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  • richardmitnick 2:58 pm on October 5, 2017 Permalink | Reply
    Tags: , An Update on the Event Horizon Telescope, EHT - Event Horizon Telescope   

    From AAAS: “An Update on the Event Horizon Telescope” 

    AAAS

    AAAS

    October 5, 2017
    Sheperd Doeleman
    Harvard-Smithsonian CfA

    The Event Horizon Telescope (EHT) is an international collaboration aiming to capture the first image of a black hole by creating a virtual Earth-sized radio telescope. We recently launched a new website that contains background material, the latest news from our team, and educational resources.

    At present, the EHT team is processing observations from a week-long observing campaign in April 2017 that linked together eight telescopes in Hawaii, Arizona, Spain, Mexico, Chile, and the South Pole via the technique of very-long-baseline interferometry (VLBI). This global array targeted two supermassive black holes, one at the center of the Milky Way and the other in M87, a giant elliptical galaxy about 50 million light-years away in Virgo. For each of these, the EHT has the magnifying power and sensitivity to form images of the millimeter-wavelength light emitted by hot gas near the event horizon. Einstein’s general theory of relativity predicts that the EHT should see a silhouette formed by the intense gravity of the black hole warping the light from infalling hot gas. The dynamics of matter may also be detected as hot blobs of material orbit the black hole and shear into turbulent flows.

    1
    The South Pole Telescope illuminated by aurora australis and the Milky Way. Jupiter is brightly visible at lower left. The outside temperature is -60°C. [Daniel Michalik / South Pole Telescope]

    Most data recorded at all the sites have been shipped to two central processing facilities, one at MIT Haystack Observatory and another at the Max Planck Institute for Radio Astronomy, where the signals are combined in VLBI correlators. We are still waiting for the hard disks containing data from the South Pole, where they have been stored during the long polar winter when there are no flights to/from the Amundsen-Scott station. Some data, however, were sent back from the South Pole via satellite, so we have confirmed that all the sites in the EHT worked well, and analysis of the data is getting started.

    On the technical side, the EHT has broken new ground by making VLBI observations at the shortest wavelengths to date. And the array has been extended to bandwidths, or data capture rates, that are more than 10 times what was possible just a few years ago. Parallel advances in theory are providing direction for analysis techniques through detailed modeling and simulations of black hole accretion. For more information on current EHT work in both of these areas, as well as updates, we encourage you to visit the project website.

    Event Horizon Telescope Array

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

    ESO/APEX
    Atacama Pathfinder EXperiment

    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

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    See the full article here .

    The American Association for the Advancement of Science is an international non-profit organization dedicated to advancing science for the benefit of all people.

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  • richardmitnick 11:14 am on August 23, 2017 Permalink | Reply
    Tags: , , , , , EHT - Event Horizon Telescope, ,   

    From astrobites: “Students on the Hunt for Black Holes” 

    Astrobites bloc

    Astrobites

    Aug 22, 2017
    Ana Torres Campos
    Crossposts, Personal Experiences

    Inside the Large Millimeter Telescope Alfonso Serrano (LMT), at an altitude of 4500 meters above sea level, Queen’s Don’t Stop Me Now can be heard in the background while a group of people cheer and shake hands after successfully concluding an observation run for one of the most important astronomical projects in the last years: The Event Horizon Telescope (EHT).

    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

    This project aims to obtain, for the first time ever, the image of the projected shadow of the supermassive black hole at the center of our galaxy, as well as the one in Messier 87.

    SGR A* NASA’s Chandra X-Ray Observatory

    1
    Messier 87, sources of images posted in graphic.

    In this post I share my personal experience as a guest of the team responsible for the observations of the EHT that were taken with the LMT in April of this year.

    2
    Figure 1 The LMT control room onApril 11th, 2017 at the end of the EHT 2017 observing run. Left to right: Antonio Hernández, Sergio Dzib, Emir Moreno, Edgar Castillo, Gopal Narayanan, Katie Bouman and Sandra Bustamante. Credit: Ana Torres Campos.

    Why should you care about the Event Horizon Telescope?
    The New York Times and National Geographic, among others, have written articles about the EHT, so don’t be surprised if one of these days your relatives or friends ask you about the project. Its greatness lies in not only being the first opportunity to observe an unknown event, or proving Einstein’s general relativity at never- imagined scales, but in demonstrating that, in times of discord, a close collaboration among a large number of nations is essential for scientific advancement.

    The Event Horizon Telescope is a network of eight [with ALMA it is now nine] millimeter-wave radio observatories located on four continents and representing over 20 nations. These observatories work together as a single Earth-sized telescope using the Very Large Baseline Interferometry (VLBI) technique. One of these facilities is the LMT, a 32-meter single-dish millimeter-wavelength telescope led by the Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE, Mexico) and the University of Massachusetts Amherst (UMass, U.S.A.). Each night, the LMT synchronized (with a precision higher than 10-12 seconds) with the other telescopes using a hydrogen maser and recorded approximately 30 Terabytes of data which were stored in Mark 6 data systems developed by the Massachusetts Institute of Technology (MIT) Haystack Observatory.

    4
    Massachusetts Institute of Technology (MIT) Haystack Observatory.

    The observing run at the LMT

    The observing run was set to begin on April 4 with a 10-day window to accomplish five observing sessions. Some of the EHT team members got to the telescope site days before to check on the instruments (a 1.3-mm receiver, the backend system and the hydrogen maser) and get acclimated to the high altitude and time change (since the observations were to be performed at night time). My adventure began on May 31 when I met the EHT-LMT observing team, led by Dr. Gopal Narayanan (UMass researcher and the developer of the 1.3-mm receiver). I was really surprised that the crew consisted mainly of PhD students; Sandy, Aleks, and Michael are in their first years and Katie is a Computer Science PhD candidate. The first thing that came to mind was: how come young students are in charge of such an important task?! I got the answer to my question after spending a few days with them. Not only they are outstandingly capable but also they know how to work as a team.

    Since the observing sessions were to be ~17 hours long, the team split into two groups: Group 1 (David, Lindy, Aleks and Michael) began the observing session at 5:30 pm and ended at 2 am, and Group 2 (Edgar,Gopal, Katie and Sandy) started to observe at 1 am and finished at 10 am. This schedule allowed all of the team members to sleep for at least 6 hours, join with the Command Center (and the other observatories) at the 2:30 pm video conference for the go/no-go decision (given the weather conditions at the different sites), and having a one hour overlap in between observing groups’ shifts.

    5
    (Top) Left to Right: the 1.3-mm receiver, Sandra Bustamante, Aleksandar Popstefanija and Gopal Narayanan. (Bottom-Left) Sergio Dzib, Antonio Hernández and Gopal Narayanan, at the back stands the backend system with the Mark 6. (Bottom-Right) Gopal Narayanan checking the hydrogen maser.

    Both groups had an expert telescope operator (Edgar or David), but in one group was the backend system expert (Lindy) while in the other was the receiver expert (Gopal). This made the students a little nervous at first because if any problem arose then they would have had to face it alone before calling the expert (whom would very likely be sleeping at Base Camp).

    The first target of the observing run was a binary black hole called OJ 287.

    6
    http://www.as.up.krakow.pl/sz/oj287.html

    This object is scientifically interesting all on its own, but because it is a deeply studied object, it will instead be used to calibrate the observations of the project’s primary observing targets. These are Sagittarius A* (Sgt A*), the supermassive black hole at the center of our galaxy, and the supermassive black hole in M87, the most important object of the first night since Sgt A* observations were planned for the following days.

    This object is scientifically interesting all on its own, but because it is a deeply studied object, it will instead be used to calibrate the observations of the project’s primary observing targets. These are Sagittarius A* (Sgr A*), the supermassive black hole at the center of our galaxy, and the supermassive black hole in Messier 87, the most important object of the first night since Sgr A* observations were planned for the following days.

    7
    (Left) Members of the EHT project infront of the LMT. From left to right: Aleksandar Popstefanija, Michael Janssen, Sandra Bustamante, Lindy Blackburn, Katie Bouman, Gopal Narayanan and Edgar Castillo. (Middle) Lindy explains the data recording instructions to the students. (Right) Telescope operators David Sánchez and Edgar Castillo. Credit: Ana Torres Campos.

    Along with the observations came the uncomfortable situations that nobody talks about but that every observational astronomer has suffered from: power failure, difficulty to perfectly focus the telescope, and coffee shortage, the last one being the most stressful of them all. The good thing was that the exceptional skills of the telescope staff (including the operators) managed to quickly fix these inconveniences and halfway through the observing run reinforcement arrived: Antonio (a PhD student at IRyA/Université Toulouse III – Paul Sabatier) and Sergio (a postdoc at MPIFRA). Nevertheless, tiredness increased every day, but the 24-hour interactions among the team members helped them feel relaxed, increasing the moments of laughter and jokes.

    In my personal opinion, one of the keys to the EHT success is the excellent communication between the project team members, based not only on frequent videoconferences, emails and chats on Slack, but also a very well organized web or “wiki” where you can find the manuals of the instruments, tutorials on the observing run procedures, and even contact telephone numbers.

    What I learned from the EHT-LMT team
    1. An observing run will only be successful if the team works efficiently.
    2. It is necessary to be capable of occupying different roles on a team.
    3. Being assertive when listening and giving instructions will save you time.
    4. Relaxing and fun moments will improve the job performance of the team.
    Finally, I would like to thank Gopal, Katie, Michael, Sandy, Lindy, Aleks, David, Edgar, Antonio, Michael and Sergio for sharing with me such an incredible experience and to the LMT site and Base Camp crew for the outstanding job they do.

    See the full article here .

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    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 1:56 pm on August 15, 2017 Permalink | Reply
    Tags: Black hole imaging, EHT - Event Horizon Telescope, , Global mm-VLBI Array (GMVA),   

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

    ESO 50 Large

    European Southern Observatory

    1.8.2017 Challenges in Obtaining an Image of a Supermassive Black Hole

    “Seeing a black hole” has been a long-cherished desire for many astronomers, but now, thanks to the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA) projects, it may no longer be just a dream.

    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

    Global mm-VLBI Array

    To make it possible to image the shadow of the event horizon of Sagittarius A*, many researchers and cutting-edge technologies have been mobilised — because obtaining an image of a black hole is not as easy as snapping a photo with an ordinary camera.

    Sagittarius A* has a mass of approximately four million times that of the Sun, but it only looks like a tiny dot from Earth, 26 000 light-years away. To capture its image, incredibly high resolution is needed. As explained in the fifth post of this blog series, the key is to use Very-Long-Baseline Interferometry (VLBI), a technique that combines the observing power of and the data from telescopes around the world to create a virtual giant radio telescope.

    The resolution of a telescope can be calculated from the radio wavelength the telescope is observing at and the size of the telescope — or in VLBI, the distance between the antennas. However, while actually observing, several kinds of noise and errors interfere with the telescope’s performance and affect the resolution.

    In VLBI, each antenna is equipped with an extremely precise atomic clock to record the time at which radio signals from the target object were received. The gathered data are synthesised using the times as a reference, so that the arrival time of the radio waves to each antenna can be accurately adjusted.

    But this process isn’t always straightforward because the Earth’s atmosphere blocks a certain range of wavelengths. Several kinds of molecules such as water vapour absorb a fraction of radio waves that pass through the atmosphere, with shorter wavelengths more susceptible to absorption. To minimise the effect of atmospheric absorption, radio telescopes are built at high and dry sites, but even then they are still not completely immune from the effect.

    The tricky part of this absorption effect is that the direction of a radio wave is slightly changed when it passes through the atmosphere containing water vapour. This means that the radio waves arrive at different times at each antenna, making it difficult to synthesise the data later using the time signal as a reference. And even worse: since VLBI utilises antennas located thousands of kilometres apart, it has to take into account the differences in the amount of water vapour in the sky above each site, as well as the large fluctuations of water vapour content during the observation period. In optical observations, these fluctuations make the light of a star flicker and lower the resolution. Radio observations have similar problems.

    “We have only a few ways to reduce this effect in VLBI observations,” explains Satoki Matsushita at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) of Taiwan. “If there is a compact object emitting intense radiation near the target object, we can remove most of the effect of refraction of radio waves by water vapour by using such an intense radiation source as a reference. However, no such intense reference source has been found near Sagittarius A* so far. And even if there is a reference source, there are still necessary conditions that must be satisfied: the telescopes need to have the ability to observe the target object and reference object at the same time; or the telescopes need to have the high-speed drive mechanism to quickly switch the observation between the target object and the reference object. Unfortunately, not all telescopes participating in the EHT/GMVA observations have this capability. One of the methods to remove the effect is to equip each antenna with an instrument to measure the amount of water vapour, but ALMA is the only telescope that has adopted this method at this point.”

    Another major challenge in imaging a black hole is obtaining a high-quality image. By combining the data collected by antennas thousands of kilometres apart, VLBI achieves a resolution equivalent to a radio telescope several thousands of kilometres in diameter. However, VLBI also has a lot of large blank areas that are not covered by any of the antennas. These missing parts make it difficult for VLBI to reproduce a high-fidelity image of a target object from the synthesised data. This is a common problem for all radio interferometers, including ALMA, but it can be more serious in VLBI where the antennas are located very far apart.

    It might be natural to think that a higher resolution means a higher image quality, as is the case with an ordinary digital camera, but in radio observations the resolution and image quality are quite different things. The resolution of a telescope determines how close two objects can be to each other and yet still be resolved as separate objects, while the image quality defines the fidelity in reproducing the image of the structure of the observed object. For example, imagine a leaf, which has a variety of veins. The resolution is the ability to see thinner vein patterns, while the image quality is the ability to capture the overall spread of the leaf. In normal human experience, it would seem bizarre if you could see the very thin veins of a leaf but couldn’t grasp a complete view of the leaf — but such things happen in VLBI, since some portions of data are inevitably missing.

    2
    This infographic illustrates how ALMA contributes to the EHT observations. With its shorter baseline, ALMA is sensitive to larger scales than the EHT and so ALMA can fill in the lower-resolution, larger-scale structures that the EHT misses. Credit: NRAO.

    Researchers have been studying data processing methods to improve image quality for almost as long as the history of the radio interferometer itself, so there are some established methods that are already widely used, while others are still in an experimental phase. In the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA) projects, which are both aiming to capture the shadow of a black hole’s event horizon for the first time, researchers began to develop effective image analysis methods using simulation data well before the start of the observations.

    4
    A simulated image of the supermassive black hole Sagittarius A*, which is likely to be obtained in the most recent EHT observations. The dark gap at the centre is the shadow of the black hole. Credit: Kazunori Akiyama (MIT Haystack Observatory).

    The observations with the EHT and the GMVA were completed in April 2017. The data collected by the antennas around the world has been sent to the US and Germany, where data processing will be conducted with dedicated data-processing computers called correlators. The data from the South Pole Telescope, one of the participating telescopes in the EHT, will arrive at the end of 2017, and then data calibration and data synthesis will begin in order to produce an image, if possible. This process might take several months to achieve the goal of obtaining the first image of a black hole, which is eagerly awaited by black hole researchers and the general astronomical community worldwide.

    This lengthy time span between observations and results is normal in astronomy, as the reduction and analysis of the data is a careful, time-consuming process. Right now, all we can do is wait patiently for success to come — for a long-held dream of astronomers to be transformed into a reality.

    Until then, this is the last post in our blog series about the EHT and GMVA projects. When the results become available in early 2018, we’ll be back with what will hopefully be exciting new information about our turbulent and fascinating galactic centre.

    See the full article here .

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

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

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

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    ALMA on the Chajnantor plateau at 5,000 metres.

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

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    Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

     
  • richardmitnick 3:00 pm on July 21, 2017 Permalink | Reply
    Tags: Blog Update June 30 2017, EHT - Event Horizon Telescope   

    From EHT: EHT Update June 30, 2017 

    Event Horizon Telescope/blog

    June 30, 2017
    Shep Doeleman
    EHT Director

    It is an exciting time in the Event Horizon Telescope (EHT) project. After many years of preparation, our team mounted a week-long observing campaign in April of this year that linked together 8 telescopes in Hawaii, the South Pole, Arizona, Spain, Mexico and Chile. This global array targeted two supermassive black holes, one at the center of the Milky Way galaxy, and the other at the heart of Messier 87, a giant elliptical galaxy about 50 million light years away. For each of these black holes, the EHT has the magnifying power and sensitivity to form images of the mm wavelength light emitted by the hot gas near the event horizon. Data recorded at all the sites has been shipped back to two central processing facilities at MIT and the Max Planck Institute for Radio Astronomy where signals from all participating telescopes are being combined. The power of this technique is that the EHT delivers an angular resolution comparable to a telescope as large as the distance between the EHT sites.

    There are no guarantees of what the EHT will see. Eintstein’s General Theory of Relativity predicts that the EHT should see a silhouette formed by the intense gravity of the black hole warping the light from infalling hot gas. The dynamics of matter may also be detected as hot blobs of material orbit the black hole and shear into turbulent flows. But the proof will be in the team’s analysis of the data, and that is still just getting started. Because the collected data are combined long after the observations are made, the technique used by the EHT (Very Long Baseline Interferometry, or VLBI) is well known for its quality of delayed gratification.

    On the technical side, the EHT has broken new ground by making VLBI observations at the shortest wavelengths to date. And the array has been extended to bandwidths, or data capture rates, that are more than 10 times what was possible just a few years ago. Extension to include the South Pole Telescope means that the EHT is truly an Earth-sized instrument.

    Parallel advances in theory are providing direction for analysis techniques through detailed modeling and simulations of black hole accretion. Information on current EHT work in both of these areas can be found on this website.

    During the observations, EHT members at all sites ticked through detailed checklists each day to ensure things were ready: Hydrogen maser atomic clocks stable, high speed data recorders on line, signal processing instruments tuned up, synchronization to GPS complete. The EHT can tell if the position of an entire telescope is off by a millimeter, and if the timing of electronic systems are shifted by a trillionth of a second, so all of this matters. And after waiting over a decade to make these observations, you go through the checklist twice. The one thing beyond anyone’s control is the weather. At a central command room at the Smithsonian Astrophysical Observatory in Cambridge, MA, weather data was collected each day from around the array and an often agonizing decision made on whether to fire off an evening of observations based on predictions and the experience of staff at all the sites. Will the heavy clouds surrounding a mountain top telescope dissipate, or will they settle in for the night? Is the weather risky at many sites, or maybe just one? And even if the sky above clears up, might ground conditions early in the evening leave a dish iced up and unusable? In the end, the weather was overwhelmingly excellent and we triggered 5 days of observing out of a possible 10-day window.

    So far, the data processing centers have confirmed that all the sites in the EHT worked well, except of course for the South Pole, where the hard disks used to record the data are being stored until the station re-opens in September and flights are allowed in and out. This is very welcome news, but at this stage no results on the two main targets, SgrA* and M87, are available. Over the coming months, the EHT team will continue data processing and refining analysis tools with focus then shifting to investigations of predicted strong gravity black hole signatures.

    The EHT website will be updated with developments, and also has background material, news, science results and educational resources.

    See the full article here.

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    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

     
  • richardmitnick 8:30 pm on July 7, 2017 Permalink | Reply
    Tags: , , , , EHT - Event Horizon Telescope, , GMVA-Global mm-VLBI Array, SagA*   

    From ESO: “5. How to build an Earth-sized radio telescope” 

    ESO 50 Large

    European Southern Observatory

    A black hole is an extraordinary object with extremely strong gravity, but when observed from Earth it would look like a tiny dot. To capture an image of a black hole, a telescope with extraordinarily high resolution is required. But how can such a revolutionary telescope be created?

    As we discovered in the previous post, the larger the diameter of the telescope, the better the resolution. This is true both for optical and radio telescopes, which means that a tremendously large telescope is needed to observe a small object that can barely be seen from Earth — like a black hole.

    The Atacama Large Millimeter/submillimeter Array (ALMA), which is operated in Chile by a global partnership, combines multiple antennas spread over distances from 150 metres to 16 kilometres. This allows it to simulate a single giant telescope much larger than any individual dish that could be built, achieving a resolution equivalent to up to a 16-km diameter telescope. ALMA’s resolution reaches 1/100 of 1/3600 of a degree angle — 5000 times better than the human eye!

    And yet even with such an exceptionally good “eyesight”, ALMA would need to improve its resolution 100 fold in order to capture a black hole at the centre of the Milky Way galaxy.

    To simulate a telescope with 100 times the resolution of ALMA, telescopes must be spread over a much larger area — far beyond the Chilean Andes, beyond even South America and extending to North America and Europe. Using the Very-Long-Baseline Interferometry (VLBI) technique, telescopes of several thousand kilometres in diameter can be simulated. The Event Horizon Telescope (EHT) and Global mm-VLBI Array (GMVA) both form Earth-sized telescopes that combine the observing power and the data collected by a range of telescopes across the world, including ALMA. The participating telescopes are listed below.

    3
    Telescopes contributing to the EHT and GMVA observations of Sagittarius A*. The connected telescopes simulate a telescope equivalent to the dimensions of the whole western hemisphere of the Earth. Credit: ESO/O. Furtak

    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

    Global mm-VLBI Array


    GMVA ALMA, VLBA (eight locations in U.S.), GBT 100m (West Virginia, U.S.), IRAM 30m (Spain), OAN 40m (Spain), Max Planck Institute for Radio Astronomy 100m (Germany)

    But how does VLBI work? With ALMA, it’s relatively straightforward: each antenna receives signals from a target object and then sends them via optical fibres to a central location on site, where they are processed and combined by a dedicated supercomputer. However, when telescopes are located thousands of kilometres apart — halfway across the world from each other — it’s impossible to connect them via optical fibres to a central location and transmit such enormous volumes of data. VLBI therefore uses a different technique: the data are first recorded at each individual telescope and stored on recording devices on site. These devices are then shipped or flown back to one place and played back all together in a computer for data synthesis.

    4
    A schematic diagram of the VLBI mechanism. Each antenna, spread out over vast distances, has an extremely precise atomic clock. Analogue signals collected by the antenna are converted to digital signals and stored on hard drives together with the time signals provided by the atomic clock. The hard drives are then shipped to a central location to be synchronised. An astronomical observation image is obtained by processing the data gathered from multiple locations. Credit: ALMA (ESO/NAOJ/NRAO), J.Pinto & N.Lira.

    A key component of the VLBI technique are the clocks — and these are no ordinary clocks. To synthesise the data gathered simultaneously by contributing telescopes around the world, each telescope requires a clock set to the accurate time with astonishing precision. These clocks measure small differences in the arrival time of the radio waves coming from the target object to each antenna of the array. Every telescope taking part in VLBI is equipped with an extremely precise, specially-developed atomic clock — so accurate that over a period of 100 million years, each clock would be off by less than 1 second!

    6
    Hydrogen maser atomic clock installed at the ALMA Array Operations Site (AOS), along with the technicians who installed it. Credit: ALMA (ESO/NAOJ/NRAO), C. Padilla.

    Another key element in VLBI is the device used to record the data. The first VLBI experiments were carried out in the 1960s and used magnetic tapes to record observations, but since entering the 21st century, more and more VLBI observations have been recorded on hard drives because of their larger storage capacity and lower prices. The hard drives used in the EHT and GMVA observations are based on magnetic-disk technology and incorporate primarily low-cost PC components.

    One important aspect of such a recording device is the speed with which it records data. The faster the data recording speed, the more extensive the range of frequency signals that can be recorded, which improves the overall sensitivity of the observations. Some of the hard drives used in the EHT observations can record data at up to a total rate of 16 gigabits per second! Of course, the storage capacity of the hard drives is also important. The capacity of the hard drives ALMA used for the EHT/GMVA observations exceeds 1 petabyte (1 million gigabytes) in total.

    The dedicated supercomputer to process the recorded data is called a “correlator”. The EHT correlator was developed by the Massachusetts Institute of Technology in the US, while the GMVA correlator was developed by the Max Planck Institute for Radio Astronomy located in Bonn, Germany. The enormous amount of data obtained is firstly recorded at the telescopes around the world, and then sent to these two locations where it is read from each disk to the correlator at up to 4096 MB per second. The data is then processed by the correlator to form an astronomical image.

    The VLBI technique can use these cutting-edge technologies to form an Earth-sized telescope capable of achieving extremely high resolution. This raises the question: Can any type of celestial object be revealed in detail by VLBI observations? Unfortunately, the answer is no. Some objects will be a good target of the VLBI observations, while others will not.

    If you’ve ever used a microscope to observe a small object, you might be familiar with the experience of raising the magnification — only to see a dimmer view. The same thing happens with telescopes. Increasing the resolution means seeing an object in a view that is divided into many smaller parts. This inevitably results in decreasing the amount of light received from each part of the target object. Eventually, as the resolution increases, fainter objects becomes invisible.

    For this reason, the extraordinarily high resolution of VLBI is mainly suitable for observing bright objects. VLBI is often used to observe objects that emit intense radio waves, such as astrophysical masers (similar to the kind of lasers that we are familiar with, but at microwave wavelengths) occurring around young and old stars, and high-speed jets of gas ejected from supermassive black holes. Since a high-temperature gas disk around a supermassive black hole is thought to emit strong radio waves, the EHT and GMVA observations aim to use the VLBI technique to capture the elusive black hole at the centre of the galaxy.

    This is the fifth post of a blog series following the Event Horizon Telescope and the Global mm-VLBI Array projects. The next topic will focus on the supermassive black hole Sagittarius A* located at the centre of the Milky Way, a high-priority target object of the EHT/GMVA observations.

    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

     
  • richardmitnick 9:56 am on June 8, 2017 Permalink | Reply
    Tags: , , , , , EHT - Event Horizon Telescope, , , Nautlius, , , Sean Carroll at Caltech, , Will Quantum Mechanics Swallow Relativity   

    From Nautilus: “Will Quantum Mechanics Swallow Relativity?” 

    Nautilus

    Nautilus

    June 8, 2017
    By Corey S. Powell
    Illustration by Nicholas Garber

    The contest between gravity and quantum physics takes a new turn.

    It is the biggest of problems, it is the smallest of problems.

    At present physicists have two separate rulebooks explaining how nature works. There is general relativity, which beautifully accounts for gravity and all of the things it dominates: orbiting planets, colliding galaxies, the dynamics of the expanding universe as a whole. That’s big. Then there is quantum mechanics, which handles the other three forces—electromagnetism and the two nuclear forces. Quantum theory is extremely adept at describing what happens when a uranium atom decays, or when individual particles of light hit a solar cell. That’s small.

    Now for the problem: Relativity and quantum mechanics are fundamentally different theories that have different formulations. It is not just a matter of scientific terminology; it is a clash of genuinely incompatible descriptions of reality.

    The conflict between the two halves of physics has been brewing for more than a century—sparked by a pair of 1905 papers by Einstein, one outlining relativity and the other introducing the quantum—but recently it has entered an intriguing, unpredictable new phase. Two notable physicists have staked out extreme positions in their camps, conducting experiments that could finally settle which approach is paramount.

    Basically you can think of the division between the relativity and quantum systems as “smooth” versus “chunky.” In general relativity, events are continuous and deterministic, meaning that every cause matches up to a specific, local effect. In quantum mechanics, events produced by the interaction of subatomic particles happen in jumps (yes, quantum leaps), with probabilistic rather than definite outcomes. Quantum rules allow connections forbidden by classical physics. This was demonstrated in a much-discussed recent experiment, in which Dutch researchers defied the local effect. They showed two particles—in this case, electrons—could influence each other instantly, even though they were a mile apart. When you try to interpret smooth relativistic laws in a chunky quantum style, or vice versa, things go dreadfully wrong.

    Relativity gives nonsensical answers when you try to scale it down to quantum size, eventually descending to infinite values in its description of gravity. Likewise, quantum mechanics runs into serious trouble when you blow it up to cosmic dimensions. Quantum fields carry a certain amount of energy, even in seemingly empty space, and the amount of energy gets bigger as the fields get bigger. According to Einstein, energy and mass are equivalent (that’s the message of e=mc2), so piling up energy is exactly like piling up mass. Go big enough, and the amount of energy in the quantum fields becomes so great that it creates a black hole that causes the universe to fold in on itself. Oops.

    Craig Hogan, a theoretical astrophysicist at the University of Chicago and the director of the Center for Particle Astrophysics at Fermilab, is reinterpreting the quantum side with a novel theory in which the quantum units of space itself might be large enough to be studied directly. Meanwhile, Lee Smolin, a founding member of the Perimeter Institute for Theoretical Physics in Waterloo, Canada, is seeking to push physics forward by returning back to Einstein’s philosophical roots and extending them in an exciting direction.

    To understand what is at stake, look back at the precedents. When Einstein unveiled general relativity, he not only superseded Isaac Newton’s theory of gravity; he also unleashed a new way of looking at physics that led to the modern conception of the Big Bang and black holes, not to mention atomic bombs and the time adjustments essential to your phone’s GPS. Likewise, quantum mechanics did much more than reformulate James Clerk Maxwell’s textbook equations of electricity, magnetism, and light. It provided the conceptual tools for the Large Hadron Collider, solar cells, all of modern microelectronics.

    What emerges from the dustup could be nothing less than a third revolution in modern physics, with staggering implications. It could tell us where the laws of nature came from, and whether the cosmos is built on uncertainty or whether it is fundamentally deterministic, with every event linked definitively to a cause.

    2
    THE MAN WITH THE HOLOMETER: Craig Hogan, a theoretical astrophysicist at Fermilab, has built a device to measure what he sees as the exceedingly fine graininess of space. “I’m hoping for an experimental result that forces people to focus the theoretical thinking in a different direction,” Hogan says.The Department of Astronomy and Astrophysics, the University of Chicago

    A Chunky Cosmos

    Hogan, champion of the quantum view, is what you might call a lamp-post physicist: Rather than groping about in the dark, he prefers to focus his efforts where the light is bright, because that’s where you are most likely to be able to see something interesting. That’s the guiding principle behind his current research. The clash between relativity and quantum mechanics happens when you try to analyze what gravity is doing over extremely short distances, he notes, so he has decided to get a really good look at what is happening right there. “I’m betting there’s an experiment we can do that might be able to see something about what’s going on, about that interface that we still don’t understand,” he says.

    A basic assumption in Einstein’s physics—an assumption going all the way back to Aristotle, really—is that space is continuous and infinitely divisible, so that any distance could be chopped up into even smaller distances. But Hogan questions whether that is really true. Just as a pixel is the smallest unit of an image on your screen and a photon is the smallest unit of light, he argues, so there might be an unbreakable smallest unit of distance: a quantum of space.

    In Hogan’s scenario, it would be meaningless to ask how gravity behaves at distances smaller than a single chunk of space. There would be no way for gravity to function at the smallest scales because no such scale would exist. Or put another way, general relativity would be forced to make peace with quantum physics, because the space in which physicists measure the effects of relativity would itself be divided into unbreakable quantum units. The theater of reality in which gravity acts would take place on a quantum stage.

    Hogan acknowledges that his concept sounds a bit odd, even to a lot of his colleagues on the quantum side of things. Since the late 1960s, a group of physicists and mathematicians have been developing a framework called string theory to help reconcile general relativity with quantum mechanics; over the years, it has evolved into the default mainstream theory, even as it has failed to deliver on much of its early promise. Like the chunky-space solution, string theory assumes a fundamental structure to space, but from there the two diverge. String theory posits that every object in the universe consists of vibrating strings of energy. Like chunky space, string theory averts gravitational catastrophe by introducing a finite, smallest scale to the universe, although the unit strings are drastically smaller even than the spatial structures Hogan is trying to find.

    Chunky space does not neatly align with the ideas in string theory—or in any other proposed physics model, for that matter. “It’s a new idea. It’s not in the textbooks; it’s not a prediction of any standard theory,” Hogan says, sounding not the least bit concerned. “But there isn’t any standard theory right?”

    If he is right about the chunkiness of space, that would knock out a lot of the current formulations of string theory and inspire a fresh approach to reformulating general relativity in quantum terms. It would suggest new ways to understand the inherent nature of space and time. And weirdest of all, perhaps, it would bolster an au courant notion that our seemingly three-dimensional reality is composed of more basic, two-dimensional units. Hogan takes the “pixel” metaphor seriously: Just as a TV picture can create the impression of depth from a bunch of flat pixels, he suggests, so space itself might emerge from a collection of elements that act as if they inhabit only two dimensions.

    Like many ideas from the far edge of today’s theoretical physics, Hogan’s speculations can sound suspiciously like late-night philosophizing in the freshman dorm. What makes them drastically different is that he plans to put them to a hard experimental test. As in, right now.

    Starting in 2007, Hogan began thinking about how to build a device that could measure the exceedingly fine graininess of space. As it turns out, his colleagues had plenty of ideas about how to do that, drawing on technology developed to search for gravitational waves. Within two years Hogan had put together a proposal and was working with collaborators at Fermilab, the University of Chicago, and other institutions to build a chunk-detecting machine, which he more elegantly calls a “holometer.” (The name is an esoteric pun, referencing both a 17th-century surveying instrument and the theory that 2-D space could appear three-dimensional, analogous to a hologram.)

    Beneath its layers of conceptual complexity, the holometer is technologically little more than a laser beam, a half-reflective mirror to split the laser into two perpendicular beams, and two other mirrors to bounce those beams back along a pair of 40-meter-long tunnels. The beams are calibrated to register the precise locations of the mirrors. If space is chunky, the locations of the mirrors would constantly wander about (strictly speaking, space itself is doing the wandering), creating a constant, random variation in their separation. When the two beams are recombined, they’d be slightly out of sync, and the amount of the discrepancy would reveal the scale of the chunks of space.

    For the scale of chunkiness that Hogan hopes to find, he needs to measure distances to an accuracy of 10-18 meters, about 100 million times smaller than a hydrogen atom, and collect data at a rate of about 100 million readings per second. Amazingly, such an experiment is not only possible, but practical. “We were able to do it pretty cheaply because of advances in photonics, a lot of off the shelf parts, fast electronics, and things like that,” Hogan says. “It’s a pretty speculative experiment, so you wouldn’t have done it unless it was cheap.” The holometer is currently humming away, collecting data at the target accuracy; he expects to have preliminary readings by the end of the year.

    Hogan has his share of fierce skeptics, including many within the theoretical physics community. The reason for the disagreement is easy to appreciate: A success for the holometer would mean failure for a lot of the work being done in string theory. Despite this superficial sparring, though, Hogan and most of his theorist colleagues share a deep core conviction: They broadly agree that general relativity will ultimately prove subordinate to quantum mechanics. The other three laws of physics follow quantum rules, so it makes sense that gravity must as well.

    For most of today’s theorists, though, belief in the primacy of quantum mechanics runs deeper still. At a philosophical—epistemological—level, they regard the large-scale reality of classical physics as a kind of illusion, an approximation that emerges from the more “true” aspects of the quantum world operating at an extremely small scale. Chunky space certainly aligns with that worldview.

    Hogan likens his project to the landmark Michelson-Morley experiment of the 19th century, which searched for the aether—the hypothetical substance of space that, according to the leading theory of the time, transmitted light waves through a vacuum. The experiment found nothing; that perplexing null result helped inspire Einstein’s special theory of relativity, which in turn spawned the general theory of relativity and eventually turned the entire world of physics upside down. Adding to the historical connection, the Michelson-Morley experiment also measured the structure of space using mirrors and a split beam of light, following a setup remarkably similar to Hogan’s.

    “We’re doing the holometer in that kind of spirit. If we don’t see something or we do see something, either way it’s interesting. The reason to do the experiment is just to see whether we can find something to guide the theory,” Hogan says. “You find out what your theorist colleagues are made of by how they react to this idea. There’s a world of very mathematical thinking out there. I’m hoping for an experimental result that forces people to focus the theoretical thinking in a different direction.”

    Whether or not he finds his quantum structure of space, Hogan is confident the holometer will help physics address its big-small problem. It will show the right way (or rule out the wrong way) to understand the underlying quantum structure of space and how that affects the relativistic laws of gravity flowing through it.

    _______________________________________________________________________

    The Black Hole Resolution

    Here on Earth, the clash between the top-down and bottom-up views of physics is playing out in academic journals and in a handful of complicated experimental apparatuses. Theorists on both sides concede that neither pure thought nor technologically feasible tests may be enough to break the deadlock, however. Fortunately, there are other places to look for a more definitive resolution. One of the most improbable of these is also one of the most promising—an idea embraced by physicists almost regardless of where they stand ideologically.

    “Black hole physics gives us a clean experimental target to look for,” says Craig Hogan, a theoretical astrophysicist at the University of Chicago and the director of the Center for Particle Astrophysics at Fermilab. “The issues around quantum black holes are important,” agrees Lee Smolin, a founding member of the Perimeter Institute for Theoretical Physics in Waterloo, Canada.

    Black holes? Really? Granted, these objects are more commonly associated with questions than with answers. They are not things you can create in the laboratory, or poke and prod with instruments, or even study up close with a space probe. Nevertheless, they are the only places in the universe where Hogan’s ideas unavoidably smash into Smolin’s and, more importantly, where the whole of quantum physics collides with general relativity in a way that is impossible to ignore.

    At the outer boundary of the black hole—the event horizon—gravity is so extreme that even light cannot escape, making it an extreme test of how general relativity behaves. At the event horizon, atomic-scale events become enormously stretched out and slowed down; the horizon also divides the physical world into two distinct zones, inside and outside. And there is a very interesting meeting place in terms of the size of a black hole. A stellar-mass black hole is about the size of Los Angeles; a black hole with the mass of the Earth would be roughly the size of a marble. Black holes literally bring the big-small problem in physics home to the human scale.

    The importance of black holes for resolving that problem is the reason why Stephen Hawking and his cohorts debate about them so often and so vigorously. It turns out that we don’t actually need to cozy up close to black holes in order to run experiments with them. Quantum theory implies that a single particle could potentially exist both inside and outside the event horizon, which makes no sense. There is also the question of what happens to information about things that fall into a black hole; the information seems to vanish, even though theory says that information cannot be destroyed. Addressing these contradictions is forcing theoretical physicists to grapple more vigorously than ever before with the interplay of quantum mechanics and general relativity.

    Best of all, the answers will not be confined to the world of theory. Astrophysicists have increasingly sophisticated ways to study the region just outside the event horizon by monitoring the hot, brilliant clouds of particles that swirl around some black holes. An even greater breakthrough is just around the corner: the Event Horizon Telescope. This project is in the process of linking together about a dozen radio dishes from around the world, creating an enormous networked telescope so powerful that it will be able to get a clear look at Sagittarius A*, the massive black hole that resides in the center of our galaxy. Soon, possibly by 2020, the Event Horizon Telescope should deliver its first good portraits. What they show will help constrain the theories of black holes, and so offer telling clues about how to solve the big-small problem.

    Human researchers using football stadium-size radio telescopes, linked together into a planet-size instrument, to study a star-size black hole, to reconcile the subatomic-and-cosmic-level enigma at the heart of physics … if it works, the scale of the achievement will be truly unprecedented.

    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

    _______________________________________________________________________

    3
    THE SYNTHESIZER: Black holes are the only place where the whole of quantum physics collides with general relativity in a way that is impossible to ignore. An artist’s impression shows the surroundings of the supermassive black hole at the heart of the active galaxy in the southern constellation of Centaurus. Observations at a European Southern Observatory in Chile have revealed not only the torus of hot dust around the black hole but also a wind of cool material in the polar regions. ESO/M. Kornmesser

    A Really, Really Big Show

    If you are looking for a totally different direction, Smolin of the Perimeter Institute is your man. Where Hogan goes gently against the grain, Smolin is a full-on dissenter: “There’s a thing that Richard Feynman told me when I was a graduate student. He said, approximately, ‘If all your colleagues have tried to demonstrate that something’s true and failed, it might be because that thing is not true.’ Well, string theory has been going for 40 or 50 years without definitive progress.”

    And that is just the start of a broader critique. Smolin thinks the small-scale approach to physics is inherently incomplete. Current versions of quantum field theory do a fine job explaining how individual particles or small systems of particles behave, but they fail to take into account what is needed to have a sensible theory of the cosmos as a whole. They don’t explain why reality is like this, and not like something else. In Smolin’s terms, quantum mechanics is merely “a theory of subsystems of the universe.”

    A more fruitful path forward, he suggests, is to consider the universe as a single enormous system, and to build a new kind of theory that can apply to the whole thing. And we already have a theory that provides a framework for that approach: general relativity. Unlike the quantum framework, general relativity allows no place for an outside observer or external clock, because there is no “outside.” Instead, all of reality is described in terms of relationships between objects and between different regions of space. Even something as basic as inertia (the resistance of your car to move until forced to by the engine, and its tendency to keep moving after you take your foot off the accelerator) can be thought of as connected to the gravitational field of every other particle in the universe.

    That last statement is strange enough that it’s worth pausing for a moment to consider it more closely. Consider a thought problem, closely related to the one that originally led Einstein to this idea in 1907. What if the universe were entirely empty except for two astronauts. One of them is spinning, the other is stationary. The spinning one feels dizzy, doing cartwheels in space. But which one of the two is spinning? From either astronaut’s perspective, the other is the one spinning. Without any external reference, Einstein argued, there is no way to say which one is correct, and no reason why one should feel an effect different from what the other experiences.

    The distinction between the two astronauts makes sense only when you reintroduce the rest of the universe. In the classic interpretation of general relativity, then, inertia exists only because you can measure it against the entire cosmic gravitational field. What holds true in that thought problem holds true for every object in the real world: The behavior of each part is inextricably related to that of every other part. If you’ve ever felt like you wanted to be a part of something big, well, this is the right kind of physics for you. It is also, Smolin thinks, a promising way to obtain bigger answers about how nature really works, across all scales.

    “General relativity is not a description of subsystems. It is a description of the whole universe as a closed system,” he says. When physicists are trying to resolve the clash between relativity and quantum mechanics, therefore, it seems like a smart strategy for them to follow Einstein’s lead and go as big as they possibly can.

    Smolin is keenly aware that he is pushing against the prevailing devotion to small-scale, quantum-style thinking. “I don’t mean to stir things up, it just kind of happens that way. My role is to think clearly about these difficult issues, put my conclusions out there, and let the dust settle,” he says genially. “I hope people will engage with the arguments, but I really hope that the arguments lead to testable predictions.”

    At first blush, Smolin’s ideas sound like a formidable starting point for concrete experimentation. Much as all of the parts of the universe are linked across space, they may also be linked across time, he suggests. His arguments led him to hypothesize that the laws of physics evolve over the history of the universe. Over the years, he has developed two detailed proposals for how this might happen. His theory of cosmological natural selection, which he hammered out in the 1990s, envisions black holes as cosmic eggs that hatch new universes. More recently, he has developed a provocative hypothesis about the emergence of the laws of quantum mechanics, called the principle of precedence—and this one seems much more readily put to the test.

    Smolin’s principle of precedence arises as an answer to the question of why physical phenomena are reproducible. If you perform an experiment that has been performed before, you expect the outcome will be the same as in the past. (Strike a match and it bursts into flame; strike another match the same way and … you get the idea.) Reproducibility is such a familiar part of life that we typically don’t even think about it. We simply attribute consistent outcomes to the action of a natural “law” that acts the same way at all times. Smolin hypothesizes that those laws actually may emerge over time, as quantum systems copy the behavior of similar systems in the past.

    One possible way to catch emergence in the act is by running an experiment that has never been done before, so there is no past version (that is, no precedent) for it to copy. Such an experiment might involve the creation of a highly complex quantum system, containing many components that exist in a novel entangled state. If the principle of precedence is correct, the initial response of the system will be essentially random. As the experiment is repeated, however, precedence builds up and the response should become predictable … in theory. “A system by which the universe is building up precedent would be hard to distinguish from the noises of experimental practice,” Smolin concedes, “but it’s not impossible.”

    Although precedence can play out at the atomic scale, its influence would be system-wide, cosmic. It ties back to Smolin’s idea that small-scale, reductionist thinking seems like the wrong way to solve the big puzzles. Getting the two classes of physics theories to work together, though important, is not enough, either. What he wants to know—what we all want to know—is why the universe is the way it is. Why does time move forward and not backward? How did we end up here, with these laws and this universe, not some others?

    The present lack of any meaningful answer to those questions reveals that “there’s something deeply wrong with our understanding of quantum field theory,” Smolin says. Like Hogan, he is less concerned about the outcome of any one experiment than he is with the larger program of seeking fundamental truths. For Smolin, that means being able to tell a complete, coherent story about the universe; it means being able to predict experiments, but also to explain the unique properties that made atoms, planets, rainbows, and people. Here again he draws inspiration from Einstein.

    “The lesson of general relativity, again and again, is the triumph of relationalism,” Smolin says. The most likely way to get the big answers is to engage with the universe as a whole.

    And the Winner Is …

    If you wanted to pick a referee in the big-small debate, you could hardly do better than Sean Carroll, an expert in cosmology, field theory, and gravitational physics at Caltech. He knows his way around relativity, he knows his way around quantum mechanics, and he has a healthy sense of the absurd: He calls his personal blog Preposterous Universe.

    Right off the bat, Carroll awards most of the points to the quantum side. “Most of us in this game believe that quantum mechanics is much more fundamental than general relativity is,” he says. That has been the prevailing view ever since the 1920s, when Einstein tried and repeatedly failed to find flaws in the counterintuitive predictions of quantum theory. The recent Dutch experiment demonstrating an instantaneous quantum connection between two widely separated particles—the kind of event that Einstein derided as “spooky action at a distance”—only underscores the strength of the evidence.

    Taking a larger view, the real issue is not general relativity versus quantum field theory, Carroll explains, but classical dynamics versus quantum dynamics. Relativity, despite its perceived strangeness, is classical in how it regards cause and effect; quantum mechanics most definitely is not. Einstein was optimistic that some deeper discoveries would uncover a classical, deterministic reality hiding beneath quantum mechanics, but no such order has yet been found. The demonstrated reality of spooky action at a distance argues that such order does not exist.

    “If anything, people under-appreciate the extent to which quantum mechanics just completely throws away our notions of space and locality [the notion that a physical event can affect only its immediate surroundings]. Those things simply are not there in quantum mechanics,” Carroll says. They may be large-scale impressions that emerge from very different small-scale phenomena, like Hogan’s argument about 3-D reality emerging from 2-D quantum units of space.

    Despite that seeming endorsement, Carroll regards Hogan’s holometer as a long shot, though he admits it is removed from his area of research. At the other end, he doesn’t think much of Smolin’s efforts to start with space as a fundamental thing; he regards the notion as absurd as trying to argue that air is more fundamental than atoms. As for what kind of quantum system might take physics to the next level, Carroll remains broadly optimistic about string theory, which he says “seems to be a very natural extension of quantum field theory.” In all these ways, he is true to the mainstream, quantum-based thinking in modern physics.

    Yet Carroll’s ruling, while almost entirely pro-quantum, is not purely an endorsement of small-scale thinking. There are still huge gaps in what quantum theory can explain. “Our inability to figure out the correct version of quantum mechanics is embarrassing,” he says. “And our current way of thinking about quantum mechanics is simply a complete failure when you try to think about cosmology or the whole universe. We don’t even know what time is.” Both Hogan and Smolin endorse this sentiment, although they disagree about what to do in response. Carroll favors a bottom-up explanation in which time emerges from small-scale quantum interactions, but declares himself “entirely agnostic” about Smolin’s competing suggestion that time is more universal and fundamental. In the case of time, then, the jury is still out.

    No matter how the theories shake out, the large scale is inescapably important, because it is the world we inhabit and observe. In essence, the universe as a whole is the answer, and the challenge to physicists is to find ways to make it pop out of their equations. Even if Hogan is right, his space-chunks have to average out to the smooth reality we experience every day. Even if Smolin is wrong, there is an entire cosmos out there with unique properties that need to be explained—something that, for now at least, quantum physics alone cannot do.

    By pushing at the bounds of understanding, Hogan and Smolin are helping the field of physics make that connection. They are nudging it not just toward reconciliation between quantum mechanics and general relativity, but between idea and perception. The next great theory of physics will undoubtedly lead to beautiful new mathematics and unimaginable new technologies. But the best thing it can do is create deeper meaning that connects back to us, the observers, who get to define ourselves as the fundamental scale of the universe.

    See the full article here .

    Please help promote STEM in your local schools.

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 2:31 pm on June 2, 2017 Permalink | Reply
    Tags: , EHT - Event Horizon Telescope, ,   

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

    ESO 50 Large

    European Southern Observatory

    6.2.17
    No writer credit

    [These blog posts are in reverse order because that is how I found them. I still have not found the link to the blog itself to do a proper job.]

    4. How do Radio Telescopes work?
    23.5.2017

    Can you imagine yourself hearing only the bass of a music recording? Or only seeing objects of a particular colour? Well, in a way, you experience this every day. The human eye can only detect a narrow part of the electromagnetic spectrum: a section we call visible light. But a broad range of electromagnetic waves exist with the same nature — for example radio waves, which have much longer wavelengths than the light we can detect with our eyes. Radio wavelengths range from 1 millimetre to over 10 metres, while visible light wavelengths are only a few hundred nanometres — one nanometre is 1/10 000th the thickness of a piece of paper!

    Radio waves are not visible to us directly, but in 1867 their existence was predicted by James Clerk Maxwell. By the end of the 19th century, scientists had developed instruments that could transmit and detect electromagnetic waves at the radio end of the spectrum. A few decades later, it was discovered that these instruments could not only be used for communication, but could also be directed towards space — hidden parts of the Universe were suddenly revealed!

    The first detection of radio waves from an astronomical object was in 1932, when Karl Jansky observed radiation coming from the Milky Way.

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

    Then came the phenomenal discovery of the cosmic microwave background [CMB] in 1964, worthy of a Nobel Prize in Physics.

    CMB per ESA/Planck

    ESA/Planck

    Soon afterwards, Jocelyn Bell Burnell observed the first pulsar with an array of radio aerials in 1967, which led to another Nobel Prize. And this was only the beginning — a dazzling array of discoveries have been made since.

    2
    This panoramic view of the Chajnantor plateau shows some of the 66 antennas of the Atacama Large Millimeter/submillimeter Array (ALMA). Credit: ESO/B. Tafreshi (twanight.org)

    But how do radio telescopes work?

    In order to detect signals from astronomical objects, every radio telescope requires an antenna and at least one receiver. They come in a variety of shapes and sizes, reflecting the need to be able to detect a great breadth of radio waves across many wavelengths.

    The antennas of most radio telescopes working at wavelengths shorter than 1 metre are paraboloidal dishes. The curved reflector concentrates incoming radio waves at a focal point. For shorter wavelengths, such as millimetre waves collected by ALMA and VLBI networks like the EHT and GMVA, the perfection of the dish’s surface is critical: any warp, bump, or dent in the parabola will scatter these tiny waves away from the focus, and valuable information is lost.

    In addition to the main dish, most radio telescopes have secondary reflectors that send the concentrated waves to receivers. These receivers select, detect and amplify the radio signals of the desired frequencies. The receiver delivers these signals in an analogue format, which is converted into a digital signal and fed into a computer. Astronomers can then stitch these signals together to create a map of the sky measured by radio brightness.

    Radio telescopes point at a radio source for hours in order to detect the faintest signals coming from the near and distant Universe. This technique is a similar to keeping the shutter of a camera open for a long exposure at night. After combining these signals with a computer, astronomers can analyse the radiation emitted by many astronomical phenomena — such as stars, galaxies, nebulae and supermassive black holes.

    3
    The view of the centre of our galaxy with a closer view of the object known as Sagittarius A*, the bright radio source that corresponds to the supermassive black hole. Credit: NRAO/AUI/NSF

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

    Here’s the problem in radio astronomy: because radio wavelengths are so long, it is difficult to achieve a high resolution of the objects being observed. Even the shortest radio wavelengths observed by the largest single telescopes only result in an angular resolution slightly better than that of the unaided eye. The resolution (or degree of detail in the image) of a single telescope can be calculated by dividing the length of the radio wave by the diameter of the antenna. When this ratio is small, the angular resolution is large and therefore finer details can be observed. The larger the diameter of the telescope, the better the resolution, therefore radio telescopes tend to be much larger than telescopes suited for other, shorter wavelengths like visible light.

    The longest wavelengths, on scales of metres, pose a particular challenge because it is hard to achieve good resolution from a single dish. The largest moveable dish is the Green Bank Telescope (100 metres across).



    GBO radio telescope, Green Bank, West Virginia, USA

    Dishes that don’t move can be much, much larger. The world’s biggest radio dish is the newly-constructed Five-hundred-meter Aperture Spherical Telescope (FAST) in China: a fixed dish supported by a natural basin in the landscape.

    FAST radio telescope, now operating, located in the Dawodang depression in Pingtang county Guizhou Province, South China

    FAST can observe radio waves up to 4.3 metres in wavelength. There are also other similar dishes, such as the historic 300-metre Arecibo Observatory, which was the largest telescope for five decades until FAST was completed in 2016.

    NAIC/Arecibo Observatory, Puerto Rico, USA

    But building antennas any larger than this is not feasible, so here we reach a limit when it comes to observing at longer and longer wavelengths. But what can be improved is the angular resolution, opening the door of investigation into the finest details of the low-energy Universe.

    A Nobel Prize winning technique called interferometry opened this door: if the signals from many antennas spread over a large area are combined, then the antennas can operate together like a gigantic telescope — an array. Modern arrays usually bring the signals together at a central location in digital form using optical fibres, and then process them in a special-purpose supercomputer called a correlator.

    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

    One such array is the Atacama Large Millimeter/submillimeter Array on the Chajnantor plateau in the Atacama Desert. ALMA comprises 66 high-precision antennas up to 16 kilometres apart, working together as an interferometer. The resolution of an interferometer depends not on the diameter of individual antennas, but on the maximum separation between them. Moving the antennas further apart increases the resolution.

    The signals from the antennas are brought together and processed by the ALMA correlator. The antennas work together in unison, giving ALMA a maximum resolution which is even better than that achieved at visible wavelengths by the NASA/ESA Hubble Space Telescope. This is because the maximum distance between the antennas can be very large, increasing the resolving power of the interferometer and allowing it to detect smaller details.

    The ability to link antennas over baselines of many kilometres is crucial to obtain extremely good resolution and a high degree of detail in the images. This gives astronomers the possibility to go even further than arrays like ALMA; by combining the signals from radio telescopes all across the world, the distances between the antennas can be Earth-sized — and even larger, in the case of space-based antennas like Spektr-R.

    The telescopes do not have to be physically connected; rather, the signals recorded at each telescope are later “played back” in the correlator. This technique, called very-long-baseline interferometry (VLBI), provides exquisite angular resolution and paves the way for phenomenal new discoveries — including the detailed observation of the supermassive black hole at the centre of our galaxy.

    This is the fourth post of a blog series following the Event Horizon Telescope and the Global mm-VLBI Array projects. Next time, we’ll talk about how to build an Earth-sized radio telescope.

    Global mm-VLBI Array

    3. What’s so interesting about the event horizon?
    2.5.2017

    We know that black holes are fascinating objects, capable of bending not only our minds but also reality itself. They squeeze matter into an extraordinarily miniscule space, resulting in an object with an immense gravitational pull. Around this object is a boundary beyond which nothing can escape, not even light: the event horizon. Besides attracting enormous quantities of matter, the event horizon is attracting a lot of attention from astronomers around the world. But why?

    As we discovered in the previous post, black holes are impossible to observe directly. Photons aren’t emitted, and therefore nothing reaches the astronomer’s telescope (except, of course, small amounts of Hawking radiation). But scientists can learn a lot from the bright material surrounding black holes.

    When matter comes under the gravitational spell of a black hole, material will either be sucked directly into it or will be pulled into a doomed orbit like water circling a drain. The gravitational pull near the event horizon is so strong that the matter around it reaches relativistic speeds (i.e. speeds comparable to the speed of light). The friction between the material heats it to incredibly high temperatures, turning it into glowing plasma. Close to the event horizon photons are pulled into nearly circular orbits, and this form a bright photon ring which outlines the black “shadow” of inside the event horizon itself.

    4
    Simulated image of an accreting black hole. The event horizon is in the middle of the image, and the shadow can be seen with a rotating accretion disk surrounding it. Credit: Bronzwaer/Davelaar/Moscibrodzka/Falcke/Radboud University

    Einstein’s theory of general relativity predicts the existence of event horizons around black holes. But until now, the resolution of our telescopes has not been high enough to “see” a black hole. Despite the fact that the event horizon can be millions of kilometres in diameter, black holes are elusive. They are very far away and often hidden behind significant amounts of interstellar gas and dust. At 26 000 light-years from Earth, our galaxy’s supermassive black hole — called Sagittarius A* — is just a tiny pinprick on the sky.

    By linking up different telescopes across the globe, the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA) can achieve the resolution necessary to perceive the pinprick of Sagittarius A*. Without doubt, these observations are incredibly exciting. They will allow for the study of black holes in more detail — as well as acting as a test for Einstein’s theory of General Relativity.

    “Einstein’s wonderful general relativity has been around for about a hundred years now and is very unintuitive, but despite that, it has managed to overcome all tests so far,” explains Ciriaco Goddi, astronomer from the EHT. “However, these tests have not been done in such strong gravitational fields.”

    A pressing issue in physics is that the theories of general relativity and quantum mechanics seem to be fundamentally incompatible. To get to the bottom of this issue, physicists need to study the places where these theories overlap or break down. However, the conventional view is that this will not be observed at the event horizon of a supermassive black hole: quantum effects are expected to be important only near the horizon of lighter (about 10 microgram) black holes — of which we currently have no evidence for their existence. Yet some theorists argue that there will be deviations from classical general relativity close to the event horizon even for supermassive black holes, and these are potentially observable with the EHT.

    “If there is any deviation from Einstein’s predictions near the black hole, where gravitation is at its strongest, we would need a new theory of gravity,” Goddi says, “and that means that we would need to describe space and time in different terms.”

    General relativity predicts that the “shadow” of a black hole is circular, but other theories predict the shadow could be “squashed” along either the vertical axis (prolate) or the horizontal axis (oblate). Studying the shadow can therefore test general relativity as well as alternate theories of gravity. Plus, since the diameter of the black hole’s shadow is proportional to its mass, observing a black hole’s shadow may allow astronomers to directly estimate its mass.

    5
    This infographic shows a simulation of the outflow (bright red) from a black hole and the accretion disk around it, with simulated images of the three potential shapes of the event horizon’s shadow. Credit: ESO/N. Bartmann/A. Broderick/C.K. Chan/D. Psaltis/F. Ozel

    ALMA astronomer Violette Impellizzeri adds: We think that there is a supermassive black hole at the centre of every galaxy. But the inner workings of these black holes remain a mystery. However, we need to ask ourselves the question of why there is a supermassive black hole at the centre of every galaxy. And it’s become more and more clear that black holes play a fundamental role in the formation of galaxies, and how they evolved. So, the links between the black holes, the galaxies, and the Universe are vital to understand.”

    The VLBI observations with the EHT and GMVA will make phenomenal new discoveries, addressing the current and pressing problems of gravitational theory.

    This is the third post of a blog series following the EHT and GMVA projects. Next time, we’ll explore how radio telescopes work.

    2. What is a black hole?
    11.4.2017

    6

    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.

    7
    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.

    8
    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!

    1. What are the Event Horizon Telescope and the Global mm-VLBI Array?
    30.3.2017

    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. 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) [above]and the Global mm-VLBI Array (GMVA) [above], working at different wavelengths. 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. 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.

    9
    This infographic details the locations of the participating telescopes of the Event Horizon Telescope and the Global mm-VLBI Array. Credit: ESO/O. Furtak

    10
    ALMA’s solitude: This panoramic view of the Chajnantor Plateau shows the site of the Atacama Large Millimeter/submillimeter Array (ALMA), a place of solitude 5000 metres above sea level in the Chilean Andes. Credit: ESO/B. Tafreshi (twanight.org)

    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.

    11
    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.

    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

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    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

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

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

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

    Ethan Siegel
    Apr 29, 2017

    1
    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?

    2
    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.

    3
    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.

    4
    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.

    4
    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.

    5
    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.

    6
    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.

    6
    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.

    7
    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: , , , , , EHT - Event Horizon Telescope, ,   

    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.

    1
    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.

    3
    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:

    4
    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.

    5
    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.

    6
    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 .

    Please help promote STEM in your local schools.
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    Stem Education Coalition
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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

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