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  • richardmitnick 12:52 pm on July 16, 2018 Permalink | Reply
    Tags: , , , , , European VLBI, , New images from a super-telescope, ,   

    From Netherlands Institute for Radio Astronomy: “New images from a super-telescope” 

    ASTRON bloc

    From Netherlands Institute for Radio Astronomy

    1

    New images from a super-telescope bring astronomers a step closer to understanding dark matter.

    Astronomers using a global network of radio telescopes have produced one of the sharpest astronomical images ever. The resulting image demonstrates that dark matter is distributed unevenly across a distant galaxy.

    The image was created by combining data from a global radio telescope network, comprised of the European VLBI Network, and the Very Long Baseline Array and Green Bank Telescope in the United States, in an effort to address some of the fundamental questions about dark matter. The international team of astronomers aim to determine how much dark matter is present in galaxies and how it is distributed. According to current theories, a galaxy, such as our Milky Way, should have thousands of dwarf galaxies orbiting around it, yet to date only approximately 100 have been found.

    European VLBI

    NRAO/VLBA

    Green Bank Radio Telescope, West Virginia, USA

    “It has been suggested that these dwarf galaxies could be dark matter dominated and, therefore, highly difficult to observe. However, throughout the distant Universe, we can discover the presence of these small mass structures only by using the gravitational lensing effect,” explains Cristiana Spingola, lead author on the paper, from the Kapteyn Astronomical Institute, Groningen.

    Gravitational lensing allows astronomers to observe incredibly distant radio sources that cannot be directly detected.

    Gravitational Lensing NASA/ESA

    By observing how the radio emission from the distant source is bent by the gravitational field of a massive object – the lens – located between the source and the Earth, it is possible to determine information about both the distant source and the lens. In this study the researchers used the radio source MG J0751+2716, at such great a distance that it has taken the light 11.7 billion years to reach the Earth. This object is comprised of a black hole with a powerful ejection of material, known as a jet. The lens consists of a group of galaxies located at a look-back time of 3.9 billion years from Earth.

    In the study, the astronomers were able to determine the distance, brightness and projected size of the radio source, together with the composition of dark matter across the lens, which appeared clumpy and uneven.

    “For the first time we were able to observe large gravitationally lensed arcs on extremely small angular scales. The background source – the black hole with radio jets – is distorted into these arcs on the image because of the gravitational effect of the foreground galaxies (the lens). It is a rare possibility to get such an extended arc.” Spingola added, “the unprecedented detail of these extended gravitational arcs allowed us to infer with high precision the distribution of the matter of the galaxy acting as a lens.”

    It is only possible to obtain such high-resolution data by coordinating multiple telescopes to observe the same radio source simultaneously. In this case, 24 radio antennas from across the globe were connected using a technique called Very Long Baseline Interferometry (VLBI). Data from all the telescopes was collated in a process known as correlation, at a super computer housed at the Joint Institute for VLBI ERIC in Dwingeloo, the Netherlands.

    To better understand the properties for dark matter, the team are now applying sophisticated numerical algorithms to quantify the nature of the clumpy dark matter. But, they are also on the hunt for more extended gravitational arcs just like this.

    “There are only a limited number of gravitational lenses suitable for this study, and while we have started this search using the European VLBI Network and the Very Long Baseline Array we expect that there will be more giant radio arcs in the future,” explained John McKean, project lead from the Netherlands Institute for Radio Astronomy (ASTRON) and the Kapteyn Astronomical Institute.

    This study was led by John McKean from the Kapteyn Astronomical Institute, University of Groningen and the Netherlands Institute for Radio Astronomy (ASTRON), Dwingeloo on behalf of the international research team SHARP (Strong Lensing at High Angular Resolution Project) led by Chris Fassnacht (University of California, Davis), and also including Matt Auger (University of Cambridge), Leon Koopmans (University of Groningen), David Lagattuta (University of Lyon) and Simona Vegetti (Max Planck Institute for Astrophysics). Their findings can be found in Issue 4, Volume 478 of the Monthly Notices of the Royal Astronomical Society, published by Oxford University Press.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    LOFAR is a radio telescope composed of an international network of antenna stations and is designed to observe the universe at frequencies between 10 and 250 MHz. Operated by ASTRON, the network includes stations in the Netherlands, Germany, Sweden, the U.K., France, Poland and Ireland.
    ASTRON-Westerbork Synthesis Radio Telescope
    Westerbork Synthesis Radio Telescope (WSRT)

    ASTRON was founded in 1949, as the Foundation for Radio radiation from the Sun and Milky Way (SRZM). Its original charge was to develop and operate radio telescopes, the first being systems using surplus wartime radar dishes. The organisation has grown from twenty employees in the early 1960’s to about 180 staff members today.

     
  • richardmitnick 1:59 pm on April 29, 2017 Permalink | Reply
    Tags: Ask Ethan: What should a black hole’s event horizon look like?, , , European VLBI, ,   

    From Ethan Siegel: “Ask Ethan: What should a black hole’s event horizon look like?” 

    Ethan Siegel
    Apr 29, 2017

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    An illustration of a black hole. Despite how dark it is, all black holes are thought to have formed from normal matter alone, but illustrations like these are only partially accurate. Image credit: NASA / JPL-Caltech.

    You might think that it should be all black, but then how would we see it?

    “It is conceptually interesting, if not astrophysically very important, to calculate the precise apparent shape of the black hole… Unfortunately, there seems to be no hope of observing this effect.” -Jim Bardeen

    Earlier this month, telescopes from all around the world took data, simultaneously, of the Milky Way’s central black hole.

    Here is the Event Horizon Telescope Array

    Event Horizon Telescope map

    The locations of the radio dishes that will be part of the Event Horizon Telescope array. Image credit: Event Horizon Telescope sites, via University of Arizona at https://www.as.arizona.edu/event-horizon-telescope.

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Also involved:

    European VLBI

    Of all the black holes that are known in the Universe, the one at our galactic center — Sagittarius A* — is special.

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

    From our point of view, its event horizon is the largest of all black holes. It’s so large that telescopes positioned at different locations on Earth should be able to directly image it, if they all viewed it simultaneously. While it will take months to combine and analyze the data from all the different telescopes, we should get our first image of an event horizon by the end of 2017. So what will it looks like? That’s the question of Dan Barrett, who’s seen some illustrations and is a bit puzzled:

    Shouldn’t the event horizon completely surround the black hole like an egg shell? All the artist renderings of a black hole are like slicing a hard boiled egg in half and showing that image. How is it that the event horizon does not completely surround the black hole?

    There are a few different classes of illustrations floating around, to be sure. But which ones, if any, are correct?

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    Artwork illustrating a simple black circle, perhaps with a ring around it, is an oversimplified picture of what an event horizon looks like. Image credit: Victor de Schwanberg.

    The oldest type of illustration is simply a circular, black disk, blocking out all the background light from behind it. This makes sense if you think about what a black hole actually is: a collection of mass that’s so great and so compact that the escape velocity from its surface is greater than the speed of light! Since nothing can move that quickly, not even the forces or interactions between the particles inside the black hole, the inside of a black hole collapses to a singularity, and an event horizon is created around the black hole. From this spherical region of space, no light can escape, and so it should appear as a black circle, from any perspective, superimposed on the background of the Universe.

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    A black hole isn’t just a mass superimposed over an isolated background, but will exhibit gravitational effects that stretch, magnify and distort background light due to gravitational lensing. Image credit: Ute Kraus, Physics education group Kraus / Axel Mellinger.

    But there’s more to the story than that. Because of their gravity, black holes will magnify and distort any background light, due to the effect of gravitational lensing. This is a more detailed and accurate illustration of what a black hole looks like, as it also possesses an apparent event horizon sized appropriately with the curvature of space in General Relativity.

    Unfortunately, these illustrations are flawed, too: they fail to account for foreground material and for accretion around the black hole. Some illustrations, though, do successfully add these in.

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    An illustration of an active black hole, one that accretes matter and accelerates a portion of it outwards in two perpendicular jets, may describe the black hole at the center of our galaxy in many regards. Image credit: Mark A. Garlick.

    Because of their tremendous gravitational effects, black holes will form accretion disks in the presence of other sources of matter. Asteroids, gas clouds, or even entire stars will be torn apart by the tidal forces coming from an object as massive as a black hole. Due to the conservation of angular momentum, and of collisions between the various infalling particles, a disk-like object will emerge around the black hole, which will heat up and emit radiation. In the innermost regions, particles occasionally fall in, adding to the mass of the black hole, while the material in front of the black hole will obscure part of the sphere/circle you’d otherwise see.

    But the event horizon itself isn’t transparent, and you shouldn’t be able to see the matter behind it.

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    The black hole, as illustrated in the movie Interstellar, shows an event horizon fairly accurately for a very specific class of rotating black holes. Image credit: Interstellar / R. Hurt / Caltech.

    It might seem surprising that a Hollywood film — Interstellar — has a more accurate illustration of a black hole than many of the professional pieces of artwork created for/by NASA, but misconceptions abound, even among professionals, when it comes to black holes. Black holes don’t suck matter in; they simply gravitate. Black holes don’t tear things apart because of any extra force; it’s simply tidal forces — where one part of the infalling object is closer to the center than another — that does it. And most importantly, black holes rarely exist in a “naked” state, but rather exist in the vicinity of other matter, such as at the center of our galaxy.

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    An X-ray / Infrared composite image of the black hole at the center of our galaxy: Sagittarius A*. It has a mass of about four million Suns, and is found surrounded by hot, X-ray emitting gas. Image credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI.

    So with all of that in mind, what are the hard-boiled-egg images that have been going around? Remember, we can’t image the black hole itself, because it doesn’t emit light! All we can do is look at a particular wavelength, and see a combination of the emitting light that comes from around, behind and in front of the black hole itself. The expected signal, indeed, does resemble a split hard-boiled egg.

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    Some of the possible profile signals of the black hole’s event horizon as simulations of the Event Horizon Telescope indicate. Image credit: High-Angular-Resolution and High-Sensitivity Science Enabled by Beamformed ALMA, V. Fish et al., arXiv:1309.3519

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

    This has to do with what it is we’re imaging. We can’t look in X-rays, because there are simply too few X-ray photons overall. We can’t look in visible light, because the galactic center is opaque it it. And we can’t look in the infrared, because the atmosphere blocks infrared light. But what we can do is look in the radio, and we can do it all over the world, simulataneously, to get the optimal resolution possible.

    The black hole at the galactic center has an angular size of about 37 micro-arc-seconds, while the resolution of this telescope array is around 15 micro-arc-seconds, so we should be able to see it! At radio frequencies, the overwhelming majority of that radiation comes from charged matter particles being accelerated around the black hole. We don’t know how the disk will be oriented, whether there will be multiple disks, whether it will be more like a swarm of bees or more like a compact disk. We also don’t know whether it will prefer one “side” of the black hole, as viewed from our perspective, over another.

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    Five different simulations in general relativity, using a magnetohydrodynamic model of the black hole’s accretion disk, and how the radio signal will look as a result. Image credit: GRMHD simulations of visibility amplitude variability for Event Horizon Telescope images of Sgr A*, L. Medeiros et al., arXiv:1601.06799.

    We fully expect the event horizon to be real, to be of a specific size, and to block all the light coming from behind it. But we also expect that there will be some signal in front of it, that the signal will be messy due to the messy environment around the black hole, and that the orientation of the disk with respect to the black hole will play an important role in determining what we see.

    One side is brighter as the disk rotates towards us; one side is fainter as the disk rotates away. The entire “outline” of the event horizon may be visible as well, thanks to the effect of gravitational lensing. Perhaps most importantly, whether the disk is seen “edge-on” or “face-on” with respect to us will drastically alter the signal, as the 1st and 3rd panels below illustrate.

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    The orientation of the accretion disk as either face-on (left two panels) or edge-on (right two panels) can vastly alter how the black hole appears to us. Image credit: ‘Toward the event horizon — the supermassive black hole in the Galactic Center’, Class. Quantum Grav., Falcke & Markoff (2013).

    There are other effects we can test for, including:

    whether the black hole has the right size as predicted by general relativity,
    whether the event horizon is circular (as predicted), or oblate or prolate instead,
    whether the radio emissions extend farther than we thought,

    or whether there are any other deviations from the expected behavior. This is a brand new frontier in physics, and we’re poised to actually test it directly. One thing’s for certain: no matter what it is that the Event Horizon Telescope sees, we’re bound to learn something new and wonderful about some of the most extreme objects and conditions in the Universe!

    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 1:11 pm on April 15, 2017 Permalink | Reply
    Tags: , , , , , , European VLBI,   

    From ESO: “Taking the First Picture of a Black Hole” 

    ESO 50 Large

    European Southern Observatory

    30.3.2017

    1. What are the Event Horizon Telescope and the Global mm-VLBI Array?

    At the centre of our galaxy lurks a cosmic monster: a supermassive black hole called Sagittarius A* with a mass about four million times that of the Sun.

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

    Its gravity is so intense that not even light can escape its pull, but if it wasn’t for its strong gravitational influence on the stars and gas around it, we would have no idea that it was there! Now, an ambitious new endeavour is underway to take a never-seen-before image, of the event horizon of the black hole itself.

    Two international collaborations of radio telescopes have linked up to create Earth-sized virtual telescopes: the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA), working at different wavelengths.

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    This infographic details the locations of the participating telescopes of the Event Horizon Telescope and the Global mm-VLBI Array. Credit: ESO/O. Furtak

    Global mm-VLBI Array

    Event Horizon Telescope Array

    Event Horizon Telescope map

    The locations of the radio dishes that will be part of the Event Horizon Telescope array. Image credit: Event Horizon Telescope sites, via University of Arizona at https://www.as.arizona.edu/event-horizon-telescope.

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    Future Array/Telescopes

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    The impressive line-up of telescopes, which stretch across the globe from the South Pole to Hawaii to Europe, will work together to target the supermassive black hole at the heart of the Milky Way.

    To do this, astronomers will exploit a technique known as Very-long-baseline Interferometry (VLBI), where telescopes thousands of kilometres apart can link together and act as one.

    European VLBI

    This cooperative technique can achieve a far higher resolution than any single facility could obtain on its own — a resolution 2000 times that of the NASA/ESA Hubble Space Telescope! This super-high resolution is crucial for detecting the black hole, which — despite being about 20 times bigger than the Sun — lies a long way away, over 26 000 light-years from Earth.

    The plan to image a black hole has been in the works for years, but it’s only recently that technology has brought the ambitious endeavour within reach. Plus, a radio telescope heavyweight has just joined the team: the Atacama Large Millimeter/submillimeter Array (ALMA).

    Located high up on the Chajnantor plateau in Chile’s Atacama Desert, ALMA’s 66 antennas and exquisite receivers make it the largest and most sensitive component of the EHT/GMVA collaboration, increasing the overall sensitivity by a factor of 10. Despite being a state-of-the-art facility, ALMA has undergone several upgrades to take part in the collaboration. Specialist equipment has been installed, including new hard drives that are necessary to store the sheer amount of data produced by the observations, as well as an extremely accurate atomic clock, which is critical to link ALMA to the entire VLBI network.

    The first groundbreaking observations will be made in April 2017: observations at 3 millimetre wavelengths will be made with the GMVA from 1–4 April 2017, and with the EHT at 1.3 millimetre wavelengths from 5–14 April 2017. The GMVA will investigate the properties of the accretion and outflow around the Galactic Centre, while the EHT will attempt to image, for the very first time, the shadow of the black hole’s event horizon.

    There is a long, hard road ahead to process the massive amounts of data that will be acquired during the observation periods, and results are expected to become available towards the end of 2017.

    The outcome of these observations is eagerly awaited by the astronomy community worldwide, as their scientific potential is incredibly exciting and the collaboration are pursuing some awesome goals. These could include testing Einstein’s theory of general relativity, which predicts a roughly circular “shadow” around the black hole. Other goals include learning about how material accretes around black holes, as well as the formation of extremely fast jets of gas that blast out from them.

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    Simulated images of the shadow of a black hole: General relativity predicts that the shadow should be circular (middle), but a black hole could potentially also have a prolate (left) or oblate (right) shadow. Future EHT images will test this prediction. Credit: D. Psaltis and A. Broderick.

    This is the first post of a blog series that will take you along for the astronomical ride, giving insight into how cutting-edge research is done and what risks are involved.

    In the following posts, we’ll explore questions such as: What makes black holes so interesting? How do radio telescopes see the Universe? And what do we really know about the supermassive monster lurking at the centre of the Milky Way?

    11.4.2017

    2. What is a black hole?

    Right now, astronomers are attempting to take the first image of the event horizon of the supermassive black hole at the centre of the Milky Way — but what exactly are black holes?

    Black holes are some of the most bizarre and fascinating objects in the Universe. Essentially, they’re reality-bending concentrations of matter squeezed into a very tiny space, creating an object with an immense gravitational pull. Around a black hole is a boundary called an event horizon — the surface beyond which nothing can escape the black hole’s clutches, not even light.

    Take a tour of the anatomy of a black hole with our handy infographic:

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    Credit: ESO, ESA/Hubble, M. Kornmesser/N. Bartmann

    Since no light can escape from a black hole, we can’t see them directly. But their huge gravitational influence gives away their presence. Black holes are often orbited by stars, gas and other material in tight paths that become more crowded and frantic as they’re dragged closer to the event horizon. This creates a superheated accretion disc around the black hole, which emits vast amounts of radiation of different wavelengths.

    By observing this radiation from the activity around black holes, astronomers have determined that there are two main types: stellar mass and supermassive.

    A stellar mass black hole is the corpse of a star more than about 30 times as massive as our Sun. At the end of its life, such stars violently collapse and don’t stopped collapsing until all of their constituent matter has condensed down into an unimaginably tiny space. It’s easiest to discover stellar mass black holes that are part of an X-ray binary system, where the black hole is guzzling down material from its companion star.

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    Artist’s impression of the formation of a stellar black hole in a binary system. Credit: ESO/L. Calçada/M.Kornmesser

    The second type is called a supermassive black hole. These gargantuan black holes are up to billions of times more massive than an average star, and how they formed is much less clear and is a matter of ongoing study. One theory proposes they formed from enormous clouds of matter that collapsed when galaxies first formed; another theory suggests that colliding stellar mass black holes can merge into one enormous object.

    Today, these supermassive monsters reside at the centres of almost every galaxy — including our own Milky Way. They exert tremendous influence on their home galaxies, especially when they gorge on gas and stars.

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    Artist’s impression of a gas cloud after a close approach to the black hole at the centre of the Milky Way. The star orbiting the black hole are shown, along with blue lines that mark their fast, tight orbits. Credit: ESO/MPE/Marc Schartmann

    26 000 light-years away from Earth, Sagittarius A* (Sgr A* for short) is the supermassive black hole in the hot, violent centre of the Milky Way. It’s over 4 million times more massive than our Sun, over 20 million kilometres across, and is spinning at a large fraction of the speed of light. It’s shrouded from optical telescopes by dense clouds of dust and gas, so observatories that can observe different wavelengths — either longer (such as ALMA) or shorter (X-ray telescopes) — are essential to study its properties.

    Soon, through the combined power of ALMA and other millimetre-wavelength telescopes across the globe, we may become much better acquainted with the monstrous heart of our galaxy. The Global mm-VLBI Array is currently investigating the process of how gas, dust and other material accrete onto supermassive black holes, as well as the formation of the extremely fast gas jets that flow from them. The Event Horizon Telescope, on the other hand, is working towards a different goal: imaging the shadow of the event horizon, the point of no return.

    This is the second post of a blog series following the EHT and GMVA projects. Stay tuned to find out more about why the event horizon of a black hole is so interesting!

    Event Horizon Telescope website
    GMVA website
    BlackHoleCam — an EU-funded project to finally image, measure and understand astrophysical black holes
    Read more about ALMA
    Find out more about ALMA’s VLBI capabilities

    See the full article here .

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

    ESO LaSilla
    ESO/Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres

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

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

    ESO NTT
    ESO/NTT at Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres

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

    ALMA Array
    ALMA on the Chajnantor plateau at 5,000 metres

    ESO E-ELT
    ESO/E-ELT to be built at Cerro Armazones at 3,060 m

    ESO APEX
    APEX Atacama Pathfinder 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert

     
    • Nikola Milovic 8:48 am on April 16, 2017 Permalink | Reply

      I wish I could make contact with scientists who are trying to learn something more about black holes. The main reason for this contact is my view that science still does not know what a black hole is and how and why it occurs.
      It is true that this is a place where even light can not escape. But, one must know the limits of long acting black hole and what happens within those boundaries towards the center of the black hole and outside those borders where both matter and light still “confused” and do not know which way to go. To be deciphered. What if scientists to “see” with new telescopes, is again out of the black hole and its limits where the “forbidden transition both sides of the border.
      It is true that this is an enormous amount of gravity, but how and why this occurs, science can not know if you do not know the structure of the universe.
      The black hole has a spherical shape and is situated so that all sides around this sphere can “suck every form of matter. The fact that science sees as the horizon, not what is in reality, neither of the black hole can form any kind of matter, nor can they be two black holes collide.

      Like

  • richardmitnick 3:11 pm on January 4, 2017 Permalink | Reply
    Tags: , European VLBI, , , ,   

    From NRAO: “Precise Location, Distance Provide Breakthrough in Study of Fast Radio Bursts” 

    NRAO Icon
    National Radio Astronomy Observatory

    NRAO Banner

    4 January 2017

    1
    Visible-light image of host galaxy.
    Credit: Gemini Observatory/AURA/NSF/NRC.

    For the first time, astronomers have pinpointed the location in the sky of a Fast Radio Burst (FRB), allowing them to determine the distance and home galaxy of one of these mysterious pulses of radio waves. The new information rules out several suggested explanations for the source of FRBs.

    “We now know that this particular burst comes from a dwarf galaxy more than three billion light-years from Earth,” said Shami Chatterjee, of Cornell University. “That simple fact is a huge advance in our understanding of these events,” he added. Chatterjee and other astronomers presented their findings to the American Astronomical Society’s meeting in Grapevine, Texas, in the scientific journal Nature, and in companion papers in the Astrophysical Journal Letters.

    Fast Radio Bursts are highly-energetic, but very short-lived (millisecond) bursts of radio waves whose origins have remained a mystery since the first one was discovered in 2007. That year, researchers scouring archived data from Australia’s Parkes Radio Telescope in search of new pulsars found the first known FRB — one that had burst in 2001.

    There now are 18 known FRBs. All were discovered using single-dish radio telescopes that are unable to narrow down the object’s location with enough precision to allow other observatories to identify its host environment or to find it at other wavelengths. Unlike all the others, however, one FRB, discovered in November of 2012 at the Arecibo Observatory in Puerto Rico, has recurred numerous times.

    NAIC/Arecibo Observatory, Puerto Rico, USA
    NAIC/Arecibo Observatory, Puerto Rico, USA

    The repeating bursts from this object, named FRB 121102 after the date of the initial burst, allowed astronomers to watch for it using the National Science Foundation’s (NSF) Karl G. Jansky Very Large Array (VLA), a multi-antenna radio telescope system with the resolving power, or ability to see fine detail, needed to precisely determine the object’s location in the sky.

    In 83 hours of observing time over six months in 2016, the VLA detected nine bursts from FRB 121102.

    “For a long time, we came up empty, then got a string of bursts that gave us exactly what we needed,” said Casey Law, of the University of California at Berkeley.

    “The VLA data allowed us to narrow down the position very accurately,” said Sarah Burke-Spolaor, of the National Radio Astronomy Observatory (NRAO) and West Virginia University.

    Using the precise VLA position, researchers used the Gemini North telescope in Hawaii to make a visible-light image that identified a faint dwarf galaxy at the location of the bursts. The Gemini observations also determined that the dwarf galaxy is more than 3 billion light-years from Earth.

    Gemini/North telescope at Mauna Kea, Hawaii, USA
    Gemini/North telescope at Mauna Kea, Hawaii, USA

    “Before we knew the distance to any FRBs, several proposed explanations for their origins said they could be coming from within or near our own Milky Way Galaxy. We now have ruled out those explanations, at least for this FRB,” said Shriharsh Tendulkar, of McGill University in Montreal, Canada.

    In addition to detecting the bright bursts from FRB 121102, the VLA observations also revealed an ongoing, persistent source of weaker radio emission in the same region.

    Next, a team of observers used the multiple radio telescopes of the European VLBI Network (EVN), along with the 1,000-foot-diameter William E. Gordon Telescope of the Arecibo Observatory, and the NSF’s Very Long Baseline Array (VLBA) to determine the object’s position with even greater accuracy.

    European VLBI
    European VLBI

    NRAO VLBA
    NRAO VLBA

    “These ultra high precision observations showed that the bursts and the persistent source must be within 100 light-years of each other,” said Jason Hessels, of the Netherlands Institute for Radio Astronomy and the University of Amsterdam.

    “We think that the bursts and the continuous source are likely to be either the same object or that they are somehow physically associated with each other,” said Benito Marcote, of the Joint Institute for VLBI ERIC, Dwingeloo, Netherlands.

    The top candidates, the astronomers suggested, are a neutron star, possibly a highly-magnetic magnetar, surrounded by either material ejected by a supernova explosion or material ejected by a resulting pulsar, or an active nucleus in the galaxy, with radio emission coming from jets of material emitted from the region surrounding a supermassive black hole.

    “We do have to keep in mind that this FRB is the only one known to repeat, so it may be physically different from the others,” cautioned Bryan Butler of NRAO.

    “Finding the host galaxy of this FRB, and its distance, is a big step forward, but we still have much more to do before we fully understand what these things are,” Chatterjee said.

    “This impressive result shows the power of several telescopes working in concert — first detecting the radio burst and then precisely locating and beginning to characterize the emitting source,” said Phil Puxley, a program director at the National Science Foundation that funds the VLA, VLBA, Gemini and Arecibo observatories. “It will be exciting to collect more data and better understand the nature of these radio bursts.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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), the Robert C. Byrd Green Bank Telescope (GBT), and the Very Long Baseline Array (VLBA)*.

    ALMA Array

    NRAO ALMA

    GBO radio telescope, Green Bank, West Virginia, USA
    GBO Radio Observatory telescope, Green Bank, West Virginia, USA, formerly supported by NSF, but now on its own

    NRAO VLA
    NRAO VLA

    The NRAO is building two new major research facilities in partnership with the international community that will soon open new scientific frontiers: the Atacama Large Millimeter/submillimeter Array (ALMA), and the Expanded Very Large Array (EVLA). Access to ALMA observing time by the North American astronomical community will be through the North American ALMA Science Center (NAASC).
    *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.

     
  • richardmitnick 6:59 am on July 6, 2016 Permalink | Reply
    Tags: , , , European VLBI,   

    From RAS: “Earth-size telescope tracks the aftermath of a star being swallowed by a supermassive black hole” 

    Royal Astronomical Society

    Royal Astronomical Society

    05 July 2016
    Media contact

    Robert Cumming
    Communications Officer
    Onsala Space Observatory
    Chalmers University of Technology
    Sweden
    Tel: +46 70 493 3114 or +46 (0)31 772 5500
    robert.cumming@chalmers.se

    Science contact

    Jun Yang
    Onsala Space Observatory
    Chalmers University of Technology
    Sweden
    Tel: +46 (0)31 7725531
    jun.yang@chalmers.se

    Radio astronomers have used a radio telescope network the size of the Earth to zoom in on a unique phenomenon in a distant galaxy: a jet activated by a star being consumed by a supermassive black hole. The record-sharp observations reveal a compact and surprisingly slowly moving source of radio waves, with details published in a paper in the journal Monthly Notices of the Royal Astronomical Society. The results will also be presented at the European Week of Astronomy and Space Science in Athens, Greece, on Friday 8 July 2016.

    1
    This artist’s impression shows the remains of a star that came too close to a supermassive black hole. Extremely sharp observations of the event Swift J1644+57 with the radio telescope network EVN (European VLBI Network) have revealed a remarkably compact jet, shown here in yellow. Image credit: ESA/S. Komossa/Beabudai Design.

    The international team, led by Jun Yang (Onsala Space Observatory, Chalmers University of Technology, Sweden), studied the new-born jet in a source known as Swift J1644+57 with the European VLBI Network (EVN), an Earth-size radio telescope array.

    European VLBI
    European VLBI

    When a star moves close to a supermassive black hole it can be disrupted violently. About half of the gas in the star is drawn towards the black hole and forms a disc around it. During this process, large amounts of gravitational energy are converted into electromagnetic radiation, creating a bright source visible at many different wavelengths.

    One dramatic consequence is that some of the star’s material, stripped from the star and collected around the black hole, can be ejected in extremely narrow beams of particles at speeds approaching the speed of light. These so-called relativistic jets produce strong emission at radio wavelengths.

    The first known tidal disruption event that formed a relativistic jet was discovered in 2011 by the NASA satellite Swift. Initially identified by a bright flare in X-rays, the event was given the name Swift J1644+57. The source was traced to a distant galaxy, so far away that its light took around 3.9 billion years to reach Earth.

    Jun Yang and his colleagues used the technique of very long baseline interferometry (VLBI), where a network of detectors separated by thousands of kilometres are combined into a single observatory, to make extremely high-precision measurements of the jet from Swift J1644+57.

    2
    Three years of extremely precise EVN measurements of the jet from Swift J1644+5734 show a very compact source with no signs of motion. Lower panel: false colour contour image of the jet (the ellipse in the lower left corner shows the size of an unresolved source). Upper panel: position measurement with dates. One microarcsecond is one 3 600 000 000th part of a degree. Image credit: EVN/JIVE/J. Yang.

    “Using the EVN telescope network we were able to measure the jet’s position to a precision of 10 microarcseconds. That corresponds to the angular extent of a 2-Euro coin on the Moon as seen from Earth. These are some of the sharpest measurements ever made by radio telescopes”, says Jun Yang.

    Thanks to the amazing precision possible with the network of radio telescopes, the scientists were able to search for signs of motion in the jet, despite its huge distance.

    “We looked for motion close to the light speed in the jet, so-called superluminal motion. Over our three years of observations such movement should have been clearly detectable. But our images reveal instead very compact and steady emission – there is no apparent motion”, continues Jun Yang.

    The results give important insights into what happens when a star is destroyed by a supermassive black hole, but also how newly launched jets behave in a pristine environment. Zsolt Paragi, Head of User Support at the Joint Institute for VLBI ERIC (JIVE) in Dwingeloo, Netherlands, and member of the team, explains why the jet appears to be so compact and stationary.

    “Newly formed relativistic ejecta decelerate quickly as they interact with the interstellar medium in the galaxy. Besides, earlier studies suggest we may be seeing the jet at a very small angle. That could contribute to the apparent compactness”, he says.

    The record-sharp and extremely sensitive observations would not have been possible without the full power of the many radio telescopes of different sizes which together make up the EVN, explains Tao An from the Shanghai Astronomical Observatory, P.R. China.

    “While the largest radio telescopes in the network contribute to the great sensitivity, the larger field of view provided by telescopes like the 25-m radio telescopes in Sheshan and Nanshan (China), and in Onsala (Sweden) played a crucial role in the investigation, allowing us to simultaneously observe Swift J1644+57 and a faint reference source,” he says.

    Swift J1644+57 is one of the first tidal disruption events to be studied in detail, and it won’t be the last.

    “Observations with the next generation of radio telescopes will tell us more about what actually happens when a star is eaten by a black hole – and how powerful jets form and evolve right next to black holes”, explains Stefanie Komossa, astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany.

    “In the future, new, giant radio telescopes like FAST (Five hundred meter Aperture Spherical Telescope) and SKA (Square Kilometre Array) will allow us to make even more detailed observations of these extreme and exciting events,” concludes Jun Yang.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

     
  • richardmitnick 9:02 pm on June 27, 2014 Permalink | Reply
    Tags: , , , , European VLBI, ,   

    From physicsworld.com: “Couple emerges from trio of supermassive black holes” 

    physicsworld
    physicsworld.com

    Jun 27, 2014
    Tushna Commissariat

    A trio of closely orbiting supermassive black holes has been spotted in a galaxy nearly 4.2 billion light-years away. The discovery was made by an international team of astronomers, which points out that such triple systems are very rare because most galaxies have just one black hole at their centre. This system is particularly interesting to astronomers because two of the three black holes are very closely bound, forming a “tight” binary pair within the system.

    tsmbh

    Astronomers know that supermassive black holes – the largest type of black hole, which can be billions of solar masses – lie at the heart of most galaxies, including our own Milky Way. Most galaxies are believed to evolve via collisions and mergers between smaller galaxies, so some of the larger galaxies should contain multiple supermassive black holes. Having two or more such gravitational powerhouses in a galaxy would have profound effects on its structure and dynamics. As a pair of supermassive black holes orbit one another, for example, the binary system’s gravity would disrupt the gas and stars at the centre of the host galaxy. This, in turn, could lead to a burst of star formation or even the ejection of one of the black holes from the galaxy.
    Heavyweight triplets

    To date, only a few galaxies with two supermassive black holes have been found, and just four triple black-hole systems are currently known. The closest known spacing between black holes in a binary system is 2.4 kiloparsecs – about 1/10th the diameter of the main disc of the Milky Way. The new system, detected by Roger Deane of the University of Cape Town, South Africa, and colleagues, consists of two supermassive black holes separated by a mere 140 parsecs, while the third of the trio is 7 kiloparsecs from the close-knit pair. The two black holes in the pair are orbiting one another at high speed – more than 100,000 m s–1.

    The team made its discovery while studying six galaxies that were thought to host binary supermassive black-hole systems based on near-infrared and optical observations. The researchers found that one of the black holes was actually two, and hence that particular system is a triple. Because the astronomers did not have to search through many candidates to find the system, they believe that tightly knit binaries and indeed triple systems of black holes could be more common than previously thought.

    Giant radio telescope

    The team employed a technique known as very long baseline interferometry (VLBI) to study the trio. VLBI creates a giant radio telescope spanning thousands of kilometres across the globe by combining the signals from large radio antennas that can be separated by up to 10,000 km. This allows astronomers to see detail 50 times finer than that possible with the Hubble Space Telescope. The current observations were done with the European VLBI Network (EVN) and the data were correlated at the Joint Institute for VLBI in Europe (JIVE) in the Netherlands.

    European VLBI
    European VLBI

    Deane told physicsworld.com that the discovery demonstrates the power of VLBI to differentiate between multiple objects in systems that are huge distances from Earth. Before the latest discovery, a pair of supermassive black holes with the closest orbit (about 7 parsecs apart) was spotted in a galaxy some 750 million light-years from Earth. “Our system is 4.2 billion light-years away, which is much more distant than the closest known pair, demonstrating that the VLBI technique can be used to probe close black-hole pairs across a fair fraction of cosmic time,” he says.
    Spinning jets

    The presence of the bound pair was also revealed via a much more prominent feature – the large-scale radio jets emanating from the black holes. Such astrophysical jets are a common feature of supermassive black holes – accreted matter collecting around the event horizon of the black hole is ejected along its axis of rotation as it tries to fall into the hole. The triple system has three such jets, and Deane and colleagues found that the presence of the tight pair is imprinted onto the properties of the jets. Indeed, the orbital motion of the black holes in the pair twists the jets into a helical or corkscrew-like “S” shape. This provides astronomers with a “smoking gun” for a binary black-hole system that could be used in future searches.

    Deane also points out that this extreme triple system could be creating gravitational waves – ripples in the very fabric of space–time. Future telescopes, such as the Square Kilometre Array, should be able to detect these ripples for black holes that are even closer together. “It fills me with great excitement as this is just scratching the surface of a long list of discoveries that will be made possible with the Square Kilometre Array,” Deane says.

    The research is published in Nature.

    See the full article here.

    See also this article from iafrica, which, to me, confuses this issue. This article credits SKA, makes no mention of the European VLBI.

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
    IOP Institute of Physics


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