Black star (semiclassical gravity)

A black star is a gravitational object composed of matter. It is a theoretical alternative to the black hole concept from general relativity. The theoretical construct was created through the use of semiclassical gravity theory. A similar structure should also exist for the Einstein–Maxwell–Dirac equations system, which is the (super)classical limit of quantum electrodynamics, and for the Einstein–Yang–Mills–Dirac system, which is the (super)classical limit of the standard model.

A black star doesn't need to have an event horizon, and may or may not be a transitional phase between a collapsing star and a singularity. A black star is created when matter compresses at a rate significantly less than the freefall velocity of a hypothetical particle falling to the center of its star, because quantum processes create vacuum polarization, which creates a form of degeneracy pressure, preventing spacetime (and the particles held within it) from occupying the same space at the same time. This vacuum energy is theoretically unlimited, and if built up quickly enough, will stop gravitational collapse from creating a singularity. This may entail an ever-decreasing rate of collapse, leading to an infinite collapse time, or asymptotically approaching a radius bigger than zero.

A black star with a radius slightly greater than the predicted event horizon for an equivalent-mass black hole will appear very dark, because almost all light produced will be drawn back to the star, and any escaping light will be severely gravitationally redshifted. It will appear almost exactly like a black hole. It will feature Hawking radiation, as virtual particle pairs created in its vicinity may still be split, with one particle escaping and the other being trapped. Additionally, it will create thermal Planckian radiation that will closely resemble the expected Hawking radiation of an equivalent black hole.

The predicted interior of a black star will be composed of this strange state of spacetime, with each length in depth heading inward appearing the same as a black star of equivalent mass and radius with the overlayment stripped off. Temperatures increase with depth towards the centre.

Sources

  • Carlos Barceló, Stefano Liberati, Sebastiano Sonego and Matt Visser, Scientific American (October 2009) Black Stars, Not Black Holes
  • Barceló, C.; Liberati, S.; Sonego, S.; Visser, M. (2008). "Fate of gravitational collapse in semiclassical gravity". Physical Review D. 77 (4): 044032. arXiv:0712.1130. Bibcode:2008PhRvD..77d4032B. doi:10.1103/PhysRevD.77.044032.
  • Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (2009) "Small, dark, and heavy: But is it a black hole?", Bibcode2009arXiv0902.0346V, arXiv:0902.0346
  • https://NeutronStarsAndBlackStars.com

See also

Dark-energy star

A dark-energy star is a hypothetical compact astrophysical object, which a minority of physicists think might constitute an alternative explanation for observations of astronomical black hole candidates.

The concept was proposed by physicist George Chapline. The theory states that infalling matter is converted into vacuum energy or dark energy, as the matter falls through the event horizon. The space within the event horizon would end up with a large value for the cosmological constant and have negative pressure to exert against gravity. There would be no information-destroying singularity.

Gravastar

A gravastar is an object hypothesized in astrophysics as an alternative to the black hole theory by Pawel O. Mazur and Emil Mottola. 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".

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Outline of black holes

The following outline is provided as an overview of and topical guide to black holes:

Black hole – mathematically defined region of spacetime exhibiting such a strong gravitational pull that no particle or electromagnetic radiation can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although crossing the event horizon has enormous effect on the fate of the object crossing it, it appears to have no locally detectable features. 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 on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe.

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