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  • richardmitnick 9:41 am on January 27, 2020 Permalink | Reply
    Tags: , , , , , Milky Way, We live in our very own spiral arm of the galaxy-albeit a relatively minor one-our spiral arm is formally called the Orion-Cygnus Arm., Where is our solar system?   

    From EarthSky: “Which spiral arm of the Milky Way contains our sun?” 

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    From EarthSky

    January 27, 2020

    We live in a seemingly nondescript neighborhood in the Milky Way galaxy, in a small spiral arm called the Orion Arm.

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    Artist’s concept of our Milky Way galaxy, as seen from far galactic north (the direction of the constellation Coma Berenices) via NASA/ JPL-Caltech/ R. Hurt

    Our Milky Way galaxy is the island of stars we call home. If you imagined it as a disk with spiral arms emanating from the center, our sun is about a third of the way from the center to the visible edge. Our solar system is located between two prominent spiral arms, in what astronomers once thought was a mere bridge of stars, gas, and dust clouds. In recent decades, research advances have revealed that we live in our very own spiral arm of the galaxy, albeit a relatively minor one. Our spiral arm is formally called the Orion-Cygnus Arm. It’s also known simply as the Orion Arm or Local Arm, and you sometimes still hear the name Orion Bridge.

    The Milky Way is a spiral galaxy. In fact, the Milky Way is a barred spiral galaxy, which means it has a central bar. There’s still a lot we don’t know about the structure of our galaxy. According to the best current knowledge, the Milky Way is about 150,000 to 200,000 light-years across, and about 2,000 light-years deep, and has 100 to 400 billion stars. There may be four primary spiral arms emanating from its center bar with an unknown number of smaller offshoot arms.

    Where, within this vast spiral structure, do our sun and its planets reside? We’re about 26,000 light-years from the center of the galaxy, on the inner edge of the Orion-Cygnus Arm.

    It’s sandwiched by two primary spiral arms, the Sagittarius and Perseus Arms. The artists’ concepts above and below show the Orion-Cygnus Arm, the home spiral arm of our sun in the Milky Way galaxy.

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    In this diagram, you can more clearly see the 4 major spiral arms of the Milky Way. The Perseus Arm is shown in cyan, and the Carina-Sagittarius Arm in pink. Towards the top, the sun’s location is marked on the orange-colored Orion-Cygnus Arm. Image via Rursus/ Wikimedia Commons.

    The Orion Arm of the Milky Way is thought to be some 3,500 light-years wide. Initially, astronomers thought it was about 10,000 light-years in length. A new study – published in 2016 [Science Advances]– suggests it’s more than 20,000 light-years long.

    Astronomers are continuing to piece together the structure of the Milky Way by painstakingly measuring the positions and distances to many stars and gas clouds. Distances are determined from parallax measurements by telescopes on the ground and in space. One currently-operational space telescope, Gaia, is expected to provide a wealth of new information to better characterize the Milky Way’s structure and size.

    ESA/GAIA satellite

    In fact, it’s Gaia’s stated goal to provide a 3-dimensional map of our Milky Way.

    The Orion Arm is named for the constellation Orion the Hunter, which is one of the most prominent constellations of Northern Hemisphere winter (Southern Hemisphere summer). Some of the brightest stars and most famous celestial objects of this constellation (Betelgeuse, Rigel, the stars of Orion’s Belt, the Orion Nebula) are neighbors of sorts to our sun, located within the Orion Arm. That’s why we see so many bright objects within the constellation Orion – because when we look at it, we’re looking into our own local spiral arm.

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    Artist’s concept of our galactic neighborhood. Some of the best-known astronomical objects in our sky lie in the Orion Arm, including our sun. Image via R. Hurt/ Wikimedia Commons.

    See the full article here .


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    Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.

     
  • richardmitnick 6:36 pm on January 14, 2020 Permalink | Reply
    Tags: , , , , Faraday rotation effect, Galactic magnetic field, Interstellar Medium (ISM), , Milky Way, THOR survey, University of Calgary in Canada, Warm Ionized Medium (WIM)   

    From Max Planck Institute for Astronomy: “Hot gas feeds spiral arms of the Milky Way” 

    From Max Planck Institute for Astronomy

    January 14, 2020

    Dr. Markus Nielbock
    Press and public relations officer
    Phone:+49 6221 528-134
    Email: pr@mpia.de

    Max Planck Institute for Astronomy, Heidelberg

    Max Planck Institute for Astronomy
    Prof. Dr. Henrik Beuther
    Phone:+49 6221 528-447
    Email: beuther@mpia.de

    Max Planck Institute for Astronomy, Heidelberg

    Magnetic fields point the way to the material that sustains star formation in the Milky Way.

    An international research team, with significant participation of astronomers from the Max Planck Institute for Astronomy (MPIA), has gained important insights into the origin of the material in the spiral arms of the Milky Way, from which new stars are ultimately formed. By analysing properties of the galactic magnetic field, they were able to show that the dilute so-called Warm Ionized Medium (WIM), in which the Milky Way is embedded, condenses near a spiral arm. While gradually cooling, it serves as a supply of the colder material of gas and dust that feeds star formation.

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    False-colour representation of the radio emission in the Milky Way from the THOR survey at a wavelength of about 21 cm. The upper band (1.4 GHz continuum) shows the emission from different sources, while the lower bands show the distribution of atomic hydrogen. Credit: Y. Wang/MPIA

    The Milky Way is a spiral galaxy, a disc-shaped island of stars in the cosmos, in which most bright and young stars cluster in spiral arms. There they form from the dense Interstellar Medium (ISM), which consists of gas (especially hydrogen) and dust (microscopic grains with high abundances of carbon and silicon). In order for new stars to form continuously, material must be constantly flushed into the spiral arms to replenish the supply of gas and dust.

    Milky Way NASA/JPL-Caltech /ESO R. Hurt. The bar is visible in this image

    A group of astronomers from the University of Calgary in Canada, the Max Planck Institute for Astronomy (MPIA) in Heidelberg and other research institutions have now been able to show that the supply comes from a much hotter component of the ISM, which usually envelops the entire Milky Way.

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    This Warm Ionized Medium (WIM) has an average temperature of 10,000 degrees. High-energy radiation from hot stars causes the hydrogen gas of the WIM to be largely ionised. The results suggest that the WIM condenses in a narrow area near a spiral arm and gradually flows into it while cooling.

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    Segment of the THOR survey near the Sagittarius arm of the Milky Way. The crosses indicate the position of sources of polarised radio emission. Their sizes correspond to the magnitude of the Faraday rotation effect. The strongest signals were measured in a rather inconspicuous strip to the right of the bright objects in the middle of the image. The strong radio sources indicate the position of the spiral arm. Credit: J. Stil/University of Calgary/MPIA

    The scientists discovered the dense WIM by measuring the so-called Faraday rotation, an effect named after the English physicist Michael Faraday. This involves changing the orientation of linearly polarised radio emissions when they pass through a plasma (ionised gas) traversed by a magnetic field. One speaks of polarised radiation when the electric field oscillates in only one plane. Ordinary light is not polarised. The magnitude of the change in polarisation also depends on the observed wavelength.

    In the present study, recently published in The Astrophysical Journal Letters, astronomers were able to detect an unusually strong signal in a rather inconspicuous area of the Milky Way.The analysis is based on the THOR survey (The HI/OH Recombination Line Survey of the Milky Way), which has been conducted at MPIA for several years now and in which a large area of the Milky Way is observed at several radio wavelengths. Polarised radio sources such as distant quasars or neutron stars serve as “probes” for determining the Faraday rotation. This allows astronomers not only to detect the otherwise difficult to measure magnetic fields in the Milky Way, but also to study the structure and properties of the hot gas. “We were very surprised by the strong signal in a rather quiet area of the Milky Way,” says Henrik Beuther from MPIA, who is leading the THOR project. “These results show us that there is still a lot to be discovered in studying the structure and dynamics of the Milky Way.”tect an unusually strong signal in a rather inconspicuous area of the Milky Way, which is located directly on the side of the Sagittarius arm of the Milky Way facing the Galactic Centre. The spiral arm itself stands out in the imaging data due to strong radio emission generated by embedded hot stars and supernova remnants. However, the astronomers found the strongest shift in polarisation outside this prominent zone. They conclude from this that the increased Faraday rotation does not originate within this active part of the spiral arm. Instead, it originates from condensed WIM, which, like the magnetic field, belongs to a less obvious component of the spiral arm.

    The analysis is based on the THOR survey (The HI/OH Recombination Line Survey of the Milky Way), which has been conducted at MPIA for several years now and in which a large area of the Milky Way is observed at several radio wavelengths. Polarised radio sources such as distant quasars or neutron stars serve as “probes” for determining the Faraday rotation. This allows astronomers not only to detect the otherwise difficult to measure magnetic fields in the Milky Way, but also to study the structure and properties of the hot gas. “We were very surprised by the strong signal in a rather quiet area of the Milky Way,” says Henrik Beuther from MPIA, who is leading the THOR project. “These results show us that there is still a lot to be discovered in studying the structure and dynamics of the Milky Way.”

    Collaboration

    This study was made possible by a cooperation of the following research institutions:

    Department of Physics and Astronomy, The University of Calgary, Canada; Max Planck Institute for Astronomy, Heidelberg, Germany; Department of Physics and Astronomy, West Virginia University, USA; Green Bank Observatory, USA; Center for Gravitational Waves and Cosmology, West Virginia University, USA; Argelander Institute for Astronomy, University of Bonn, Germany; Centre for Astronomy, University of Heidelberg, Germany; Jet Propulsion Laboratory, California Institute of Technology, USA; Interdisciplinary Centre for Scientific Computing, University of Heidelberg, Germany; Research School of Astronomy and Astrophysics, The Australian National University, Canberra, Australia; Max Planck Institute for Radio Astronomy, Bonn, Germany; Jodrell Bank Centre for Astrophysics, The University of Manchester, United Kingdom

    See the full article here .

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    Max Planck Institute for Astronomy campus

    The Max Planck Institute for Astronomy
    How do stars and planets form? What can we learn about planets orbiting stars other than the Sun? How do galaxies form, and how have they changed in the course of cosmic history?

    Those are the central questions guiding the work of the scientists and engineers at the Max Planck Institute for Astronomy (MPIA) in Heidelberg. The institute was founded in 1967, and it is one of roughly 80 institutes of the Max Planck Society, Germany’s largest organizations for basic research.

    MPIA has a staff of around 290, three quarters of which are working in sci-tech. At any given time, the institute features numerous junior scientists and guest scientists both from Germany and abroad.

     
  • richardmitnick 12:31 pm on December 20, 2019 Permalink | Reply
    Tags: "These are the stars the Pioneer and Voyager spacecraft will encounter", , , , , , , , , Milky Way, , NASA Pioneer 10 and 11,   

    From MIT Technology Review: “These are the stars the Pioneer and Voyager spacecraft will encounter” 

    MIT Technology Review
    From MIT Technology Review

    Dec 20, 2019
    Emerging Technology from the arXiv

    As four NASA spacecraft exit our solar system, a 3D map [below] of the Milky Way reveals which others they’re likely to visit tens of thousands of years on.

    Laniakea supercluster. From Nature The Laniakea supercluster of galaxies R. Brent Tully, Hélène Courtois, Yehuda Hoffman & Daniel Pomarède at http://www.nature.com/nature/journal/v513/n7516/full/nature13674.html. Milky Way is the red dot.

    Milky Way NASA/JPL-Caltech /ESO R. Hurt. The bar is visible in this image

    NASA Pioneer 10

    NASA Pioneer 11

    NASA/Voyager 1

    NASA/Voyager 2

    During the 1970s, NASA launched four of the most important spacecraft ever built. When Pioneer 10 began its journey to Jupiter, astronomers did not even know whether it was possible to pass through the asteroid belt unharmed.

    The inner Solar System, from the Sun to Jupiter. Also includes the asteroid belt (the white donut-shaped cloud), the Hildas (the orange “triangle” just inside the orbit of Jupiter), the Jupiter trojans (green), and the near-Earth asteroids. The group that leads Jupiter are called the “Greeks” and the trailing group are called the “Trojans” (Murray and Dermott, Solar System Dynamics, pg. 107)
    This image is based on data found in the en:JPL DE-405 ephemeris, and the en:Minor Planet Center database of asteroids (etc) published 2006 Jul 6. The image is looking down on the en:ecliptic plane as would have been seen on 2006 August 14. It was rendered by custom software written for Wikipedia. The same image without labels is also available at File:InnerSolarSystem.png. Mdf at English Wikipedia

    Only after it emerged safe was Pioneer 11 sent on its way.

    Both sent back the first close-up pictures of Jupiter, with Pioneer 11 continuing to Saturn. Voyager 1 and 2 later took even more detailed measurements, and extended the exploration of the solar system to Uranus and Neptune.

    All four of these spacecraft are now on their way out of the solar system, heading into interstellar space at a rate of about 10 kilometers per second. They will travel about a parsec (3.26 light-years) every 100,000 years, and that raises an important question: What stars will they encounter next?

    This is harder to answer than it seems. Stars are not stationary but moving rapidly through interstellar space. Without knowing their precise velocity, it’s impossible to say which ones our interstellar travelers are on course to meet.

    Enter Coryn Bailer-Jones at the Max Planck Institute for Astronomy in Germany and Davide Farnocchia at the Jet Propulsion Laboratory in Pasadena, California. These guys have performed this calculation using a new 3D map of star positions and velocities throughout the Milky Way.

    Max Planck Institute for Astronomy


    Max Planck Institute for Astronomy campus, Heidelberg, Baden-Württemberg, Germany

    NASA JPL


    NASA JPL-Caltech Campus

    This has allowed them to work out for the first time which stars the spacecraft will rendezvous with in the coming millennia. “The closest encounters for all spacecraft take place at separations between 0.2 and 0.5 parsecs within the next million years,” they say.

    Their results were made possible by the observations of a space telescope called Gaia.

    ESA/GAIA satellite

    Since 2014, Gaia has sat some 1.5 million from Earth recording the position of 1 billion stars, planets, comets, asteroids, quasars, and so on. At the same time, it has been measuring the velocities of the brightest 150 million of these objects.

    The result is a three-dimensional map of the Milky Way and the way astronomical objects within it are moving. It is the latest incarnation of this map, Gaia Data Release 2 or GDR2, that Bailer-Jones and Farnocchia have used for their calculations.

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    ESA/Gaia/DPAC

    The map makes it possible to project the future positions of stars in our neighborhood and to compare them with the future positions of the Pioneer and Voyager spacecraft, calculated using their last known positions and velocities.

    This information yields a list of stars that the spacecraft will encounter in the coming millennia. Bailer-Jones and Farnocchia define a close encounter as flying within 0.2 or 0.3 parsecs.

    The first spacecraft to encounter another star will be Pioneer 10 in 90,000 years. It will approach the orange-red star HIP 117795 in the constellation of Cassiopeia at a distance of 0.231 parsecs. Then, in 303,000 years, Voyager 1 will pass a star called TYC 3135-52-1 at a distance of 0.3 parsecs. And in 900,000 years, Pioneer 11 will pass a star called TYC 992-192-1 at a distance of 0.245 parsecs.

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    These fly-bys are all at a distance of less than one light-year and in some cases might even graze the orbits of the stars’ most distant comets.

    Voyager 2 is destined for a more lonely future. According to the team’s calculations, it will never come within 0.3 parsecs of another star in the next 5 million years, although it is predicted to come within 0.6 parsecs of a star called Ross 248 in the constellation Andromeda in 42,000 years.

    Andromeda Galaxy Messier 31 with Messier32 -a satellite galaxy copyright Terry Hancock.

    Milkdromeda -Andromeda on the left-Earth’s night sky in 3.75 billion years-NASA

    These interstellar explorers will eventually collide with or be captured by other stars. It’s not possible yet to say which ones these will be, but Bailer-Jones and Farnocchia have an idea of the time involved. “The timescale for the collision of a spacecraft with a star is of order 10^20 years, so the spacecraft have a long future ahead of them,” they conclude.

    The Pioneer and Voyager spacecraft will soon be joined by another interstellar traveler. The New Horizons spacecraft that flew past Pluto in 2015 is heading out of the solar system but may yet execute a maneuver so that it intercepts a Kuiper Belt object on its way.

    NASA/New Horizons spacecraft

    Kuiper Belt. Minor Planet Center

    After that last course correction takes place, Bailer-Jones and Farnocchia will be able to work out its final destination.

    Ref: arxiv.org/abs/1912.03503 : Future stellar flybys of the Voyager and Pioneer spacecraft

    See the full article here .


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    The mission of MIT Technology Review is to equip its audiences with the intelligence to understand a world shaped by technology.

     
  • richardmitnick 4:39 pm on November 20, 2019 Permalink | Reply
    Tags: , , , , , Milky Way, ,   

    From Curtin University: “Outback telescope captures Milky Way centre, discovers remnants of dead stars” 

    20 November 2019

    Lucien Wilkinson
    Media Consultant
    Supporting Humanities and Science and Engineering
    Tel: +61 8 9266 9185
    Mob: +61 401 103 683
    lucien.wilkinson@curtin.edu.au

    Yasmine Phillips
    Manager, Media Relations
    Phone: +61 8 9266 9085
    Mobile: +61 401 103 877
    Email: yasmine.phillips@curtin.edu.au

    A radio telescope in the Western Australian outback has captured a spectacular new view of the centre of the galaxy in which we live, the Milky Way.

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    The image from the Murchison Widefield Array (MWA) telescope shows what our galaxy would look like if human eyes could see radio waves.

    SKA Murchison Widefield Array, Boolardy station in outback Western Australia, at the Murchison Radio-astronomy Observatory (MRO)

    Astrophysicist Dr Natasha Hurley-Walker, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), created the images using the Pawsey Supercomputing Centre in Perth.

    Magnus Cray XC40 supercomputer at Pawsey Supercomputer Centre Perth Australia

    Galaxy Cray XC30 Series Supercomputer at Pawsey Supercomputer Centre Perth Australia

    Fujisto Raijin supercomputer

    Fujitsu Raijin Supercomputer

    “This new view captures low-frequency radio emission from our galaxy, looking both in fine detail and at larger structures,” she said.

    “Our images are looking directly at the middle of the Milky Way, towards a region astronomers call the Galactic Centre.”

    The data for the research comes from the GaLactic and Extragalactic All-sky MWA survey, or ‘GLEAM’ for short.

    The survey has a resolution of two arcminutes (about the same as the human eye) and maps the sky using radio waves at frequencies between 72 and 231 MHz (FM radio is near 100 MHz).

    “It’s the power of this wide frequency range that makes it possible for us to disentangle different overlapping objects as we look toward the complexity of the Galactic Centre,” Dr Hurley-Walker said.

    “Essentially, different objects have different ‘radio colours’, so we can use them to work out what kind of physics is at play.”

    Using the images, Dr Hurley-Walker and her colleagues discovered the remnants of 27 massive stars that exploded in supernovae at the end of their lives.

    These stars would have been eight or more times more massive than our Sun before their dramatic destruction thousands of years ago.

    Younger and closer supernova remnants, or those in very dense environments, are easy to spot, and 295 are already known.

    Unlike other instruments, the MWA can find those which are older, further away, or in very empty environments.

    Dr Hurley-Walker said one of the newly-discovered supernova remnants lies in such an empty region of space, far out of the plane of our galaxy, and so despite being quite young, is also very faint.

    “It’s the remains of a star that died less than 9,000 years ago, meaning the explosion could have been visible to Indigenous people across Australia at that time,” she said.

    An expert in cultural astronomy, Associate Professor Duane Hamacher from the University of Melbourne, said some Aboriginal traditions do describe bright new stars appearing in the sky, but we don’t know of any definitive traditions that describe this particular event.

    “However, now that we know when and where this supernova appeared in the sky, we can collaborate with Indigenous elders to see if any of their traditions describe this cosmic event. If any exist, it would be extremely exciting,” he said.

    Dr Hurley-Walker said two of the supernova remnants discovered are quite unusual “orphans”, found in a region of sky where there are no massive stars, which means future searches across other such regions might be more successful than astronomers expected.

    Other supernova remnants discovered in the research are very old, she said.

    “This is really exciting for us, because it’s hard to find supernova remnants in this phase of life—they allow us to look further back in time in the Milky Way.”

    The MWA telescope is a precursor to the world’s largest radio telescope, the Square Kilometre Array, which is due to be built in Australia and South Africa from 2021.

    “The MWA is perfect for finding these objects, but it is limited in its sensitivity and resolution,” Dr Hurley-Walker said.

    “The low-frequency part of the SKA, which will be built at the same site as the MWA, will be thousands of times more sensitive and have much better resolution, so should find the thousands of supernova remnants that formed in the last 100,000 years, even on the other side of the Milky Way.”

    The new images of the Galactic Centre can be viewed via a web browser using the GLEAMoscope app or through an android device using the GLEAM app3.

    See the full article here .

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    Curtin University (formerly known as Curtin University of Technology and Western Australian Institute of Technology) is an Australian public research university based in Bentley and Perth, Western Australia. The university is named after the 14th Prime Minister of Australia, John Curtin, and is the largest university in Western Australia, with over 58,000 students (as of 2016).

    Curtin was conferred university status after legislation was passed by the Parliament of Western Australia in 1986. Since then, the university has been expanding its presence and has campuses in Singapore, Malaysia, Dubai and Mauritius. It has ties with 90 exchange universities in 20 countries. The University comprises five main faculties with over 95 specialists centres. The University formerly had a Sydney campus between 2005 & 2016. On 17 September 2015, Curtin University Council made a decision to close its Sydney campus by early 2017.

    Curtin University is a member of Australian Technology Network (ATN), and is active in research in a range of academic and practical fields, including Resources and Energy (e.g., petroleum gas), Information and Communication, Health, Ageing and Well-being (Public Health), Communities and Changing Environments, Growth and Prosperity and Creative Writing.

    It is the only Western Australian university to produce a PhD recipient of the AINSE gold medal, which is the highest recognition for PhD-level research excellence in Australia and New Zealand.

    Curtin has become active in research and partnerships overseas, particularly in mainland China. It is involved in a number of business, management, and research projects, particularly in supercomputing, where the university participates in a tri-continental array with nodes in Perth, Beijing, and Edinburgh. Western Australia has become an important exporter of minerals, petroleum and natural gas. The Chinese Premier Wen Jiabao visited the Woodside-funded hydrocarbon research facility during his visit to Australia in 2005.

     
  • richardmitnick 5:13 pm on October 25, 2019 Permalink | Reply
    Tags: "How the Milky Way devours its neighbors", , , Milky Way   

    From Astronomy Magazine: “How the Milky Way devours its neighbors” 

    Astronomy magazine

    From Astronomy Magazine

    October 25, 2019
    Ray Jayawardhana

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    OMEGA CENTAURI (NGC 5139) — the Milky Way’s biggest and brightest globular cluster — may be the nucleus of a dwarf galaxy captured long ago by the Milky Way. Daniel Phillips

    On a clear moonless night, the arc of the Milky Way overhead seems the very picture of serenity. Yet its gentle glow masks a life of turmoil. Episodes of violence, plunder, and cannibalism pervade astronomers’ emerging picture of our galaxy’s history.

    Unraveling this story, with the help of painstaking observations and sophisticated computer simulations, could shed light on how the Milky Way acquired its present form. It could also help astronomers understand galaxy evolution in general.

    4
    THE MILKY WAY climbs majestically above the 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile. Despite its peaceful appearance, our galaxy has devoured untold numbers of dwarf galaxies. K. Don/NOAO/AURA/NSF

    The classical view of the galaxy’s origin, proposed more than four decades ago, starts with a single large gas cloud that collapsed when the universe was in its infancy. In 1978, however, Leonard Searle and Robert Zinn, then at the Carnegie Observatories in Pasadena, California, introduced a new twist.

    The astronomers suggested that some globular clusters — dense knots of hundreds of thousands of stars in the galactic halo — joined the Milky Way after its central regions and disk already had taken shape. Ever since, various astronomers have argued that ­certain globular clusters are stolen goods, wrested away from other smaller galaxies as they merged with the Milky Way.

    Clusters orbiting the galactic center “backward” — opposite to the orbits of the Sun and most other stars — are among the most likely interlopers. Many researchers think Omega Centauri (NGC 5139), the most massive globular known, could be the nucleus of a disrupted dwarf galaxy.

    This more chaotic picture agrees better with current theory about how galaxies evolved from an initially near-homogeneous universe. The favored model goes by the name “cold dark matter” (CDM).

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex Mittelmann Cold creation

    This theory assumes dark matter — the mysterious substance whose gravity dominates over normal matter — consists of slow-moving (hence “cold”) particles.

    From the bottom up

    The CDM scenario, explored in numerous theoretical calculations and simulations, suggests structure formed from the bottom up. Large galaxies grew from the mergers of smaller clumps. Galaxies grouped into clusters and still-larger superclusters. One challenge for the CDM model is that it predicts many more dwarf galaxies in our cosmic neighborhood than astronomers observe.

    It could be that the Milky Way and other large galaxies, like the nearby Andromeda Galaxy (M31), already have gobbled up most of their smaller brethren or distorted them so much they are difficult to spot even in our own backyard.

    A massive galaxy exerts powerful tidal forces because the gravitational pull acting on the near side of a neighbor significantly exceeds that acting on the far side. These forces overwhelm the gravity binding a dwarf galaxy together and rip it apart. The tides draw gas and stars into long trails or streams that eventually disperse. Once the “loot” mixes in with the big galaxy’s contents, tracing its origin proves far from easy.

    The vast majority of mergers that built our galaxy probably happened early in its history. But the Milky Way continues to des­troy and swallow its remaining neighbors.

    6
    THE LARGE MAGELLANIC CLOUD provides a major portion of the Magellanic Stream, a 600,000-light-year-long concentration of gas perhaps stripped by the Milky Way from this irregular satellite galaxy and its neighbor, the Small Magellanic Cloud.
    Andreas B’ker & Axel Martin

    Big news from small galaxies

    The Magellanic Stream has often been held up as the poster child of an ongoing merger.

    10

    The stream consists of gas stripped from two irregular satellite galaxies well known to Southern Hemisphere observers: the Large and Small Magellanic Clouds. First identified more than 40 years ago, the stream trails the motions of the galaxies for some 600,000 light-years. The so-called Leading Arm stretches between the clouds and our galaxy.

    Some models suggest the Milky Way created these filaments. But a decade ago, Nitya Kallivayalil, then at MIT, and her colleagues found that the Magellanic Clouds are moving unexpectedly fast. Unless our galaxy has far more mass than we think, the clouds may be on their first pass — and tides alone likely could not produce the stream.

    The Milky Way also seems to be disrupting other Local Group dwarfs. University of Virginia astronomer Steven Majewski leads one of several groups that have discovered tidal debris from several of these dwarfs, including those in the constellations Carina, Leo, Ursa Minor, and Sculptor.

    Perhaps the most dramatic case of a cannibalized Milky Way satellite is the Sagittarius Dwarf Spheroidal Galaxy.

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    Sagittarius Dwarf Spheroidal Galaxy

    Rodrigo Ibata, then a graduate student at Cambridge ­University, found it almost by accident.

    In 1994, Ibata was studying the motions and chemical compositions of stars in our galaxy’s bulge. While collecting spectra of his sample stars at the Anglo-Australian Telescope in Australia, Ibata noticed a few of the reddest stars had velocities different from all the others.


    AAO Anglo Australian Telescope near Siding Spring, New South Wales, Australia, Altitude 1,100 m (3,600 ft)

    Even stranger, the stars appeared to be moving together. On the next couple of nights, he took spectra of more red stars. They all shared the same unusual motion.

    When Ibata returned to Cambridge, he and his colleagues scanned archival photographic plates of that region of sky, then plotted the positions of red stars similar in brightness to those he had found with peculiar velocities. This exercise revealed the contours of a hitherto unknown galaxy. It lies roughly perpendicular to the Milky Way’s disk and about 100,000 light-years away, on the far side of the galactic center.

    It had been hiding behind the Milky Way’s thick veil of stars and dust. What’s more, the newly found dwarf spheroidal galaxy, named Sagittarius after the constellation that contains its center, has a rather contorted appearance. This represents clear evidence of bullying by the dwarf’s massive neighbor.

    During the past 20 years, astronomers have attempted to chart the dwarf galaxy’s full extent. Recent maps show its debris scattered in a giant arc that wraps around the Milky Way. Ibata’s team and others argue that several globular clusters previously thought to belong to our galaxy actually came from the Sagittarius dwarf. Other stolen clusters and individual stars may exist, but they’re already so well mixed in with the Milky Way’s own that astronomers can’t trace their origins.

    The surprise discovery of the Sagittarius dwarf raised the possibility others like it may lurk undetected. Astronomers imagined spaghetti-like strands crisscrossing the Milky Way, each filament retaining a faint memory of the path taken by its long-since-destroyed parent galaxy or globular cluster. Scientists tried to identify streams of stars with peculiar motions and odd chemical abundance patterns, which might betray their alien origins.

    The tides turn to Sloan

    For researchers in pursuit of these elusive fossils, the Sloan Digital Sky Survey has turned out to be a treasure trove.

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    Initiated in 2000 and now in its fourth phase, the multi-wavelength survey covers one-third of the sky.

    Michael Odenkirchen and Eva Grebel, then at the Max Planck Institute for Astronomy in Germany, and their colleagues quickly discovered two tidal trails. The trails emerge from a sparse and remote glob­ular cluster cataloged as Palomar 5.

    12
    Palomar 5, Serpens Dwarf

    One of these trails has now been traced across more than 20° of sky, spanning some 25,000 light-years.

    Scientists think Palomar 5 lost much of the observed debris in the past 2 billion years. Simulations suggest this ­cluster will break apart completely the next time it crosses the Milky Way’s disk, just 100 million years from now. Other researchers have since identified an even larger debris arc associated with the glob­ular cluster NGC 5466.

    7
    THE ANDROMEDA GALAXY (M31) looks serene when viewed from Earth, but it disguises a history of rampant cannibalism.
    T.A. Rector/B.A. Wolpa/NOAO/AURA/NSF

    In 2003, Heidi Jo Newberg of Rensselaer Polytechnic Institute in Troy, New York, Brian Yanny of Fermilab outside Chicago, and their colleagues reported the discovery of a “ring” of stars beyond the visible edge of the Milky Way’s disk. They named it the Monoceros Stream because its center lies toward that constellation.

    13
    Monoceros Ring

    The Monoceros Stream’s stars stood out in the Sloan data because they have unusual colors. The colors arise from the stars’ lack of heavy ­elements — meaning all those natural elements heavier than helium. Some ­scientists think the stream originates from a dwarf galaxy in the constellation Canis Major that’s being torn apart by the Milky Way’s gravitational tides.

    In 2006, Mario Juric of Prince­ton University and his colleagues reported discovery of a remarkable increase in stellar density toward the constellation Virgo. The structure turned up in a 3-D map of about 48 million stars the team made from Sloan data.

    At an estimated distance of 30,000 light-years, the density structure lies well within the Milky Way’s confines. The most likely explanation is that these “extra” stars belong to a slowly dissolving dwarf galaxy.

    A team led by Kathy Vivas of the Center for Astronomical Investigations in Vene­zuela had noticed hints of such a beast a few years earlier. The researchers were searching for a type of pulsating variable star known as RR Lyrae stars. “We saw a high density of RR Lyrae stars in the region — more than 20 of them — and speculated that they belonged to a small galaxy being cannibalized by the Milky Way,” she says. In light of the Sloan findings, “It appears that the stellar stream we detected is itself part of a larger structure.”

    Field of streams

    Later in 2006, Cambridge University’s Vasily Belokurov and Daniel Zucker and their collaborators identified a number of other trails and lumps in Sloan images taken toward the north galactic pole, not far from the direction of the previously known Sagittarius and Monoceros streams. So many tidal trails populate this region that the researchers dubbed it the “field of streams.”

    One of these trails covers 30° of sky. It contains two globular clusters deficient in heavy elements and could be the “orphan” of yet another disrupted dwarf galaxy. At least three more faint Milky Way satellites, all showing signs of distortion, turn up in the Sloan survey. Taken together, these findings are “a striking demonstration of multiple merger events going on in the Milky Way right now,” Yanny says.

    6

    Astronomers now have little doubt our galaxy has enriched itself at the expense of others. “In fact, the majority of globular clusters might be relics of accretion events,” claims Julio Navarro, an astrophysicist at the University of Victoria.

    As supporting ­evidence, Navarro points to the agreement between the distribution of globular clusters around the Milky Way and the density profile of accreted stars in his group’s simulations of
    galaxy formation. He finds a similar match between models and observations of our galaxy’s near twin, the Andromeda Galaxy. This suggests galactic cannibalism might be rampant.

    Our exotic neighbors

    But, the “stolen goods” may not be found just in the galaxy’s outer reaches. Some interlopers may lurk in the solar neighborhood, too. Timothy Beers of the University of Notre Dame and his collab­orators identified a group of stars in the Milky Way’s disk that shares the chemical abundance pattern of stars in Omega Centauri, and may have come from the same disrupted parent galaxy.

    Another such grouping includes the relatively nearby red giant star Arcturus. The members of this group move through space in a similar manner to one another, but much slower than most other stars in their vicinity. They also share a distinct chemical imprint.

    “You can make a plausible though not conclusive case that these stars came from a disrupted satellite galaxy,” says Navarro. His simulations show tidal debris not only can accumulate in the galaxy’s halo, but also contribute to the disk. “It may be that most metal-poor stars in the Milky Way’s disk originated in various accreted satellites,” he argues.

    Sloan researchers have also discovered two distinct populations of stars in the galaxy’s halo. The groups orbit the galaxy’s center in opposite directions, providing more evidence for multiple mergers in the past. Unfortunately, it’s probably impossible to pin down just how many neighbors the Milky Way has devoured during its long history. There could have been hundreds of small early mergers, or just a few major collisions that dominated.

    A study of 20,000 stars in four dwarf spheroidal galaxies found a puzzling paucity of extremely metal-poor stars. This suggests the Milky Way’s current small neighbors may differ fundamentally from those it devoured in the distant past.

    Detailed observations of large numbers of stars in the galactic halo could provide more clues to the Milky Way’s history. A survey project known as RAVE, for RAdial Velocity Experiment, has measured the velocities and compositions of 483,330 stars. Meanwhile, Sloan’s APOGEE-2 survey will collect spectra of another 300,000 stars in both the northern and southern skies by the time it wraps up in the autumn of 2020.

    Our galaxy clearly has had a colorful, if not dramatic, history. But the story is far from complete. The challenge for astronomers will be to weave it together from a million pieces scattered in space and time.

    The cannibal next door

    With evidence of the Milky Way’s cannibalism all around us, it seems logical our galaxy’s near twin, the massive Andromeda Galaxy (M31), should show signs, too. The nearest large galaxy to our own, the spiral behemoth M31, lies approximately 2.5 million light-years away. That vast distance makes it difficult for astronomers to discern relic stars left behind by past mergers.

    Despite the challenges, astronomers have made progress. In 1993, a team led by Tod Lauer of the National Optical Astronomy Observatories in Tucson discovered what appear to be two dense knots — called a double nucleus — at M31’s center. The researchers needed the Hubble Space Telescope’s sharp eyes to separate the two structures. Some astronomers spec­ulated that one of the clumps originated in a satellite galaxy that had collided with M31.

    One problem with this story: The two clumps should have merged in less than 100 million years — a short time compared with the several-billion-year age of the stars in those knots. Most researchers now prefer an alternate explanation, proposed by Scott Tremaine of Princeton University. He thinks both knots belong to a single elongated disk of stars having a supermassive black hole at one focus.

    More convincing evidence of M31’s cannibalism came to light in 2001. At that time, astronomers were conducting a deep panoramic imaging survey of the Andromeda Galaxy’s halo with the 2.5-meter Isaac Newton Telescopeon La Palma in the Canary Islands.

    ING Isaac Newton 2.5m telescope at Roque de los Muchachos Observatory on La Palma in the Canary Islands, Spain, Altitude 2,344 m (7,690 ft)

    Rodrigo Ibata of Strasbourg Observatory in France and his collaborators discovered an extended stream of stars protruding from Andromeda. Astronomers have dubbed this feature the Giant Southern Stream.

    Some researchers have proposed that the Giant Southern Stream consists of stars torn from one of Andromeda’s two close companions, the dwarf satellite galaxies M32 and NGC 205. According to Puragra Guhathakurta of the University of California at Santa Cruz, there’s no hard evidence for this explanation.

    The more likely scenario, Guhathakurta says, is that Andromeda has completely devoured a dwarf galaxy. If this is true, the Giant Southern Stream may be just one segment of an extended debris trail looping around the giant galaxy. The trail marks the dwarf galaxy’s extended death spiral into Andromeda.

    A team led by Guhathakurta has reported evidence linking the Giant Southern Stream to several other locations in Andromeda where large numbers of stars appear to move as a group. The researchers believe these features are parts of a continuous star stream. “We think we are seeing the debris trail of a small, chemically rich galaxy that fell into Andromeda,” Guhathakurta says.

    More recently, the Sloan survey revealed a giant, ­diffuse clump of stars just outside M31’s disk that could be the remnants of another satellite galaxy being torn apart by Andromeda’s tides. The exact nature of this structure remains a mystery, however. Many astronomers continue to search Andromeda for clues to its voracious and chaotic history.

    See the full article here .


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  • richardmitnick 10:15 am on August 28, 2019 Permalink | Reply
    Tags: , , , , , Milky Way   

    From European Space Agency: “Gaia untangles the starry strings of the Milky Way” 

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    From European Space Agency

    28 August 2019

    Marina Kounkel
    Western Washington University, USA
    Email: marina.kounkel@wwu.edu

    Kevin Covey
    Western Washington University, USA
    Email: kevin.covey@wwu.edu

    Timo Prusti
    Gaia Project Scientist
    European Space Agency
    Email: timo.prusti@esa.int


    Gaia tracing starry strings in the Milky Way.

    Rather than leaving home young, as expected, stellar ‘siblings’ prefer to stick together in long-lasting, string-like groups, finds a new study of data from ESA’s Gaia spacecraft.

    ESA/GAIA satellite

    Exploring the distribution and past history of the starry residents of our galaxy is especially challenging as it requires astronomers to determine the ages of stars. This is not at all trivial, as ‘average’ stars of a similar mass but different ages look very much alike.

    To figure out when a star formed, astronomers must instead look at populations of stars thought to have formed at the same time – but knowing which stars are siblings poses a further challenge, since stars do not necessarily hang out long in the stellar cradles where they formed.

    1
    This diagram shows a face-on view of stellar ‘families’ – clusters (dots) and co-moving groups (thick lines) of stars – within about 3000 light-years from the Sun, which is located at the centre of the image. The diagram is based on data from the second data release of ESA’s Gaia mission. Each family is identified with a different colour and comprises a population of stars that formed at the same time. Purple hues represent the oldest stellar populations, which formed around 1 billion years ago; blue and green hues represent intermediate ages, with stars that formed hundreds of millions of years ago; orange and red hues show the youngest stellar populations, which formed less than a hundred million years ago. Thin lines show the predicted velocities of each group of stars over the next 5 million years, based on Gaia’s measurements. The lack of structures at the centre is an artefact of the method used to trace individual populations, not due to a physical bubble. A recent study using data from Gaia’s second data release uncovered nearly 2000 previously unidentified clusters and co-moving groups of stars and determined the ages for hundreds of thousands of stars, making it possible to track stellar ‘siblings’ and uncover their surprising arrangements. The study revealed that the most massive among these familial groups of stars may keep moving together through the galaxy in long, string-like configurations for billions of years after their birth.

    “To identify which stars formed together, we look for stars moving similarly, as all of the stars that formed within the same cloud or cluster would move in a similar way,” says Marina Kounkel of Western Washington University, USA, and lead author of the new study [The Astronomical Journal].

    “We knew of a few such ‘co-moving’ star groups near the Solar System, but Gaia enabled us to explore the Milky Way in great detail out to far greater distances, revealing many more of these groups.”

    Marina used data from Gaia’s second release to trace the structure and star formation activity of a large patch of space surrounding the Solar System, and to explore how this changed over time. This data release, provided in April 2018, lists the motions and positions of over one billion stars with unprecedented precision.

    The analysis of the Gaia data, relying on a machine learning algorithm, uncovered nearly 2000 previously unidentified clusters and co-moving groups of stars up to about 3000 light years from us – roughly 750 times the distance to Proxima Centauri, the nearest star to the Sun. The study also determined the ages for hundreds of thousands of stars, making it possible to track stellar ‘families’ and uncover their surprising arrangements.

    2
    Stellar families in Gaia’s sky

    “Around half of these stars are found in long, string-like configurations that mirror features present within their giant birth clouds,” adds Marina.

    “We generally thought young stars would leave their birth sites just a few million years after they form, completely losing ties with their original family – but it seems that stars can stay close to their siblings for as long as a few billion years.”

    The strings also appear to be oriented in particular ways with respect to our galaxy’s spiral arms – something that depends upon the ages of the stars within a string. This is especially evident for the youngest strings, comprising stars younger than 100 million years, which tend to be oriented at right angles to the spiral arm nearest to our Solar System.

    3
    Stellar groups and strings in the Milky Way – edge-on view

    The astronomers suspect that the older strings of stars must have been perpendicular to the spiral arms that existed when these stars formed, which have now been reshuffled over the past billion years.

    “The proximity and orientation of the youngest strings to the Milky Way’s present-day spiral arms shows that older strings are an important ‘fossil record’ of our galaxy’s spiral structure,” says co-author Kevin Covey, also of Western Washington University, USA.

    “The nature of spiral arms is still debated, with the verdict on them being stable or dynamic structures not settled yet. Studying these older strings will help us understand if the arms are mostly static, or if they move or dissipate and re-form over the course of a few hundred million years – roughly the time it takes for the Sun to orbit around the galactic centre a couple of times.”

    Gaia was launched in 2013, and is on a mission to chart a three-dimensional map of our galaxy, pinpointing the locations, motions, and dynamics of roughly one percent of the stars within the Milky Way, along with additional information about many of these stars. Further Gaia releases, including more and increasingly precise data, are planned for the coming decade, providing astronomers with the information they need to unfold the star-formation history of our galaxy.

    “Gaia is a truly ground-breaking mission that is revealing the history of the Milky Way – and its constituent stars – like never before,” adds Timo Prusti, Gaia project scientist at ESA.

    “As we will determine the ages for a larger number of stars distributed throughout our galaxy, not just those residing in compact clusters, we’ll be in an even better position to analyse how these stars have evolved over time.”

    See the full article here .


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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 11:37 am on July 24, 2019 Permalink | Reply
    Tags: "Production Sites of Stars are Rare", , , , , High-density gas- the material for stars- accounts for only 3% of the total mass of gas distributed in the Milky Way, Milky Way, , Nobeyama Radio Obeservatory (NRO) 45-m telescope   

    From National Astronomical Observatory of Japan: “Production Sites of Stars are Rare” 

    NAOJ

    From National Astronomical Observatory of Japan

    1
    Distribution of gas clouds obtained from the FUGIN project. The high-density gas (right) is detected only in small parts of the low-density gas (left). (Credit: NAOJ)

    Astronomers using the Nobeyama Radio Obeservatory (NRO) 45-m telescope [below] found that high-density gas, the material for stars, accounts for only 3% of the total mass of gas distributed in the Milky Way. This result provides key information for understanding the unexpectedly low production rate of stars.

    Milky Way Credits: NASA/JPL-Caltech /ESO R. Hurt. The bar is visible in this image

    Stars are born in gas clouds. The high-density gas pockets form in the extended, low-density gas clouds, and stars form in the very dense gas cores which evolve within the high-density gas. However, observations of distant galaxies detected 1000 times fewer stars than the production value expected from the total amount of low-density gas. To interpret the discrepancy, observations which detect both of the high-density and low-density gas with high-spatial resolution and wide area coverage were needed. However, such observations are difficult, because the high-density gas structures are dozens of times smaller than the low-density gas structures.

    The Milky Way survey project “FUGIN” conducted using the NRO 45-m telescope and the multi-beam receiver FOREST overcame these difficulties. Kazufumi Torii, a project assistant professor at NAOJ, and his team analyzed the big data obtained in the FUGIN project, and measured the accurate masses of the low-density and high-density gas for a large span of 20,000 light-years along the Milky Way. They revealed for the first time that the high-density gas accounts for only 3% of the total gas.

    These results imply the production rate of high-density gas in the low-density gas clouds is small, creating only a small number of opportunities to form stars. The researcher team will continue working on the FUGIN data to investigate the cause of inefficient formation of the high-density gas.

    Science paper PASJ

    See the full article here .

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    NAOJ

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level


    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array
    sft
    Solar Flare Telescope

    Nobeyama Radio Telescope - Copy
    Nobeyama Radio Observatory

    Nobeyama Solar Radio Telescope Array
    Nobeyama Radio Observatory: Solar

    Misuzawa Station Japan
    Mizusawa VERA Observatory

    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

     
  • richardmitnick 11:18 am on March 13, 2019 Permalink | Reply
    Tags: "Streams of Stars Snaking Through the Galaxy Could Help Shine a Light on Dark Matter", Adrian Price-Whelan calls GD-1 "the Goldilocks stream" because it's in just the right place., , , At about 33000 light-years (10 kiloparsecs) GD-1 is the longest stellar stream in the galactic halo, , , Dark matter makes up the bulk of the mass in the universe but it has never been directly observed, , , Milky Way, scores of dark matter seeds are scattered through galaxies like the Milky Way, , The stellar stream known as GD-1 is a thin flow of material tucked inside the Galactic halo   

    From smithsonian.com: “Streams of Stars Snaking Through the Galaxy Could Help Shine a Light on Dark Matter” 

    smithsonian
    From smithsonian.com

    March 12, 2019
    Nola Taylor Redd

    When the Milky Way consumes another galaxy, tendrils of stellar streams survive the merger, containing clues about the universe’s mysterious unseen matter.

    1
    An ultraviolet image of the Andromeda galaxy, the closest major galaxy to the Milky Way, taken by NASA’s Galaxy Evolution Explorer space telescope. Like our own galaxy, Andromeda is a spiral galaxy with a flat rotating disk of stars and gas and a concentrated bulge of stars at the center. (NASA/JPL-Caltech)

    When a small galaxy strays too close to the Milky Way, the gravity from our larger galaxy reels it in. Gas and stars are ripped from the passing galaxy as it falls inward toward its doom, creating streams of material that stretch between the galactic pair. These streams continue to tear away stars until the infalling object has been completely consumed. After the merger is over, some of the only remaining signs of the devoured object are the stellar streams snaking through the Milky Way, a small sample of stars from a galaxy long gone.

    In addition to being a record of the past, one of these streams may provide the first direct evidence for small scale clusters of dark matter—the elusive material that is believed to account for 85 percent of all matter in the universe. A recent analysis of a trail of stars reveals that it interacted with a dense object in the last few hundred million years. After ruling out the most likely suspects, the researchers determined that the relatively recently made gap in the stream may have been caused by a small clump of dark matter. If confirmed, the eddies of this stellar stream could help scientists sort through the competing theories about dark matter and perhaps even close in on the characteristics of the mysterious material.

    The stellar stream known as GD-1 is a thin flow of material tucked inside the Galactic halo, the loose collection of stars and gases surrounding the disk of the Milky Way. Using data released last April from the European Space Agency’s Gaia space telescope, which is in the process of assembling the most detailed map of the Milky Way’s stars ever made, astronomers were able to use precise positional data to reconstruct the movement of the stars in GD-1.

    ESA/GAIA satellite

    Torn from a cloud of material, the stream is the last remnant of an object that was likely consumed by our galaxy in the last 300 million years—an eyeblink on astronomical timescales.

    Gaia found two small breaks in the stream, the first unambiguous observation of gaps in a stellar stream, as well as a dense collection of stars called a spur. Together, these features suggest that a small but massive object shook up the material of the stream.

    “I think this is the first direct dynamical evidence for the small-scale [structure] of dark matter,” says Adrian Price-Whelan, an astronomer at the Flatiron Institute in New York. Working with Ana Bonaca of the Harvard-Smithsonian Center for Astrophysics, Price-Whelan investigated the newfound structures in GD-1 to determine their source and presented the results earlier this year at the winter meeting of the American Astronomical Society.

    At about 33,000 light-years (10 kiloparsecs), GD-1 is the longest stellar stream in the galactic halo. While Price-Whelan and his colleagues were able to use models to show that one of the gaps formed during the generation of the stream, the other gap remained a mystery. However, along with the puzzle, Gaia also revealed a solution: the spur.

    When an object travels past or through a stellar stream, it disrupts the stars. Price-Whelan compares the disruption to a strong jet of air blowing across a stream of water. The water—or stars—plume outward along the path of the disruptor, creating a gap. Some move so fast that they escape the stream and go flying off into space, lost forever. Others are pulled back into the stream to form eddy-like features astronomers call spurs. After a few hundred million years, most spurs merge back into the stream, and only the gap remains, though some can be longer-lived.

    When it comes to spotting structures in stellar streams, Price-Whelan calls GD-1 “the Goldilocks stream” because it’s in just the right place. GD-1 is within the stars of the Milky Way, but moving in the opposite direction, making it easier for astronomers to pick out the stars in the stream from the surrounding objects. “At any given location, it’s moving differently from the way most of the other stars in that part of the sky are moving,” Price-Whelan says.

    The researchers modeled what type of objects could be responsible for the relatively newborn spur spotted in GD-1. They determined that the responsible object had to weigh in with a mass somewhere between 1 million and 100 million times the mass of the sun. Stretching only about 65 light-years (20 pc) in length, the object would have been incredibly dense. The interaction between the stream and the dense object would have likely happened within the last few hundred million years out of the 13.8-billion-year lifetime of the universe.

    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Dark matter isn’t the only object that could have disrupted the stellar stream. A globular cluster or dwarf galaxy swooping nearby could also have created the gap and spur. Price-Whelan and his colleagues turned their eyes toward all known such objects and calculated their orbits, finding that none came close enough to GD-1 in the last billion years to shake things up. A chance encounter with a primordial black hole could have sent the stream’s stars flying, but it would have been an extremely rare event.

    According to dark matter simulations that allow for small structures, scores of dark matter seeds are scattered through galaxies like the Milky Way. A stream like GD-1 is expected to encounter at least one such seed within the last 8 billion years, making dark matter a far more likely perturber based on encounter rates than any other object.

    Dark matter makes up the bulk of the mass in the universe, but it has never been directly observed. The two leading theories for its existence are the warm dark matter model and the Lambda cold dark matter model (ΛCDM), which is the model preferred by most scientists.

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex Mittelmann Cold creation

    Under ΛCDM, dark matter forms clumps that can be as large as a galaxy or as small as a soda can. Warm dark matter models suggest that the material has less massive particles and lacks the can-sized structures that the ΛCDM model suggests. Finding evidence for small scale structures of dark matter could help weed out certain models and start to narrow in on some of the characteristics of the tantalizing stuff.

    “Streams might be the only avenue that we could [use to] study the lowest mass end of what dark matter is doing,” Price-Whelan says. “If we want to be able to confirm or reject or rule out different theories of dark matter, we really need to know what’s happening at [the low] end.”

    Gaia’s data helped identify the stars of the spur, but it’s not detailed enough to compare the velocity differences between them and the stars in the stream, which could help confirm that dark matter perturbed the structure. Price-Whelan and his colleagues want to use NASA’s Hubble Space Telescope to further study the movement of the faint stars in GD-1. Although Gaia has opened the door to wide-scale examination of the movement of stars across the Milky Way, Price-Whelan says that it can’t compete with the HST when it comes to very faint stars. “You can drill much deeper when you have a dedicated telescope like Hubble,” he says.

    The differences in how the stars of the stream and spur move could help astronomers determine how much energy the perturbing object carried, as well as allow researchers to calculate its orbit. These pieces of information could be used to track down the disruptive dark matter clump and study its immediate environment.

    In addition to making a more in-depth study of GD-1, astronomers plan to apply the same techniques enabled by Gaia’s data to some of the more than 40 other streams surrounding the Milky Way. Spotting spurs and gaps in other streams and tying them to dark matter could further improve our understanding of how the mysterious substance interacts with the visible galaxy.

    After decades of puzzling over the mystery of dark matter, the gaps and spurs in stellar streams like GD-1 may finally help to reveal the secrets of the substance that makes up most of the universe. “This is one of the most exciting things that has come out of Gaia,” Price-Whelan says.

    See the full article here .

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    Smithsonian magazine and Smithsonian.com place a Smithsonian lens on the world, looking at the topics and subject matters researched, studied and exhibited by the Smithsonian Institution — science, history, art, popular culture and innovation — and chronicling them every day for our diverse readership.

     
  • richardmitnick 1:47 pm on January 4, 2019 Permalink | Reply
    Tags: , , , , , Milky Way, The Large Magellanic Cloud could hit our galaxy in two billion years’ time., The Milky Way is on a collision course with a neighbouring galaxy that could fling our Solar System into space   

    From Durham University: “Milky Way heading for catastrophic collision” 

    Durham U bloc

    From Durham University

    4 January 2019

    1
    Hubble Space Telescope image representing a merger between two galaxies (M51a and M51b) similar in mass to the Milky Way and the Large Magellanic Cloud. Credit: NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA)

    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Large Magellanic Cloud by by German astrophotographer Eckhard Slawik

    There’s an enemy in our midst. Quietly circling around our galaxy, it could send our Solar System hurtling out of the Milky Way and into the obscurity of interstellar space.

    Its name is the Large Magellanic Cloud (LMC), and even though it is one of the more researched satellite galaxies buzzing around our own, astrophysicists are only now seeing it for what it truly is: an unusually large cosmic threat.

    The Milky Way is on a collision course with a neighbouring galaxy that could fling our Solar System into space.

    The Large Magellanic Cloud could hit our galaxy in two billion years’ time.

    On the off chance that humans survive for another two billion years, our descendants will be in for a treat.

    If the catastrophic collision wakes up the black hole sleeping at the center of our galaxy, this dark beast will begin devouring everything in sight, growing ten times larger than it already is.

    As it feeds on surrounding gas, the stage will be set and the show will begin – what the researchers describe as a “spectacular display of cosmic fireworks.”

    “This phenomenon will generate powerful jets of high energy radiation emanating from just outside the black hole,” explains lead author Marius Cautun, a cosmologist at Durham University.

    “While this will not affect our Solar System, there is a small chance that we might not escape unscathed from the collision between the two galaxies which could knock us out of the Milky Way and into interstellar space.”

    Our galaxy is long overdue for such a collision. So far, it has managed to get by relatively unscathed in the grand scheme of things. Especially when you consider the company that it keeps.

    The Milky Way is surrounded by a group of smaller satellite galaxies, orbiting quietly around us.

    These galaxies can lead separate lives for many billions of years, but on occasion, they can find themselves sinking into the centre of their host galaxy, until at last they collide and are swallowed up completely.

    In this way, galaxies are constantly evolving and growing, but the Milky Way’s poor appetite makes it quite atypical.

    In comparison to our own galaxy, for instance, Andromeda can devour galaxies weighing nearly 30 times more.

    “We think that up to now our galaxy has had only a few mergers with very low mass galaxies,” says co-author Alis Deason, a computational cosmologist at Durham University.

    “This represents very slim pickings when compared to nearby galaxies of the same size as the Milky Way.”

    This galactic collision would happen much sooner than the predicted impact between the Milky Way and another neighbour, Andromeda, which scientists say will hit our galaxy in eight billion years.

    Andromeda Galaxy Adam Evans

    Active black hole

    The coming together with the Large Magellanic Cloud could wake up our galaxy’s dormant black hole, which would begin devouring surrounding gas and increase in size by up to ten times.

    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory

    Sgr A* from ESO VLT

    As it feeds, the now-active black hole would throw out high-energy radiation.

    While these cosmic fireworks are unlikely to affect life on Earth, researchers say there is a small chance that the initial collision could send our Solar System hurtling into space.

    Dark matter

    The Large Magellanic Cloud is the Milky Way’s brightest satellite galaxy and only entered our neighbourhood about 1.5 billion years ago. It sits about 163,000 light years from our galaxy.

    Until recently, astronomers thought that it would either orbit the Milky Way for many billions of years, or, since it moves so fast, escape from our galaxy’s gravitational pull.

    However, recent measurements indicate that the Large Magellanic Cloud has nearly twice as much dark matter than previously thought.

    Solar System

    Researchers say that since it has a larger than expected mass, the Large Magellanic Cloud is rapidly losing energy and is doomed to collide with our galaxy, which could have consequences for our Solar System.

    Lead researcher Dr Marius Cautun, a postdoctoral fellow in our Institute for Computational Cosmology, said: “There is a small chance that we might not escape unscathed from the collision between the two galaxies, which could knock us out of the Milky Way and into space.”

    Read the full research paper MNRAS.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Durham U campus

    Durham University is distinctive – a residential collegiate university with long traditions and modern values. We seek the highest distinction in research and scholarship and are committed to excellence in all aspects of education and transmission of knowledge. Our research and scholarship affect every continent. We are proud to be an international scholarly community which reflects the ambitions of cultures from around the world. We promote individual participation, providing a rounded education in which students, staff and alumni gain both the academic and the personal skills required to flourish.

     
  • richardmitnick 1:53 pm on December 16, 2018 Permalink | Reply
    Tags: , , , , , , Milky Way,   

    From EarthSky: “What is the Local Group?” 

    1

    From EarthSky

    How many galaxies are now known to lie within our Local Group of galaxies? How does our Milky Way rank, size-wise? And what about the vast superclusters beyond?

    1
    One view of the Local Group- a bit to constricted.The 3 largest galaxies in the Local Group are, in descending order, Messier 31 the Andromeda galaxy, the Milky Way, and Messier 33 also known as the Triangulum Galaxy

    Iconic view of the Local Group. Andrew Z. Colvin 3 March 2011

    We know where our galaxy is located, but only locally speaking. The Milky Way galaxy is one of more than 54 galaxies known as the Local Group. The three largest members of the group are our Milky Way (second-biggest), the Andromeda galaxy (biggest) and the Triangulum Galaxy. The other galaxies in the Local Group are dwarf galaxies, and they’re mostly clustered around the three larger galaxies.

    The Local Group does have a gravitational center. It’s somewhere between the Milky Way and the Andromeda Galaxy.

    The Local Group has a diameter of about 10 million light-years.

    Astronomers have also discovered that our Local Group is on the outskirts of a giant supercluster of galaxies, known as the Virgo Supercluster.

    Virgo Supercluster NASA

    Virgo Supercluster, NASA, Wikipedia

    At least 100 galaxy groups and clusters are located within the Virgo Supercluster. Its diameter is thought to be about 110 million light-years.

    The Virgo Supercluster may be part of an even-larger structure that astronomers call the Laniakea Supercluster.

    Laniakea supercluster. From Nature The Laniakea supercluster of galaxies R. Brent Tully, Hélène Courtois, Yehuda Hoffman & Daniel Pomarède at http://www.nature.com/nature/journal/v513/n7516/full/nature13674.html. Milky Way is the red dot.

    It consists of perhaps 100,000 galaxies stretched out over some 520 million light-years.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.

    Stem Education Coalition

    Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.orgin 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. “Being an EarthSky editor is like hosting a big global party for cool nature-lovers,” she says.

     
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