Magnetospheric eternally collapsing object
Magnetospheric eternally collapsing objects or MECOs were proposed in 2003 as alternative models for black holes by Darryl Leiter and Stanley Robertson. They are a variant of the eternally collapsing objects or ECOs proposed by Abhas Mitra first in 1998. His peer reviewed paper published in Journal of Mathematical Physics of the American Institute of Physics supports this contention that the so-called black holes should be ECOs by showing that true Schwarzschild black holes have gravitational mass M = 0. He argues that (i) The so-called massive Black Hole Candidates (BHCs) must be quasi-black holes rather than exact black holes and (ii) During preceding gravitational collapse, entire mass energy and angular momentum of the collapsing objects must be radiated away before formation of exact mathematical black holes. And since the formation of a mathematical zero-mass black hole requires infinite proper time, continued gravitational collapse becomes eternal, and the so-called black hole candidates must be Eternally Collapsing Objects (ECO). 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 proposed observable difference between MECOs and black holes is that the 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 simply continue collapsing and 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 further the collapse the slower the continuing collapse, so that collapse to a singularity would take an infinite time and, unlike a black hole, the MECO never fully collapses. Rather, according to the model it slows down and enters an eternal collapse.
A MECO can carry electric and magnetic properties.
A MECO has a finite size, can carry angular momentum and rotate.
The rotation of an electromagnetically active MECO creates an electric field.
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' interpretation.
It is expected that future observations by instruments such as the Event Horizon Telescope will either prove that Black Holes exist or provide evidence the MECO model is more realistic.
Reception of the MECO model
There are now incontrovertible evidences that many X-ray binaries and quasars contain massive or super-massive ultra-compact objects. Popularly such ultra-compacts objects are referred to as "Black Holes". Thus any claim such as "quasars do not contain black holes" is met with suspicion. Accordingly, the description of black hole candidates as ECOs or MECOs has not been widely adopted.
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'.
- 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.
- Mitra, A. (1998). "Final state of spherical gravitational collapse and likely sources of Gamma Ray bursts". arXiv:astro-ph/9803014 [astro-ph].
- 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.
- A. Mitra, J. Math. Phys. 50, 042502 (2009) (American Institute of Physics)"Comments on The Euclidean gravitational action as black hole entropy, singularities, and space-time voids".
- A. Mitra, Phys. Rev. D 74, 024010 (2006) (American Physical Soc., USA) "Why gravitational contraction must be accompanied by emission of radiation in both Newtonian and Einstein gravity".
- A. Mitra, MNRAS, 367, L66-L68 (2006) (Royal Astronomical Soc., London) "A generic relation between baryonic and radiative energy densities of stars".
- A. Mitra, MNRAS, 369, 492–496 (2006) (Royal Astronomical Soc. London)"Radiation pressure supported stars in Einstein gravity: eternally collapsing objects".
- A. Mitra, New Astronomy, Volume 12, 146–160 (2006) (Elsevier, Netherlands) "Sources of stellar energy, Einstein Eddington timescale of gravitational contraction and eternally collapsing objects".
- A. Mitra & N.K. Glendenning, MNRAS 404, L50-L54 (2010) (Royal Astronomical Soc., London)"Likely formation of general relativistic radiation pressure supported stars or 'eternally collapsing objects'".
- 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) "The Mass of the Oppenheimer-Snyder Hole: Only Finite Mass Quasi-Black Holes".