What might be the origin of Fermi bubbles?

Fermi-LAT satellite has product new interesting data about Milky Way central region commented already by Lubos. The following is the abstract of the article Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind? by Meng Su, Tracy R. Slatyer and Douglas P. Finkbeiner.

Data from the Fermi-LAT reveal two large gamma-ray bubbles, extending 50 degrees above and below the Galactic center, with a width of about 40 degrees in longitude. The gamma-ray emission associated with these bubbles has a significantly harder spectrum (dN/dE ≈&E^-2) than the IC emission from electrons in the Galactic disk, or the gamma-rays produced by decay of pions from proton-ISM collisions. There is no significant spatial variation in the spectrum or gamma-ray intensity within the bubbles, or between the north and south bubbles. The bubbles are spatially correlated with the hard-spectrum microwave excess known as the WMAP haze; the edges of the bubbles also line up with features in the ROSAT X-ray maps at 1.5-2 keV. We argue that these Galactic gamma-ray bubbles were most likely created by some large episode of energy injection in the Galactic center, such as past accretion events onto the central massive black hole, or a nuclear starburst in the last ≈&10 Myr. Dark matter annihilation/decay seems unlikely to generate all the features of the bubbles and the associated signals in WMAP and ROSAT; the bubbles must be understood in order to use measurements of the diffuse gamma-ray emission in the inner Galaxy as a probe of dark matter physics. Study of the origin and evolution of the bubbles also has the potential to improve our understanding of recent energetic events in the inner Galaxy and the high-latitude cosmic ray population.

The article contains a long highly technical description of findings. I of course do not have real understanding about this side. The results however seem to be rather clear. There is bubble and its mirror image (bringing in the mind of Lubos infinity symbol) with a center in the galactic nucleus. In these regions there is no significang spatial variation of the gamma ray intensity. The radius of the bubbles is about 5 kparsecs. The X-ray maps in energy range 1.5-2 keV suggest features consistent with the identification as Fermi bubbles. Also the WMAP microwave excess known as microwave haze is consistent with Fermi bubbles.

What could be the mechanism producing the gamma rays?

1. I do not regard the explanation in terms of a catastrophic event terribly convincing since I find it difficult to understand the symmetry with respect to the galactic plane for this option. Rather, the notion of many-sheeted space-time would suggest that quasi-static structures are involved.

2. Fractality of TGD Universe would encourage to consider analogies with the physics of stellar objects, maybe even planets. The nearest and best known example is Earth itself with its magnetic fields and associated van Allen radiation belts. Could Fermi bubbles correspond to a dipole magnetic field with dipole in the direction of galactic plane? Could the dipole correspond to the galactic bar? The estimates for its size vary in surprisingly large range of 1-5 kparsecs but are reasonably near to the size scales of the bubbles which is around 10 kparsecs.

3. One could perhaps imagine the analogs of van Allen radiation belts with very energetic particles originating from the galactic bar a nd traveling along flux quanta (back and forth?) and radiating gamma rays, whose energies would vary up to 100 GeV at least. In the magnetohydrodynamic approximation the charged particles would move along the field lines of the magnetic field. There is however energy conserving Lorentz force present (plus possibly the Coulomb force caused by electric field) and this causes the emission of radiation.

4. In TGD framework the decay of string like object defined by bar could generate extremely energetic particles -say electrons- propagating along the flux quanta. The emission of gamma rays would be especially intensive near turning points where the direction of motion of charged particle is changing most intensely. This would occur near galactic plane where the direction of the magnetic field is changing.

One could bring more TGD to this picture.

1. In TGD vision galaxies are like pearls in the necklace represented by long cosmic strings. These cosmic strings are not the cosmic strings are in GUTs but string like 3-surfaces predicted by TGD dominating the very early cosmolgy and gradually developing an increasing size for their Minkowski space projection with in the ideal case is 2-D. These cosmic strings would be responsible for the magnetic fields filling the Universe but very poorly understood in the standard cosmology. The jet orthogonal to the plane of galaxy would be associated with the "big cosmic string" defining the necklace.

2. Also the galaxies themselves could correspond to decay producs of cosmic strings. They could be closed or open: maybe the two cases correspond to elliptic and spiral galaxies. The galactic bar for spiral galaxies could correspond to decay products of open cosmic string. A straight cosmic string with length L corresponds to an object with mass which is roughly 10^-4 times the mass of black hole with radius L. If the cosmic string is highly entangled, its mass can approach to that of black hole and supermassive galactic black hole with a size of about 150 light seconds could correspond to a highly entangled piece of cosmic string.

3. Open cosmic strings could decay to ordinary matter at their ends. During quasar phase this process would be especially effective and could be partially responsible for gamma ray beams in the direction of the string and producing gamma ray bursts. Kind of cosmic fire crackers would be in question and galactic bar could represent remnants of this kind of fire-cracker still emitting matter travelling along the flux quanta of the galactic magnetic field and producing the gamma radiation.

4. There should be strong magnetic fields associated with these objects. In TGD Universe they would correspond to space-time sheets defining flux tubes or flux sheets of magnetic field. Charged particles would travel along these flux sheets and dissipate their energy by emitting gamma rays.

An interesting question is whether it makes sense to speak about cyclotron states at the flux tubes of the magnetic field and assign the X rays or microwaves with the cyclotron emission.

1. The d'Alembertian for a relativistic motion in constant magnetic field reduces to free motion in longitudinal direction and harmonic oscillator in the transversal directions. By generalizing the non-relativistic formula one one obtain the dispersion relation

   E = (p²+2n × h× eB)^1/2 .

   Here p is the momentum parallel to the flux tube. The magnetic contribution to the energy is completely neglibible in gamma ray range unless magnetic field is very strong.

2. The unit of transversal magnetic energy corresponding to Δ n=1 in the formula for the energy is h× eB/E obtained by replacing mass with energy in the classical formula. For relativistic energies these energies form a continuum. Magnetic confinement suggests that the value of the galactic magnetic field should be such that the transversal contribution to the energy is comparable to the longitudinal energy. For magnetic field of 1 Tesla L= sqrt(h/eB) corresponds to magnetic length of order nm which corresponds to energy of order 10² eV. For ordinary value of Planck constant 100 GeV would require a magnetic field with magnitude of order 10⁹ Tesla. 10⁸ Tesla is the value of B assigned with typical pulsars but there is also a class of pulsars with 1000 stronger magnetic field. One might expect magnetic fields with at strength of at least 10⁸ Tesla in the galactic nucleus.

3. How the scaling of scaling of Planck constant for dark matter affects the situation? Large values of Planck constant correspond to integer multiples h=nh₀ of ordinary Planck constants and coverings of the imbedding space. This would suggest that the total magnetic flux remains constant and is only divided between N sheets so that the formula for the energy is unaffected for a given sheet of the covering.