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.[1] They are a variant of the eternally collapsing objects or ECOs proposed by Abhas Mitra first in 1988.[2][3][4] Mitra claimed to have proved that finite mass black holes cannot form from the spherically symmetric gravitational collapse of a star. 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.[5][6][7][8][9]

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.[2]

Theoretical model

Eternal collapse

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.[5][6][7][8][9]

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.[5][6][7][8][9]

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.[5][6][7][8][9]

Magnetic field

Since it has no event horizon, a MECO can carry electric and magnetic properties.

Since it has not collapsed to a point, a MECO has a finite size, which in turn allows it to carry angular momentum and to rotate.

The rotation of an electromagnetically active MECO creates a magnetic field.

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.[10][11] 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.[10]

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 on two key proofs (i) No trapped surface is formed in general relativistic gravitational collapse and (ii) The world-line of an in-falling test particle, which must be `Time-like' would tend to be `Light-like' at the Event Horizon (EH) of an assumed black hole (ds_{EH}^2 \to 0). The physical interpretation of the latter proof is that the `physical speed' of the test particle as defined by Landau & Lifshitz and all other general relativistic experts would approach the speed of light.[3] In order to avoid this, Crawford and Tereno proposed that the speed of one in-falling particle should be measured by another in-falling observer.[12] If so, the speed of the in-falling test particle could remain sub-luminal everywhere, even at the central singularity. While this could be another definition of `velocity', Mitra claimed that it has got nothing to with his proof which is independent of the definition of `velocity' (ds_{EH}^2 \to 0).[4][13] In fact later Crawford too admitted that ` it is important to emphasize that the interior structure of realistic black holes has not been satisfactorily determined, and is still open to considerable debate'.[14]

See also

References

  1. ↑ 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.
  2. ↑ 2.0 2.1 Mitra, A. (1998). "Final state of spherical gravitational collapse and likely sources of Gamma Ray bursts". arXiv:astro-ph/9803014 [astro-ph].
  3. ↑ 3.0 3.1 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.
  4. ↑ 4.0 4.1 A. Mitra,Foundations of Physics Letters, Volume 15, pp 439–471 (2002) (Springer, Germany)"On the final state of spherical gravitational collapse".
  5. ↑ 5.0 5.1 5.2 5.3 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".
  6. ↑ 6.0 6.1 6.2 6.3 A. Mitra, MNRAS, 367, L66-L68 (2006) (Royal Astronomical Soc., London) "A generic relation between baryonic and radiative energy densities of stars".
  7. ↑ 7.0 7.1 7.2 7.3 A. Mitra, MNRAS, 369, 492–496 (2006) (Royal Astronomical Soc. London)"Radiation pressure supported stars in Einstein gravity: eternally collapsing objects".
  8. ↑ 8.0 8.1 8.2 8.3 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".
  9. ↑ 9.0 9.1 9.2 9.3 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'".
  10. ↑ 10.0 10.1 Shiga, D.; "Mysterious quasar casts doubt on black holes", New Scientist: Space, 2006. (retrieved 2 December 2014)
  11. ↑ 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.
  12. ↑ 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.
  13. ↑ 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".
  14. ↑ Rosa Doran, Francisco S. N. Lobo, Paulo Crawford, Foundations of Physics 38, 160, 2008 (gr-qc/0609042)"Interior of a Schwarzschild Black Hole Revisited".