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Article: Can accretion disk properties observationally distinguish black holes from naked singularities?

TitleCan accretion disk properties observationally distinguish black holes from naked singularities?
Authors
Issue Date2010
PublisherAmerican Physical Society. The Journal's web site is located at http://prd.aps.org
Citation
Physical Review D (Particles, Fields, Gravitation and Cosmology), 2010, v. 82 n. 12, article no. 124047, p. 124047-1-124047-20 How to Cite?
AbstractNaked singularities are hypothetical astrophysical objects, characterized by a gravitational singularity without an event horizon. Penrose has proposed a conjecture, according to which there exists a cosmic censor who forbids the occurrence of naked singularities. Distinguishing between astrophysical black holes and naked singularities is a major challenge for present day observational astronomy. In the context of stationary and axially symmetrical geometries, a possibility of differentiating naked singularities from black holes is through the comparative study of thin accretion disks properties around rotating naked singularities and Kerr-type black holes, respectively. In the present paper, we consider accretion disks around axially-symmetric rotating naked singularities, obtained as solutions of the field equations in the Einstein-massless scalar field theory. A first major difference between rotating naked singularities and Kerr black holes is in the frame dragging effect, the angular velocity of a rotating naked singularity being inversely proportional to its spin parameter. Because of the differences in the exterior geometry, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution and equilibrium radiation spectrum) are different for these two classes of compact objects, consequently giving clear observational signatures that could discriminate between black holes and naked singularities. For specific values of the spin parameter and of the scalar charge, the energy flux from the disk around a rotating naked singularity can exceed by several orders of magnitude the flux from the disk of a Kerr black hole. In addition to this, it is also shown that the conversion efficiency of the accreting mass into radiation by rotating naked singularities is always higher than the conversion efficiency for black holes, i.e., naked singularities provide a much more efficient mechanism for converting mass into radiation than black holes. Thus, these observational signatures may provide the necessary tools from clearly distinguishing rotating naked singularities from Kerr-type black holes. © 2010 The American Physical Society.
Persistent Identifierhttp://hdl.handle.net/10722/142487
ISSN
2014 Impact Factor: 4.643
2015 SCImago Journal Rankings: 1.882
ISI Accession Number ID
Funding AgencyGrant Number
government of the Hong Kong Special Administrative RegionHKU 701808P
Funding Information:

The work of T.H. was supported by the General Research Fund Grant No. HKU 701808P of the government of the Hong Kong Special Administrative Region.

Grants

 

DC FieldValueLanguage
dc.contributor.authorKovacs, Zen_US
dc.contributor.authorHarko, TCen_US
dc.date.accessioned2011-10-28T02:46:54Z-
dc.date.available2011-10-28T02:46:54Z-
dc.date.issued2010en_US
dc.identifier.citationPhysical Review D (Particles, Fields, Gravitation and Cosmology), 2010, v. 82 n. 12, article no. 124047, p. 124047-1-124047-20en_US
dc.identifier.issn1550-7998-
dc.identifier.urihttp://hdl.handle.net/10722/142487-
dc.description.abstractNaked singularities are hypothetical astrophysical objects, characterized by a gravitational singularity without an event horizon. Penrose has proposed a conjecture, according to which there exists a cosmic censor who forbids the occurrence of naked singularities. Distinguishing between astrophysical black holes and naked singularities is a major challenge for present day observational astronomy. In the context of stationary and axially symmetrical geometries, a possibility of differentiating naked singularities from black holes is through the comparative study of thin accretion disks properties around rotating naked singularities and Kerr-type black holes, respectively. In the present paper, we consider accretion disks around axially-symmetric rotating naked singularities, obtained as solutions of the field equations in the Einstein-massless scalar field theory. A first major difference between rotating naked singularities and Kerr black holes is in the frame dragging effect, the angular velocity of a rotating naked singularity being inversely proportional to its spin parameter. Because of the differences in the exterior geometry, the thermodynamic and electromagnetic properties of the disks (energy flux, temperature distribution and equilibrium radiation spectrum) are different for these two classes of compact objects, consequently giving clear observational signatures that could discriminate between black holes and naked singularities. For specific values of the spin parameter and of the scalar charge, the energy flux from the disk around a rotating naked singularity can exceed by several orders of magnitude the flux from the disk of a Kerr black hole. In addition to this, it is also shown that the conversion efficiency of the accreting mass into radiation by rotating naked singularities is always higher than the conversion efficiency for black holes, i.e., naked singularities provide a much more efficient mechanism for converting mass into radiation than black holes. Thus, these observational signatures may provide the necessary tools from clearly distinguishing rotating naked singularities from Kerr-type black holes. © 2010 The American Physical Society.-
dc.languageengen_US
dc.publisherAmerican Physical Society. The Journal's web site is located at http://prd.aps.org-
dc.relation.ispartofPhysical Review D (Particles, Fields, Gravitation and Cosmology)en_US
dc.rightsPhysical Review D (Particles, Fields, Gravitation and Cosmology). Copyright © American Physical Society.-
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.titleCan accretion disk properties observationally distinguish black holes from naked singularities?en_US
dc.typeArticleen_US
dc.identifier.emailKovacs, Z: zkovacs@hku.hken_US
dc.identifier.emailHarko, TC: harko@hkucc.hku.hken_US
dc.identifier.authorityHarko, TC=rp01333en_US
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.1103/PhysRevD.82.124047-
dc.identifier.scopuseid_2-s2.0-78651322098-
dc.identifier.hkuros196867en_US
dc.identifier.volume82en_US
dc.identifier.issue12-
dc.identifier.spage124047-1en_US
dc.identifier.epage124047-20en_US
dc.identifier.isiWOS:000286744400005-
dc.publisher.placeUnited States-
dc.relation.projectBrane world cosmology: post-inflationary reheating and gravitational lensing-

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