Magnetospheric eternally collapsing object
The magnetospheric eternally collapsing object (MECO) is an alternative model for black holes initially proposed by Indian scientist Abhas Mitra in 1998 and later generalized by Darryl Leiter and Stanley Robertson. A proposed observable difference between MECOs and black holes is that a MECO can produce its own intrinsic magnetic field. An uncharged black hole cannot produce its own magnetic field, though its accretion disc can.
In the theoretical model a MECO begins to form in much the same way as a black hole, with a large amount of matter collapsing inward toward a single point. However, as it becomes smaller and denser, a MECO does not form an event horizon.
As the matter becomes denser and hotter, it glows more brightly. Eventually its interior approaches the Eddington limit. At this point the internal radiation pressure is sufficient to slow the inward collapse almost to a standstill.
In fact, the collapse gets slower and slower, so a singularity could only form in an infinite future. Unlike a black hole, the MECO never fully collapses. Rather, according to the model it slows down and enters an eternal collapse.
Mitra's paper proposing eternal collapse appeared in the Journal of Mathematical Physics. In this paper, Mitra proposes that so-called black holes are eternally collapsing while Schwarzschild black holes have a gravitational mass M = 0. He argued that all proposed black holes are instead quasi-black holes rather than exact black holes and that during the gravitational collapse to a black hole, the entire mass energy and angular momentum of the collapsing objects is radiated away before formation of exact mathematical black holes. Mitra proposes that in his formulation since a mathematical zero-mass black hole requires infinite proper time to form, continued gravitational collapse becomes eternal, and the observed black hole candidates must instead be eternally collapsing objects (ECOs). For physical realization of this, he argued that in an extremely relativistic regime, continued collapse must be slowed to a near halt by radiation pressure at the Eddington limit.
A MECO can carry electric and magnetic properties, has a finite size, can carry angular momentum and rotate.
Astronomer Rudolph Schild of the Harvard–Smithsonian Center for Astrophysics claimed in 2006 to have found evidence consistent with an intrinsic magnetic field from the black hole candidate in the quasar Q0957+561. Chris Reynolds of the University of Maryland has criticised the MECO interpretation, suggesting instead that the apparent hole in the disc could be filled with very hot, tenuous gas, which would not radiate much and would be hard to see, however Leiter in turn questions the viability of Reynolds's interpretation.
Reception of the MECO model
Mitra's proof that black holes cannot form is based in part on the argument that in order for a black hole to form, the collapsing matter must travel faster than the speed of light with respect to a fixed observer. In 2002; Paulo Crawford and Ismael Tereno cited this as an example of a "wrong and widespread view", and explain that in order for a frame of reference to be valid, the observer must be moving along a timelike worldline. At or inside the event horizon of a black hole, it is not possible for such an observer to remain fixed; all observers are drawn toward the black hole. Mitra argues that he has proven that the world-line of an in-falling test particle would tend to be lightlike at the event horizon, independent of the definition of "velocity".
- Mitra, A. (1998). "Final state of spherical gravitational collapse and likely sources of Gamma Ray bursts". arXiv:astro-ph/9803014.
- Mitra, A. (2000). "Non-occurrence of trapped surfaces and black holes in spherical gravitational collapse: An abridged version". Foundations of Physics Letters. 13 (6): 543. arXiv:astro-ph/9910408. doi:10.1023/A:1007810414531.
- Leiter, D.; Robertson, S. (2003). "Does the principle of equivalence prevent trapped surfaces from being formed in the general relativistic collapse process?". Foundations of Physics Letters. 16 (2): 143. arXiv:astro-ph/0111421. doi:10.1023/A:1024170711427.
- A. Mitra, Phys. Rev. D 74, 024010 (2006) (American Physical Soc., USA) Mitra, Abhas (2006). "Why gravitational contraction must be accompanied by emission of radiation in both Newtonian and Einstein gravity". Physical Review D. 74 (2). arXiv:gr-qc/0605066. doi:10.1103/PhysRevD.74.024010.
- A. Mitra, MNRAS, 367, L66-L68 (2006) (Royal Astronomical Soc., London) Mitra, A. (2006). "A generic relation between baryonic and radiative energy densities of stars". Monthly Notices of the Royal Astronomical Society: Letters. 367: L66–L68. arXiv:gr-qc/0601025. doi:10.1111/j.1745-3933.2006.00141.x.
- A. Mitra, MNRAS, 369, 492–496 (2006) (Royal Astronomical Soc. London)Mitra, A. (2006). "Radiation pressure supported stars in Einstein gravity: eternally collapsing objects". Monthly Notices of the Royal Astronomical Society. 369: 492–496. arXiv:gr-qc/0603055. doi:10.1111/j.1365-2966.2006.10332.x.
- A. Mitra, New Astronomy, Volume 12, 146–160 (2006) (Elsevier, Netherlands) Mitra, Abhas; Robertson, Stanley (November 2006). "Sources of stellar energy, Einstein Eddington timescale of gravitational contraction and eternally collapsing objects". New Astronomy. 12 (2): 146–160. arXiv:astro-ph/0608178. Bibcode:2006NewA...12..146M. CiteSeerX 10.1.1.256.3740. doi:10.1016/j.newast.2006.08.001.
- A. Mitra & N.K. Glendenning, MNRAS 404, L50-L54 (2010) (Royal Astronomical Soc., London)Mitra, Abhas; Glendenning, Norman K. (2010). "Likely formation of general relativistic radiation pressure supported stars or 'eternally collapsing objects'". Monthly Notices of the Royal Astronomical Society: Letters. 404: L50–L54. arXiv:1003.3518. doi:10.1111/j.1745-3933.2010.00833.x. Archived from the original on 2013-11-04.
- A. Mitra, J. Math. Phys. 50, 042502 (2009) (American Institute of Physics)Mitra, Abhas (2009). "Comments on The Euclidean gravitational action as black hole entropy, singularities, and space-time voids". Journal of Mathematical Physics. 50 (4): 042502. arXiv:0904.4754. doi:10.1063/1.3118910.
- Shiga, D.; "Mysterious quasar casts doubt on black holes", New Scientist: Space, 2006. (retrieved 2 December 2014)
- Schild, R.E.; Leiter, D.J.; Robertson, S.L. (2006). "Observations supporting the existence of an intrinsic magnetic moment inside the central compact object within the Quasar Q0957+561". Astronomical Journal. 132 (1): 420–32. arXiv:astro-ph/0505518. Bibcode:2006AJ....132..420S. doi:10.1086/504898.
- Crawford, P.; Tereno, I. (2002). "Generalized observers and velocity measurements in General Relativity". General Relativity and Gravitation. 34 (12): 2075–88. arXiv:gr-qc/0111073. Bibcode:2002GReGr..34.2075C. doi:10.1023/A:1021131401034.
- A. Mitra and K. K. Singh, Int. J. Mod. Phys. D 22, 1350054 (2013) (World Scientific) Mitra, Abhas; Singh, K. K. (2013). "The Mass of the Oppenheimer-Snyder Hole: Only Finite Mass Quasi-Black Holes". International Journal of Modern Physics D. 22 (9): 1350054. doi:10.1142/S0218271813500545.