Magnetospheric eternally collapsing object

Last updated

The magnetospheric eternally collapsing object (MECO) is an alternative model for black holes initially proposed by Indian scientist Abhas Mitra in 1998 [1] [2] [3] and later generalized by American researchers Darryl J. Leiter and Stanley L. Robertson. [4] 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. [1]

Contents

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

Mitra provides a review of the evolution of black hole alternatives including his model of eternal collapse and MECOs. [10]

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. [11] 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. [5] [6] [7] [8] [9]

Magnetic field

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

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. [12] [13] 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. [12]

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. [2] 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. [14] 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". [3] [15]

See also

Related Research Articles

<span class="mw-page-title-main">Black hole</span> Object that has a no-return boundary

A black hole is a region of spacetime where gravity is so strong that nothing, including light and other electromagnetic waves, has enough energy to escape it. Einstein's theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. A black hole has a great effect on the fate and circumstances of an object crossing it, but it has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly.

<span class="mw-page-title-main">General relativity</span> Theory of gravitation as curved spacetime

General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalises special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second order partial differential equations.

In general relativity, a naked singularity is a hypothetical gravitational singularity without an event horizon.

Hawking radiation is the theoretical thermal black-body radiation released outside a black hole's event horizon. This is counterintuitive because once ordinary electromagnetic radiation is inside the event horizon, it cannot escape. It is named after the physicist Stephen Hawking, who developed a theoretical argument for its existence in 1974. Hawking radiation is predicted to be extremely faint and is many orders of magnitude below the current best telescopes' detecting ability.

The no-hair theorem states that all stationary black hole solutions of the Einstein–Maxwell equations of gravitation and electromagnetism in general relativity can be completely characterized by only three independent externally observable classical parameters: mass, electric charge, and angular momentum. Other characteristics are uniquely determined by these three parameters, and all other information about the matter that formed a black hole or is falling into it "disappears" behind the black-hole event horizon and is therefore permanently inaccessible to external observers after the black hole "settles down". Physicist John Archibald Wheeler expressed this idea with the phrase "black holes have no hair", which was the origin of the name.

In astronomy, the term compact object refers collectively to white dwarfs, neutron stars, and black holes. It could also include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects have a high mass relative to their radius, giving them a very high density, compared to ordinary atomic matter.

A gravastar is an object hypothesized in astrophysics by Pawel O. Mazur and Emil Mottola as an alternative to the black hole theory. It has usual black hole metric outside of the horizon, but de Sitter metric inside. On the horizon there is a thin shell of matter. The term "gravastar" is a portmanteau of the words "gravitational vacuum star". Further theoretical considerations of gravastars include the notion of a nestar, or a second gravastar nested within the first one.

The Immirzi parameter is a numerical coefficient appearing in loop quantum gravity (LQG), a nonperturbative theory of quantum gravity. The Immirzi parameter measures the size of the quantum of area in Planck units. As a result, its value is currently fixed by matching the semiclassical black hole entropy, as calculated by Stephen Hawking, and the counting of microstates in loop quantum gravity.

Numerical relativity is one of the branches of general relativity that uses numerical methods and algorithms to solve and analyze problems. To this end, supercomputers are often employed to study black holes, gravitational waves, neutron stars and many other phenomena described by Einstein's theory of general relativity. A currently active field of research in numerical relativity is the simulation of relativistic binaries and their associated gravitational waves.

A ring singularity or ringularity is the gravitational singularity of a rotating black hole, or a Kerr black hole, that is shaped like a ring.

An exotic star is a hypothetical compact star composed of exotic matter, and balanced against gravitational collapse by degeneracy pressure or other quantum properties.

<span class="mw-page-title-main">Gravitational-wave astronomy</span> Branch of astronomy using gravitational waves

Gravitational-wave astronomy is an emerging field of science, concerning the observations of gravitational waves to collect relatively unique data and make inferences about objects such as neutron stars and black holes, events such as supernovae, and processes including those of the early universe shortly after the Big Bang.

A nonsingular black hole model is a mathematical theory of black holes that avoids certain theoretical problems with the standard black hole model, including information loss and the unobservable nature of the black hole event horizon.

<span class="mw-page-title-main">Gravitoelectromagnetism</span> Analogies between Maxwells and Einsteins field equations

Gravitoelectromagnetism, abbreviated GEM, refers to a set of formal analogies between the equations for electromagnetism and relativistic gravitation; specifically: between Maxwell's field equations and an approximation, valid under certain conditions, to the Einstein field equations for general relativity. Gravitomagnetism is a widely used term referring specifically to the kinetic effects of gravity, in analogy to the magnetic effects of moving electric charge. The most common version of GEM is valid only far from isolated sources, and for slowly moving test particles.

<span class="mw-page-title-main">Relativistic images</span> Images of gravitational lensing

Relativistic images are images of gravitational lensing which result due to light deflections by angles .

In astrophysics, an event horizon is a boundary beyond which events cannot affect an observer. Wolfgang Rindler coined the term in the 1950s.

<span class="mw-page-title-main">Binary black hole</span> System consisting of two black holes in close orbit around each other

A binary black hole (BBH), or black hole binary, is a system consisting of two black holes in close orbit around each other. Like black holes themselves, binary black holes are often divided into stellar binary black holes, formed either as remnants of high-mass binary star systems or by dynamic processes and mutual capture; and binary supermassive black holes, believed to be a result of galactic mergers.

A black hole firewall is a hypothetical phenomenon where an observer falling into a black hole encounters high-energy quanta at the event horizon. The "firewall" phenomenon was proposed in 2012 by physicists Ahmed Almheiri, Donald Marolf, Joseph Polchinski, and James Sully as a possible solution to an apparent inconsistency in black hole complementarity. The proposal is sometimes referred to as the AMPS firewall, an acronym for the names of the authors of the 2012 paper. The potential inconsistency pointed out by AMPS had been pointed out earlier by Samir Mathur who used the argument in favour of the fuzzball proposal. The use of a firewall to resolve this inconsistency remains controversial, with physicists divided as to the solution to the paradox.

Manasse Mbonye is a theoretical astrophysicist born in Gahini, Rwanda. He is currently Executive Secretary of the National Council for Science and Technology in Kigali.

<span class="mw-page-title-main">Accretion disk</span> Structure formed by diffuse material in orbital motion around a massive central body

An accretion disk is a structure 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 other forces induce instabilities causing orbiting material in the disk to spiral inward toward the central body. Gravitational and frictional forces compress and raise the temperature of the material, causing the emission of electromagnetic radiation. The frequency range of that radiation depends on the central object's mass. Accretion disks of young stars and protostars radiate in the infrared; those around neutron stars and black holes in the X-ray part of the spectrum. The study of oscillation modes in accretion disks is referred to as diskoseismology.

References

  1. 1 2 Mitra, Abhas (1998). "Final state of spherical gravitational collapse and likely sources of Gamma Ray bursts". arXiv: astro-ph/9803014 .
  2. 1 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. 1 2 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. 1 2 3 4 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. 1 2 3 4 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. 1 2 3 4 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. 1 2 3 4 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. 1 2 3 4 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. 1 2 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.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.