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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 American researchers Darryl J. Leiter and Stanley L. 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 disk can.

Theoretical model

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 provides a review of the evolution of black hole alternatives including his model of eternal collapse and MECOs.

Eternal collapse

Mitra's paper claiming non-occurrence of event horizons and exact black holes later appeared in Pramana - Journal of 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.

Magnetic field

A MECO can carry electric and magnetic properties, has a finite size, can carry angular momentum and rotate.

Observational evidence

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 hypothesis 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".

See also

• Apparent horizon
• Firewall paradox
• Planck star
• No-hair theorem

References

1. ^ Mitra, Abhas (1998). "Final state of spherical gravitational collapse and likely sources of Gamma Ray bursts". arXiv:astro-ph/9803014.
2. ^ Mitra, Abhas (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. S2CID 13945362.
3. ^ Mitra, Abhas (2002). "On the final state of spherical gravitational collapse". Foundations of Physics Letters. 15 (5): 439–471. arXiv:astro-ph/0207056. Bibcode:2002FoPhL..15..439M. doi:10.1023/A:1023968113757. S2CID 119363978.
4. Leiter, Darryl J.; Robertson, Stanley L. (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. S2CID 123650253.
5. ^ Mitra, Abhas (2006). "Why gravitational contraction must be accompanied by emission of radiation in both Newtonian and Einstein gravity". Physical Review D. 74 (2): 024010. arXiv:gr-qc/0605066. Bibcode:2006PhRvD..74b4010M. doi:10.1103/PhysRevD.74.024010. S2CID 119364634.
6. ^ Mitra, Abhas (2006). "A generic relation between baryonic and radiative energy densities of stars". Monthly Notices of the Royal Astronomical Society: Letters. 367 (1): L66–L68. arXiv:gr-qc/0601025. Bibcode:2006MNRAS.367L..66M. doi:10.1111/j.1745-3933.2006.00141.x. S2CID 8776989.
7. ^ Mitra, Abhas (2006). "Radiation pressure supported stars in Einstein gravity: eternally collapsing objects". Monthly Notices of the Royal Astronomical Society. 369 (1): 492–496. arXiv:gr-qc/0603055. Bibcode:2006MNRAS.369..492M. doi:10.1111/j.1365-2966.2006.10332.x. S2CID 16271230.
8. ^ Mitra, Abhas; Robertson, Stanley L. (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. S2CID 15066591.
9. ^ 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 (1): L50–L54. arXiv:1003.3518. Bibcode:2010MNRAS.404L..50M. doi:10.1111/j.1745-3933.2010.00833.x. S2CID 119164101.
10. Mitra, Abhas (2021). The Rise and Fall of the Black Hole Paradigm. Pan Macmillan Publishing India Pvt. Ltd. ISBN 978-9389104141.
11. Mitra, Abhas (2009). "Quantum information paradox: Real or fictitious?". Pramana - Journal of Physics. 73 (3): 615–622. arXiv:0911.3518. Bibcode:2009Prama..73..615M. doi:10.1007/s12043-009-0113-9. S2CID 119117345.
12. ^ Shiga, David (2006). "Mysterious quasar casts doubt on black holes". New Scientist. Retrieved 2 December 2014.
13. Schild, Rudolph E.; Leiter, Darryl J.; Robertson, Stanley 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. S2CID 119355221.
14. Crawford, Paulo; Tereno, Ismael (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. S2CID 2556392.
15. 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. Bibcode:2013IJMPD..2250054M. doi:10.1142/S0218271813500545. S2CID 118493061.

v t e Black holes
Outline
Types	BTZ black hole Schwarzschild Rotating Charged Virtual Kugelblitz Supermassive Primordial Direct collapse Rogue Malament–Hogarth spacetime
Size	Micro Extremal Electron Stellar Microquasar Intermediate-mass Supermassive Active galactic nucleus Quasar LQG Blazar OVV
Formation	Stellar evolution Gravitational collapse Neutron star Related links Tolman–Oppenheimer–Volkoff limit White dwarf Related links Supernova Micronova Hypernova Related links Gamma-ray burst Binary black hole Quark star Supermassive star Quasi-star Supermassive dark star X-ray binary
Properties	Astrophysical jet Gravitational singularity Ring singularity Theorems Event horizon Photon sphere Innermost stable circular orbit Ergosphere Penrose process Blandford–Znajek process Accretion disk Hawking radiation Gravitational lens Microlens Bondi accretion M–sigma relation Quasi-periodic oscillation Thermodynamics Bekenstein bound Bousso's holographic bound Immirzi parameter Schwarzschild radius Spaghettification
Issues	Black hole complementarity Information paradox Cosmic censorship ER = EPR Final parsec problem Firewall (physics) Holographic principle No-hair theorem
Metrics	Schwarzschild (Derivation) Kerr Reissner–Nordström Kerr–Newman Hayward
Alternatives	Nonsingular black hole models Black star Dark star Dark-energy star Gravastar Magnetospheric eternally collapsing object Planck star Q star Fuzzball Geon
Analogs	Optical black hole Sonic black hole
Lists	Black holes Most massive Nearest Quasars Microquasars
Related	Outline of black holes Black Hole Initiative Black hole starship Black holes in fiction Big Bang Big Bounce Compact star Exotic star Quark star Preon star Gravitational waves Gamma-ray burst progenitors Gravity well Hypercompact stellar system Membrane paradigm Naked singularity Population III star Supermassive star Quasi-star Supermassive dark star Rossi X-ray Timing Explorer Superluminal motion Timeline of black hole physics White hole Wormhole Tidal disruption event Planet Nine
Notable	Cygnus X-1 XTE J1650-500 XTE J1118+480 A0620-00 Sagittarius A* Centaurus A Phoenix Cluster PKS 1302-102 OJ 287 SDSS J0849+1114 TON 618 MS 0735.6+7421 NeVe 1 Hercules A 3C 273 Q0906+6930 Markarian 501 ULAS J1342+0928 PSO J030947.49+271757.31 AT2018hyz Swift J1644+57
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