471 research outputs found
Note on a new parametrization for testing the Kerr metric
We propose a new parametrization for testing the Kerr nature of astrophysical
black hole candidates. The common approaches focus on the attempt to constrain
possible deviations from the Kerr solution described by new terms in the
metric. Here we adopt a different perspective. The mass and the spin of a black
hole make the spacetime curved and we want to check whether they do it with the
strength predicted by general relativity. As an example, we apply our
parametrization to the black hole shadow, an observation that may be possible
in a not too distant future.Comment: 8 pages, 3 figure
Dangerous implications of a minimum length in quantum gravity
The existence of a minimum length and a generalization of the Heisenberg
uncertainty principle seem to be two fundamental ingredients required in any
consistent theory of quantum gravity. In this letter we show that they would
predict dangerous processes which are phenomenologically unacceptable. For
example, long--lived virtual super--Planck mass black holes may lead to rapid
proton decay. Possible solutions of this puzzle are briefly discussed.Comment: 5 pages, no figure. v3: refereed versio
A revision of the Generalized Uncertainty Principle
The Generalized Uncertainty Principle arises from the Heisenberg Uncertainty
Principle when gravity is taken into account, so the leading order correction
to the standard formula is expected to be proportional to the gravitational
constant . On the other hand, the emerging picture suggests a
set of departures from the standard theory which demand a revision of all the
arguments used to deduce heuristically the new rule. In particular, one can now
argue that the leading order correction to the Heisenberg Uncertainty Principle
is proportional to the first power of the Planck length . If so, the
departures from ordinary quantum mechanics would be much less suppressed than
what is commonly thought.Comment: 6 pages, 1 figur
Shadows of CPR black holes and tests of the Kerr metric
We study the shadow of the Cardoso-Pani-Rico (CPR) black hole for different
values of the black hole spin , the deformation parameters
and , and the viewing angle . We find that the main impact of
the deformation parameter is the change of the size of the
shadow, while the deformation parameter affects the shape of its
boundary. In general, it is impossible to test the Kerr metric, because the
shadow of a Kerr black hole can be reproduced quite well by a black hole with
non-vanishing or . Deviations from the Kerr
geometry could be constrained in the presence of high quality data and in the
favorable case of a black hole with high values of and . However, the
shadows of some black holes with non-vanishing present peculiar
features and the possible detection of these shadows could unambiguously
distinguish these objects from the standard Kerr black holes of general
relativity.Comment: 10 pages, 7 figures. v2: refereed version with minor change
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