of the law and its Sky Quality Group continuously monitors the parameters that define observing quality at the IAC Observatories.

    The IAC’s research programme includes astrophysical research and technological development projects.

    The IAC is also involved in researcher training, university teaching and outreachactivities.

    The IAC has devoted much energy to developing technology for the design and construction of a large 10.4 metre diameter telescope, the ( Gran Telescopio CANARIAS, GTC), which is sited at the Observatorio del Roque de los Muchachos.


    Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, SpainGran Telescopio CANARIAS, GTC

     
  • richardmitnick 4:55 pm on July 6, 2017 Permalink | Reply
    Tags: Gravitational lens helps reveal "fireworks" in the early universe, Gravitational Lensing, Hubble Pushed Beyond Limits to Spot Clumps of New Stars in Distant Galaxy,   

    From Hubble: “Hubble Pushed Beyond Limits to Spot Clumps of New Stars in Distant Galaxy” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    NASA/ESA Hubble Telescope

    Jul 6, 2017

    Contact

    Christine Pulliam
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4366
    cpulliam@stsci.edu

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

    Dr. Jane Rigby
    NASA’s Goddard Space Flight Center, Greenbelt, Maryland
    301-286-1507 (office) / 240-475-3917 (cell)
    jane.r.rigby@nasa.gov

    Traci Johnson
    University of Michigan, Ann Arbor, Michigan
    612-325-1402
    tljohn@umich.edu

    1
    Gravitational lens helps reveal “fireworks” in the early universe
    When the universe was young, stars formed at a much higher rate than they do today. By peering across billions of light-years of space, Hubble can study this early era. But at such distances, galaxies shrink to smudges that hide key details. Astronomers have teased out those details in one distant galaxy by combining Hubble’s sharp vision with the natural magnifying power of a gravitational lens. The result is an image 10 times better than what Hubble could achieve on its own, showing dense clusters of brilliant, young stars that resemble cosmic fireworks.

    2

    When it comes to the distant universe, even the keen vision of NASA’s Hubble Space Telescope can only go so far. Teasing out finer details requires clever thinking and a little help from a cosmic alignment with a gravitational lens.

    By applying a new computational analysis to a galaxy magnified by a gravitational lens, astronomers have obtained images 10 times sharper than what Hubble could achieve on its own. The results show an edge-on disk galaxy studded with brilliant patches of newly formed stars.

    “When we saw the reconstructed image we said, ‘Wow, it looks like fireworks are going off everywhere,’” said astronomer Jane Rigby of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

    The galaxy in question is so far away that we see it as it appeared 11 billion years ago, only 2.7 billion years after the big bang. It is one of more than 70 strongly lensed galaxies studied by the Hubble Space Telescope, following up targets selected by the Sloan Giant Arcs Survey, which discovered hundreds of strongly lensed galaxies by searching Sloan Digital Sky Survey imaging data covering one-fourth of the sky.

    The gravity of a giant cluster of galaxies between the target galaxy and Earth distorts the more distant galaxy’s light, stretching it into an arc and also magnifying it almost 30 times. The team had to develop special computer code to remove the distortions caused by the gravitational lens, and reveal the disk galaxy as it would normally appear.

    The resulting reconstructed image revealed two dozen clumps of newborn stars, each spanning about 200 to 300 light-years. This contradicted theories suggesting that star-forming regions in the distant, early universe were much larger, 3,000 light-years or more in size.

    “There are star-forming knots as far down in size as we can see,” said doctoral student Traci Johnson of the University of Michigan, lead author of two of the three papers describing the research.

    Without the magnification boost of the gravitational lens, Johnson added, the disk galaxy would appear perfectly smooth and unremarkable to Hubble. This would give astronomers a very different picture of where stars are forming.

    While Hubble highlighted new stars within the lensed galaxy, NASA’s James Webb Space Telescope will uncover older, redder stars that formed even earlier in the galaxy’s history. It will also peer through any obscuring dust within the galaxy.

    “With the Webb Telescope, we’ll be able to tell you what happened in this galaxy in the past, and what we missed with Hubble because of dust,” said Rigby.

    These findings appear in a paper published in The Astrophysical Journal Letters[http://imgsrc.hubblesite.org/hvi/uploads/science_paper/file_attachment/241/Rigby_2017_ApJ_843_79_published_July_10.pdf], and two additional papers published in The Astrophysical Journal [http://imgsrc.hubblesite.org/hvi/uploads/science_paper/file_attachment/240/T_Johnson_published_ApJ_paper_July_10.pdf] and [http://imgsrc.hubblesite.org/hvi/uploads/science_paper/file_attachment/242/T_Johnson_published_ApJL_July_10.pdf].

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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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    AURA Icon

    NASA image

     
  • richardmitnick 2:28 pm on July 4, 2017 Permalink | Reply
    Tags: , , , , , Gravitational Lensing, Image of the initial SN Refsdal observations via the Hubble Space Telescope as well as the newly discovered magnified star LS1   

    From astrobites: “The Farthest Star Ever Seen” 

    Astrobites bloc

    Astrobites

    Jul 4, 2017
    Gourav Khullar

    Title: An individual star at redshift 1.5 extremely magnified by a galaxy-cluster lens
    Authors: P. L. Kelly, J. M . Diego, S. Rodney et al.
    First Author’s Institution: University of California, Berkeley, USA

    Status: Submitted to Nature, closed access (with an open arXiv version in the link above)

    I write this astrobite in my living room, assisted heavily by the lenses in my spectacles. It’s quite a marvelous thing – a pair of glasses. For the last decade or so, a pair of glasses have been necessary for me to marvel at the wonders of the world (and universe, now that studying astrophysics allows me to do that at leisure). Then, imagine my surprise when I came across the cosmic equivalent of my glasses and what a marvel they are! Gravitational lenses are some of the most massive structures in the universe, teaching us about the most distant and the most massive objects in the cosmos.

    Radio galaxies gravitationally lensed by a very large foreground galaxy cluster Hubble

    Gravitational lensing, as you may know, is a phenomenon predicted by Albert Einstein’s theory of General Relativity, where a massive object creates a gravitational potential well in the space it occupies. Every particle that passes through this potential well will follow a distorted path, since this potential well is essentially modifying the path available to particles itself. This ‘distortion’ also applies to photons. Hence, even light coming from background objects – like a star or a galaxy – gets distorted (or bent) on its way to us, if it encounters a ‘gravitational lens’ in its way. The effect was first detected by Sir Arthur Eddington in 1919 via observations of the same patch of sky during the night as well as during the day behind the sun – the idea was to check if the sun bent the light coming from stars behind it, by observing the patch of sky around the sun during a solar eclipse. The slight distortions – just like a regular magnifying glass or a pair of myopia-correcting glasses would cause – were found, and gravitational lensing was first observed! Since then, we have discovered multiple gigantic structures that act like lenses. Since this effect is based on an object creating distortions in space around them proportional to the mass they contain, the more massive the object, the greater the distorting effect. Hence, most lenses that we have studied well so far are galaxies, or even galaxy clusters which are the most massive collapsed objects in the universe. For more details, check out this video (Credits: ESO).

    It is important to note that since a galaxy cluster can act as a gravitational lens, just like a magnifying glass it also has the capacity to ‘magnify’ background objects. Imagine a faint galaxy that we are not able to detect with regular telescopes. Now imagine the same galaxy when it happens to lie in the line of sight of a galaxy cluster. Based on its location and distance from the ‘lens’, a faint background galaxy can get magnified by several times, allowing its minimal flux to reach us at last. It is common for astrophysicists in this field to study large objects like faint blue galaxies at redshifts of 2-3 that get magnified by nearby galaxy clusters, which would not have been possible otherwise. This advancing field is only getting better with improved understanding of galaxy clusters as lenses – the calculations of their masses, and how this mass may be distributed throughout the cluster. Today’s study has gone one step further, into uncharted territory. Today’s study has observed a gravitationally lensed star!

    2
    Fig 2. Image of the initial SN Refsdal observations via the Hubble Space Telescope, as well as the newly discovered magnified star LS1.

    From Hubble observations of a multiple-imaged supernova via gravitational lensing (see this astrobite for more details on Supernova Refsdal), Kelly et al. were successful in observing another extremely fascinating object too – a blue unresolved source of light, whose flux kept fluctuating. By taking spectra of that object, they concluded that it was a B-type star whose light was magnified approximately 2000 times on its way to us! In comparison, a typical galaxy is expected to be magnified by ~50 times. What makes this object undoubtedly a star are specific features seen in the spectra – namely the huge drop in flux around a rest-frame wavelength of ~3650 Angstroms called the Balmer break. Moreover, since the huge drop in flux is actually seen at a much higher wavelength, that allows for the calculation of the ‘redshift‘, or distance of the object. It turns out that this star, called LS1, is at a redshift of ~1.5, the farthest star ever discovered. For context, 99% of the stars you see in the night sky, are within the Milky Way. The farthest star we have discovered until now, is in a nearby galaxy few hundred thousand light years away. LS1, on the other hand, is 36 billion light years away!

    3
    Fig 3. The complete Spectral Energy Distribution (or a Flux map) of the observed star LS1. You can see that different models of stars with different temperatures and properties have been fit to the observations, in order to ascertain the nature of the faint blue star. The ‘Balmer break’ can be seen at ~9000A instead of a rest-frame wavelength of ~3650A, corresponding to a redshift of ~1.5.

    Other properties of the star have also been observed – its temperature (~11000 K), its transverse velocity or motion in the sky (~1000 km/s) and the reason why this star magnified to the extent it did. In construction of mass models of galaxies (or clusters) that could cause gravitational lensing, there are certain surfaces around the lens that are called ‘caustics’. These surfaces correspond to a ‘mathematically infinite’ magnification in ideal lens models, and if an object is present on these unique surfaces, even a very faint object can pop out in lens observations! LS1 is no different – the models built in this paper suggest exactly that. This study also calculates the probability of a star to lie on a caustic, as well as the probability of such a massive hot star in the background existing at that distance. It is needless to say that observing such a distant star can tell us volumes about the nature of stellar population at high redshifts, as wells as test gravitational lens models to their extremes!

    Keep an eye out for more on this in the near future. After all, it’s the farthest star ever seen by a human, guys!

    See the full article here .

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    STEM Icon

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    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.

     
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