A black star is a gravitational object composed of matter. It is a theoretical alternative to the

black hole A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can defo ...

concept from

general relativity 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. ...

. The theoretical construct was created through the use of

semiclassical gravity Semiclassical gravity is the approximation to the theory of quantum gravity in which one treats matter fields as being quantum and the gravitational field as being classical. In semiclassical gravity, matter is represented by quantum matter fiel ...

theory. A similar structure should also exist for the Einstein–Maxwell–Dirac equations system, which is the (super) classical limit of

quantum electrodynamics In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and spec ...

, and for the Einstein–Yang–Mills–Dirac system, which is the (super) classical limit of the standard model. A black star does not require an

event horizon In astrophysics, an event horizon is a boundary beyond which events cannot affect an 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 compact ob ...

, and may or may not be a transitional phase between a collapsing

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

and a singularity. A black star is created when matter compresses at a rate significantly less than the

free fall In Newtonian physics, free fall is any motion of a body where gravity is the only force acting upon it. In the context of general relativity, where gravitation is reduced to a space-time curvature, a body in free fall has no force acting on i ...

velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity i ...

of a hypothetical particle falling to the center of its star, because quantum processes create

vacuum polarization In quantum field theory, and specifically quantum electrodynamics, vacuum polarization describes a process in which a background electromagnetic field produces virtual electron–positron pairs that change the distribution of charges and curr ...

, which creates a form of

degeneracy pressure Degenerate matter is a highly dense state of fermionic matter in which the Pauli exclusion principle exerts significant pressure in addition to, or in lieu of, thermal pressure. The description applies to matter composed of electrons, protons, ne ...

, preventing

spacetime In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why diffe ...

(and the particles held within it) from occupying the same space at the same time. This

vacuum energy Vacuum energy is an underlying background energy that exists in space throughout the entire Universe. The vacuum energy is a special case of zero-point energy that relates to the quantum vacuum. The effects of vacuum energy can be experiment ...

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 Hawking radiation is theoretical black body radiation that is theorized to be released outside a black hole's event horizon because of relativistic quantum effects. It is named after the physicist Stephen Hawking, who developed a theoretical ar ...

, 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.

Temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on ...

s increase with depth towards the center.

Sources

* Carlos Barceló, Stefano Liberati, Sebastiano Sonego and Matt Visser, Scientific American (October 2009) ''Black Stars, Not Black Holes'' * * Visser, Matt; Barcelo, Carlos; Liberati, Stefano; Sonego, Sebastiano (2009
"Small, dark, and heavy: But is it a black hole?"
,

Sources

See also