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  • richardmitnick 7:37 am on March 12, 2018 Permalink | Reply
    Tags: , , , Bow shocks, , , ,   

    From NASA: “Cosmic Bow Shocks” 

    NASA image
    NASA

    No writer credit


    No video credit

    Imagine an object moving at super-sonic speed. This object, as it moves through a medium, causes the material in the medium to pile up, compress, and heat up. The result is a type of shock wave, known as a bow shock.

    A bow shock gets it’s name from bow waves, the curved ridge of water in front of a fast-moving boat created by the force of the bow pushing forward through the water. Bow waves and bow shocks can look similar, however bow waves only occur on the surface of water while bow shocks occur in 3 dimensions.

    There are bow shocks everywhere, even in space–and these cosmic bow shocks can tell scientists cosmic secrets.

    Even the emptiest regions of space contain protons, electrons, atoms, molecules and other matter. When planets, stars, and the plasma clouds ejected from supernovae fly at a high speed through this surrounding medium, cosmic bow shocks are generated in that medium.

    The solar wind forms a bow shock in front of Earth’s magnetosphere.

    Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase

    “The fast-moving plasma of the solar wind blows past Earth, but it cannot penetrate our magnetosphere,” explains Maxim Markevitch of NASA’s Goddard Space Flight Center.

    NASA Goddard Campus


    “The solar wind has a magnetic field, and the Earth’s magnetosphere is almost like a solid body for that wind. So the solar wind forms a bow shock in front of the outer edge of the magnetosphere.”

    Studying Earth’s bow shock can unlock the secrets of the solar wind, allowing us to better understand its complicated effects on our planet.

    The high-speed collisions of stars with the interstellar medium create impressive bow shocks. Hot supergiant star Kappa Cassiopeia creates a shock that can be seen by the infrared detectors on NASA’s Spitzer Space Telescope.

    NASA/Spitzer Infrared Telescope

    In this Spitzer image, the pile-up of heated material around Kappa Cassiopeia is indicated in red.

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    http://www.spitzer.caltech.edu/images/5730-sig14-003-The-Shocking-Behavior-of-a-Speedy-Star
    Kappa Cassiopeiae, or HD 2905 to astronomers, is a runaway star—a massive, hot supergiant gone rogue. What really makes the star stand out in this image is the surrounding, streaky red glow of material in its path. Such structures are called bow shocks, and they can often be seen in front of the fastest, most massive stars in the galaxy.

    Bow shocks form where the magnetic fields and wind of particles flowing off a star collide with the diffuse, and usually invisible, gas and dust that fill the space between stars. How these shocks light up tells astronomers about the conditions around the star and in space. Slow-moving stars like our sun have bow shocks that are nearly invisible at all wavelengths of light, but fast stars like Kappa Cassiopeiae create shocks that can be seen by Spitzer’s infrared detectors.
    Incredibly, this shock is created about 4 light-years ahead of Kappa Cassiopeiae, showing what a sizable impact this star has on its surroundings.

    Studying stellar bow shocks can reveal the secret motions of the underlying stars, telling us how fast they’re moving, which way, and what they’re moving through.

    An example of a bow shock on an even grander scale is seen in this cluster of galaxies located in the Carina constellation, called 1E 0657-558.

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    Anne’s Astronomy News
    The Bullet cluster (1E 0657-558) consists of two colliding galaxy clusters in Carina.

    This X-ray image from the Chandra observatory captures the moment of a gigantic collision of two smaller clusters, the two white regions in the image.

    NASA/Chandra Telescope

    Markevitch says, “The clusters are filled with hot plasma, and one of them — the cluster on the right — is smaller and denser. As it flies through the less-dense cloud of plasma that is the bigger cluster it forms a bow shock.”

    Scientists study such cluster shocks to deduce their velocity in the plane of the sky. And the fine structure of the shocks reveals a lot about the interesting, complicated physical processes in the plasmas present in clusters as well as in many other astrophysical objects across the universe.

    For more on shocking phenomena found beyond our solar system, stay tuned to science.nasa.gov.

    See the full article here .

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    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

    President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

    Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

    NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble, Chandra, Spitzer, and associated programs. NASA shares data with various national and international organizations such as from the [JAXA]Greenhouse Gases Observing Satellite.

     
  • richardmitnick 10:57 am on July 3, 2017 Permalink | Reply
    Tags: , , , Bow shocks, , , , The giant star Zeta Ophiuchi   

    From Spitzer via Manu: “Massive Star Makes Waves” 12.18.12 


    Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.

    NASA/Spitzer Telescope

    Spitzer

    12.18.12
    No writer credit

    1

    The giant star Zeta Ophiuchi is having a “shocking” effect on the surrounding dust clouds in this infrared image from NASAs Spitzer Space Telescope. Stellar winds flowing out from this fast-moving star are making ripples in the dust as it approaches, creating a bow shock seen as glowing gossamer threads, which, for this star, are only seen in infrared light.

    Zeta Ophiuchi is a young, large and hot star located around 370 light-years away. It dwarfs our own sun in many ways — it is about six times hotter, eight times wider, 20 times more massive, and about 80,000 times as bright. Even at its great distance, it would be one of the brightest stars in the sky were it not largely obscured by foreground dust clouds.

    This massive star is travelling at a snappy pace of about 54,000 mph (24 kilometers per second), fast enough to break the sound barrier in the surrounding interstellar material. Because of this motion, it creates a spectacular bow shock ahead of its direction of travel (to the left). The structure is analogous to the ripples that precede the bow of a ship as it moves through the water, or the sonic boom of an airplane hitting supersonic speeds.

    The fine filaments of dust surrounding the star glow primarily at shorter infrared wavelengths, rendered here in green. The area of the shock pops out dramatically at longer infrared wavelengths, creating the red highlights.

    A bright bow shock like this would normally be seen in visible light as well, but because it is hidden behind a curtain of dust, only the longer infrared wavelengths of light seen by Spitzer can reach us.

    Bow shocks are commonly seen when two different regions of gas and dust slam into one another. Zeta Ophiuchi, like other massive stars, generates a strong wind of hot gas particles flowing out from its surface. This expanding wind collides with the tenuous clouds of interstellar gas and dust about half a light-year away from the star, which is almost 800 times the distance from the sun to Pluto. The speed of the winds added to the stars supersonic motion result in the spectacular collision seen here.

    Our own sun has significantly weaker solar winds and is passing much more slowly through our galactic neighborhood so it may not have a bow shock at all. NASAs twin Voyager spacecraft are headed away from the solar system and are currently about three times farther out than Pluto. They will likely pass beyond the influence of the sun into interstellar space in the next few years, though this is a much gentler transition than that seen around Zeta Ophiuchi.

    For this Spitzer image, infrared light at wavelengths of 3.6 and 4.5 microns is rendered in blue, 8.0 microns in green, and 24 microns in red.

    See the full article here .

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    The Spitzer Space Telescope is a NASA mission managed by the Jet Propulsion Laboratory located on the campus of the California Institute of Technology and part of NASA’s Infrared Processing and Analysis Center.

    NASA image

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  • richardmitnick 2:08 pm on October 23, 2016 Permalink | Reply
    Tags: Bow shocks, ,   

    From Science Alert: “Astrophysicists have witnessed plasma ripples moving along Earth’s bow shock” 

    ScienceAlert

    Science Alert

    20 OCT 2016
    JOSH HRALA

    1
    APS/Carin Cain

    These things actually exist.

    Astrophysicists have witnessed tiny ripples forming on Earth’s ‘bow shock’ – the plasma shockwaves produced when solar winds smash into Earth’s magnetic field.

    While the ripples have long been hypothesised, actually finding them in space has proven a challenge. Now, researchers have been able to study them for the first time, and it could help us to finally understand cosmic rays.

    The breakthrough came thanks to thanks to NASA’s Magnetospheric MultiScale satellites (MMS).

    NASA/MMS

    nasa-mms-satellites
    NASA/MMS

    “With the new MMS spacecraft we can, for the first time, resolve the structure of the bow shock at these small scales,” said team leader Andreas Johlander, from the Swedish Institute of Space Physics (IRF).

    So, what are these ripples and where do they come from?

    Much of the visible matter in the Universe is actually plasma, a hot ionised gas. This plasma can produce shockwaves around other objects in space – such as planets, stars, and supernovae – when it interacts with the magnetic fields around them.

    Just imagine it like a wave of water travelling around the bow of a ship, where the water is plasma and the ship’s bow is Earth’s magnetic field (or magnetosphere), sending the plasma rushing to either side as it displaces it.

    These shockwaves are known to act basically like particle accelerators, and shockwaves around supernovae are commonly thought to produce cosmic rays, high energy atoms or particles that travel near the speed of light through space.

    But the thing is, we don’t really understand exactly how the particles in these shockwaves get so fast.

    Based on previously developed mathematical models, researchers think that tiny ripples in these shockwaves might be to blame for this acceleration, though finding and actually witnessing them has been impossible because they are super small and fast, making them hard to spot with traditional technologies.

    That is, until now, because the new team was able to witness these ripples inside Earth’s bow shock.

    To pull off this feat and to analyse these ripples further, the team employed NASA’s MMS – a group of four satellites that fly in a tetrahedral formation around Earth’s magnetosphere to sample plasma activity.

    This represents the first time researchers have been able to successfully witness these ripples, providing proof – once and for all – of their existence other than in mathematical calculations.

    But it’s just the first step – now we have to figure out how they work.

    With further study, the team says that understanding how these ripples in plasma shocks help accelerate and heat particles might shine new light on how cosmic rays form around supernovae.

    “These direct observations of shock ripples in a space plasma allow us to characterise the physical properties of the ripples. This brings us one step closer to understanding how shocks can produce cosmic rays,” said Johlander.

    The team’s work was published in Physical Review Letters.

    See the full article here .

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  • richardmitnick 6:39 pm on September 21, 2015 Permalink | Reply
    Tags: , , , Bow shocks   

    From AAS NOVA: Bow Shock Leads the Way for a Speeding Hot Jupiter 

    AASNOVA

    Amercan Astronomical Society

    21 September 2015
    Susanna Kohler

    1
    Artist’s impression of a hot Jupiter preceded by a bow shock, as it orbits its host star supersonically. Scientists have recently discovered evidence of a shock ahead of the exoplanet HD 189733b. [NASA, ESA and A. Schaller (for STScI)]

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    Bow shock per ESA, no image credit

    As hot Jupiters whip around their host stars, their speeds can exceed the speed of sound in the surrounding material, theoretically causing a shock to form ahead of them. Now, a study has reported the detection of such a shock ahead of transiting exoplanet HD 189733b, providing a potential indicator of the remarkably strong magnetic field of the planet.

    Rushing Planets

    Due to their proximity to their hosts, hot Jupiters move very quickly through the stellar wind and corona surrounding the star.

    When this motion is supersonic, the material ahead of the planet can be compressed by a bow shock — and for a transiting hot Jupiter, this shock will cross the face of the host star in advance of the planet’s transit.

    In a recent study, a team of researchers by Wilson Cauley of Wesleyan University report evidence of just such a pre-transit. The team’s target is exoplanet HD 189733b, one of the closest hot Jupiters to our solar system. When the authors examined high-resolution transmission spectra of this system, they found that prior to the optical transit of the planet, there was a large dip in the transmission of the first three hydrogen Balmer lines. This could well be the absorption of an optically-thick bow shock as it moves past the face of the star.

    Tremendous Magnetism

    Operating under this assumption, the authors create a model of the absorption expected from a hot Jupiter transiting with a bow shock ahead of it. Using this model, they show that a shock leading the planet at a distance of 12.75 times the planet’s radius reproduces the key features of the transmission spectrum.

    This stand-off distance is surprisingly large. Assuming that the location of the bow shock is set by the point where the planet’s magnetospheric pressure balances the pressure of the stellar wind or corona that it passes through, the planetary magnetic field would have to be at least 28 Gauss. This is seven times the strength of Jupiter’s magnetic field!

    Understanding the magnetic fields of exoplanets is important for modeling their interiors, their mass loss rates, and their interactions with their host stars. Current models of exoplanets often assume low-value fields similar to those of planets within our solar system. But if the field strength estimated for HD 189733b’s field is common for hot Jupiters, it may be time to update our models!

    See the full article here .

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