jackbauer 2

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Messages posté(e)s par jackbauer 2


  1. Je reviens à mon post précédent. Le papier II est dédié à l'instrumentation ; Comme on peut le lire ci-dessous ils ne manquent pas d'idées pour améliorer leur dispositif dans les années qui viennent :

    (la traduction automatique n'est pas assez bonne et j'ai pas trop le temps de corriger) 

     

    6. Future Developments


     The EHT array is continuing to develop. With the ability to image SMBHs on horizon scales now confirmed (Papers I; III; III; V; VI), the focus of EHT development will shift to enabling observations that can refine constraints on fundamental black hole properties, processes of black hole accretion and outflow, and tests of general relativity. This depends on achieving higher angular resolution, enhancing image fidelity, and enabling dynamic imaging of time-variable phenomena. Higher resolution will allow more detailed studies and modeling of sub-horizon structures as well as sensitive tests for asymmetries in shadow features. Greater image fidelity will bring fainter emission near the horizon into focus for the study of accretion and jet processes, and it will enable a sensitive comparison across imaging epochs, which is especially germane for M87 with its dynamical timescale of days to weeks. For SgrA*, the light-crossing time of ∼20s requires a dynamic approach to image reconstruction, with the potential of observing the near real-time evolution of a black hole. The planned and in-progress addition of telescope facilities at new geographic sites will improve the (u, v), or Fourier, coverage, and thus imaging fidelity. Over the course of the next two years, the EHT expects to add two more facilities: a beamformed NOEMA in France, which, once completed, will be the equivalent of an approximately 50m dish, and a 12m diameter dish on Kitt Peak in Arizona. A newly realized and important consequence of designing high-bandwidth systems is that adding telescopes with modest diameters (;6m ) creates VLBI baselines with sufficient sensitivity to detect the primary EHT targets. An expansion of the EHT can, therefore, include the possibility of deploying numerous smaller apertures, enabling not only improved image quality but also snapshot capability, which is a precursor to constructing black hole movies (Bouman et al. 2018; Johnson et al. 2018). Additional plans to enhance the data throughput of VLBI backend and phased array systems are underway, linked to new generations of wideband millimeter and submillimeter receivers and industry trends that will allow for rapid design and implementation. With the inclusion of more sites and wider bandwidths, the computational requirements for VLBI correlation will increase: linearly with bandwidth, and as the square of the number of stations. The exploration of scalable approaches to address future EHT correlation needs is underway (Gill et al. 2019). The combination of these efforts is aimed at the substantial expansion of aperture plane sampling of the EHT and improved imaging. To significantly improve angular resolution requires development in different directions. Planned extension of the EHT to operation at 0.87mm wavelength, a standard receiving band at many facilities, would increase the angular resolution of the array by ∼40%. VLBI tests at 0.87mm are underway and this capability is expected at a subset of EHT sites over the next 3–5yr (see Table 4). An alternate approach to increased angular resolution is to deploy EHT antennas in space where baseline length is not limited to the diameter of the Earth, potentially allowing horizon-scale imaging of additional SMBH candidates (Johannsen et al. 2012). Space platforms also offer the possibility of rapidly sampling the Fourier plane, thereby opening the potential for dynamical imaging of black hole accretion and outflow processes (D. Palumbo et al. 2019, in preparation; F. Roelofs et al. 2019, in preparation; M. Shea et al. 2019, in preparation). EHT observation strategies continue to be refined. With further development of remote monitoring and control tools, the EHT can explore triggering observations during the best conditions throughout the year outside the current March–April window. One consequence of this flexibility would be that observations for SgrA* and M87 could be optimized separately in a given observing cycle, instead of grouped together as they are currently. Distributing the observations over a larger portion of the year also increases the likelihood that the EHT would detect emission transients or flaring on intermediate timescales should they occur, and affords, in general, the opportunity to study M87 on timescales that correspond to the expected ISCO period of order one to several weeks (Table 1). Not all EHT sites may be able to participate in such flexible campaigns, but even a subset of the array, especially if augmented with many smaller dishes, could provide useful observations for variability studies.

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  2. il y a une heure, Alain MOREAU a dit :

    Que peut-on espérer pour le moment ?

     

    Extrait du papier I page 9, dans la conclusion :

     

     Higher-resolution images can be achieved by going to a shorter wavelength, i.e., 0.8 mm (345GHz), by adding more telescopes and, in a more distant future, with space-based interferometry (Kardashev et al. 2014; Fish et al. 2019; Palumbo et al. 2019; F. Roelofs et al. 2019b, in preparation).

     

    Another primary EHT source, SgrA*, has a precisely measured mass three orders of magnitude smaller than that of M87*, with dynamical timescales of minutes instead of days. Observing the shadow of SgrA* will require accounting for this variability and mitigation of scattering effects caused by the interstellar medium (Johnson 2016; Lu et al. 2016; Bouman et al. 2018). Time dependent nonimaging analysis can be used to potentially track the motion of emitting matter near the black hole, as reported recently through interferometric observations in the near-infrared (Gravity Collaboration et al. 2018b). Such observations provide separate tests and probes of GR on yet another mass scale (Broderick & Loeb 2005; Doeleman et al. 2009b; Roelofs et al. 2017; Medeiros et al. 2017).

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  3. il y a 30 minutes, Pulsarx a dit :

    A quoi  devrait-on s'attendre si on augmentait drastiquement le nombre de coupoles à la surface de la terre, en terme d'image, résolution etc ?  Mon 2eme point sur le "gros merdier" me pousse à penser qu'on ne verrait pas beaucoup moins flou ... mais je n'en sais rien au final ! 

    Des idées ?

     

    Et bien oui, théoriquement on verrait l'image au centre : c'est le modèle informatique. Mais c'est hors de notre portée pour longtemps...

     

     

    b2.jpg


  4. Curieusement, dans leur com disponible en ligne, il manque un montage ou une simulation avec l'énorme jet de M87

     

    extrait de Wiki :

     

    "...Le jet de matière qui émerge du cœur de Messier 87 s'étend sur au moins 5 000 al et est composé de matière éjectée de la galaxie par un trou noir supermassif. Ce jet est hautement collimaté, il semble contraint à un angle d'environ 16 ° sur 2 pc du cœur et un angle de 6–7 ° à 12 pc. Il y a des preuves de l'existence d'un jet opposé, mais cet objet reste invisible de la Terre à cause du faisceau relativiste (en)…"