The magnetospheric eternally collapsing object (MECO) is an alternative model for

black hole A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...

s 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 A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

. An uncharged black hole cannot produce its own magnetic field, though its

accretion disk An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and ...

can.

Theoretical model

In the theoretical model a MECO begins to form in much the same way as a

, 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 In astrophysics, an event horizon is a boundary beyond which events cannot affect an outside observer. Wolfgang Rindler coined the term in the 1950s. In 1784, John Michell proposed that gravity can be strong enough in the vicinity of massive c ...

. As the matter becomes denser and hotter, it glows more brightly. Eventually its interior approaches the

Eddington limit The Eddington luminosity, also referred to as the Eddington limit, is the maximum luminosity a body (such as a star) can achieve when there is balance between the force of radiation acting outward and the gravitational force acting inward. The stat ...

. At this point the internal

radiation pressure Radiation pressure (also known as light pressure) is mechanical pressure exerted upon a surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of ...

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 Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a body, until the discovery of the atom and particle physics. It was found that different atoms and different elementary parti ...

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

at the

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 Rudolph E. Schild (born 10 January 1940) is an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, who has been active since the mid-1960s. He has authored or contributed to over 250 papers, of which 150 are in refereed journals. ...

of the

Harvard Harvard University is a private Ivy League research university in Cambridge, Massachusetts, United States. Founded in 1636 and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher lear ...

– Smithsonian

Center for Astrophysics Center or centre may refer to: Mathematics *Center (geometry), the middle of an object * Center (algebra), used in various contexts ** Center (group theory) ** Center (ring theory) * Graph center, the set of all vertices of minimum eccentricit ...

claimed in 2006 to have found evidence consistent with an intrinsic magnetic field from the black hole candidate in the

quasar A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...

Q0957+561 The Twin Quasar (also known as Twin QSO, Double Quasar, SBS 0957+561, TXS 0957+561, Q0957+561 or QSO 0957+561 A/B), was discovered in 1979 and was the first identified gravitational lens, gravitationally lensed double quasar, not to be confused ...

. 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 In physics and astronomy, a frame of reference (or reference frame) is an abstract coordinate system, whose origin (mathematics), origin, orientation (geometry), orientation, and scale (geometry), scale have been specified in physical space. It ...

to be valid, the observer must be moving along a

timelike In mathematical physics, the causal structure of a Lorentzian manifold describes the possible causal relationships between points in the manifold. Lorentzian manifolds can be classified according to the types of causal structures they admit (''ca ...

worldline The world line (or worldline) of an object is the path that an object traces in 4-dimensional spacetime. It is an important concept of modern physics, and particularly theoretical physics. The concept of a "world line" is distinguished from co ...

. At or inside the

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 In mathematical physics, the causal structure of a Lorentzian manifold describes the possible causal relationships between points in the manifold. Lorentzian manifolds can be classified according to the types of causal structures they admit (''ca ...

at the event horizon, independent of the definition of "velocity".

References