Magnetospheric eternally collapsing object

Magnetospheric eternally collapsing object (MECO) is an alternative model for black hole proposed in 2003 by Darryl Leiter and Stanley Robertson a variant of the eternally collapsing object (ECO) proposed by Abhas Mitra in 1998. 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.

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