Magnetospheric eternally collapsing object

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A Magnetospheric Eternally Collapsing Object or MECO is a proposed alternative to a black hole. In essence, this theory states that massive objects that suffer gravitational collapse never actually form black holes since the build up of gravitationally trapped radiation pressure slows the collapse to a very small rate when the object becomes sufficiently compact (see Eddington luminosity). The main differences between MECO's and black holes lies in the fact that a MECO has a distantly observable intrinsic magnetic field, while emitting Eddington limited radiation from a highly redshifted surface which makes this "glow" from the MECO surface difficult to observe (black holes can't have magnetic fields and emit only weak Hawking radiation). Recent evidence of intrinsic magnetic fields inside of to what are thought to be super-massive black holes in the centers of some quasars has brought attention to the possibility that they may actually contain MECOs.

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[edit] History

The term Eternally Collapsing Object (ECO) was first coined by astrophysicist Abhas Mitra in 1998.[1] He argued that the observed black hole candidates must actually be quasistatic ultra compact objects, called ECOs, though they are asymptotically approaching the true black hole state. He mentioned that "Much more importantly, the ECOs may possess magnetic fields whose value could be modest (in extragalactic cases) or extremely high (in stellar mass ECOs). In contrast, the intrinsic magnetic field of black holes is zero. And ECOs might be identified as objects different from black holes by virtue of the existence of such intrinsic magnetic fields". He also claimed that the beamed emission from the Gamma Ray Bursts could be better understood if they are associated with birth of highly magnetized ECOs rather than non-magnetized black holes."[2] The essential idea was that the non-singular ECOs are something like the Relativistic version of Neutron Stars. In several other preprints[3] and papers,[4] he claimed ECOs that are black holes with physical surfaces and intrinsic magnetic fields.

The observational and theoretical arguments suggesting that the galactic black hole candidates are Eternally Collapsing Objects containing strong intrinsic equipartition magnetic field in lieu of an event horizon was first shown in a paper published by two American astrophysicists, Robertson and Leiter.[5] In this context of this new development, it was natural to add the term "Magnetospheric" to ECO to make it MECO, as was done by Darryl Leiter, Abhas Mitra and Stanley Robertson in 2001.[6]

However, Mitra later withdrew his name from a subsequent revised version of the preprint he had written with Leiter and Robertson. The reason that Mitra withdrew his name was that he wanted the MECO picture to be a generic extension of the more general ECO concept, which would have no crucial assumptions and is thus model independent. But Leiter & Robertson were keen to make a specific model of MECO with some assumptions in order to immediately apply it to astrophysical observations, and their paper bearing the same title was subsequently published.[7]

Robertson and Leiter elaborated on this aspect by using the idea of disk-magnetospheric interaction.[8] Further, by invoking the well known "magnetic propeller" mechanism, they offered a novel explanation for a hitherto unexplained universal correlation between observed radio and X-ray luminosities in black hole candidates.[9] In turn, such works suggest, from an observational point of view, that black hole candidates are actually magnetized ECOs. Yet one might argue that the evidence that black hole candidates are actually magnetized ECOs is circumstantial, like much of the other "evidences" in astrophysics. One might also argue that, in principle, there might be alternative explanations based on other models.


[edit] The Strong Principle of Equivalence Implies The Existence of MECO

In general relativity, preservation of the strong principle of equivalence (SPOE) requires that special relativity must hold locally for all time-like observers in all of spacetime. The existence of MECO is implied by the idea that Nature requires that the SPOE must be dynamically preserved everywhere in spacetime for the timelike world lines of massive particles or fluids under the influence of both gravitational and non-gravitational forces. Preservation of the SPOE requires that the frame of reference of the co-moving observer in the massive collapsing fluid must always be connected to the frame of reference of a stationary observer by special relativistic transformations with a physical 3-speed that is less than the speed of light (Schild, R., Leiter, D., & Robertson, S. 2006, AJ, 132, 420 -(SLR06).

Since the left-hand side of the Einstein equation cannot by itself dynamically enforce the preservation of the SPOE, it follows that for collapsing objects there must exist SPOE-preserving non-gravitational processes in nature which must always be included in the energy–momentum tensor on the right-hand side of the Einstein equation. It was in this manner that the general relativistic MECO solutions to the Einstein-Maxwell equations were discovered, as was shown in the papers (Robertson, S., & Leiter, D. (2002), ApJ, 565, 447; Robertson, S., & Leiter, D. (2003) ApJ, 596, L203; Robertson, S., & Leiter, D. (2004), MNRAS, 350, 1391; and developed in more detail in Appendices 1–10 of Schild et al. (2005),(Schild, R., Leiter, D., & Robertson, S. (2005), arXiv astro-ph/0505518. There it was shown that for a collapsing body, the structure and radiation transfer properties of the energy–momentum tensor on the right-hand side of the Einstein field equations, could describe a collapsing radiating object which contained equipartition magnetic fields that generated a highly red-shifted Eddington limited secular collapse process. This collapse process was shown to preserve the SPOE by dynamically preventing trapped surfaces, that lead to event horizons, from forming. In Appendices 1–10 of Schild et al. (2005) it was shown that, by using the Einstein–Maxwell equations and quantum electrodynamics in the context of general relativistic plasma astrophysics, it was possible to virtually stop and maintain a slow (many Hubble times!), steady collapse of a compact physical plasma object outside of its Schwarzschild radius. The non-gravitational force was Compton photon pressure generated by synchrotron radiation from an intrinsic equipartition magnetic dipole field contained within the compact object. The rate of collapse is controlled by radiation at the local Eddington limit, but from a highly red shifted surface with an extremely small photon escape cone. In Appendix 9 and 10 of Schild et al. (2005) it was shown that the equatorial poloidal magnetic field, associated with a locally Eddington limited secular rate of collapse of the exterior surface, was strong enough to spontaneously create bound electron-positron pairs in the surface plasma of the MECO which contribute to the general relativistic surface drift currents, within the pair dominated plasma at the MECO surface. These electron-positron drift currents on the MECO surface generate the magnetic fields which create the MECO’s distantly observed intrinsic magnetic moment. Within the context of the MECO’s Eddington limited secular balance, the action of this QED pair production process was shown to be sufficient to stabilize the collapse rate of the MECO surface. For the collapsing, radiating pair dominated plasma associated with the MECO, the corresponding exterior solution to the Einstein equation is described by the time dependent Vaidya metric, where no coordinate transformation between MECO Vaidya metric and the black hole Kerr–Schild metric exists.

Since the highly red shifted Eddington limited MECO Vaidya metric solutions preserve the SPOE they do not have event horizons and the MECO exhibit distantly observed slowly rotating intrinsic magnetic dipole moments which can interact with their surrounding accretion disk environments. In this way the super massive MECO existing in the center of quasar Q0957 revealed itself by generating unique observable magnetic effects on the accretion disk environment (i.e. the Schild-Vakulik Structure discussed in (SLR06)) which observationally distinguished it from that of a central Black Hole.

[edit] Quasar Q0957+561

The more or less direct evidence to this effect came in 2005 largely because of the efforts of the American astronomer Rudy Schild (R. Schild, D. Leiter and S. Robertson, Astronomical J., 132, 420 (2006).

"Schild monitored the quasar's brightness for 20 years, and led an international consortium of observers operating 14 telecopes to keep the object under steady around-the-clock watch at critical times."[10]

The quasar Q0957+561 revealed its structure with very high resolution because of gravitational microlensing by the stars of an intervening galaxy along its line of sight. This structure has broad similarity with the one expected from a magnetized neutron star endowed with an accretion disc.

The accretion flow in the equatorial plane is halted by the magnetic pressure of the central compact object and the inner radius of the disk is determined by the Alfven Radius. The accretion plasma flow then gets guided by the central dipole magnetic field towards the poles of the central magnetized compact object. During this process, the joint effect of spin and magnetic field may fling part of the accretion flow in an outward relativistic jet. Probably the fastest known astrophysical jet has a bulk Lorentz Factor of > 10, and it is associated with a X-ray binary Cir X-1 which contains a magnetized neutron star rather than a black hole candidate. This shows that presence of strong central magnetic field may be necessary to launch strong jets. There may be a wind outflow from the accretion disk itself. The magnetic push due to the central dipole field may also lend the wind an oppositely moving twin cusp-like structure. This "cusp like" picture may be compared with the "hour glass" picture of magnetic field structure recently observed in a collapsing magnetized Molecular cloud.[11]

Thus, the observations of the accretion disc of this quasar made with the aid of a gravitational lens seem to indicate that Q0957+561 has a magnetic field, which a black hole cannot have. The researchers deduced the existence of a magnetic field from the fact that the accretion disk has a gap of 4000 AU around the central object. A small part of the disk just outside of the gap seems to be glowing, which is interpreted as being a sign that the material is heated by a strong magnetic field. Such a glow is also expected because most of the accretion power is released at the inner edge of the disk, truncated by the magnetic pressure of the central compact object. In contrast, for black hole accretion, even though, the inner edge of the disk formally lies at 3 Rg, where Rg is the Schwarzschild Radius, the flow is actually never truncated and, on the other hand, proceeds first to the event horizon and then, all the way up to the central singularity. The flow might get quasispherical in between and a glow is expected from region lying between the event horizon and the inner edge of the disk.


[edit] Further reading

  • "Magnetospheric Eternally Collapsing Objects (MECOs): Likely New Class of Source of Cosmic Ray Particle Acceleration", A. Mitra, Proc. 29th Int. Cos. Ray Conf., Vol 3. pp.125-128 (2005), arXiv:physics/0506183
  • "The Magnetospheric Eternally Collapsing Object (MECO) Model of Galactic Black Hole Candidates and Active Galactic Nuclei", S.L. Robertson and D.J. Leiter, in "New Developments in Black Hole Research", ed. P.V. Kreitler (Nova Sc., NY, 2006), pp. 1-43, [ISBN 1-59454-641-X], arXiv:astro-ph/0602453
  • "Sources of Stellar Energy, Einstein - Eddington Time Scale of Gravitational Contraction and Eternally Collapsing Objects", A. Mitra, New Astronomy, Vol. 12(2), pp.146-160 (2006) arXiv:astro-ph/0608178
  • "Eternally Collapsing Objects or Black Holes: A Review of 90 Years of Misconceptions", A. Mitra, Invited Review Article in "Focus on Black Hole Research", ed. P.V. Kreitler (Nova Sc. NY, 2006), p. 1-94, [ISBN 1-59454-460-3]
  • "Radiation Pressure Supported Stars in Einstein Gravity: Eternally Collapsing Objects", A. Mitra, Mon. Not. Roy. Astron. Soc., Vol. 369, pp. 492-496 (2006) arXiv:gr-qc/0603055

[edit] References

  1. ^ "Final State of Spherical Gravitational Collapse and Likely Sources of Gamma Ray Bursts", A. Mitra, arXiv:astro-ph/9803014 (1998)
  2. ^ "Non-occurrence of Trapped Surfaces and Black Holes in Spherical Gravitational Collapse: An Abridged Version", A. Mitra, Found. Phys. Lett., 13(6),543 (2000), arXiv:astro-ph/9910408
  3. ^ "On the Question of Trapped Surfaces and Black Holes", A. Mitra (2001), arXiv:astro-ph/0105532
  4. ^ "On the Nature of the Compact Condensations at the Centre of Galaxies", A. Mitra, Bull. Astron. Soc. India, 30, 173 (2002), astro-ph/0205261, "On the Final State of Spherical Gravitational Collapse", A. Mitra, Found. Phys. Lett., 15, 439, (2002), arXiv:astro-ph/0207056
  5. ^ "Evidence for Intrinsic Magnetic Moments in Black Hole Candidates", S. Robertson and D. Leiter, Astrophysical J., 565, 447 (2002), arXiv:astro-ph/0102381
  6. ^ "Does the Principle of Equivalence Prevent Trapped Surfaces From being Formed in the General Relativistic Collapse Process?", D. Leiter, A. Mitra and S. Robertson, (2001), arXiv:astro-ph/0111421
  7. ^ "Does the Principle of Equivalence Prevent Trapped Surfaces From being Formed in the General Relativistic Collapse Process?", D. Leiter and S. Robertson, Foundations of Physics Lett., Vol. 16, pp.143 (2003)
  8. ^ "On Intrinsic Magnetic Moment in Black Hole Candidates", S. Robertson and D. Leiter, Astrophysical J. Lett., 596, L203 (2003), arXiv:astro-ph/0310078
  9. ^ "On the Origin of the Radio/X-Ray Luminosity Correlation in Black Hole Candidates", S. Robertson and D. Leiter, Mon. Not. Roy. Astron. Soc., 350, 1391, 2004, arXiv:astro-ph/0402445
  10. ^ Center for Astrophysics, Harvard, Press Release, July 25, 2006
  11. ^ Center for Astrophysics (CfA), Harvard, Press Release, Aug 10, 2006

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