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 in 1998. Mitra claimed to have proved that black holes cannot form from the spherically symmetric gravitational collapse of a star. Based on this, he argued that the collapse must be slowed to a near halt by radiation pressure at the Eddington limit.
It has been suggested that the theory is based on an incorrect approach to velocity in general relativity.
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.
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.
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
The description of black hole candidates as ECOs or MECOs has not been widely adopted, and has been criticized. In 2006, Gerry Gilmore of the Institute for Astronomy at the University of Cambridge stated that the MECO concept is "almost certainly wrong." 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.
- 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].
- Jeff Hodgson; "Magnetospheric Eternally Collapsing Objects", presentation slides, 2008  (Retrieved 3 December 2014)
- 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.
- 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.
- Sample, I. (30 July 2006). "US team's quasar probe sinks black hole theory". The Age.com.
- 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.