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  • richardmitnick 6:22 am on September 10, 2016 Permalink | Reply
    Tags: , , , Star Formation   

    From CfA: “Statistical Properties of Star Formation in Molecular Clouds” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    September 2, 2016
    No writer credit

    1
    An image of the giant molecular cloud complex, Mon R2. A far-infrared study of the numbers of dense clumps across this cloud has found statistical correlations that depend on the relative dominance of turbulence versus gravity. Adam Block, Mt. Lemmon SkyCenter, U. Arizona

    Stars form within the dense regions of diffuse molecular clouds, but the physical processes that determine the locations, rate, and efficiency of star formation are poorly understood. Recent thinking envisions an approximately two-step process: first, a network of dense filaments form due to large-scale turbulence and then fragmentation into cores occurs as gravity starts to dominate. In the dense gas the structure formation is affected by motions induced primarily by three processes: supersonic turbulence, self-gravity, and magnetic fields, although the role of each process is still debated.

    Recent research suggests that the statistical properties of the column density (for example, the numbers of cores denser than a fixed value) offer a key to unraveling structure formation mechanisms. Computer simulations of star formation show that if the number of dense cores having any particular density value is random, then turbulence is probably dominant, but if denser cores tend to cluster non-randomly, then gravity is probably dominant.

    CfA astronomers Scott Wolk and Phil Myers and their colleagues have analyzed the Herschel Space Observatory’s five wavelength far infrared images of the giant molecular cloud Mon R2, looking for evidence of non-randomness in core formation.

    ESA/Herschel
    ESA/Herschel

    The far infrared images can be combined to map the dust densities (or more precisely, the dust column densities). The astronomers found that in lower density regions — in this Mon R2 characterized by a clear density cut-off — the distribution was indeed random, signaling the dominance of turbulence over most of the giant cloud. However, in the denser regions, self-gravity appears to be predominant. Moreover, the deviation from randomness can be quantified, and the scientists found that the measure of the variation correlates with the numbers of young stars seen in the vicinity. They even discovered some instances when a second value of this measure was needed for the densest regions. Although relating these findings to more fundamental issues like the star formation efficiency will require additional research, the new paper demonstrates that far infrared imaging techniques can provide critical insights into early stages of star formation.

    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.

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  • richardmitnick 7:30 am on March 29, 2016 Permalink | Reply
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    From ESA: “Star-forming ribbon” 

    ESA Space For Europe Banner

    European Space Agency

    29/03/2016
    M. Juvela (U. Helsinki, Finland)

    1

    Star formation is taking place all around us. The Milky Way is laced with clouds of dust and gas that could become the nursery of the next generation of stars. Thanks to ESA’s Herschel space observatory, we can now look inside these clouds and see what is truly going on.

    ESA/Herschel
    ESA/Herschel

    It may seem ironic but when searching for sites of future star formation, astronomers look for the coldest spots in the Milky Way. This is because before the stars ignite the gas that will form their bulk must collapse together. To do that, it has to be cold and sluggish, so that it cannot resist gravity.

    As well as gas, there is also dust. This too is extremely cold, perhaps just 10–20 degrees above absolute zero. To optical telescopes it appears completely dark, but the dust reveals itselfat far-infrared wavelengths.

    One of the surprises is that the coldest parts of the cloud form filaments that stretch across the warmer parts of the cloud. This image shows a cold cloud filament, known to astronomers as G82.65-2.00. The blue filament is the coldest part of the cloud and contains 800 times as much mass as the Sun. The dust in this filament has a temperature of –259ºC. At this low temperature, if the filament contains enough mass it is likely that this section will collapse into stars.

    This image is colour-coded so that the longest infrared wavelength, corresponding to the coldest region, is shown in blue, and the shortest wavelength, corresponding to slightly warmer dust, is shown in red.

    The field of view on display here is a little more than two times the width of the full Moon. It is one of 116 regions of space observed by Herschel as part of the Galactic Cold Cores project. Each field was chosen because ESA’s cosmic microwave background mapper, Planck, showed that these regions of the galaxy possessed extremely cold dust.

    ESA/Planck
    ESA/Planck

    See the full article here .

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

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  • richardmitnick 11:06 am on March 3, 2016 Permalink | Reply
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    From ALMA: “ALMA Spots Baby Star’s Growing Blanket” 

    ALMA Array

    ALMA

    01 March 2016
    Valeria Foncea

    Education and Public Outreach Officer

    Joint ALMA Observatory

    Santiago, Chile

    Tel: +56 2 467 6258

    Cell: +56 9 75871963
    Email: vfoncea@alma.cl

    Masaaki Hiramatsu

    Education and Public Outreach Officer, NAOJ Chile
    Observatory
Tokyo, Japan

    Tel: +81 422 34 3630

    E-mail: hiramatsu.masaaki@nao.ac.jp

    Richard Hook
    Public Information Officer, ESO

    Garching bei München, Germany

    Tel: +49 89 3200 6655

    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    Charles E. Blue
    Public Information Officer
    National Radio Astronomy Observatory
    Charlottesville, Virginia, USA
    Tel: +1 434 296 0314
    Cell: +1 202 236 6324
    E-mail: cblue@nrao.edu

    Protoplanetary disc from ALMA
    Typical protoplanetary disc. ALMA

    Researchers using the Atacama Large Millimeter/submillimeter Array (ALMA) have made the first direct observations delineating the gas disk around a baby star from the infalling gas envelope. This finding fills an important missing piece in our understanding of the early phases of stellar evolution.

    A team led by Yusuke Aso (a graduate student at the University of Tokyo) and Nagayoshi Ohashi (a professor at the Subaru Telescope, National Astronomical Observatory of Japan) observed the baby star named TMC-1A located 450 light years away from us, in the constellation Taurus (the Bull). TMC-1A is a protostar, a star still in the process of forming. Large amounts of gas still surround TMC-1A.

    Stars form in dense gas clouds. Baby stars grow by taking in the surrounding gas, like a fetus receiving nutrition from the mother’s placenta. In this process, gas cannot flow directly into the star. Instead it first accumulates and forms a disk around the star, and then the disk feeds into the star. However, it is still unknown when in the process of star formation this disk appears and how it evolves. Lack of sensitivity and resolution in radio observations has made it difficult to observe these phenomena.

    “The disks around young stars are the places where planets will be formed,” said Aso, the lead author of the paper that appeared in the Astrophysical Journal. “To understand the formation mechanism of a disk, we need to differentiate the disk from the outer envelope precisely and pinpoint the location of its boundary.”

    Using ALMA, the team directly observed the boundary between the inner rotating disk and the outer infalling envelope with high accuracy for the first time. Since gas from the outer envelope is continuously falling into the disk, it had been difficult to identify the transition region in previous studies. In particular, the tenuous but high speed gas in rotating disks is not easy to see. But ALMA has enough sensitivity to highlight such a component and illustrate the speed and distribution of gas in the disk very precisely. This enabled the team to distinguish the disk from the infalling envelope.

    The team found that the boundary between the disk and envelope is located 90 astronomical units from the central baby star. This distance is three times longer than the orbit of Neptune, the outermost planet in the Solar System. The observed disk obeys Keplerian rotation: the material orbiting closer to the central star revolves faster than material further out.

    The high-sensitivity observations provided other important information about the object. From detailed measurement of the rotation speed, the research team could calculate that the mass of the baby star is 0.68 times the mass of the Sun. The team also determined the gas infall rate to be a millionth of the mass of the Sun per year, with a speed of 1 km per second. Gravity causes gas to fall towards the central baby star, but the measured speed is much less than the free-fall speed. Something must be slowing the gas down. The researchers suspect that a magnetic field around the baby star might be what is slowing the gas.

    “We expect that as the baby star grows, the boundary between the disk and the infall region moves outward,” said Aso. “We are sure that future ALMA observations will reveal such evolution.”

    These observational results were published as Aso et al. ALMA Observations of the Transition from Infall Motion to Keplerian Rotation around the Late-phase Protostar TMC-1A in the Astrophysical Journal.

    See the full article here .

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    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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  • richardmitnick 12:33 pm on February 25, 2016 Permalink | Reply
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    From NAOJ/Subaru: “Subaru-HiCIAO Spots Young Stars Surreptitiously Gluttonizing Their Birth Clouds” 

    NAOJ

    NAOJ

    February 24, 2016
    No writer credit found

    An international team led by researchers at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) has used a new infrared imaging technique to reveal dramatic moments in star and planet formation. These seem to occur when surrounding material falls toward very active baby stars, which then feed voraciously on it even as they remain hidden inside their birth clouds. The team used the HiCIAO (High Contrast Instrument for the Subaru Next-Generation Adaptive Optics) camera on the Subaru 8-meter Telescope in Hawaii to observe a set of newborn stars. The results of their work shed new light on our understanding of how stars and planets are born.

    NAOJ Subaru HiCIAO Camera
    NAOJ Subaru HiCIAO Camera

    NAOJ Subaru star and planet formation
    A schematic diagram of star and planet formation based on Green (2001). (Credit: ASIAA)

    The Process of Star Birth

    Stars are born when giant clouds of dust and gas collapse under the pull of their own gravity. Planets are believed to be born at nearly the same time as their stars in the same disk of material. However, there are still a number of mysteries about the detailed physical processes that occur as stars and planets form.

    The giant collections of dust and gas where stars form are called “molecular clouds” because they are largely made up of molecules of hydrogen and other gases. Over time, gravity in the densest regions of these clouds gathers in the surrounding gas and dust, via a process called “accretion”. It is often assumed that this process is smooth and continuous.

    However, this steady infall explains only a small fraction of the final mass of each star that is born in the cloud. Astronomers are still working to understand when and how the remaining material is gathered in during the process of star and planet birth.

    A few stars are known to be associated with a sudden and violent “feeding” frenzy from inside their stellar nursery. When they gluttonize on the surrounding material, their visible light increases very suddenly and dramatically, by a factor of about a hundred. These sudden flareups in brightness are called “FU Orionis outbursts” because they were first discovered toward the star FU Orionis.

    Not many stars are found to be associated with such outbursts — only a dozen out of thousands. However, astronomers speculate that all baby stars may experience such outbursts as part of their growth. The reason we only see FU Ori outbursts toward a few newborn stars is simply because they are relatively quiet most of the time.

    One key question about this mysterious facet of starbirth is “What are the detailed physical mechanisms of these outbursts?” The answer lies in the region surrounding the star. Astronomers know the optical outbursts are associated with a disk of material close to the star, called the accretion disk. It becomes significantly brighter when the disk gets heated up to temperatures similar to those of lava flows here on Earth (around 700 to 1200 C or 1292 to 2182 F) like the one flowing from Kilauea volcano area in the island of Hawaii. Several processes have been proposed as triggers for such outbursts and astronomers have been investigating them over the past few decades.

    Finding a Mechanism for FU Ori Outbursts

    An international team lead by Drs. Hauyu Baobab Liu and Hiro Takami, two researchers at ASIAA, used a novel imaging technique available at the Subaru Telescope to tackle this issue. The technique – imaging polarimetry with coronagraphy – has tremendous advantages for imaging the environments in the disks. In particular, its high angular resolution and sensitivity allow astronomers to “see” the light from the disk more easily. How does this work?

    Circumstellar material is a mixture of gas and dust. The amount of dust is significantly smaller than the amount of gas in the cloud, so it has little effect on the motion of the material. However, dust particles scatter (reflect) light from the central star, illuminating all the surrounding material. The HiCIAO camera mounted on the Subaru 8.2-meter telescope, one of the largest optical and near-infrared (NIR) telescopes in the world, is well-suited to observing this dim circumstellar light. It successfully allowed the team to observe four stars experiencing FU Ori outbursts.

    Details of Four FU Ori Outbursts

    The team’s target stars are located 1,500-3,500 light-years from our solar system. The images of these outbursting newborns were surprising and fascinating, and nothing like anything previously observed around young stars. Three have unusual tails. One shows an “arm”, a feature created by the motion of material around the star. Another shows odd spiky features, which may result from an optical outburst blowing away circumstellar gas and dust. They show a messy and chaotic environment, much like a human baby eating food.

    To understand the structures observed around these newborn stars, theorists on the team extensively studied one of several mechanisms proposed to explain FU Ori outbursts. It suggests that gravity in circumstellar gas and dust clouds creates complicated structures that look like cream stirred into coffee. These oddly shaped collections of material fall onto the star at irregular intervals. The team also conducted further computer simulations for scattered light from the outburst. Although more simulations are required to match the simulations to the observed images, these images show that this is a promising explanation for the nature of FU Ori outbursts.

    Studying these structures may also reveal how some planetary systems are born. Astronomers know some exoplanets (planets around other stars) are found extremely far away from their central stars. Sometimes they orbit more than a thousand times the distance between the Sun and Earth, and significantly larger than the orbit of Neptune (which is about 30 times the distance between the Sun and Earth). These distances are also much larger than orbits explained by standard theories of planet formation. Simulations of complicated circumstellar structures like the ones seen in the HiCIAO views also predict that some dense clumps in the material may become gas giant planets. This would naturally explain the presence of exoplanets with such large orbits.

    In spite of these exciting new results, there is a still great deal more work to do to understand the mechanisms of star and planet birth. More detailed comparisons between observation and theory are needed. Further observations, particularly with the Atacama Large Millimeter/Submillimeter Array, will take our gaze more deeply into circumstellar gas and dust clouds.

    ALMA Array
    ALMA

    The array allows observations of the surrounding dust and gas with unprecedented angular resolution and sensitivity. Astronomers are also planning to construct telescopes significantly larger than Subaru in the coming decades – including the Thirty Meter Telescope (TMT) and the European Extremely Large Telescope [E-ELT].

    TMT
    TMT

    ESO E-ELT
    E-ELT

    These should allow detailed studies of regions very close to newborn stars.

    Note:

    Astronomical Unit (AU) is a unit of distance. 1 AU corresponds to the average distance between the Earth and the Sun.

    Paper and Research Team:

    This research was supported by the Ministry of Science and Technology (MoST) of Taiwan (Grant Nos. 103-2112-M-001-029 and 104-2119-M-001-018). E.I.V. acknowledges the support from the Russian Ministry of Education and Science Grant 3.961.2014/K and RFBR grant 14-02-00719. R.D. was supported by Hubble Fellowship. M.M.D. acknowledges support from the Submillimeter Array through an SMA Postdoctoral Fellowship.
    These observational results were published by Liu et al. as Circumstellar Disks of the Most Vigorously Accreting Young Stars in the Science Advances on February 5, 2016.

    This research was conducted by:

    Hauyu Baobab Liu (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan / European Southern Observatory, EU)
    Michihiro Takami (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan)
    Tomoyuki Kudo (Subaru Telescope, National Astronomical Observatory of Japan, USA)
    Jun Hashimoto (National Astronomical Observatory of Japan, Japan)
    Ruobing Dong (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan / Hubble Fellow / Department of Astronomy, UC Berkeley, USA)
    Eduard I. Vorobyov (Department of Astrophysics, University of Vienna, Austria / Research Institute of Physics, Southern Federal University, Russia)
    Tae-Soo Pyo (Subaru Telescope, National Astronomical Observatory of Japan, USA)
    Misato Fukagawa (National Astronomical Observatory of Japan, Japan)
    Motohide Tamura (National Astronomical Observatory of Japan, Japan / Department of Astronomy, Graduate School of Science, The University of Tokyo, Japan)
    Thomas Henning (Max-Planck-Institut für Astronomie, Germany)
    Michael M. Dunham (Harvard-Smithsonian Center for Astrophysics, USA)
    Jennifer Karr (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan)
    Nobuhiko Kusakabe (National Astronomical Observatory of Japan, Japan)
    Toru Tsuribe (College of Science, Ibaraki University, Japan)

    See the full article here .

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

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

    NAOJ Subaru Telescope

    NAOJ Subaru Telescope interior
    Subaru

    ALMA Array
    ALMA

    sft
    Solar Flare Telescope

    Nobeyama Radio Telescope - Copy
    Nobeyama Radio Observatory

    Nobeyama Solar Radio Telescope Array
    Nobeyama Radio Observatory: Solar

    Misuzawa Station Japan
    Mizusawa VERA Observatory

    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

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

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

     
  • richardmitnick 12:38 am on February 16, 2016 Permalink | Reply
    Tags: , , , , Star Formation   

    From CfA: “Star Formation in Distant Galaxy Clusters” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    February 12, 2016
    No writer credit found

    The first stars appeared about one hundred million years after the big bang, and ever since then stars and star formation processes have lit up the cosmos, producing heavy elements, planets, black holes, and arguably all of the other interesting characters in today’s universe. When the universe was about three billion years old (currently it is 13.8 billion years old), star formation activity peaked at rates about ten times above current levels. Why this happened, and whether the physical processes back then were different from those today or just more active (and why), are among the most pressing questions in astronomy, and are among the drivers of future facilities from large ground-based telescopes to NASA’s James Webb Space Telescope.

    NASA Webb telescope annotated
    NASA/ESA/CSA Webb

    The local environment of a galaxy plays a critical role in regulating its star formation. Studies in the local universe find, for example, that in dense galaxy cluster environments (a cluster can contain as many as a thousand galaxies) the star formation is suppressed, consistent with the idea that interactions and other mechanisms are stripping away the raw material for new stars (the neutral gas) and sweeping it into the intergalactic environment. In the distant universe, however, the picture is murkier, and some studies have even found the opposite, perhaps explaining in part the higher star formation rates then. Although studies of individual galaxies in the early universe have made progress, it is usually because these are extremely active and luminous galaxies. A cluster of galaxies, by contrast, might host one or two bright members but most of the membership is ordinary, faint, and hard to study. In fact, clusters are usually even difficult to identify.

    CfA astronomers Matt Ashby, Brian Stalder, Tony Stark and their team of colleagues have studied star formation in very dense galaxy clusters in the early universe, dating from about six billion years after the big bang, in an effort to resolve the issue of star formation in cluster environments. They started with a sample of ultraluminous galaxies from the earlier, three billion year-old epoch (or even younger), discovered with the South Pole Telescope.

    South Pole Telescope
    South Pole Telescope

    These more distant galaxies were detected in part because their light has been gravitationally lensed by closer clusters; that is how the team was able to locate these clusters in the first place. Knowing where to look, the scientists used infrared data from the Herschel and Planck Space Telescopes (and others) to examine the faint infrared signals from the clusters.

    ESA Herschel
    ESA/Herschel

    ESA Planck
    ESA/Planck

    That light is presumed to come from star formation, allowing the scientists to determine its level of activity and properties. Their principal finding is that the star formation activity is actually enhanced, not suppressed, in these clusters, up to several thousand new stars are forming per year in these clusters over-and-above the normal levels for these sets of galaxies. They also find that star formation is active out to the edges of clusters, perhaps fifteen million light-years across, and that the effect of this faint infrared emission needs to be taken into consideration in studies of origins of the cosmic background.
    Reference(s):

    Probing star formation in the dense environments of z ∼ 1 lensing haloes aligned with dusty star-forming galaxies detected with the South Pole Telescope, N. Welikala, M. Bethermin, D. Guery, M. Strandet, K. A. Aird, M. Aravena, M. L. N. Ashby, M. Bothwell, A. Beelen, L. E. Bleem, C. de Breuck, M. Brodwin, J. E. Carlstrom, S. C. Chapman, T. M. Crawford, H. Dole, O. Dore, W. Everett, I. Flores-Cacho, A. H. Gonzalez, J. Gonz´alez-Nuevo, T. R. Greve, B. Gullberg, Y. D. Hezaveh, G. P. Holder, W. L. Holzapfel, R. Keisler, G. Lagache, J. Ma, M. Malkan, D. P. Marrone, L. M. Mocanu, L. Montier, E. J. Murphy, N. P. H. Nesvadba, A. Omont, E. Pointecouteau, J. L. Puget, C. L. Reichardt, K. M. Rotermund, D. Scott, P. Serra, J. S. Spilker, B. Stalder, A. A. Stark, K. Story, K. Vanderlinde, J. D. Vieira and A. Weiß, MNRAS 455, 1629, 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 5:26 pm on January 3, 2016 Permalink | Reply
    Tags: , , Star Formation   

    From Astronomy Now: “The great galaxy shutdown” 

    Astronomy Now bloc

    Astronomy Now

    2 January 2016
    Keith Cooper

    Temp 1
    The spiral galaxy M94, imaged by the Hubble Space Telescope in 2015, is still forming stars, but in many other galaxies star formation has stopped. Image: ESA/Hubble and NASA.

    NASA Hubble Telescope
    NASA/ESA Hubble

    Stars are not forming in the same great numbers that they did billions of years ago and several advances in 2015 have shed light on why this downturn took place.

    It seems that there is more than one way to shut down a galaxy, but the reduction in cold molecular gas available to form stars is always the key. The environment that a galaxy exists in can also play a role. In galaxy clusters the gas may just be too hot, according to a study published in the 5 March edition of the journal Nature. An alternative theory, published in the 14 May issue of Nature, suggests hot gas could also ‘strangle’ a galaxy falling into a cluster by cutting it off from intergalactic sources of cold gas.

    The black holes that lie within galaxies are also a powerful influence. A report published in the 26 March issue of Nature connected a powerful wind of radiation from an active black hole in a galaxy 2.3 billion light years away to the outflows of what would otherwise be gas used to form stars seen streaming away from the galaxy. Another study, this time in the 17 April edition of the journal Science, used the Hubble Space Telescope and the ESO/Very Large Telescope [VLT] in Chile to find evidence to back up the black hole scenario, in that galaxies seem to shut down their star formation from the inside-out.

    ESO VLT Interferometer
    ESO/VLT

    Meanwhile, from the pages of the 20 August issue of the Monthly Notices of the Royal Astronomical Society,came the suggestion that many spiral galaxies have morphed into elliptical galaxies over the past eight billion years or so, mostly through a process of mergers that use up much of the available star-forming disc. Afterwards, there’s little gas left to form new stars.

    See the full article here .

    Another view of M94

    Temp 2
    Beautiful spiral galaxy M94 (Messier 94) lies a mere 15 million light-years distant in the northern constellation of the hunting dogs, Canes Venatici. A popular target for astronomers, the brighter inner part of the face-on galaxy is about 30,000 light-years across. Traditionally, deep images have been interpreted as showing M94’s inner spiral region surrounded by a faint, broad ring of stars. But a new multi-wavelength investigation has revealed previously undetected spiral arms sweeping across the outskirts of the galaxy’s disk, an outer disk actively engaged in star formation. At optical wavelengths, M94’s outer spiral arms are followed in this remarkable discovery image, processed to enhance the outer disk structure. Background galaxies are visible through the faint outer arms, while the three spiky foreground stars are in our own Milky Way galaxy. R Jay Gabany (Blackbird Observatory.)

    Blackbird Observatory
    Blackbird Observatory

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  • richardmitnick 11:20 am on September 19, 2015 Permalink | Reply
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    From Astronomy Now: “Dust discs of nearby red dwarfs could reveal planetary secrets” 

    Astronomy Now bloc

    Astronomy Now

    1
    Artist’s depiction of a dusty ‘circumstellar’ disc orbiting a young red dwarf star. Illustration credit: NASA/JPL-Caltech/T. Pyle (SSC).

    An accidental find of a collection of young red dwarf stars close to our solar system could give us a rare glimpse of slow-motion planet formation. Astronomers from The Australian National University (ANU) and University of New South Wales (UNSW), Canberra found large discs of dust around two of the stars, telltale signs of planets in the process of forming.

    “We think the Earth and all the other planets formed from discs like these so it is fascinating to see a potential new solar system evolving,” said the lead researcher Dr. Simon Murphy, from the ANU Research School of Astronomy and Astrophysics.

    “However, other stars of this age usually don’t have discs any more. The red dwarf discs seem to live longer than those of hotter stars like the Sun. We don’t understand why,” said Dr. Murphy.

    2
    Artist’s conception of an exoplanet orbiting a cool red dwarf star like TWA 35/36 in the study. Illustration credit: David A. Aguilar (CfA/Harvard-Smithsonian).

    The discovery of objects like these two challenges current theories about planet formation, said co-author Professor Warrick Lawson from UNSW Canberra. “It suggests the planet forming process can endure a lot longer than previously thought,” he said.

    The red dwarfs may also host planets that have already formed from the dusty discs, Dr. Murphy added. “I think a lot of telescopes will be turned toward them in the next few years to look for planets,” he said.

    The giveaway that the red dwarfs had discs around them was an unusual glow in the infrared spectrum of the stars.

    Although the discs were not observed directly, Dr. Murphy said such close red dwarfs offered a good chance of catching a rare direct glimpse of a disc, or even a planet, by employing specialised telescopes. “Because they are fainter than other stars and there is not as much glare, young red dwarfs are ideal places to directly pick out recently formed planets,” he said.

    3
    The location of one of the red dwarfs, called 2M1239-5702, is near Gacrux — a red giant star at the top of the Southern Cross. Image credit: Akira Fujii.

    Professor Lawson said the ability to detect these dim stars has improved dramatically in recent decades, revealing a wealth of information. “Less than 20 years ago, the notion that the nearest part of the galaxy would be littered with young stars was a completely novel one,” he said.

    “Most of these objects lie in the southern sky and thus are best accessed by telescopes in the Southern Hemisphere, including those operated by ANU and Australia more broadly,” added Professor Lawson.

    The research is published in the Monthly Notices of the Royal Astronomical Society.

    See the full article here .

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  • richardmitnick 2:29 pm on September 14, 2015 Permalink | Reply
    Tags: , , , Star Formation   

    From AAS NOVA: ” Forming Stars From the Cosmic Web” 

    AASNOVA

    Amercan Astronomical Society

    14 September 2015
    Susanna Kohler

    1
    Simulation of the cosmic web. A recent study has found evidence of star formation in galaxies as a result of cold gas flowing in from the cosmic web. [Springel et al. 2005/The Millennium Simulation Project]

    Scientists have recently identified a connection between metal-poor regions in a set of dwarf galaxies and bursts of star-formation activity within them. These observations provide long-awaited evidence supporting predictions of how stars formed in the early universe and in dwarf galaxies today.

    Metal-Poor Clues

    The primary driver of star formation over cosmic history is thought to be the accretion onto galaxies of cold gas streaming from the cosmic web. The best way to confirm this model would be to observe a cloud of cosmic gas flowing into an otherwise-quiescent galaxy and launching a wave of star formation. But because cold gas doesn’t emit much radiation, it’s difficult to detect directly.

    Now, a team of scientists have found a clever way around this problem: they searched galaxies for a correlation between areas of active star formation and metal-poor regions. Why? Because metal-poor regions could be a smoking gun indicating a recently accreted cloud of cold gas from the cosmic web.

    2
    Distribution of metallicity along the major axis of one of the target galaxies. The red bar in the top image shows the position of the spectrograph slit along the galaxy, with the arrow showing the direction of growing distance in the plot below. The plot shows the metallicity variation (red symbols) and star-formation rate (blue line) along the galaxy’s major axis. The metallicity drop coincides with the brightest knot of the galaxy. [Sánchez Almeida et al. 2015]

    Impacting Clouds

    The authors of this study, led by Jorge Sánchez Almeida (Instituto de Astrofísica de Canarias and University of La Laguna, Spain), used the Great Canary Telescope to obtain high-quality spectra of ten dwarf galaxies with especially low average metallicities.

    Great Canary Telescope
    Great Canary Telescope Interior
    Great Canary Telecope

    They aligned the spectrograph slit along the major axes of the galaxies in order to measure abundances as a function of position within each galaxy.

    The team found that, in nine out of the ten cases, the galaxies displayed sharp drops (by factors of 3–10) in metallicity along a portion of their lengths. The metallicity drops corresponded to bright knots representing starburst regions, in which surface star formation rates are larger than that of the rest of the galaxy by factors of 10–100.

    The authors conclude that in these galaxies, a cold cosmic gas cloud with low metallicity impacted the galaxy’s outer region. This impact caused the cloud to compress, triggering the star formation we now observe. At the same time, the gas from the cloud diluted the region’s metallicity, resulting in the low abundances now measured. The authors determine that the cloud impacted within the last 100 Myr — otherwise enough time would have passed for the gas to mix azimuthally as it rotated around the galaxy.

    Citation

    J. Sánchez Almeida et al 2015 ApJ 810 L15. doi:10.1088/2041-8205/810/2/L15

    See the full article here .

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  • richardmitnick 9:12 am on May 22, 2015 Permalink | Reply
    Tags: , , , Star Formation   

    From CAASTRO: “Old, gas-rich galaxies likely had early star formation boom” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    22 May 2015
    No Writer Credit

    The most massive stars (with masses up to a hundred times the mass of our sun) explode as supernovae at the end of their life and release huge amounts of energy and material into their neighbourhoods. These phenomena are so energetic that they can alter the rate of star formation and impact the chemical composition of galaxies since heavy elements are synthesised in the interior of stars via nuclear fusion reactions. Astronomical observations suggest that many supernova explosions adding up can halt the formation of new stars and expel enriched gas out of galaxies. Indirect observations seem also to suggest that a supermassive black hole resides at the centre of virtually all galaxies. We still do not know how these objects formed but we believe that their masses are greater than 1 million solar masses and the energy emitted by gas falling into them could produce outflows at even higher velocity than the supernova driven outflows (thousands of km/s).

    1

    In a recent University of Melbourne led paper, Dr Edoardo Tescari and colleagues present the first results of the CAASTRO supported AustraliaN GADGET-3 early Universe Simulations project, or ANGUS for short. The team ran numerical simulations of the Universe in its early stages (up to 13 billion years ago) to study formation and evolution of galaxies and how they interact with their environment. They focused in particular on the so called “feedback” effects associated with the formation of stars and supermassive black holes at the centre of galaxies.

    Including the effects of both, supernovae and supermassive black holes, their simulations tested different configurations of feedback (early/late and weak/strong). The researchers found that efficient feedback at early times is needed to reproduce new observations of the global amount of star formation in the “young” Universe. They propose the following theoretical scenario to explain their results: galaxies that formed 13 billion years ago contained a lot of gas that was quickly converted into many stars. The back-reaction of the star formation processes (i.e. feedback) has since suppressed subsequent star formation especially in low mass galaxies.

    Publication details:
    E. Tescari, A. Katsianis, S. Wyithe, K. Dolag, L. Tornatore, P. Barai, M. Viel, S. Borgani in MNRAS (2014) Simulated star formation rate functions at z ~ 4 – 7, and the role of feedback in high-z galaxies

    See the full article here.

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    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

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  • richardmitnick 12:02 pm on September 5, 2014 Permalink | Reply
    Tags: , , , , , Star Formation   

    From Astrobiology: “Evidence of forming planet discovered 335 light years from Earth” 

    Astrobiology Magazine

    Astrobiology Magazine

    Sep 5, 2014
    See quotes from co-authors below

    An international team of scientists led by a Clemson University astrophysicist has discovered new evidence that planets are forming around a star about 335 light years from Earth.

    The team found carbon monoxide emission that strongly suggests a planet is orbiting a relatively young star known as HD100546. The candidate planet is the second that astronomers have discovered orbiting the star.

    Theories of how planets form are well-developed. But if the new study’s findings are confirmed, the activity around HD100546 would mark one of the first times astronomers have been able to directly observe planet formation happening.

    New discoveries from the star could allow astronomers to test their theories and learn more about the formation of solar systems, including our own, said Sean Brittain, an associate professor of astronomy and astrophysics at Clemson.

    “This system is very close to Earth relative to other disk systems,” he said. “We’re able to study it at a level of detail that you can’t do with more distant stars. This is the first system where we’ve been able to do this.

    “Once we really understand what’s going on, the tools that we are developing can then be applied to a larger number of systems that are more distant and harder to see.”

    For more than a decade, the team has focused some of Earth’s most powerful telescopes on a disk-shaped cloud of gas and dust that surrounds HD100546.

    sd
    Sean Brittain works at his computer in Kinard Hall. Credit: Clemson University

    The star is about 2.5 times larger and 30 times brighter than the sun, Brittain said. It’s in the constellation Musca, or The Fly, and can only be seen from the Southern Hemisphere.

    Brittain made three trips to Chile as far back as 2003 to gather data for the research. He used telescopes at the Gemini Observatory and the European Southern Observatory.

    The new planet astronomers believe they have found what would be an uninhabitable gas giant at least three times the size of Jupiter, Brittain said. Its distance from the star would be about the same distance that Saturn is from the sun.

    The team used a technique called “spectro-astrometry,” which enables small changes in the position of the carbon monoxide emission to be measured. A source of excess carbon monoxide emission was detected that appears to vary in position and velocity. The varying position and velocity are consistent with orbital motion around the star.

    The favored hypothesis is that emission comes from a “circumplanetary” disk of gas orbiting a giant planet, Brittain said.

    “Another possibility is that we’re seeing the wake from tidal interactions between the object and the circumstellar disk of gas and dust orbiting the star,” he said.

    Members of the team reported their findings in a recent edition of The Astrophysical Journal.

    The name of the article is NIR Spectroscopy of the HAeBe Star 100546. III. Further Evidence of an Orbiting Companion? The authors are Brittain; John S. Carr of the Naval Research Laboratory in Washington, D.C.; Joan R. Najita of the National Optical Astronomy Observatory in Tucson, Arizona; and Sascha P. Quanz and Michael R. Meyer, both of ETH Zurich, Institute for Astronomy.

    The next step in the study would be to take a picture using the new high-contrast imagers on the European Southern Observatory’s Very Large Telescope or Gemini South Telescope, Brittain said.

    ESO VLT Interferometer
    ESO VLT Interior
    ESO/VLT

    Gemini South telescope
    Gemini South Interior
    Gemini South

    Circumplanetary disks of rotating viscous material have long been thought to surround giant planets at birth, but little observational evidence for their existence has been found outside the solar system. They are believed to be the birthplaces of planetary moons, such as those that orbit Jupiter.

    “There are different models of circumplanetary disks, but we’ve never seen one,” Brittain said.

    Disks form in all kinds of environments in the universe as a consequence of a fundamental law of physics known as “the conservation of angular momentum.”

    The law states that a spinning object will keep spinning just as hard unless a force acts on it. If the object gets smaller, it will spin faster and vice versa.

    The same principle that causes ice skaters to speed up when they pull in their arms and legs also causes disks to form around objects as material falls on to them. This is true for disks around supermassive black holes at the center of galaxies, circumstellar disks around young stars and circumplanetary disks around forming planets.

    Mark Leising, the chair of Clemson’s astronomy and astrophysics department, said Brittain’s work will raise the department’s international profile.

    “I congratulate Dr. Brittain and his team on their excellent work,” Leising said. “Astronomers are now very good at finding already-formed planets around many nearby stars, but it has been difficult to watch the planets in the process of forming.

    “Using very clever techniques and the most advanced telescopes on Earth, they have accomplished that. It’s great to see our faculty working with leading institutions around the world to make discoveries at the forefront of astronomy.”

    Evidence of another planet forming was previously found farther out from HD100546. A blob of gas and dust that has grown denser over time was discovered about the distance Pluto is from the sun.

    “It is in the process of collapsing,” Brittain said. “Maybe in a million years you’ll have another planet and disk.”

    The outer candidate planet would be a gas giant planet about the size of Jupiter. It’s among the evidence that points to multiple and perhaps sequential planet formation.

    A team that was led by Quanz and included Meyer reported the discovery of the outer candidate planet last year in The Astrophysical Journal Letters.

    Quotes from the co-authors:

    John Carr, Naval Research Laboratory

    “The possibility that we have caught a planet in the act of formation is an exciting result. What makes this work doubly interesting is the evidence that we are seeing gas as it swirls around and flows onto the planet to feed its continuing growth. This could be observational confirmation for the existence of circumplanetary disks that are predicted to surround giant planets at birth. An important point in this research is that we were able to track the object over a period of several years and show that it is indeed orbiting around the star as expected for a planet.”

    Joan Najita (520-318-8416), National Optical Astronomy Observatory

    “We stumbled onto this project when a paper in the literature predicted that forming planets would induce a detectable signature in the CO emission from disks. Because we had studied HD100546 for many years, we could immediately test this idea in one system. It was uncanny that the first system we studied actually showed the signature of orbital motion. It’s not every day that you look for something exciting and actually find it! But the test of any interpretation is to make a prediction and see if it is verified. We are thrilled that the data recently reported confirm the signature of orbital motion that we predicted based on our earlier work.”

    Sascha P. Quanz (+41 (0)78 9565274), ETH Zurich, Institute for Astronomy

    “The HD100546 system keeps being a treasure for planet formation research! Not only does this star host one of the best studied circumstellar gas and dust disks, but now we have direct evidence for two young planets orbiting this two-and-a-half solar mass star. If our interpretation is correct, these two planets have different evolutionary stages with the inner one being older than the outer one. This means that for the first time we can now study directly different phases of gas giant planet formation – and this around a single star!”

    Contact information: sascha.quanz@astro.phyz.ethz.ch

    Michael R. Meyer (+41 (0)79 560 6188), ETH Zurich, Institute for Astronomy

    “Twenty-five years ago, there was great skepticism whether planets around other stars would be common and whether we would be able to detect them if they were. Now we are starting to place observational constraints on their earliest phases of formation. If the implication that we have detected molecules in a circumplanetary disk can be confirmed, we can begin to ask whether these disks play a role in determining the final masses of forming planets.”

    The findings reported today are based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, Chile, under program number 090.C-0571(A). Support for the work came from the National Science Foundation under grant number AST-0954811. Basic research in infrared astronomy at the Naval Research Laboratory is supported by 6.1 base funding. Support also came from the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics. The content in this article is solely the responsibility of the researchers and does not necessarily represent the official views of any agency.

    See the full article here.

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