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  • richardmitnick 12:37 pm on February 16, 2018 Permalink | Reply
    Tags: AAS NOVA, An Eccentric Planet Skims a Giant Star, , , ,   

    From AAS NOVA: “An Eccentric Planet Skims a Giant Star” 

    AASNOVA

    AAS NOVA

    16 February 2018
    Susanna Kohler

    1
    Artist’s impression of a gas-giant exoplanet passing close to the surface of its host star. The recently discovered exoplanet HD 76020b passes within 4 stellar radii of its host’s surface in its orbit. [ESA, NASA, G. Tinetti (University College London, UK & ESA) and M. Kornmesser (NASA/ESA Hubble)].

    NASA/ESA Hubble Telescope

    As part of a major survey of evolved stars, scientists have discovered the most eccentric planet known to orbit a giant. What can we learn from this unusual object before it’s eventually consumed by its host?

    2
    An example of the diversity of just a few of the planetary systems discovered by the Kepler mission. [NASA].

    Planetary Diversity

    In the early stages of exoplanet science, it was easy to assume that all systems around other stars would be similar to our own solar system: rocky worlds close in, gas giants further out — and all with co-planar, low-eccentricity orbits.

    As we observed the first exoplanets and learned about their properties, however, it quickly became apparent that most other systems don’t resemble our own. The more exoplanets we observe, the more we become aware of the diversity of planetary systems — with planet compositions, masses, and orbits unlike any in the solar system.

    3
    Orbit of HD 76920b, oriented properly and overlaid with the solar system inner planets’ orbits to scale. A comet and asteroid from our solar system are shown as having comparably eccentric orbits. [Wittenmyer et al. 2017]

    Relative Sizes Matter

    Some systems are easier to study than others. Since exoplanet detection and characterization techniques rely on looking for the imprint of planets on stellar signals, systems consisting of a small star and large planet are favored. For this reason, exoplanets orbiting solar-like or dwarf stars are especially well studied — but we don’t have nearly as much information about planets orbiting massive, hot stars.

    To combat this lack of data, several teams have begun surveys particularly targeting evolved, massive stars. One of these is known as the Pan-Pacific Planet Search, a survey that uses the 3.9m Anglo-Australian Telescope in Australia to study the spectra of metal-rich subgiants in the southern hemisphere.


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

    Fresh among the discoveries from this survey is a planet orbiting HD 76920, reported on in a recent publication led by Robert Wittenmyer (University of Southern Queensland and University of New South Wales, Australia).

    4
    Orbital eccentricity vs. planet’s periastron distance for the 116 confirmed planets orbiting giant stars. HD 76920b, the most eccentric of them, is shown with the red dot. [Wittenmyer et al. 2017]

    An Extreme Orbit

    Wittenmyer and collaborators conducted follow-up spectroscopy with two additional telescopes to confirm the properties of HD 76920. The team reports that HD 76920b — a giant planet of perhaps 4 Jupiter masses, with a period of 415 days and an eccentricity of e = 0.86 — is the most eccentric planet ever discovered orbiting a giant star.

    How did HD 76920b achieve its extreme orbit? The go-to explanation for such an orbit is gravitational influence from a distant, massive stellar companion — and yet the authors find no evidence in their observations for a second star in the system. Instead, the team suggests that HD 76020b arrived on its current orbit via planet–planet scattering interactions earlier in the system’s lifetime.

    Toasty Future

    Lastly, Wittenmyer and collaborators use modeling to explore HD 76020b’s future. This planet’s orbit is already so extreme that it nearly skims the surface of its host, dipping to within 4 stellar radii of the star’s surface at its closest approach. The authors show that the planet will be engulfed by its host on a timescale of ~100 million years due to a combination of the star’s expanding radius and tidal interactions.

    Gathering more observations of this extreme planet — and hunting for others like it — will help us to continue to learn about the formation and evolution of the diverse planetary systems our universe houses.

    Citation

    Robert A. Wittenmyer et al 2017 AJ 154 274. http://iopscience.iop.org/article/10.3847/1538-3881/aa9894/meta

    Related journal articles

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    See the full article for further references with links.

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    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

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  • richardmitnick 8:45 am on February 8, 2018 Permalink | Reply
    Tags: A New Look at Speeding Outflows, AAS NOVA, , , , , , , UFOs- ultra-fast outflows   

    From AAS NOVA: ” A New Look at Speeding Outflows” 

    AASNOVA

    AAS NOVA

    7 February 2018
    Susanna Kohler

    1
    Artist’s impression of a galaxy that is releasing material via two strongly collimated jets (shown in red/orange) as well as via wide-angle, ultra-fast outflows (shown in gray/blue). The inset shows a closeup of the accretion disk and central supermassive black hole at the galaxy’s core. [ESA/AOES Medialab].

    The compact centers of active galaxies — known as active galactic nuclei, or AGN — are known for the dynamic behavior they exhibit as the supermassive black holes at their centers accrete matter. New observations of outflows from a nearby AGN provide a more detailed look at what happens in these extreme environments.

    Outflows from Giants

    2
    The powerful radio jets of Cygnus A, which extend far beyond the galaxy. [NRAO/AUI].

    AGN consist of a supermassive black hole of millions to tens of billions of solar masses surrounded by an accretion disk of in-falling matter. But not all the material falling toward the black hole accretes! Some of it is flung from the AGN via various types of outflows.

    The most well-known of these outflows are powerful radio jets — collimated and incredibly fast-moving streams of particles that blast their way out of the host galaxy and into space. Only around 10% of AGN are observed to host such jets, however — and there’s another outflow that’s more ubiquitous.

    Fast-Moving Absorbers

    Perhaps 30% of AGN — both those with and without observed radio jets — host wider-angle, highly ionized gaseous outflows known as ultra-fast outflows (UFOs). Ultraviolet and X-ray radiation emitted from the AGN is absorbed by the UFO, revealing the outflow’s presence: absorption lines appear in the ultraviolet and X-ray spectra of the AGN, blue-shifted due to the high speeds of the absorbing gas in the outflow.

    3
    Quasar PG 1211+143, indicated by the crosshairs at the center of the image, in the color context of its surroundings. [SDSS/S. Karge]

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

    But what is the nature of UFOs? Are they disk winds? Or are they somehow related to the radio jets? And what impact do they have on the AGN’s host galaxy?

    X-ray and Ultraviolet Cooperation

    New observations are now providing fresh information about one particular UFO. A team of scientists led by Ashkbiz Danehkar (Harvard-Smithsonian Center for Astrophysics [CfA]) recently used the Chandra and Hubble space telescopes to make the first simultaneous observations of the same outflow — a UFO in quasar PG 1211+143 — in both X-rays and in ultraviolet.

    Danehkar and collaborators found absorption lines in both sets of data revealing an outflow moving at ~17,000 km/s (for reference, that’s ~5.6% of the speed of light, and more than 1,500 times faster than Elon Musk’s roadster will be traveling at its maximum speed in the orbit it was launched onto yesterday by the Falcon Heavy). Having the information both from the X-ray and the ultraviolet data provides the opportunity to better asses the UFO’s physical characteristics.

    A Link Between Black Holes and Galaxies?

    4
    The X-ray spectrum for PG 1211+143 was obtained by Chandra HETGS (top); the ultraviolet spectrum was obtained by HST-COS G130M (bottom). [Adapted from Danehkar et al. 2018]

    NASA/Chandra Telescope

    NASA/ESA Hubble Telescope

    The authors use models of the data to demonstrate the plausibility of a scenario in which a shock driven by the radio jet gives rise to the fast bulk outflows detected in the X-ray and ultraviolet spectra.

    They also estimate the impact that the outflows might have on the AGN’s host galaxy, demonstrating that the energy injected into the galaxy could be somewhere between 0.02% and 0.6% of the AGN’s total luminosity. At the higher end of this range, this could have an evolutionary impact on the host galaxy, suggesting a possible link between the black hole’s behavior and how its host galaxy evolves.

    In order to draw definitive conclusions, we will need higher-resolution observations that can determine the total size and extent of these outflows. For that, we may need to wait for 2023, when a proposed X-ray spectrometer that might fit the bill, Arcus, may be launched.

    Citation

    Ashkbiz Danehkar et al 2018 ApJ http://iopscience.iop.org/article/10.3847/1538-4357/aaa427/meta

    See the full article here .

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    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 1:10 pm on February 5, 2018 Permalink | Reply
    Tags: AAS NOVA, , , , , Featured Image: Revealing Hidden Objects with Color   

    From AAS NOVA: “Featured Image: Revealing Hidden Objects with Color” 

    AASNOVA

    AAS NOVA

    5 February 2018
    Susanna Kohler

    1
    Stunning color astronomical images can often be the motivation for astronomers to continue slogging through countless data files, calculations, and simulations as we seek to understand the mysteries of the universe. But sometimes the stunning images can, themselves, be the source of scientific discovery. This is the case with the below image of Lynds’ Dark Nebula 673, located in the Aquila constellation, that was captured with the Mayall 4-meter telescope at Kitt Peak National Observatory by a team of scientists led by Travis Rector (University of Alaska Anchorage).


    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA, Altitude 2,120 m (6,960 ft)

    After creating the image with a novel color-composite imaging method that reveals faint Hα emission (visible in red in both images here), Rector and collaborators identified the presence of a dozen new Herbig-Haro objects — small cloud patches that are caused when material is energetically flung out from newly born stars. The image adapted above shows three of the new objects, HH 1187–89, aligned with two previously known objects, HH 32 and 332 — suggesting they are driven by the same source. For more beautiful images and insight into the authors’ discoveries, check out the article linked below!

    2
    Full view of Lynds’ Dark Nebula 673. Click for the larger view this beautiful composite image deserves! [T.A. Rector (University of Alaska Anchorage) and H. Schweiker (WIYN and NOAO/AURA/NSF)]

    Citation

    T. A. Rector et al 2018 ApJ 852 13. http://iopscience.iop.org/article/10.3847/1538-4357/aa9ce1/meta

    Related Journal Articles
    Further references are at the full article complete with links

    See the full article here .

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    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 1:36 pm on January 26, 2018 Permalink | Reply
    Tags: AAS NOVA, Arecibo 327 MHz Drift Pulsar Survey, , , , , Lightweight Double Neutron Star Found, PSR J1411+2551   

    From AAS NOVA: “Lightweight Double Neutron Star Found” 

    AASNOVA

    AAS NOVA

    26 January 2018
    Susanna Kohler

    1
    Artist’s animation of a pair of neutron stars locked in a binary orbit. [NASA/Dana Berry, Sky Works Digital ].

    More than forty years after the first discovery of a double neutron star, we still haven’t found many others — but a new survey is working to change that.

    The Hunt for Pairs

    2
    The observed shift in the Hulse-Taylor binary’s orbital period over time as it loses energy to gravitational-wave emission. [Weisberg & Taylor, 2004].

    In 1974, Russell Hulse and Joseph Taylor discovered the first double neutron star: two compact objects locked in a close orbit about each other. Hulse and Taylor’s measurements of this binary’s decaying orbit over subsequent years led to a Nobel prize — and the first clear evidence of gravitational waves carrying energy and angular momentum away from massive binaries.

    Forty years later, we have since confirmed the existence of gravitational waves directly with the Laser Interferometer Gravitational-Wave Observatory (LIGO). Nonetheless, finding and studying pre-merger neutron-star binaries remains a top priority. Observing such systems before they merge reveals crucial information about late-stage stellar evolution, binary interactions, and the types of gravitational-wave signals we expect to find with current and future observatories.

    Since the Hulse-Taylor binary, we’ve found a total of 16 additional double neutron-star systems — which represents only a tiny fraction of the more than 2,600 pulsars currently known. Recently, however, a large number of pulsar surveys are turning their eyes toward the sky, with a focus on finding more double neutron stars — and at least one of them has had success.

    4
    The pulse profile for PSR J1411+2551 at 327 MHz. [Martinez et al. 2017]

    A Low-Mass Double

    Conducted with the 1,000-foot Arecibo radio telescope in Puerto Rico, the Arecibo 327 MHz Drift Pulsar Survey has enabled the recent discovery of dozens of pulsars and transients. Among them, as reported by Jose Martinez (Max Planck Institute for Radio Astronomy) and coauthors in a recent publication, is PSR J1411+2551: a new double neutron star with one of the lowest masses ever measured for such a system.

    NAIC/Arecibo Observatory, Puerto Rico, USA, at 497 m (1,631 ft)

    Through meticulous observations over the span of 2.5 years, Martinez and collaborators were able to obtain a number of useful measurements for the system, including the pulsar’s period (62 ms), the period of the binary (2.62 days), and the system’s eccentricity (e = 0.17).

    In addition, the team measured the rate of advance of periastron of the system, allowing them to estimate the total mass of the system: M = ~2.54 solar masses. This mass, combined with the eccentricity of the orbit, demonstrate that the companion of the pulsar in PSR J1411+2551 is almost certainly a neutron star — and the system is one of the lightest known to date, even including the double neutron-star merger that was observed by LIGO in August this past year.

    Constraining Stellar Physics

    5
    Based on its measured properties, PSR J1411+2551 is most likely a recycled pulsar in a double neutron-star system. [Martinez et al. 2017].

    The intriguing orbital properties and low mass of PSR J1411+2551 have already allowed the authors to explore a number of constraints to stellar evolution models, including narrowing the possible equations of state for neutron stars that could produce such a system. These constraints will be interesting to compare to constraints from LIGO and Virgo in the future, as more merging neutron-star systems are observed.

    Meanwhile, our best bet for obtaining further constraints is to continue searching for more pre-merger double neutron-star systems like the Hulse-Taylor binary and PSR J1411+2551. Let the hunt continue!

    Citation

    J. G. Martinez et al 2017 ApJL 851 L29. http://iopscience.iop.org/article/10.3847/2041-8213/aa9d87/meta

    Related Journal Articles
    See the full article for further references with links.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 10:55 am on January 25, 2018 Permalink | Reply
    Tags: AAS NOVA, , , , , , Forming Stars Near Our Supermassive Black Hole, Photoevaporative protoplanetary disks,   

    From AAS NOVA: “Forming Stars Near Our Supermassive Black Hole” 

    AASNOVA

    AAS NOVA

    24 January 2018
    Susanna Kohler

    1
    Eleven bipolar outflows — signatures of star formation — have been discovered in the very center of our galaxy, near the supermassive black hole Sgr A*. [Yusef-Zadeh et al. 2017.]

    Is it possible to form stars in the immediate vicinity of the hostile supermassive black hole at the center of our galaxy? New evidence suggests that nature has found a way.

    2
    Infrared view of the central 300 light-years of our galaxy. [Hubble: NASA/ESA/Q.D. Wang; Spitzer: NASA/JPL/S. Stolovy]

    Too Hostile for Stellar Birth?

    Around Sgr A*, the supermassive black hole lurking at the Milky Way’s center, lies a population of ~200 massive, young, bright stars.

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

    Their very tight orbits around the black hole pose a mystery: did these intrepid stars somehow manage to form in situ, or did they instead migrate to their current locations from further out?

    For a star to be born out of a molecular cloud, the self-gravity of the cloud clump must be stronger than the other forces it’s subject to. Close to a supermassive black hole, the brutal tidal forces of the black hole dominate over all else. For this reason, it was thought that stars couldn’t form in the hostile environment near a supermassive black hole — until clues came along suggesting otherwise.

    Science as an Iterative Process

    3
    Very Large Array observations of candidate photoevaporative protoplanetary disks discovered in 2015. [Yusef-Zadeh et al. 2015]

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    Longtime AAS Nova readers might recall that one of our very first highlights on the site, back in August of 2015, was of a study [The Astrophysical Journal Letters] led by Farhad Yusef-Zadeh of Northwestern University. In this study, the authors presented observations of candidate “proplyds” — photoevaporative protoplanetary disks suggestive of star formation — within a few light-years of the galactic center.

    While these observations seemed to indicate that stars might, even now, be actively forming near Sgr A*, they weren’t conclusive evidence. Follow-up observations of these and other signs of possible star formation were hindered by the challenges of observing the distant and crowded galactic center.

    Two and a half years later, Yusef-Zadeh and collaborators are back — now aided by high-resolution and high-sensitivity observations of the galactic center made with the Atacama Large Millimeter-Submillimeter Array (ALMA).

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

    And this time, they consider what they found to be conclusive.

    4
    ALMA observations of BP1, one of 11 bipolar outflows — signatures of star formation — discovered within the central few light-years of our galaxy. BP1 is shown in context at left and zoomed in at right; click for a closer look. [Yusef-Zadeh et al. 2017.]

    Unambiguous Signatures

    The authors’ deep ALMA observations of the galactic center revealed the presence of 11 bipolar outflows within a few light-years of Sgr A*. These outflows appear as approaching and receding lobes of dense gas that were likely swept up by the jets created as stars were formed within the last ~10,000 years. Yusef-Zadeh and collaborators argue that the bipolar outflows are “unambiguous signatures of young protostars.”

    Based on these sources, the authors calculate an approximate rate of star formation of ~5 x 10-4 solar masses per year in this region. This is large enough that such low-mass star formation over the past few billion years could be a significant contributor to the stellar mass budget in the galactic center.

    6
    Locations and orientations of the 11 bipolar outflows found. [Yusef-Zadeh et al. 2017]

    The question of how these stars were able to form so near the black hole remains open. Yusef-Zadeh and collaborators suggest the possibility of events that compress the host cloud, creating star-forming condensations with enough self-gravity to resist tidal disruption by Sgr A*’s strong gravitational forces.

    To verify this picture, the next step is to build a detailed census of low-mass star formation at the galactic center. We’re looking forward to seeing how this field has progressed by the next time we report on it!

    Citation

    F. Yusef-Zadeh et al 2017 ApJL 850 L30. http://iopscience.iop.org/article/10.3847/2041-8213/aa96a2/meta

    Related Journal Articles

    Signatures of Young Star Formation Activity within Two Parsecs of Sgr A* http://iopscience.iop.org/article/10.1088/0004-637X/808/1/97
    Sgr A* and Its Environment: Low-mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow http://iopscience.iop.org/article/10.3847/0004-637X/819/1/60
    Tidal Distortion of the Envelope of an AGB Star IRS 3 near Sgr A* http://iopscience.iop.org/article/10.3847/1538-4357/aa5ea2/
    Radio Continuum Observations of the Galactic Center: Photoevaporative Proplyd-like Objects Near Sgr A* http://iopscience.iop.org/article/10.1088/2041-8205/801/2/L26/
    ALMA Observations of the Galactic Center: SiO Outflows and High-mass Star Formation near Sgr A* http://iopscience.iop.org/article/10.1088/2041-8205/767/2/L32/
    Abundant CH3OH Masers but no New Evidence for Star Formation in GCM0.253+0.016 http://iopscience.iop.org/article/10.1088/0004-637X/805/1/72/

    See the full article here .

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    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 4:14 pm on January 17, 2018 Permalink | Reply
    Tags: AAS NOVA, , , Backyard Telescopes - Citizen Science, , , Watching an Expanding Binary   

    From AAS NOVA: “Backyard Telescopes Watch an Expanding Binary” 

    AASNOVA

    AAS NOVA

    17 January 2018
    Susanna Kohler

    1
    Artist’s illustration of a class of double star called a cataclysmic variable, in which a white dwarf accretes mass from a donor star. [STScI] [Artist not credited.]

    What can you do with a team of people armed with backyard telescopes and a decade of patience? Test how binary star systems evolve under Einstein’s general theory of relativity!

    1
    Diagram of a cataclysmic variable. In an AM CVn, the donor is most likely a white dwarf as well, or a low-mass helium star. [Philip D. Hall]

    Cataclysmic variables — irregularly brightening binary stars consisting of an accreting white dwarf and a donor star — are a favorite target among amateur astronomers: they’re detectable even with small telescopes, and there’s a lot we can learn about stellar astrophysics by observing them, if we’re patient.

    Among the large family of cataclysmic variables is one unusual type: the extremely short-period AM Canum Venaticorum (AM CVn) stars. These rare variables (only ~40 are known) are unique in having spectra dominated by helium, suggesting that they contain little or no hydrogen. Because of this, scientists have speculated that the donor stars in these systems are either white dwarfs themselves or very low-mass helium stars.

    Why study AM CVn stars? Because their unusual configuration allows us to predict the behavior of their orbital evolution. According to the general theory of relativity, the two components of an AM CVn will spiral closer and closer as the system loses angular momentum to gravitational-wave emission. Eventually they will get so close that the low-mass companion star overflows its Roche lobe, beginning mass transfer to the white dwarf. At this point, the orbital evolution will reverse and the binary orbit will expand, increasing its period.

    3
    CBA member Enrique de Miguel, lead author on the study, with his backyard telescope in Huelva, Spain. [Enrique de Miguel]

    Backyard Astronomy Hard at Work

    Measuring the evolution of an AM CVn’s orbital period is the best way to confirm this model, but this is no simple task! To observe this evolution, we first need a system with a period that can be very precisely measured — best achieved with an eclipsing binary system. Then the system must be observed regularly over a very long period of time.

    Though such a feat is challenging, a team of astronomers has done precisely this. The Center for Backyard Astrophysics (CBA) — a group of primarily amateur astronomers located around the world — has collectively observed the AM CVn star system ES Ceti using seven different telescopes over more than a decade. In total, they now have measurements of ES Ceti’s period spanning 2001–2017. Now, in a publication led by Enrique de Miguel (CBA-Huelva and University of Huelva, Spain), the group details the outcomes of their patience.

    Testing the Model

    4
    This O–C diagram of the timings of minimum light relative to a test ephemeris demonstrates that ES Ceti’s orbital period is steadily increasing over time. [de Miguel et al. 2017]

    De Miguel and collaborators find that ES Ceti’s ~10.3-minute orbital period has indeed increased over time — as predicted by the model — at a relatively rapid rate: the timescale for change, described by P/(dP/dt), is ~10 million years. This outcome is consistent with the hypothesis that the mass transfer and binary evolution of such systems is driven by gravitational radiation — marking one of the first such demonstrations with a cataclysmic variable.

    What’s next for ES Ceti? Systems such as this one will make for interesting targets for the Laser Interferometer Space Antenna (LISA; planned for a 2034 launch). The gravitational radiation emitted by AM CVns like ES Ceti should be strong enough and in the right frequency range to be detected by LISA, providing another test of our models for how these star systems evolve.

    Citation

    Enrique de Miguel et al 2018 ApJ 852 19.http://iopscience.iop.org/article/10.3847/1538-4357/aa9ed6/meta

    Related Journal Articles
    Further references with links at the full article.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 8:19 am on January 10, 2018 Permalink | Reply
    Tags: AAS 231: Day 1, AAS NOVA, , , ,   

    From AAS NOVA- “AAS 231: Day 1” 

    AASNOVA

    AAS NOVA

    10 January 2018
    Susanna Kohler

    1
    A stunning infrared view of Jupiter’s south pole, captured by JunoCam, reveals swirling vortices. [NASA/Juno]

    Editor’s Note: This week we’re at the 231st AAS Meeting in National Harbor, MD. Along with a team of authors from Astrobites, we will be writing updates on selected events at the meeting and posting each day. Follow along here or at astrobites.com. The usual posting schedule for AAS Nova will resume next week.

    2
    Astrobites at the undergrad orientation.

    Undergrad Reception

    We loved getting to chat with so many students at the undergrad orientation and reception on Monday night! It was great to hear about your research projects, your goals for the future, and the things you’re passionate about. Keep on being awesome, remember that we want to hear from you about your research, and let us know if there’s anything we can do to help make your entry and progression through the field of astronomy easier.

    Kavli Foundation Lecture: The New Jupiter: Results from the Juno Mission (by Kerry Hensley)

    Scott Bolton of the Southwest Research Institute, who serves as the Principal Investigator of NASA’s Juno mission, reflected that before his graduate student days, it seemed like scientists knew everything; results were reported with so much confidence that it seemed that there were no puzzles left to solve.

    NASA/Juno

    Luckily, that’s far from the case, and the Juno mission is a great example of how new results can topple long-held beliefs and open old topics to new ideas.

    Juno sweeps close to Jupiter once every 53 days (the closest approach is known as perijove), careening just a few thousand kilometers above the cloud tops, traveling pole to pole in about two hours, and steadily marching along in longitude to make a map of the planet. The Juno mission has upended established theories about Jupiter’s atmosphere, interior structure, and magnetic field. For example, there is more lightning at Jupiter than anyone anticipated, especially in the northern hemisphere. White clouds — possibly containing ammonia ice — are ubiquitous. The magnetic field has stronger high-order components than expected, and unexpectedly peaks in strength closer to the equator than the poles. The auroral trace of the volcanic moon Io has a split tail.

    2
    The volcanic surface of Jupiter’s moon Io. Could similar worlds be detectable around exoplanets? Image Credit: NASA

    In addition to these individual discoveries, the Juno mission highlights the fact that the four seemingly separate foci of the mission — origins, interior, atmosphere, and magnetosphere — are more interconnected than originally thought.

    No Juno presentation could be complete without some gorgeous images from JunoCam. (You can access raw JunoCam images and weigh in on where the camera should look next on the JunoCam website!)

    After a long approach to Jupiter, the first look at cloud formations on Jupiter’s poles didn’t disappoint; the south pole is dotted with storms arranged in a pentagon, while the north pole sports a stormy octagon. With each successive perijove bringing new and intriguing results, Jupiter surely has more surprises and more theory-toppling in store. Dr. Bolton closed the session with a message for the current crop of young investigators: Keep working on the theories, and don’t believe your professors!

    Press Conference: Astronomy from the Stratosphere (by Susanna Kohler)

    The first press conference of the meeting kicked off with a look at some of the latest results from the SOFIA mission.


    NASA SOFIA GREAT (German Receiver for Astronomy at Terahertz Frequencies)

    NASA SOFIA High-resolution Airborne Wideband Camera-Plus HAWC+ Camera

    NASA/DLR SOFIA

    SOFIA’s one of my favorite missions — it’s a big plane flying with a garage-door-sized hole in its side for an infrared telescope to point out. What’s not to love? SOFIA’s flights put it above 99% of the Earth’s water vapor, allowing it to make infrared observations that are impossible to make from the ground.

    First up, Kimberly Ennico (NASA Ames) provided a broad overview of SOFIA and its different instruments. SOFIA’s instrumentation is renewable: the team regularly swaps out the instrument that flies on its observing runs. Today’s announcements focused on initial results from the new High-Resolution Airborne Wideband Camera-Plus (HAWC+) instrument and outcomes from the German Receiver for Astronomy at Terahertz Frequencies (GREAT) instrument.

    The HAWC+ instrument provides both far-infrared images and polarimetry data, allowing us to explore the structure of galactic magnetic fields. Enrique Lopez Rodriguez (USRA/SOFIA Science Center) presented the first detections of polarized far-infrared emission from external galaxies, which can be used to infer the large-scale structure of the galactic magnetic fields. In particular, he showed contrasting observations from two different galaxies: M82, a starburst galaxy with large magnetized outflows, and NGC 1068, a massive spiral galaxy in which we can see a magnetized spiral arm.

    B-G Andersson (SOFIA / USRA) gave an overview of some of the theory behind polarization and how it traces magnetic fields. In one model, radiative alignment torque theory, radiation from stars hits dust grains and causes them to spin up. Once the grains are spinning, they interact with magnetic fields, causing the grains to align. Various recent polarization measurements made with SOFIA/HAWC+ seem to support this theory.

    Evidence for this from HAWC+ observations was presented by Fabio Santos (Northwestern University), exploring magnetic fields within galaxies. SOFIA/HAWC+ looked at one of the closest star-forming regions to us, Rho Ophiuchi, and demonstrated that the polarization of the dust grains in this interstellar cloud depends on the density within the cloud. These observations support radiative alignment theory: dust grains on the outskirts of the cloud receive more sunlight and align with magnetic fields more readily, whereas dust grains in the dense cloud interior receive less sunlight and don’t align effectively.

    Elizabeth Tarantino (University of Maryland) rounded out the session with a discussion of what SOFIA/GREAT observations have revealed about how gas cools to form clouds and collapse into the stars we observe today. The incredible resolution of the GREAT spectrometer allows us to make measurements of ionized carbon within star-forming regions in other galaxies. From these measurements, we’ve determined that both atomic and molecular gas contributes to cooling of gas — but in different ratios, depending on how actively the region is forming stars. These observations are crucial for understanding the initial stages of star formation.

    The press release corresponding to this press conference can be found here.

    Plenary Talk: A New Measurement of the Expansion Rate of the Universe, Evidence of New Physics? (by Nora Shipp)

    Adam Riess (Johns Hopkins University) is an expert in precisely measuring the expansion of the universe. In fact, he won a Nobel Prize in 2011 for his role in proving that the universe is not only expanding, but also accelerating in its expansion. These days he works on getting as precise a measurement as possible of the expansion rate in the local universe.

    3
    Turnout for Adam Riess’s talk on the expansion of the universe. [Kevin Marvel/AAS]

    In today’s plenary, Riess discussed the recent tension between the local and distant measurements of the Hubble parameter, H0. Currently there is a 3.4-sigma discrepancy between measurements by Riess’s group of H0 in the local universe and the value determined by the Planck collaboration from the cosmic microwave background (CMB).

    Riess did point out that “it’s not a discovery until 5 sigma,” however 3.4 sigma is certainly interesting, and it sounds like Riess and his group have exciting plans for reducing the errors on their measurements. In fact, Riess said that his goal is to go from 2.4% to 1% errors on the local measurement of H0 within the next 5 years, before the end of HST. An important component of this is incorporating the upcoming proper motion measurements from Gaia.

    Although he’s still working on improving his measurement before fully accepting the H0 tension, Riess made some suggestions as to possible physical explanations for the difference between the local value of H0 and the value determined from the CMB. One possibility is a new species of relativistic particle. Riess said his particle physicist colleagues have no trouble inventing new particles without messing with accepted physics. It is also possible that dark matter isn’t completely collisionless. Interactions between dark-matter particles and radiation in the early universe could lead to differences in H0.

    This is an exciting time for cosmology — it is unexpected results like this discrepancy that reveal the most exciting new insights into our universe!

    You can read more about Riess and his work in an interview by Amber Hornsby.

    Seminar for Science Writers: NASA’s Transiting Exoplanet Survey Satellite (TESS) (by Susanna Kohler)

    In addition to today’s press conferences, the AAS Press Office also hosted a seminar for science writers providing an overview of the upcoming Transiting Exoplanet Survey Satellite (TESS).

    4
    Artist’s illustration of TESS and a transiting exoplanetary system. [MIT]

    The seminar kicked off with a broad look at the TESS mission and its science objectives, provided by George Ricker (Massachusetts Institute of Technology). TESS is slated to launch in March of this year, and it will survey an enormous field of nearby, bright stars, searching for small transiting exoplanets.

    The mission pipeline doesn’t end when TESS discovers objects of interest. Sara Seager (Massachusetts Institute of Technology) described how these objects then get sent on to the TESS follow-up program, which involves hundreds of people around the world. Seager discussed the expected outcomes from TESS for planet discoveries: we may find 70 or so Earths, hundreds of super-Earths, and thousands of sub-Neptunes. The planets discovered with TESS will be orbiting bright stars, making them excellent candidates for follow-up with observatories like the James Webb Space Telescope to explore their atmospheres.

    Padi Boyd (NASA Goddard Space Flight Center) next provided an overview of TESS’s guest investigator program, which just completed peer review of its first proposal cycle, receiving more than 140 proposals from the astronomy community. TESS’s large field of view and high-cadence monitoring lends itself well to a variety of projects, like exploring variability in the stars of the Pleiades, hunting for very early-stage supernovae, and exploring the electromagnetic counterparts to gravitational-wave signals.

    5
    Kepler vs. TESS. [TESS/Elisa Quintana]

    Wrapping up the session, Elisa Quintana (NASA Goddard Space Flight Center) presented on how TESS meshes with other current and future missions. She opened by explaining that TESS isn’t a Kepler replacement: while Kepler’s planet discoveries are on average ~3,000 light-years away, TESS’s will be much loser, at ~300 light-years away on average. TESS’s field of view covers a solid angle that’s ~20x the size of Kepler’s, and the mission’s goal is specifically to hunt for small planets transiting bright stars, which can then be followed up with other current and future telescopes to learn more about the planets’ properties.

    We can look forward to TESS’s launch in the next few months, and we have high hopes for its productivity. Though the nominal mission is only 2 years, Ricker points out that the mission won’t be limited by expendables — it could last several decades in orbit if NASA chooses to continue to fund it! I don’t know about you, but I can’t wait to see what TESS shows us.

    Press Conference: An Alphabet Soup of Science from SDSS/APOGEE/BOSS/MaNGA (by Chris Lovell)

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

    Karen Masters (Astrophysical Research Consortium / SDSS-IV), spokesperson for SDSS-IV, kicked off this press conference on the Sloan Digital Sky Survey with an overview of this fourth iteration of the program, along with a sneak peek at some of the exciting science to come from the next iteration, SDSS-V.

    At the turn of the 19th century, Henrietta Leavitt was studying Cepheid variable stars, which oscillate in size and luminosity with a regular period. She noted that the period was related to the luminosity of the star, which makes these stars great for measuring distances. Sadly, it was only after her death that Leavitt’s contribution was recognised, so to go some way to rectifying this the AAS has recently decided to name this relation the Leavitt law. Much work has been done on the relation since then, but one aspect that is still poorly constrained is how the composition of the star affects the Leavitt law. Katherine Hartman (Pomona College) and Rachel Beaton (Princeton University) presented observations of Cepheids from the Apache Point Galactic Evolution Experiment (APOGEE) survey, and found that measurements of the composition of these stars give consistent results no matter at what point in the cycle they are observed.

    6
    SDSS APOGEE-2

    This is great because it means that, in future, we only need a single observation of a Cepheid to measure its composition, rather than observations over the whole cycle.

    Next up, Robert F. Wilson (University of Virginia) demonstrated the power of combining datasets from different observatories, in this instance measurements of the iron content of stars from the APOGEE instrument combined with exoplanet measurements from the Kepler space telescope. The headline result is that iron-rich stars tend to host planets with shorter periods. A mere 25% increase in the iron content can have a significant effect on the average planetary period, which is intriguing since iron makes up only around 2% of the total mass of your average main-sequence star. The physical mechanism leading to this effect is still uncertain, but Robert proposed a couple of physical explanations: either iron-rich protoplanetary disks lead to formation of planets in tighter orbits, or such systems cause planets to migrate inwards from the outer disk.

    Supermassive black holes lie at the center of almost every galaxy and are thought to have a big impact on the properties of their host galaxies. Measuring their masses throughout cosmic time is therefore key, but incredibly difficult. The next talk from Catherine Grier (Pennsylvania State University) presented results from the BOSS spectrograph that uses a technique called reverberation mapping to measure these masses.

    5
    BOSS. LBNL.

    In short, light from the accreting black hole is seen reflecting off gas in the accretion disk in real time; by studying this light, we can measure its rotation speed, which can be used to infer the mass of the black hole at the center. What’s amazing about this study is that they measure the masses of 849 black holes up to 8 billion years ago — a much bigger sample that probes much further back in time than previous studies.

    Sticking to the theme of supermassive black holes, Karen Masters presented evidence for these objects in non-star-forming dwarf galaxies. Her team used results from the MaNGA survey to observe the distribution of both stars and gas in these quiet, low-mass galaxies, and found an intriguing result: they aren’t moving together. This suggests that something is blowing out the gas, a process known as feedback. Fortunately MaNGA provides another piece to the puzzle: the ionization state of the gas. The ionization state is very high in the outflowing gas in these dwarf galaxies, which suggests the feedback is from the central black hole, rather than stars. Massive black holes were not expected to be an important driver of evolution in low-mass galaxies, so these results present a challenge to theory.

    All of the these press releases are available on the SDSS website.

    Doggett Prize Lecture: Tangible Things of American Astronomy (by Kerry Hensley)

    7
    Sara Schechner

    Astronomers are enamored with immaterial things: photons, magnetic fields, gravitational waves… But our romance with the ethereal is made possible by the material: telescopes and detectors, spacecraft and spectrometers. The careful treatment demanded by delicate and aging astronomical instruments dating back hundreds of years begs the question: why should we care about documenting and preserving obsolete artifacts from the history of astronomy? Dr. Sara Schechner, the curator of the Collection of Historical Scientific Instruments at Harvard University, answered this question with examples of astronomical paraphernalia throughout history and the effect that astronomical events have on society as a whole.

    She noted that outdated instruments and texts can provide insight into how people viewed astronomy in the past. For example, 17th century almanacs and instruments reflected the close kinship of astronomy and religion in that era; astronomy had yet to shed its theological (and sometimes ominous) associations. After the 1684 solar eclipse caused Harvard University’s commencement to be rescheduled (such a bad omen shouldn’t coincide with such an auspicious day), the Harvard president, John Rogers, suddenly died on the day of the eclipse — confirming the astronomical event as a harbinger of doom. By 1759, however, the first predicted return of Halley’s Comet was welcomed with awe.

    8
    The women computers of the Harvard College Observatory.

    Astronomical materials can also reflect other societal shifts. Glass photographic plates evoke memories of the women “computers” of the Harvard College Observatory. Brilliant yet underpaid, the women of the Harvard Observatory classified hundreds of thousands of stars and developed the spectral typing scheme still in use today. Notably, Henrietta Swan Leavitt formulated Leavitt’s Law — a connection between the period of a Cepheid variable’s pulsation and its luminosity — which was used by Edwin Hubble for his discovery of the expansion of the universe. While the work of the Harvard computers advanced the status of women in astronomy, their success didn’t necessarily advance all women; telescope advertisements catering to male astronomers in the 1960s still featured elegant women caressing telescope barrels, showcasing how astronomical materials can reflect attitudes toward women over time.

    Lastly, historical materials can highlight the public’s affinity for astronomy, as well. From amateur astronomers’ efforts to track Earth-orbiting satellites in the 1950s via project Moonwatch to advertisers using the allure of the stars to sell their products, the public’s romance with the stars is well-documented in historical artifacts. Dr. Schechner summarized her talk by saying that learning about our past helps us to live critically in the present; from the public’s reception of science to views toward women, astronomical artifacts are a lens through which we can evaluate societal changes through time.

    You can read more about Schechner and her work in an interview by Caroline Huang.

    RAS Medal Prize Lectureship: The Effect of Non-Linear Structure on Cosmological Observables (by Caroline Huang)

    If you ever take an astronomy course that covers some cosmology, probably one of the first things you’d learn is the cosmological principle — the assumption that matter is distributed isotropically and homogeneously on large scales. A somewhat less general version of this, the Copernican principle, says that we don’t live in a special place in the universe. This is one of the most basic assumptions built into Lambda-CDM, the current leading model that describes the universe.

    The truth is, however, that we don’t live in a perfectly isotropic and homogeneous universe, and that these density perturbations may (or may not) have effects on what we observe when we try to study cosmology. For example, gravitational lensing causes objects behind over-densities to look brighter, and objects behind under-densities to look fainter. The Hubble diagram of Type-Ia supernovae assumes that there is no flux bias from gravitational lensing, but theorists have actually gone back and forth on what sort of effects we might see for more than half a century. In his plenary lecture, Professor Nick Kaiser (University of Hawaii) discussed the difficulties of calculating distance as a function of redshift and the various conclusions cosmologists have come to over time regarding the effect of inhomogeneity on observables like Type-Ia supernovae.

    One way to think of this problem is to consider that our assumptions about isotropy and homogeneity lead us to conclude that a surface of constant redshift would be a sphere. While this true for something that is perfectly isotropic and homogeneous, when you have even small matter under- and over-densities, this is not the case. Since the universe is almost isotropic and homogeneous, there would only be very small perturbations, but that would cause the surface of constant redshift to look something like the surface of a golf ball: almost spherical, but with wrinkles. Since this could cause us to see a flux bias, it could have an effect on things we measure, like the Hubble constant.

    How big are these effects? In the question and answer session, Kaiser said that exactly how large these effects may be is unclear, but that he does think that it’s unlikely that they could explain the difference between the CMB and local Hubble constant measurements.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 1:23 pm on January 5, 2018 Permalink | Reply
    Tags: AAS NOVA, , , , , Galaxies Growing Up on the Edge of the Void, ,   

    From AAS NOVA: “Galaxies Growing Up on the Edge of the Void” 

    AASNOVA

    AAS NOVA

    5 January 2018
    Kerry Hensley

    1
    Light distribution of galaxies generated in the Millennium Simulation. [Max Planck Institute for Astrophysics]

    6

    As effective laboratories for studying the impact of nature on galaxy evolution without the influence of nurture, galaxies in cosmic voids stand alone. What does the dearth of galactic neighbors mean for the morphology of galaxies in cosmic voids?

    Bubbles on a Megaparsec Scale

    Cosmic voids are roughly spherical regions of the cosmic web with lower-than-average density of matter. Though far less populated than dense galaxy clusters, cosmic voids aren’t empty; delicate filaments beaded with galactic pearls cut across their centers, hosting sites of galaxy formation. Because of their low density, voids represent a laboratory within which galaxy properties and evolution are largely determined independent of the influence of neighboring galaxies.

    What is life like for a galaxy in the proximity of a cosmic void? To answer this question, Elena Ricciardelli (École Polytechnique Fédérale de Lausanne, Switzerland) and collaborators analyze the properties of galaxies residing in and around cosmic voids in the nearby (0.01 < z < 0.12) universe.

    Exploring Void Galaxy Morphology

    2
    Fraction of elliptical and spiral galaxies as a function of absolute magnitude in and outside of voids. Voids contain a higher fraction of spirals and a lower fraction of ellipticals than the control sample. [Adapted from Ricciardelli et al. 2017]

    Ricciardelli and collaborators search for the effects cosmic voids have on galaxy morphology by analyzing a sample of galaxies drawn from the Sloan Digital Sky Survey.

    4
    SDSS-III

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

    In total, they consider roughly 6,000 void galaxies and a control sample of 200,000 galaxies from environments of average density. They use the Galaxy Zoo morphological classification tool to identify the spiral and elliptical galaxies in their sample.

    Lastly, they calculate the fraction of spiral and elliptical galaxies present in their void and control samples, while correcting for the fact that faint spiral galaxies are more likely to be misclassified as ellipticals than their bright counterparts. They find that galaxies near voids are more likely to be spirals than galaxies far from voids, indicating that nearby cosmic voids have a marked effect on galaxy evolution.

    Life in and Around the Void

    5
    Clockwise from top left: elliptical fraction, spiral fraction, star-forming fraction, and stellar mass for galaxies in and around voids out to a redshift of z = 0.065. The dashed line marks the median value for each variable for the control galaxies. The dotted lines indicate the boundaries of the zone of influence of the voids. [Ricciardelli et al. 2017]

    The authors find that not only does a galaxy’s distance from the void affect its properties, but the size of the adjacent void has a measurable impact as well. Within the voids, they find a larger fraction of spiral galaxies compared to the control sample. This effect persists after removing the mass bias due to the fact that the low-density void environments are preferentially populated with low-mass galaxies; for a given mass or absolute magnitude, voids contain a higher proportion of spiral galaxies than the control sample.

    This effect is not limited to the volume within the voids; Ricciardelli and collaborators find that the properties of void-adjacent galaxies are altered out to twice the radius of the void, with a higher fraction of spiral galaxies found closer to voids. The size of a void has an effect as well; larger-than-average voids harbor a larger fraction of spiral galaxies than smaller-than-average voids.

    The authors caution that this final result depends on how the voids are defined; the effect disappears if the voids are defined using their dynamical properties rather than their size. Future research will help further disentangle the role that cosmic voids play in galaxy evolution.

    Citation

    Elena Ricciardelli et al 2017 ApJL 846 L4. http://iopscience.iop.org/article/10.3847/2041-8213/aa84ad/meta

    Related Journal Articles
    Further references with links at the full article.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 2:49 pm on December 21, 2017 Permalink | Reply
    Tags: AAS NOVA, , , , , SDSS -IV, Selections from 2017: Mapping the Universe with SDSS-IV   

    From AAS NOVA: “Selections from 2017: Mapping the Universe with SDSS-IV” 

    AASNOVA

    AAS NOVA

    20 December 2017
    Susanna Kohler

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

    Published June 2017

    Main takeaway:

    The incredibly prolific Sloan Digital Sky Survey has provided photometric observations of around 500 million objects and spectra for more than 3 million objects. The survey has now entered its fourth iteration, SDSS-IV, with the first public data release made in June 2016. A publication led by Michael Blanton (New York University) describes the facilities used for SDSS-IV, its science goals, and its three core programs.

    Why it’s interesting:

    Since data collection began in 2000, SDSS has been one of the premier surveys providing imaging and spectroscopy for objects in both the near and distant universe. SDSS has measured spectra not only for the stars in our own Milky Way, but also for galaxies that lie more than 7 billion light-years distant — making it an extremely useful and powerful tool for mapping our universe.
    What SDSS-IV is looking for:

    2
    SDSS image of an example MaNGA target galaxy (left), with some of the many things we can learn about it shown in the right and bottom panels: stellar velocity dispersion, stellar mean velocity, stellar population age, metallicity, etc. [Blanton et al. 2017]

    SDSS-IV contains three core programs:

    Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) provides high-resolution near-infrared spectra of hundreds of thousands of Milky-Way stars with the goal of improving our understanding of the history of the Milky Way and of stellar astrophysics.
    Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) obtains spatially resolved spectra for thousands of nearby galaxies to better understand the evolutionary histories of galaxies and what regulates their star formation.
    Extended Baryon Oscillation Spectroscopic Survey (eBOSS) maps the galaxy, quasar, and neutral gas distributions at redshifts out to z = 3.5 to better understand dark matter, dark energy, the properties of neutrinos, and inflation.

    Citation

    Michael R. Blanton et al 2017 AJ 154 28. https://doi.org/10.3847/1538-3881/aa7567

    Related Journal Articles

    See the full article for further references with links.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 11:05 am on December 14, 2017 Permalink | Reply
    Tags: AAS NOVA, and Fall, , , , Churn, , Star-Forming Clouds Feed   

    From AAS NOVA: “Star-Forming Clouds Feed, Churn, and Fall” 

    AASNOVA

    AAS NOVA

    13 December 2017
    Susanna Kohler

    1
    This false-color infrared image from Spitzer shows a molecular cloud, a cloud that forms in the interstellar medium and becomes the birthplace of new stars. A new study explores the physics shaping these environments. [NASA/JPL-Caltech/Harvard-Smithsonian]

    Molecular clouds, the birthplaces of stars in galaxies throughout the universe, are complicated and dynamic environments. A new series of simulations has explored how these clouds form, grow, and collapse over their lifetimes.

    1
    This composite image shows part of the Taurus Molecular Cloud. [ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey]

    ESO/APEX high on the Chajnantor plateau in Chile’s Atacama region, at an altitude of over 4,800 m (15,700 ft)

    Stellar Birthplaces

    Molecular clouds form out of the matter in between stars, evolving through constant interactions with their turbulent environments. These interactions — taking the form of accretion flows and surface forces, while gravity, turbulence, and magnetic fields interplay — are thought to drive the properties and evolution of the clouds.

    Our understanding of the details of this process, however, remains fuzzy. How does mass accretion affect these clouds as they evolve? What happens when nearby supernova explosions blast the outsides of the clouds? What makes the clouds churn, producing the motion within them that prevents them from collapsing? The answers to these questions can tell us about the gas distributed throughout galaxies, revealing information about the environments in which stars form.

    2
    A still from the simulation results showing the broader population of molecular clouds that formed in the authors’ simulations, as well as zoom-in panels of three low-mass clouds tracked in high resolution. [Ibáñez-Mejía et al. 2017]

    Models of Turbulence

    In a new study led by Juan Ibáñez-Mejía (MPI Garching and Universities of Heidelberg and Cologne in Germany, and American Museum of Natural History), scientists have now explored these questions using a series of three-dimensional simulations of a population of molecular clouds forming and evolving in the turbulent interstellar medium.

    The simulations take into account a whole host of physics, including the effects of nearby supernova explosions, self-gravitation, magnetic fields, diffuse heating, and radiative cooling. After looking at the behavior of the broader population of clouds, the authors zoom in and explore three clouds in high-resolution to learn more about the details.

    Watching Clouds Evolve

    Ibáñez-Mejía and collaborators find that mass accretion occurring after the molecular clouds form plays an important role in the clouds’ evolution, increasing the mass available to form stars and carrying kinetic energy into the cloud. The accretion process is driven both by background turbulent flows and gravitational attraction as the cloud draws in the gas in its nearby environment.

    3
    Plots of the cloud mass and radius (top) and mass accretion rate (bottom) for one of the three zoomed-in clouds, shown as a function of time over the 10-Myr simulation. [Adapted from Ibáñez-Mejía et al. 2017]

    The simulations show that nearby supernovae have two opposing effects on a cloud. On one hand, the blast waves from supernovae compress the envelope of the cloud, increasing the instantaneous rate of accretion. On the other hand, the blast waves disrupt parts of the envelope and erode mass from the cloud’s surface, decreasing accretion overall. These events ensure that the mass accretion rate of molecular clouds is non-uniform, regularly punctuated by sporadic increases and decreases as the clouds are battered by nearby explosions.

    Lastly, Ibáñez-Mejía and collaborators show that mass accretion alone isn’t enough to power the turbulent internal motions we observe inside molecular clouds. Instead, they conclude, the cloud motions must be primarily powered by gravitational potential energy being converted into kinetic energy as the cloud contracts.

    Citation

    Juan C. Ibáñez-Mejía et al 2017 ApJ 850 62. http://iopscience.iop.org/article/10.3847/1538-4357/aa93fe/meta

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