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Planck spacecraft's findings

  1. Sep 8, 2012 #1
    This can be read in the ESA site on news about the Planck probe:

    " Planck has also detected a mysterious haze of microwaves that presently defies explanation.
    It comes from the region surrounding the galactic centre and looks like a form of energy called synchrotron emission. This is produced when electrons pass through magnetic fields after having been accelerated by supernova explosions.
    The curiosity is that the synchrotron emission associated with the galactic haze exhibits different characteristics from the synchrotron emission seen elsewhere in the Milky Way.
    The galactic haze shows what astronomers call a ‘harder’ spectrum: its emission does not decline as rapidly with increasing energies.
    Several explanations have been proposed for this unusual behaviour, including higher supernova rates, galactic winds and even the annihilation of dark-matter particles.
    So far, none of them has been confirmed and it remains puzzling. "

    Could someone knowledgeable comment on this microwave haze, specifically why it is something so puzzling, and what its different synchrotron spectrum might mean?

    Thanks.
     
  2. jcsd
  3. Sep 8, 2012 #2
    My own guess would be that a harder spectrum for the synchrotron microwaves would mean they would be caused by higher energy/speed ultrarelativistic particles.
    If so, would it be puzzling because it would suggest that the GZK cutoff might have been suppressed for those particles?
     
  4. Sep 8, 2012 #3

    marcus

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    Your speculation is interesting but I can't respond directly to it. However here are some other people's reactions. Gregory Dobler (UCSB and KITP) seems to be an expert on this subject. It is not new with Planck. He has tried out all the existing explanations and found them wanting.

    http://arxiv.org/abs/arXiv:1109.4418
    A Last Look at the Microwave Haze/Bubbles with WMAP
    Gregory Dobler (KITP/UCSB)
    (Submitted on 20 Sep 2011)
    The microwave "haze" was first discovered with the initial release of the full sky data from the Wilkinson Microwave Anisotropy Probe. It is diffuse emission towards the center of our Galaxy with spectral behavior that makes it difficult to categorize as any of the previously known emission mechanisms at those wavelengths. With now seven years of WMAP data publicly available, we have learned much about the nature of the haze, and with the release of data from the Fermi Gamma-Ray Space Telescope and the discovery of the gamma-ray haze/bubbles, we have had a spectacular confirmation of its existence at other wavelengths. As the WMAP mission winds down and the Planck mission prepares to release data, I take a last look at what WMAP has to tell us about the origin of this unique Galactic feature. Much like the gamma-rays, the microwave haze/bubbles is elongated in latitude with respect to longitude by a factor of roughly two, and at high latitudes, the microwave emission cuts off sharply above ~35 degrees (compared to ~50 degrees in the gammas). The hard spectrum of electrons required to generate the microwave synchrotron is consistent with that required to generate the gamma-ray emission via inverse Compton scattering, though it is likely that these signals result from distinct regions of the spectrum (~10 GeV for the microwaves, ~1 TeV for the gammas). While there is no evidence for significant haze polarization in the 7-year WMAP data, I demonstrate explicitly that it is unlikely such a signal would be detectable above the noise.
    9 pages, 6 figures; published April 2012 in ApJ;

    He goes thru and knocks down all the explanations proposed so far one by one. Including dark matter annihilation: On page 8, right before his summary conclusions at the end he says
    ==quote==
    Dark matter annihilation: In this model, the dark halo of the Milky Way is composed of particles which have a self-annihilation cross-section and number den- sity sufficient to explain the required injected power. This scenario was first explored in the microwaves by Finkbeiner (2004b) and Hooper et al. (2007) and then expanded to include local cosmic-ray measurements by Cholis et al. (2009b). Recently, Dobler et al. (2011) showed that the gamma-ray spectrum, amplitude, and morphology can also be reproduced with dark matter annihilation if the dark halo is prolate and diffusion occurs preferentially along ordered field lines in the GC. Here the one significant failing of this model is that it does not produce sharp edges as seen in the Fermi data (the microwave morphology can be completely dominated by the magnetic field geometry). Thus, if these sharp edges persist with future data, the dark matter annihilation only model will be disfavored.
    ==endquote==

    Here is the Planck report on the haze:
    http://arxiv.org/abs/1208.5483
    Planck Intermediate Results. IX. Detection of the Galactic haze with Planck
    Planck Collaboration
    (Submitted on 27 Aug 2012)
    Using precise full-sky observations from Planck, and applying several methods of component separation, we identify and characterize the emission from the Galactic "haze" at microwave wavelengths. The haze is a distinct component of diffuse Galactic emission, roughly centered on the Galactic centre, and extends to |b| ~35 deg in Galactic latitude and |l| ~15 deg in longitude. By combining the Planck data with observations from the WMAP we are able to determine the spectrum of this emission to high accuracy, unhindered by the large systematic biases present in previous analyses. The derived spectrum is consistent with power-law emission with a spectral index of -2.55 +/- 0.05, thus excluding free-free emission as the source and instead favouring hard-spectrum synchrotron radiation from an electron population with a spectrum (number density per energy) dN/dE ~ E^-2.1. At Galactic latitudes |b|<30 deg, the microwave haze morphology is consistent with that of the Fermi gamma-ray "haze" or "bubbles," indicating that we have a multi-wavelength view of a distinct component of our Galaxy. Given both the very hard spectrum and the extended nature of the emission, it is highly unlikely that the haze electrons result from supernova shocks in the Galactic disk. Instead, a new mechanism for cosmic-ray acceleration in the centre of our Galaxy is implied.
    Comments: 15 pages, 9 figures, submitted to Astronomy and Astrophysics
     
    Last edited: Sep 8, 2012
  5. Sep 8, 2012 #4
    Thanks Marcus. Especially for the Planck collaboration very recent paper reference.
    The phrase in bold is certainly intriguing and seems to point in the same direction I hinted. I have to read the whole article carefully.

    Unfortunately my background in astrophysics is very basic, it would be great if some astrophysicist commented on this.
     
  6. Sep 8, 2012 #5
    To be more specific, could the cosmic-ray acceleration mechanism suggested by the hard synchrotron spectrum of the haze produce charged particles with energies above the GZK limit energy when detected at distances longer than the GZK horizon (163mly)? or even from nearer sources?
    I'm thinking for instance about the "Oh-my-God" particle and others detected in various experiments like AGASA and in the Pierre Auger observatory.
     
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