Magnetospheric eternally collapsing object

A Magnetospheric Eternally Collapsing Object or MECO is a proposed alternative to a black hole. In essence, this theory states that massive objects that suffer gravitational collapse never actually form black holes since the build up of gravitationally trapped radiation pressure slows the collapse to a very small rate when the object becomes sufficiently compact (see Eddington luminosity). The main differences between MECO's and black holes lies in the fact that a MECO has a distantly observable intrinsic magnetic field, while emitting Eddington limited radiation from a highly redshifted surface which makes this "glow" from the MECO surface difficult to observe (black holes can't have magnetic fields and emit only weak Hawking radiation. Recent evidence of intrinsic magnetic fields inside of what are thought to be super-massive black holes in the centers of some quasars has brought attention to the possibility that they may actually contain MECOs.

History Of the ECO

The term Eternally Collapsing Object (ECO) was first coined by astrophysicist Abhas Mitra in 1998.^[1] He suggested the possibility that black hole candidates might actually be quasistatic ultra compact objects, called ECOs, that are asymptotically approaching a true black hole state with zero mass. He also suggested the possiblity that under certain conditions ECOs may also possess intrinsic magnetic fields whose value could be modest (in extragalactic cases) or extremely high (in stellar mass ECOs). In contrast, the intrinsic magnetic field of black holes is zero. On the other hand intrinsically magnetic ECOs might be identified as objects different from black holes by virtue of the existence of their intrinsic magnetic fields". Although Mitra did not further quantitatively develop the idea of intrinsically magnetized ECOs, he continued to make reference to the possibility of their existence in later papers preprints^[2] and papers,^[3]. Mitra also claimed that the beamed emission from the Gamma Ray Bursts could be better understood if they are associated with birth of highly magnetized ECOs rather than non-magnetized black holes."^[4] The essential idea was that the non-singular ECOs are something like the Relativistic version of Neutron Stars.

Enter The MECO

Quantitative observational and theoretical arguments, supporting the existence of intrisically magnetized Eternally Collapsing Objects which contained strong intrinsic equipartition magnetic field in lieu of an event horizon, were first given in a series of seminal papers published by two American astrophysicists Darryl Leiter and Stanley Robertson, the first of which was published in 2002.^[5] In this context, it was natural to add the term "Magnetospheric" to ECO to make it MECO, as was done by Darryl Leiter, Abhas Mitra and Stanley Robertson in 2001.^[6] However Mitra withdrew his name from a subsequent revised version of the Leiter and Robertson paper because he felt that the MECO picture was a special case of the more general ECO concept, which should have no crucial assumptions and thus be model independent. Nonetheless Leiter & Robertson were keen to make a specific model of MECO in order to be able to immediately apply it to astrophysical observations, and their paper bearing the same title was subsequently published.^[7]. Robertson and Leiter elaborated on this aspect by using the idea of disk-magnetospheric interaction.^[8] Further, by invoking the well known "magnetic propeller" mechanism, they offered a novel explanation for a hitherto unexplained universal correlation between observed radio and X-ray luminosities in black hole candidates.^[9]. In the final analysis the papers of Darryl Leiter and Stanley Robertson discussed above were the first to offer observational and theoretical evidence, based General Relativity and The Strong Principle of Equivalence, that MECOs could exist in the Universe and that black hole candidates actually contained MECOs instead of Black Holes.

Why The Strong Principle Of Equivalence Implies That MECO Exist In The Universe

In general relativity, preservation of the strong principle of equivalence (SPOE) requires that special relativity must hold locally for all time-like observers in all of spacetime. On this basis Darryl Leiter and Stanley Robertson argued that existence of MECO is implied by the idea that Nature requires that the SPOE must be dynamically preserved everywhere in spacetime for the timelike world lines of massive particles or fluids under the influence of both gravitational and non-gravitational forces. Preservation of the SPOE requires that the frame of reference of the co-moving observer in the massive collapsing fluid must always be connected to the frame of reference of a stationary observer by special relativistic transformations with a physical 3-speed that is less than the speed of light (Schild, R., Leiter, D., & Robertson, S. 2006, AJ, 132, 420 -(SLR06).

Since the left-hand side of the Einstein equation cannot by itself dynamically enforce the preservation of the SPOE, it follows that for collapsing objects there must exist SPOE-preserving non-gravitational processes in nature which must always be included in the energy–momentum tensor on the right-hand side of the Einstein equation. It was in this manner that the general relativistic MECO solutions to the Einstein-Maxwell equations were discovered, as was shown in the papers (Robertson, S., & Leiter, D. (2002), ApJ, 565, 447; Robertson, S., & Leiter, D. (2003) ApJ, 596, L203; Robertson, S., & Leiter, D. (2004), MNRAS, 350, 1391; and developed in more detail in Appendices 1–10 of Schild et al. (2005),(Schild, R., Leiter, D., & Robertson, S. (2005), arXiv astro-ph/0505518. There it was shown that for a collapsing body, the structure and radiation transfer properties of the energy–momentum tensor on the right-hand side of the Einstein field equations, could describe a collapsing radiating object which contained equipartition magnetic fields that generated a highly red-shifted Eddington limited secular collapse process. This collapse process was shown to preserve the SPOE by dynamically preventing trapped surfaces, that lead to event horizons, from forming. In Appendices 1–10 of Schild et al. (2005) it was shown that, by using the Einstein–Maxwell equations and quantum electrodynamics in the context of general relativistic plasma astrophysics, it was possible to virtually stop and maintain a slow (many Hubble times!), steady collapse of a compact physical plasma object outside of its Schwarzschild radius. The non-gravitational force was Compton photon pressure generated by synchrotron radiation from an intrinsic equipartition magnetic dipole field contained within the compact object. The rate of collapse is controlled by radiation at the local Eddington limit, but from a highly red shifted surface with an extremely small photon escape cone. In Appendix 9 and 10 of Schild et al. (2005) it was shown that the equatorial poloidal magnetic field, associated with a locally Eddington limited secular rate of collapse of the exterior surface, was strong enough to spontaneously create bound electron-positron pairs in the surface plasma of the MECO which contribute to the general relativistic surface drift currents, within the pair dominated plasma at the MECO surface. These electron-positron drift currents on the MECO surface generate the magnetic fields which create the MECO’s distantly observed intrinsic magnetic moment. Within the context of the MECO’s Eddington limited secular balance, the action of this QED pair production process was shown to be sufficient to stabilize the collapse rate of the MECO surface. For the collapsing, radiating pair dominated plasma associated with the MECO, the corresponding exterior solution to the Einstein equation is described by the time dependent Vaidya metric, where no coordinate transformation between MECO Vaidya metric and the black hole Kerr–Schild metric exists.

Since the highly red shifted Eddington limited MECO Vaidya metric solutions preserve the SPOE, they do not have event horizons and the MECO exhibit distantly observed slowly rotating intrinsic magnetic dipole moments which can interact with their surrounding accretion disk environments. Hence, if supermassive MECO exist in the centers of AGN and Quasars, they should be able to observationally reveal themselves in a manner which distinguishes them from that of central supermassive Black Holes.

Observational Evidence For MECO In The Center Of Quasar Q0957+561

Direct evidence to support the existence of MECO in quasars came in 2005 largely because of the efforts of the American astronomer Rudy Schild , (R. Schild, D. Leiter and S. Robertson, Astronomical J., 132, 420 (2006).

"Schild monitored the quasar's brightness for 20 years, and led an international consortium of observers operating 14 telecopes to keep the object under steady around-the-clock watch at critical times."^[10]

The quasar Q0957+561 revealed its structure with very high resolution because of gravitational microlensing by the stars of an intervening galaxy along its line of sight. This structure has broad similarity with the one expected from a magnetized neutron star endowed with an accretion disc.

The accretion flow in the equatorial plane is halted by the magnetic pressure of the central compact object and the inner radius of the disk is determined by the Alfven Radius. The accretion plasma flow then gets guided by the central dipole magnetic field towards the poles of the central magnetized compact object. During this process, the joint effect of spin and magnetic field may fling part of the accretion flow in an outward relativistic jet. Probably the fastest known astrophysical jet has a bulk Lorentz Factor of > 10, and it is associated with a X-ray binary Cir X-1 which contains a magnetized neutron star rather than a black hole candidate. This shows that presence of strong central magnetic field may be necessary to launch strong jets. There may be a wind outflow from the accretion disk itself. The magnetic push due to the central dipole field may also lend the wind an oppositely moving twin cusp-like structure. This "cusp like" picture may be compared with the "hour glass" picture of magnetic field structure recently observed in a collapsing magnetized Molecular cloud.

Thus, the observations of the accretion disc of this quasar made with the aid of a gravitational lens seem to indicate that Q0957+561 has a magnetic field, which a black hole cannot have. The researchers deduced the existence of a magnetic field from the fact that the accretion disk has a gap of 4000 AU around the central object. A small part of the disk just outside of the gap seems to be glowing, which is interpreted as being a sign that the material is heated by a strong magnetic field. Such a glow is also expected because most of the accretion power is released at the inner edge of the disk, truncated by the magnetic pressure of the central compact object. In contrast, for black hole accretion, even though, the inner edge of the disk formally lies at 3 R_s, where R_s is the Schwarzschild Radius, the flow is actually never truncated and, on the other hand, proceeds first to the event horizon and then, all the way up to the central singularity. The flow might get quasispherical in between and a glow is expected from region lying between the event horizon and the inner edge of the disk.

Observational Evidence for The Existence of MECO In Radio Loud and Radio Quiet Quasars

In their recently published paper in Astronomical Journal [AstrJ, 135, pg 947 (2008)] R. E. Schild, D. Leiter, and S. Robertson further elaborated on the fact that the object at the heart of the radio loud quasar Q0957+561 is not a supermassive black hole, as is currently believed to be the case for all quasars. Schild and his team at the Harvard-Smithsonian Center for Astrophysics found that the jets originated 8000 AU from the poles of the centre, in a region 1000AU across. In addition they found that the accretion disc in this quasar appeared to be truncated at 2000AU from the centre, and the inner edge surrounding the apparently empty inner region of the disc contained a very thin annular region that was found to be intensely radiating. There also appeared to be a broad conic wind outflow from the accretion disc which created a luminous Broad Line Emission Region Elvis structure (cf. Martin Elvis). On the basis of these observations they came to the conclusion that "This quasar appears to be dynamically dominated by an intrinsic magnetic field which is internally anchored to its central, rotating supermassive compact object".

In "radio loud" quasars, which make up about 10% of the total quasar populations, some of that gas is forcefully ejected outward in two opposing jets at nearly the speed of light. On the other hand the remaining 90% of the quasars do not exhibit any jet structure and for that reason are "radio quiet". In order to better understand the difference between the two types of quasars, theorists struggle to understand the physics of the accretion disk and jets, while observers struggle to peer into the quasar's heart. However the manner in which the "central engine" is able to turn on radio emitting jet structures in radio loud quasars, while also being able to turn off the radio emitting jet structure in radio quiet quasars, is difficult problem for both theorists and observers because the central regions of quasars are so compact and the quasars so far away from Earth.

Using newly developed optical telescope techniques involving gravitational micro-lensing and reverberation analysis, Rudy Schild and his colleagues have also studied the internal structure of the radio quiet quasar Q2237 (known as the Einstein Cross), as well as the radio loud quasar Q0957 (known as the Twin) both of which are located more than 9 billion light-years from Earth. These two quasars, which are in distinctly different spectral states, have been observed to have central compact objects containing masses on the order of 3-4 billion Suns. For this reason most astrophysicists would consider the central objects in these two quasars to be "black holes," but Schild, Leiter, and Robertson's research has suggested otherwise. "We don't call the central objects in these quasars black holes because our observations indicate that these two quasars have central compact objects which contain internally anchored magnetic fields that are able to penetrate through the surface of their collapsed central objects and interact with the quasars accretion disk and its environment," they commented.

The researchers chose Q0957 and Q2237 because of their association with natural cosmic lenses. The gravity of nearby galaxies bends space, forming multiple images of the distant quasars and magnifying their light. Stars and planets within nearby galaxies can also affect the quasars light, causing small fluctuations in brightness (in a process called "micro-lensing") when they drift into the line of sight between Earth and the quasars.

Using this micro-lensing-reverberation technique on the radio loud quasar Q0957 Schild monitored the quasar's brightness for a period of 20 years, and led an international consortium of observers operating 14 telescopes to keep the object under steady around-the-clock watch at critical times. "With micro-lensing, we were able to discern more detail about the so-called 'black hole' in this quasar which is two- thirds of the way to the edge of the visible universe than we can from the black hole at the center of the Milky Way," said Schild. Through careful analysis, the team teased out details about the inner structure of this quasar For example, their calculations pinpointed the location where the jets form. "How when and where do these jets form? Even after 60 years of radio observations, we had no answer. Now the evidence is in, and we know," said Schild.

Schild, Leiter, and Robertson found that the jets in the radio loud quasar Q0957 appear to emerge from two regions 1,000 astronomical units in size (about 25 times larger than the Pluto-Sun distance) located 8,000 astronomical units directly above the poles of the central compact object. (An astronomical unit is defined as the average distance from the Earth to the Sun, or 93 million miles). However, that location would be expected only if the jets were powered by reconnecting magnetic field lines that were anchored to the rotating super massive compact object within the quasar. By interacting with a surrounding accretion disk, such spinning magnetic field lines spool up, winding tighter and tighter until they explosively unite, reconnect and break, releasing huge amounts of energy that power the jets. "This quasar appears to be dynamically dominated by an intrinsic magnetic field which is internally anchored to its central, rotating super massive compact object," they stated.

Since standard black hole models were found to be unable to explain the observed internal structure seen in the quasar Q0957, Schild and his colleagues, Darryl Leiter (Marwood Astrophysics Research Center and currenty a visitor at the National Radio Astronomy Observatory in Charlottesville Virginia) and Stanley Robertson (Southwestern Oklahoma State University), were led to propose a revolutionary new general relativistic theory for the quasar Q0957 in which the structure of the dominant magnetic field is intrinsic to the quasar's central, super massive compact object, rather than only being part of the accretion disk as thought by most researchers. "Our finding challenges the accepted view of black holes," said Leiter. "We've even proposed a new name for them Magnetospheric Eternally Collapsing Objects, or MECO," a magnetic generalization of the name coined in 1998 by Indian astrophysicist Abhas Mitra. This research suggests that, in addition to its mass and spin, the central compact object in Q0957 may have physical properties more like a highly red shifted, spinning magnetic dipole than like a black hole. According to this theory, a MECO does not have an event horizon, so any matter that is able to get by the magnetic propeller is gradually slowed down and stopped at the MECO's highly red shifted surface, with just a weak signal connecting the radiation from that matter to a distant observer. For this reason this signal has not been detected from Q0957 since it is very hard to observe.

Hence in [AstrJ, 135, pg 947 (2008)] Schild, Leiter, and Robertson were led to the conclusion that a simple and unified answer to the long-standing question: "Why are some quasars radio loud?" emerges naturally if the central objects of quasars are MECO, with radio-loud andradio-quiet states similar to the case of galactic black hole candidates.

References

^ "Final State of Spherical Gravitational Collapse and Likely Sources of Gamma Ray Bursts", A. Mitra, arXiv:astro-ph/9803014 (1998)
^ "On the Question of Trapped Surfaces and Black Holes", A. Mitra (2001), arXiv:astro-ph/0105532
^ "On the Nature of the Compact Condensations at the Centre of Galaxies", A. Mitra, Bull. Astron. Soc. India, 30, 173 (2002), astro-ph/0205261, "On the Final State of Spherical Gravitational Collapse", A. Mitra, Found. Phys. Lett., 15, 439, (2002), arXiv:astro-ph/0207056
^ "Non-occurrence of Trapped Surfaces and Black Holes in Spherical Gravitational Collapse: An Abridged Version", A. Mitra, Found. Phys. Lett., 13(6),543 (2000), arXiv:astro-ph/9910408
^ "Evidence for Intrinsic Magnetic Moments in Black Hole Candidates", S. Robertson and D. Leiter, Astrophysical J., 565, 447 (2002), arXiv:astro-ph/0102381
^ "Does the Principle of Equivalence Prevent Trapped Surfaces From being Formed in the General Relativistic Collapse Process?", D. Leiter, A. Mitra and S. Robertson, (2001), arXiv:astro-ph/0111421
^ "Does the Principle of Equivalence Prevent Trapped Surfaces From being Formed in the General Relativistic Collapse Process?", D. Leiter and S. Robertson, Foundations of Physics Lett., Vol. 16, pp.143 (2003)
^ "On Intrinsic Magnetic Moment in Black Hole Candidates", S. Robertson and D. Leiter, Astrophysical J. Lett., 596, L203 (2003), arXiv:astro-ph/0310078
^ "On the Origin of the Radio/X-Ray Luminosity Correlation in Black Hole Candidates", S. Robertson and D. Leiter, Mon. Not. Roy. Astron. Soc., 350, 1391, 2004, arXiv:astro-ph/0402445
^ Center for Astrophysics, Harvard, Press Release, July 25, 2006

External links

Q0957+561: Die historisch erste Linse mit Quasar (Universität zu Köln)
Research Sheds New Light On Quasars (SpaceDaily) Jul 26, 2006
Mysterious quasar casts doubt on black holes - New Scientist
arXiv:astro-ph/0505518: Observations Supporting the Existence of an Intrinsic Magnetic Moment Inside the Central Compact Object Within the Quasar Q0957+561, Rudolph E. Schild, Darryl J. Leiter, Stanley L. Robertson (25 May 2005)