Dværggalakser omkring Centaurus A roterer i en forbløffende flad skive

Fora ASTRO-FORUM NYT FRA VIDENSKABEN Dværggalakser omkring Centaurus A roterer i en forbløffende flad skive

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  • #316174

    Bjarne
    Moderator
    • Super Nova

    These synchronized galaxies are upending what we know about the universe

    By Matt Warren | Feb. 1, 2018 , 2:00 PM

    Throughout the universe, countless small galaxies rotate around larger host galaxies—our Milky Way has at least a few dozen hangers-on—and theory predicts that they should move randomly. But new research reveals a set of baby galaxies that spin regularly around their host like a carousel. The tiny galaxies surrounding Centaurus A, about 12 million light-years from Earth, were recently found to be orbiting in a surprisingly flat plane—not a random sphere. And if that wasn’t odd enough, new research shows that most of these galaxies are also moving in the same direction. Astronomers sifted through a catalog containing measurements of hundreds of galaxies to find the speed and location of 16 satellites around Centaurus A. They discovered that galaxies on one half of the plane, which is seen edge-on from Earth, tend to be moving toward us, whereas those on the other half are moving away. That suggests they are nearly all rotating in the same direction, the researchers write today in Science. What’s more, the galaxies orbiting both the Milky Way and our nearest neighbor Andromeda also seem to rotate in the same direction and in thin planes. Theoretical models of galaxy formation produce this arrangement less than 0.5% of the time, and the researchers suggest that these planes of satellites might instead be the product of ancient collisions between massive galaxies.

    Det burde hedde what we compute og ikke what we know.

     

    #316181

    Bjarne
    Moderator
    • Super Nova

    A whirling plane of satellite galaxies around Centaurus A challenges cold dark matter cosmology

    The Milky Way and Andromeda galaxy are each surrounded by a thin plane of satellite galaxies that may be corotating. Cosmological simulations predict that most satellite galaxy systems are close to isotropic with random motions, so those two well-studied systems are often interpreted as rare statistical outliers. We test this assumption using the kinematics of satellite galaxies around the Centaurus A galaxy. Our statistical analysis reveals evidence for corotation in a narrow plane: of the 16 Centaurus A’s satellites with kinematic data, 14 follow a coherent velocity pattern aligned with the long axis of their spatial distribution. In standard cosmology simulations, < 0.5% of Centaurus A-like systems show such behavior. Corotating satellite systems may be common in the Universe, challenging small-scale structure formation in the prevailing cosmological paradigm.

    Man kan her læse et preprint af artiklen.

     

    #316331

    Bjarne
    Moderator
    • Super Nova

    Cen A er langt fra den eneste galakse, hvis satellit-galakser bevæger sig i bestemte planer. Da satellitterne bevæger sig langt fra galaksens centrum vil deres baner være bestemt af tyngdekraften, og i ringe grad af gasdynamik. Sådanne baner findes kun i 0.5% af galakserne i kosmologiske simuleringer af koldt mørkt stof. Er der et problem med ΛCDM modellen eller et problem med simuleringen af koldt mørkt stof? De enkelte CDM-partikler bevæger sig meget langsomt, hvorimod simuleringerne følger banerne for “superpartikler”. Jeg er ikke overbevist om, at det ikke er hastighedsopløsningen, der er problemet.

    The Planes of Satellite Galaxies Problem, Suggested Solutions, and Open Questions

    Satellite galaxies of the Milky Way and of the Andromeda galaxy have been found to preferentially align in significantly flattened planes of satellite galaxies, and available velocity measurements are indicative of a preference of satellites in those structures to co-orbit. There is increasing evidence that such kinematically correlated satellite planes are also present around more distant hosts. Detailed comparisons show that similarly anisotropic phase-space distributions of sub-halos are exceedingly rare in cosmological simulations based on the ΛCDM paradigm. Analogs to the observed systems have frequencies of ≤ 0.5 per cent in such simulations. In contrast to other small-scale problems, the satellite planes issue is not strongly affected by baryonic processes because the distribution of sub-halos on scales of hundreds of kpc is dominated by gravitational effects. This makes the satellite planes one of the most serious small-scale problem for ΛCDM. This review summarizes the observational evidence for planes of satellite galaxies in the Local Group and beyond, and provides an overview of how they compare to cosmological simulations. It also discusses scenarios which aim at explaining the coherence of satellite positions and orbits, and why they all are currently unable to satisfactorily resolve the issue.

     

    #316336

    Bjarne
    Moderator
    • Super Nova

    Man har faktisk været opmærksom på, at kosmologiske simuleringer som Millennium-II anvender partikler med massen 8.5 millioner solmasser. Man har derfor udført zoom-simuleringer af 12 galaksepar, som ligner den Lokale Gruppe med Mælkevejen og Andromeda Galaksen plus 24 isolerede galakser med samme masser. Resultatet var det samme. Simuleringerne af en kosmologi med koldt mørkt stof kan ikke forklare de mange dværggalakser på bestemte baneplaner.

     

    #316337

    Bjarne
    Moderator
    • Super Nova

    On the Schrodinger-Poisson–Vlasov-Poisson correspondence

    The Schrodinger-Poisson equations describe the behavior of a superfluid condensate under self-gravity with a 3D wave function. As (ℏ/m)→0, with m being the boson mass, the equations have been hypothesized to approximate the collisionless Vlasov-Poisson equations also known as the collisionless Boltzmann equations. The latter describe collisionless matter with a 6D classical distribution function. We investigate the nature of this correspondence with a suite of numerical test problems in 1D, 2D, and 3D along with analytic treatments where possible. We demonstrate that, while the density field of the superfluid always shows order unity oscillations as (ℏ/m)→0 due to interference and the uncertainty principal, the potential field converges to the classical answer as (ℏ/m)2. Thus, any dynamics coupled to the superfluid potential is expected to recover the classical collisionless limit as (ℏ/m)→0. The quantum superfluid is able to capture rich phenomena such as multiple phase-sheets, shell-crossings, and warm distributions. Additionally, the quantum pressure tensor acts as a regularizer of caustics and singularities in classical solutions. This suggests the exciting prospect of using the Schrodinger-Poisson equations as a low-memory method for approximating the high-dimensional evolution of the Vlasov-Poisson equations. As a particular example we consider dark matter composed of ultra-light axions, which in the classical limit (ℏ/m)→0 is expected to manifest itself as collisionless cold dark matter.

    De numeriske simuleringer er en approximation til den kollisionsfrie Boltzmann ligning, som også går under navnet Vlasov-Poisson ligningen for klassiske partikler i et tyngdefelt, når partikelmassen går mod nul. Den klassiske Vlasov-Poisson ligning bliver til den kvantemekaniske Schrodinger-Poisson ligning, hvis det mørke stof består af ultra-lette axioner. Det var måske en ide at undersøge, om axioner kan forklare observationerne. Den mere radikale mulighed er, at Einsteins Generelle Relativitetsteori skal modificeres.

     

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