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  • richardmitnick 5:21 pm on March 22, 2017 Permalink | Reply
    Tags: , , , , , , , Dark Energy Spectroscopic Instrument (DESI), Interstellar dust, , New Study Maps Space Dust in 3-D, ,   

    From LBNL: “New Study Maps Space Dust in 3-D” 

    Berkeley Logo

    Berkeley Lab

    March 22, 2017
    Glenn Roberts Jr
    geroberts@lbl.gov
    510-486-5582


    Access mp4 video here .
    This animation shows a 3-D rendering of space dust, as viewed in a several-kiloparsec (thousands of light years) loop through and out of the Milky Way’s galactic plane. The animation uses data for hundreds of millions of stars from Pan-STARRS1 and 2MASS surveys, and is made available through a Creative Commons License. (Credit: Gregory M. Green/SLAC, KIPAC)

    Consider that the Earth is just a giant cosmic dust bunny—a big bundle of debris amassed from exploded stars. We Earthlings are essentially just little clumps of stardust, too, albeit with very complex chemistry.

    And because outer space is a very dusty place, that makes things very difficult for astronomers and astrophysicists who are trying to peer farther across the universe or deep into the center of our own galaxy to learn more about their structure, formation and evolution.

    Building a better dust map

    Now, a new study led by Edward F. Schlafly, a Hubble Fellow in the Physics Division at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), is providing a detailed, 3-D look at dust on a scale spanning thousands of light-years in our Milky Way galaxy. The study was published today in The Astrophysical Journal.

    This dust map is of critical importance for the Dark Energy Spectroscopic Instrument (DESI), a Berkeley Lab-led project that will measure the universe’s accelerating expansion rate when it starts up in 2019. DESI will build a map of more than 30 million distant galaxies, but that map will be distorted if this dust is ignored.

    “The light from those distant galaxies travels for billions of years before we see it,” according to Schlafly, “but in the last thousand years of its journey toward us a few percent of that light is absorbed and scattered by dust in our own galaxy. We need to correct for that.”

    Just as airborne dust in Earth’s sky contributes to the atmospheric haze that gives us brilliant oranges and reds in sunrises and sunsets, dust can also make distant galaxies and other space objects appear redder in the sky, distorting their distance and in some cases concealing them from view.

    Scientists are constantly developing better ways to map out this interstellar dust and understand its concentration, composition, and common particle sizes and shapes.

    1
    The dark regions show very dense dust clouds. The red stars tend to be reddened by dust, while the blue stars are in front of the dust clouds. These images are part of a survey of the southern galactic plane. (Credit: Legacy Survey/NOAO, AURA, NSF)

    Once we can solve the dust problem by creating better dust maps and learning new details about the properties of this space dust, this can give us a much more precise gauge of distances to faraway stars in the Milky Way, like a galactic GPS. Dust maps can also help to better gauge the distance to supernovae events by taking into account the effects of dust in reddening their light.

    “The overarching aim of this project is to map dust in three dimensions—to find out how much dust is in any 3-D region in the sky and in the Milky Way galaxy,” Schlafly said.

    Combined data from sky surveys shed new light on dust

    Taking data from separate sky surveys conducted with telescopes on Maui and in New Mexico, Schlafly’s research team composed maps that compare dust within one kiloparsec, or 3,262 light-years, in the outer Milky Way—including collections of gas and dust known as molecular clouds that can contain dense star- and planet-forming regions known as nebulae—with more distant dust in the galaxy.

    2
    Pan-STARRS2 and PanSTARS1 telescopes atop Haleakalā on the island of Maui, Hawaii. (Credit: Pan-STARRS)

    The resolution of these 3-D dust maps is many times better than anything that previously existed,” said Schlafly.

    This undertaking was made possible by the combination of a very detailed multiyear survey known as Pan-STARRS that is powered by a 1.4-gigapixel digital camera and covers three-fourths of the visible sky, and a separate survey called APOGEE that used a technique known as infrared spectroscopy.

    3
    A compressed view of the entire sky visible from Hawaii by the Pan-STARRS1 Observatory. The image is a compilation of half a million exposures, each about 45 seconds in length, taken over a period of four years. The disk of the Milky Way looks like a yellow arc, and the dust lanes show up as reddish-brown filaments. The background is made up of billions of faint stars and galaxies. (Credit: D. Farrow/Pan-STARRS1 Science Consortium, and Max Planck Institute for Extraterrestrial Physics)

    Infrared measurements can effectively cut through the dust that obscures many other types of observations and provides a more precise measurement of stars’ natural color. The APOGEE experiment focused on the light from about 100,000 red giant stars across the Milky Way, including those in its central halo.


    SDSS Telescope at Apache Point Observatory, NM, USA

    What they found is a more complex picture of dust than earlier research and models had suggested. The dust properties within 1 kiloparsec of the sun, which scientists measure with a light-obscuring property known as its “extinction curve,” is different than that of the dust properties in the more remote galactic plane and outer galaxy.

    New questions emerge on the makeup of space dust

    The results, researchers found, appear to be in conflict with models that expect dust to be more predictably distributed, and to simply exhibit larger grain sizes in areas where more dust resides. But the observations find that the dust properties vary little with the amount of dust, so the models may need to be adjusted to account for a different chemical makeup, for example.

    “In denser regions, it was thought that dust grains will conglomerate, so you have more big grains and fewer small grains,” Schlafly said. But the observations show that dense dust clouds look much the same as less concentrated dust clouds, so that variations in dust properties are not just a product of dust density: “whatever is driving this is not just conglomeration in these regions.”

    He added, “The message to me that we don’t yet know what’s going on. I don’t think the existing (models) are correct, or they are only right at the very highest densities.”

    Accurate measures of the chemical makeup of space dust are important, Schlafly said. “A large amount of chemistry takes place on dust grains, and you can only form molecular hydrogen on the surface of dust grains,” he said—this molecular hydrogen is essential in the formation of stars and planets.


    Access mp4 video here .
    This animation shows a 3-D rendering of dust, as viewed from a 50-parsec (163-light-year) loop around the sun. The animation uses data for hundreds of millions of stars from Pan-STARRS1 and 2MASS surveys, and is made available through a Creative Commons License: https://creativecommons.org/licenses/by-sa/4.0/. (Credit: Gregory M. Green/SLAC, KIPAC)

    Even with a growing collection of dust data, we still have an incomplete dust map of our galaxy. “There is about one-third of the galaxy that’s missing,” Schlafly said, “and we’re working right now on imaging this ‘missing third’ of the galaxy.” A sky survey that will complete the imaging of the southern galactic plane and provide this missing data should wrap up in May, he said.

    APOGEE-2, a follow-up survey to APOGEE, for example, will provide more complete maps of the dust in the local galaxy, and other instruments are expected to provide better dust maps for nearby galaxies, too.

    While the density of dust shrouds our view of the center of the Milky Way, Schlafly said there will be progress, too, in seeing deeper and collecting better dust measurements there as well.

    Researchers at the Harvard-Smithsonian Center for Astrophysics and Harvard University also participated in this work.

    4
    The planned APOGEE-2 survey area overlain on an image of the Milky Way. Each dot shows a position where APOGEE-2 will obtain stellar spectra. (Credit: APOGEE-2)

    APOGEE is a part of the Sloan Digital Sky Survey III (SDSS-III), with participating institutions including Berkeley Lab, the Alfred P. Sloan Foundation, and the National Science Foundation. PanSTARRS1 surveys are supported by the University of Hawaii Institute for Astronomy; the Pan-STARRS Project Office; the Max-Planck Society and its participating institutes in Germany; the Johns Hopkins University; the University of Durham, the University of Edinburgh, and the Queen’s University Belfast in the U.K.; the Harvard-Smithsonian Center for Astrophysics; the Las Cumbres Observatory Global Telescope Network Inc.; and the National Central University of Taiwan. Pan-STARRS is supported by the U.S. Air Force.

    See the full article here .

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  • richardmitnick 7:11 am on October 20, 2015 Permalink | Reply
    Tags: , , , Interstellar dust   

    From Astronomy: “Dust particles from afar” 

    Astronomy magazine

    Astronomy Magazine

    October 19, 2015
    Max Planck Institute for Solar System Research

    1
    The Ulysses mission was a joint project of NASA and ESA. One of the mission’s goals was to measure interstellar dust particles that make their way into the solar system.

    25 years ago, the Ulysses spacecraft was launched into space and now, for the first time, its complete set of measurements of interstellar dust has been analyzed.

    When the solar probe Ulysses embarked on its 19-year-long exploration tour in 1990, the participating researchers turned their attention not only to our Sun, but also to significantly smaller research objects: interstellar dust particles advancing from the depth of space into our solar system. Ulysses was the first mission with the goal to measure these tiny visitors and successfully detected more than 900 of them. Researchers under the leadership of the Max Planck Institute for Solar System Research (MPS) in Germany and the International Space Science Institute (ISSI) in Switzerland presented a comprehensive analysis of this largest data set of interstellar particles in three articles. Their conclusion: Within the solar system, velocity and flight direction of the dust particles can change more strongly than previously thought.

    Our solar system moves perpetually through the Milky Way. For approximately 100,000 years, it has been passing through the Local Interstellar Cloud, a cloud of interstellar matter measuring about 30 light-years in diameter.

    2
    Our solar journey through space is carrying us through a cluster of very low density interstellar clouds. Right now the Sun is inside of a cloud (Local cloud) that is so tenuous that the interstellar gas detected by IBEX is as sparse as a handful of air stretched over a column that is hundreds of light years long. These clouds are identified by their motions, indicated in this graphic with blue arrows.

    NASA IBEX
    NASA/IBEX

    Microscopic dust particles from this cloud make their way into the interior of our solar system. For researchers, they are messengers from the depths of space and provide basic information about our more distant cosmic home. In the past, several spacecraft have identified and characterized these “newcomers.” These spacecraft include Galileo and Cassini, which traveled to the gas planets Jupiter and Saturn, as well as the mission Stardust, which in 2006 returned captured interstellar dust particles to Earth.

    NASA Galileo
    NASA/Galileo

    NASA Cassini Spacecraft
    NASA/Cassini

    NASA Stardust spacecraft
    NASA/Stardust

    “Nevertheless, the data from Ulysses that we have now evaluated [for] the first time in their entirety are unique,” said Harald Krüger from MPS. For 16 years, the instrument examined the stream of particles from outside our solar system almost without interruption. Compared to this, other missions provided only snapshots. “In addition, Ulysses’ observational position was optimal,” said Veerle Sterken from the ISSI. Ulysses is the only spacecraft so far that has left the orbital plane of the planets and has flown over the Sun’s poles. While interplanetary dust produced within our planetary system is concentrated in the orbital plane, interstellar dust can be measured well outside this plane.

    “Under the influence of the Sun and the interplanetary magnetic field, the dust particles change their trajectories,” said Peter Strub from MPS. The gravitational pull and radiation pressure of the Sun, as well as the interplanetary magnetic field within the solar system, change the particles’ flight direction and speed, depending on their masses. “Since the Sun and particularly the interplanetary magnetic field are subject to an approximately twelve-year cycle, only long-term measurements can truly unravel this influence.”

    From the data of the more than 900 particles, the researchers could extract the most detailed information on mass, size, and flight direction of interstellar dust so far. Computer simulations helped to understand the various contributions of the Sun and the interplanetary field and to separate them.

    The study confirms earlier analyses, according to which the interstellar dust always traverses the solar system in approximately the same direction. It corresponds to the direction in which the solar system and the Local Interstellar Cloud move relative to each other. “Minor deviations from this main direction depend on the mass of the particles and the influence of the Sun,” said Strub.

    In 2005, however, a different picture emerged: The far-traveled particles reached the dust detector from a shifted direction. “Our simulations suggest that this effect is likely due to the variations of the solar and interplanetary magnetic field,” said Sterken. “Altered initial conditions within the Local Interstellar Cloud are likely not the reason.”

    The researchers also took a close look at the size and properties of the particles. While the majority of the dust particles has a diameter of between a half and 0.05 micrometer, there are also some remarkably large specimens of several micrometers. “Efforts to characterize the dust outside our solar system with the help of ground-based observations from Earth have not revealed such large sizes,” said Krüger. By contrast, the very small particles which astronomers typically find with telescopes cannot be found in Ulysses measurements. As computer simulations show, compared to their mass, these tiny particles become strongly electrically charged within the solar system and are deflected and thus filtered out of the main interstellar dust stream.

    The simulations also indicate that the exotic dust has a low density and is therefore porous. “Ulysses’ dust detector cannot measure the particles’ inner structure directly,” said Sterken. “However, on the computer we can try out different densities. With porous particles, the observational data can be reconstructed best.”

    The composition of the interstellar particles cannot be determined with the dust instrument onboard Ulysses. However, this is possible with the successor instrument on the Cassini spacecraft developed at the Max Planck Institute for Nuclear Physics in Heidelberg. Its measurements will allow for completely new insights into the origin and evolution of interstellar particles. Measurements with dust detectors thus provide a look into the Local Interstellar Cloud, which can only be studied by observations from Earth otherwise. In the future, dust researchers want to propose space missions to the European Space Agency to investigate interstellar dust.

    See the full article here .

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