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  • richardmitnick 9:02 am on August 4, 2017 Permalink | Reply
    Tags: , , , , , Globular clusters   

    From astrobites: “The Generation Game” 

    Astrobites bloc

    Astrobites

    Aug 3, 2017
    Paddy Alton

    Title: Young LMC clusters: the role of red supergiants and multiple stellar populations in their integrated light and CMDs
    Authors: Randa S. Asa’d, Alexandre Vazdekis, Miguel Cervi ̃no, Noelia E. D. No ̈el, Michael A. Beasley, Mahmoud Kassab
    First Author’s Institution: American University of Sharjah, UAE
    1
    Status: Accepted for publication in MNRAS, open access

    An introduction to globular clusters

    Stars are a sociable bunch, by and large. They don’t like to be alone: some hang out in pairs, or sometimes in small groups of three or four. Others still are extreme extroverts, keeping company with hundreds of thousands of other stars, for example in densely packed globular clusters (GCs) – see figure 1 for an example.

    This isn’t be the first article on star clusters to feature on astrobites – and you can be pretty sure it won’t be the last. After all, we’ve been studying them since the seventeenth century and people are still publishing papers about them!

    2
    Figure 1. The globular cluster M80 – hundreds of thousands of stars bound together by gravity, 28000 light-years from Earth. (credit: Hubble Heritage Team)

    NASA/ESA Hubble Telescope

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 1:14 pm on March 11, 2016 Permalink | Reply
    Tags: , , , Globular clusters   

    From CfA: “The Distribution of Globular Clusters” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    Omega Centauri globular cluster
    Omega Centauri globular cluster.ESO

    Globular clusters are gravitationally bound, roughly spherical ensembles of stars. Some contain as many as a million stars, and their sizes are as small as only tens of light-years in diameter. Globular clusters are typically located in the outer regions (the halos) of galaxies, and our Milky Way galaxy has about two hundred of them. Astronomers are interested in globular clusters in part because they are home to many of the oldest known stars, but also because of their locations in the halos.

    Collisions between galaxies are commonplace, and the locations of globular clusters can offer evidence of these encounters because they are strongly affected by such interactions. During a collision, a galaxy can grow by absorbing or merging with its neighbor, and some models even predict that clusters form during these interactions. Moreover, it is possible that in a merger large numbers of globular clusters originally belonging to a smaller galaxy may be captured by a larger one. The distribution of globular clusters around a galaxy holds therefore clues to their origins and to the history of the host galaxy. There is an additional benefit: Standard models of cosmology make predictions for how galaxies form and evolve that depend on fundamental properties of the universe like the amounts of dark matter and dark energy. The properties of globular cluster, mostly determined by the accretion histories and mergers of their host galaxies, also reflect the values of these fundamental cosmic quantities.

    CfA astronomers Pepi Fabbiano and Raffaele D’Abrusco (now at the University of Naples), together with their colleagues, studied the globular clusters in the core of the Fornax Cluster of galaxies, a complex of over fifty galaxies located about sixty million light-years away. Using optical and near-infrared images taken with the European Southern Observatory’s Very Large Survey Telescope, the scientists cataloged over three thousand globular clusters throughout Fornax (about two-thirds of them previously unidentified), providing a rich resource for structural analyses.

    ESO VLTI image
    VLT

    They find clear evidence for an active history of galaxy-galaxy interactions, for example in bridges between galaxies, elongated groupings, and other unusual arrangements. While these results by themselves do not refine the values of any cosmological parameters, they are consistent with the standard models, and help complete the evolutionary description of this massive nearby cluster of galaxies.
    Reference(s):

    The Extended Spatial Distribution of Globular Clusters in the Core of the Fornax Cluster, R. D’Abrusco, M. Cantiello, M. Paolillo, V. Pota, N.R. Napolitano, L. Limatola, M. Spavone, A. Grado, E. Iodice, M. Capaccioli1, R. Peletier, G. Longo, M. Hilker, S. Mieske, E.K. Grebel, T. Lisker, C. Wittmann, G. van de Ven & G. Fabbiano, ApJ 819, L31, 2016.

    See the full article here .

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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 7:39 pm on January 28, 2016 Permalink | Reply
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    From Northwestern: “Stellar Parenting: Making New Stars By ‘Adopting’ Stray Cosmic Gases” 

    Northwestern U bloc

    Northwestern University

    January 27, 2016
    No writer credit found

    Globular cluster star field
    Using observations by the Hubble Space Telescope, an international research team, including astronomers from Northwestern and the Kavli Institute for Astronomy and Astrophysics, has for the first time found young populations of stars within globular clusters that have apparently developed courtesy of star-forming gas flowing in from outside of the clusters themselves. Credit: ESA/Hubble and NASA. Acknowledgement: Judy Schmidt (geckzilla.com)

    Among the most striking objects in the universe are glittering, dense swarms of stars known as globular clusters. Astronomers had long thought globular clusters formed their millions of stars in bulk at around the same time, with each cluster’s stars having very similar ages, much like twin brothers and sisters. Yet recent discoveries of young stars in old globular clusters have scrambled this tidy picture.

    Instead of having all their stellar progeny at once, globular clusters can somehow bear second or even third sets of thousands of sibling stars. Now a new study led by researchers at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University, and including astronomers at Northwestern University, the Adler Planetarium and the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), might explain these puzzling, successive stellar generations.

    Using observations by the Hubble Space Telescope, the research team has for the first time found young populations of stars within globular clusters that have apparently developed courtesy of star-forming gas flowing in from outside of the clusters themselves.

    NASA Hubble Telescope
    NASA/ESA Hubble

    This method stands in contrast to the conventional idea of the clusters’ initial stars shedding gas as they age in order to spark future rounds of star birth.

    The study will be published in the Jan. 28 issue of the journal Nature.

    “This study offers new insight on the problem of multiple stellar populations in star clusters,” said study lead author Chengyuan Li, an astronomer at KIAA and NAOC who also is affiliated with the Chinese Academy of Sciences’ Purple Mountain Observatory.

    “Our study suggests the gaseous fuel for these new stellar populations has an origin that is external to the cluster, rather than internal.”

    In a manner of speaking, globular clusters appear capable of “adopting” baby stars — or at least the material with which to form new stars — rather than creating more “biological” children as parents in a human family might choose to do.

    “Our explanation that secondary stellar populations originate from gas accreted from the clusters’ environments is the strongest alternative idea put forward to date,” said Richard de Grijs, also an astronomer at KIAA and Chengyuan’s Ph.D. advisor. “Globular clusters have turned out to be much more complex than we once thought.”

    Globular clusters are spherical, densely packed groups of stars orbiting the outskirts of galaxies. Our home galaxy, the Milky Way, hosts several hundred. Most of these local, massive clusters are quite old, however, so the KIAA-led research team turned their attention to young and intermediate-aged clusters found in two nearby dwarf galaxies, collectively called the Magellanic Clouds.

    Specifically, the researchers used Hubble observations of the globular clusters NGC 1783 and NGC 1696 in the Large Magellanic Cloud, along with NGC 411 in the Small Magellanic Cloud.

    Scientists routinely infer the ages of stars by looking at their colors and brightnesses. Within NGC 1783, for example, Li, de Grijs and colleagues identified an initial population of stars aged 1.4 billion years, along with two newer populations that formed 890 million and 450 million years ago.

    What is the most straightforward explanation for these unexpectedly differing stellar ages? Some globular clusters might retain enough gas and dust to crank out multiple generations of stars, but this seems unlikely, said study co-author Aaron M. Geller of Northwestern University and the Adler Planetarium in Chicago.

    “Once the most massive stars form, they are like ticking time bombs, with only about 10 million years until they explode in powerful supernovae and clear out any remaining gas and dust,” Geller said. “Afterwards, the lower-mass stars, which live longer and die in less violent ways, may allow the cluster to build up gas and dust once again.”

    The KIAA-led research team proposes that globular clusters can sweep up stray gas and dust they encounter while moving about their respective host galaxies. The theory of newborn stars arising in clusters as they “adopt” interstellar gases actually dates back to a 1952 paper. More than a half-century later, this once speculative idea suddenly has key evidence to support it.

    In the study, the KIAA researchers analyzed Hubble observations of these star clusters, and then Geller and his Northwestern colleague Claude-André Faucher-Giguère carried out calculations that show this theoretical explanation is possible in the globular clusters this team studied.

    “We have now finally shown that this idea of clusters forming new stars with accreted gas might actually work,” de Grijs said, “and not just for the three clusters we observed for this study, but possibly for a whole slew of them.”

    Future studies will aim to extend the findings to other Magellanic Cloud as well as Milky Way globular clusters.

    The research is funded, in part, by the National Science Foundation.

    The title of the paper is Formation of new stellar populations from gas accreted by massive young star clusters.

    In addition to Li, de Grijs, Geller and Faucher-Giguère, other authors of the paper include Licai Deng, Yu Xin and Yi Hu, all from the Chinese Academy of Science’s National Astronomical Observatories in Beijing.

    Geller, an NSF Astronomy and Astrophysics Postdoctoral Fellow, and Faucher-Giguère, an assistant professor of physics and astronomy, are in Northwestern’s Weinberg College of Arts and Sciences and are members of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Geller also is currently at the Adler Planetarium in Chicago and previously was with the department of astronomy and astrophysics at the University of Chicago at the time of the study.

    See the full article here .

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    Northwestern South Campus
    South Campus

    On May 31, 1850, nine men gathered to begin planning a university that would serve the Northwest Territory.

    Given that they had little money, no land and limited higher education experience, their vision was ambitious. But through a combination of creative financing, shrewd politicking, religious inspiration and an abundance of hard work, the founders of Northwestern University were able to make that dream a reality.

    In 1853, the founders purchased a 379-acre tract of land on the shore of Lake Michigan 12 miles north of Chicago. They established a campus and developed the land near it, naming the surrounding town Evanston in honor of one of the University’s founders, John Evans. After completing its first building in 1855, Northwestern began classes that fall with two faculty members and 10 students.
    Twenty-one presidents have presided over Northwestern in the years since. The University has grown to include 12 schools and colleges, with additional campuses in Chicago and Doha, Qatar.

    Northwestern is recognized nationally and internationally for its educational programs.

     
  • richardmitnick 6:56 pm on January 7, 2016 Permalink | Reply
    Tags: , , , Globular clusters   

    From CfA: “Globular Clusters Could Nurture Interstellar Civilizations” 

    Smithsonian Astrophysical Observatory
    Smithsonian Astrophysical Observatory

    January 6, 2016
    Christine Pulliam
    Media Relations Manager
    Harvard-Smithsonian Center for Astrophysics
    617-495-7463
    cpulliam@cfa.harvard.edu

    Temp 1

    Globular star clusters are extraordinary in almost every way. They’re densely packed, holding a million stars in a ball only about 100 light-years across on average. They’re old, dating back almost to the birth of the Milky Way. And according to new research, they also could be extraordinarily good places to look for space-faring civilizations.

    “A globular cluster might be the first place in which intelligent life is identified in our galaxy,” says lead author Rosanne DiStefano of the Harvard-Smithsonian Center for Astrophysics (CfA).

    DiStefano presented this research today in a press conference at a meeting of the American Astronomical Society.

    Our Milky Way galaxy hosts about 150 globular clusters, most of them orbiting in the galactic outskirts. They formed about 10 billion years ago on average. As a result, their stars contain fewer of the heavy elements needed to construct planets, since those elements (like iron and silicon) must be created in earlier generations of stars. Some scientists have argued that this makes globular cluster stars less likely to host planets. In fact, only one planet has been found in a globular cluster to date.

    However, DiStefano and her colleague Alak Ray (Tata Institute of Fundamental Research, Mumbai) argue that this view is too pessimistic. Exoplanets have been found around stars only one-tenth as metal-rich as our Sun. And while Jupiter-sized planets are found preferentially around stars containing higher levels of heavy elements, research finds that smaller, Earth-sized planets show no such preference.

    “It’s premature to say there are no planets in globular clusters,” states Ray.

    Another concern is that a globular cluster’s crowded environment would threaten any planets that do form. A neighboring star could wander too close and gravitationally disrupt a planetary system, flinging worlds into icy interstellar space.

    However, a star’s habitable zone – the distance at which a planet would be warm enough for liquid water – varies depending on the star. While brighter stars have more distant habitable zones, planets orbiting dimmer stars would have to huddle much closer. Brighter stars also live shorter lives, and since globular clusters are old, those stars have died out. The predominant stars in globular clusters are faint, long-lived red dwarfs. Any potentially habitable planets they host would orbit nearby and be relatively safe from stellar interactions.

    “Once planets form, they can survive for long periods of time, even longer than the current age of the universe,” explains DiStefano.

    So if habitable planets can form in globular clusters and survive for billions of years, what are the consequences for life should it evolve? Life would have ample time to become increasingly complex, and even potentially develop intelligence.

    Such a civilization would enjoy a very different environment than our own. The nearest star to our solar system is four light-years, or 24 trillion miles, away. In contrast, the nearest star within a globular cluster could be about 20 times closer – just one trillion miles away. This would make interstellar communication and exploration significantly easier.

    “We call it the ‘globular cluster opportunity,'” says DiStefano. “Sending a broadcast between the stars wouldn’t take any longer than a letter from the U.S. to Europe in the 18th century.”

    “Interstellar travel would take less time too. The Voyager probes are 100 billion miles from Earth, or one-tenth as far as it would take to reach the closest star if we lived in a globular cluster.

    NASA Voyager 1
    Voyager 1

    That means sending an interstellar probe is something a civilization at our technological level could do in a globular cluster,” she adds.

    The closest globular cluster to Earth is still several thousand light-years away, making it difficult to find planets, particularly in a cluster’s crowded core. But it could be possible to detect transiting planets on the outskirts of globular clusters. Astronomers might even spot free-floating planets through gravitational lensing, in which the planet’s gravity magnifies light from a background star.

    A more intriguing idea might be to target globular clusters with SETI search methods, looking for radio or laser broadcasts.

    Allen Telescope Array
    SETI Institute’s Allen Telescope Array

    The concept has a long history: In 1974 astronomer Frank Drake used the Arecibo radio telescope to broadcast the first deliberate message from Earth to outer space. It was directed at the globular cluster Messier 13 (M13).

    Arecibo
    Arecibo radio telescope

    See the full article here .

    Please help promote STEM in your local schools.

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    About CfA

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy. The long relationship between the two organizations, which began when the SAO moved its headquarters to Cambridge in 1955, was formalized by the establishment of a joint center in 1973. The CfA’s history of accomplishments in astronomy and astrophysics is reflected in a wide range of awards and prizes received by individual CfA scientists.

    Today, some 300 Smithsonian and Harvard scientists cooperate in broad programs of astrophysical research supported by Federal appropriations and University funds as well as contracts and grants from government agencies. These scientific investigations, touching on almost all major topics in astronomy, are organized into the following divisions, scientific departments and service groups.

     
  • richardmitnick 8:52 am on March 20, 2015 Permalink | Reply
    Tags: , , , Globular clusters   

    From CfA: “Measuring Galaxy Evolution with Globular Clusters” 

    Smithsonian Astrophysical Observatory
    Smithsonian Astrophysical Observatory

    March 20, 2015
    No Writer Credit

    1
    The galaxy NGC 4365 in the Virgo supercluster of galaxies, showing its many globular clusters (most of the more than one hundred dots in this image are actually globular star clusters). A new study of over seven thousand globular clusters around ten Virgo galaxies finds that they are often gathered into distinct groupings whose shapes reflect the formation of the clusters and the histories of the galaxies. NASA/HST and ESO VLT

    NASA Hubble Telescope
    NASA/ESA Hubble

    ESO VLT Interferometer
    ESO/VLT

    Globular clusters are gravitationally bound ensembles of stars, as many as a million stars in some cases, grouped in roughly spherical clusters with diameters as small as only tens of light-years. Globular clusters are typically located in the outer regions (the halos) of galaxies; the Milky Way galaxy has about two hundred globular clusters orbiting it. Astronomers are interested in globular clusters in part because they are home to many of the oldest known stars, but also because of their locations in the halos. Collisions between galaxies are commonplace, and globular clusters may provide fossil evidence of these encounters because they are strongly affected by such interactions. During a collision, a galaxy can grow by absorbing or merging with its neighbor, and some models predict that clusters form during these interactions. Moreover, it is possible that in a merger large numbers of globular clusters originally belonging to a smaller galaxy may be captured by the larger galaxy. In any case, the distribution of globular clusters around a galaxy holds clues to their origins and the history of its host galaxy.

    The Virgo Cluster of galaxies, containing between one and two thousand galaxies, is located about fifty-four thousand light-years away in the direction of the constellation of Virgo.

    2

    The ten brightest galaxies of the Virgo Cluster alone contain 7053 detected globular clusters. CfA astronomers Raffaele D’Abrusco, Pepi Fabbiano, and Andreas Zezas carefully examined this set of globular clusters looking for information about the history of these galaxies. In a new paper, they report discovering distinctive structures among the globular cluster systems, meaning that the globular clusters around these galaxies are not distributed symmetrically. Their configurations often take shapes ranging from roughly linear to circular, with some more complex shapes as well. The scientists found 229 such structures in this subsample, forty-two of them classified as being medium or large and stretching over as much as seventy-five light-years. The elongated structures tend to be aligned with an axis of the host galaxy, as would be expected if a merger were responsible.

    The scientists argue that these structures are indeed the remnants of galaxies that were accreted in the past, and among other things they estimate limits on the masses of these parent galaxies. Computer simulations provide some rough level of agreement. The authors note that with more detailed computations, these structures offer a powerful new tool to advance the study of galaxy evolution.

    See the full article here.

    Please help promote STEM in your local schools.

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    About CfA

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy. The long relationship between the two organizations, which began when the SAO moved its headquarters to Cambridge in 1955, was formalized by the establishment of a joint center in 1973. The CfA’s history of accomplishments in astronomy and astrophysics is reflected in a wide range of awards and prizes received by individual CfA scientists.

    Today, some 300 Smithsonian and Harvard scientists cooperate in broad programs of astrophysical research supported by Federal appropriations and University funds as well as contracts and grants from government agencies. These scientific investigations, touching on almost all major topics in astronomy, are organized into the following divisions, scientific departments and service groups.

     
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