5,559 research outputs found
Astrophysical signatures of boson stars: quasinormal modes and inspiral resonances
Compact bosonic field configurations, or boson stars, are promising dark
matter candidates which have been invoked as an alternative description for the
supermassive compact objects in active galactic nuclei. Boson stars can be
comparable in size and mass to supermassive black holes and they are hard to
distinguish by electromagnetic observations. However, boson stars do not
possess an event horizon and their global spacetime structure is different from
that of a black hole. This leaves a characteristic imprint in the
gravitational-wave emission, which can be used as a discriminant between black
holes and other horizonless compact objects. Here we perform a detailed study
of boson stars and their gravitational-wave signatures in a fully relativistic
setting, a study which was lacking in the existing literature in many respects.
We construct several fully relativistic boson star configurations, and we
analyze their geodesic structure and free oscillation spectra, or quasinormal
modes. We explore the gravitational and scalar response of boson star
spacetimes to an inspiralling stellar-mass object and compare it to its black
hole counterpart. We find that a generic signature of compact boson stars is
the resonant-mode excitation by a small compact object on stable quasi-circular
geodesic motion.Comment: 20 pages, 8 figures. v2: minor corrections, version to be published
in Phys. Rev. D. v3: final versio
Optimal Time-dependent Sequenced Route Queries in Road Networks
In this paper we present an algorithm for optimal processing of
time-dependent sequenced route queries in road networks, i.e., given a road
network where the travel time over an edge is time-dependent and a given
ordered list of categories of interest, we find the fastest route between an
origin and destination that passes through a sequence of points of interest
belonging to each of the specified categories of interest. For instance,
considering a city road network at a given departure time, one can find the
fastest route between one's work and his/her home, passing through a bank, a
supermarket and a restaurant, in this order. The main contribution of our work
is the consideration of the time dependency of the network, a realistic
characteristic of urban road networks, which has not been considered previously
when addressing the optimal sequenced route query. Our approach uses the A*
search paradigm that is equipped with an admissible heuristic function, thus
guaranteed to yield the optimal solution, along with a pruning scheme for
further reducing the search space. In order to compare our proposal we extended
a previously proposed solution aimed at non-time dependent sequenced route
queries, enabling it to deal with the time-dependency. Our experiments using
real and synthetic data sets have shown our proposed solution to be up to two
orders of magnitude faster than the temporally extended previous solution.Comment: 10 pages, 12 figures To be published as a short paper in the 23rd ACM
SIGSPATIA
Echoes of ECOs: gravitational-wave signatures of exotic compact objects and of quantum corrections at the horizon scale
Gravitational waves from binary coalescences provide one of the cleanest
signatures of the nature of compact objects. It has been recently argued that
the post-merger ringdown waveform of exotic ultracompact objects is initially
identical to that of a black-hole, and that putative corrections at the horizon
scale will appear as secondary pulses after the main burst of radiation. Here
we extend this analysis in three important directions: (i) we show that this
result applies to a large class of exotic compact objects with a photon sphere
for generic orbits in the test-particle limit; (ii) we investigate the
late-time ringdown in more detail, showing that it is universally characterized
by a modulated and distorted train of "echoes" of the modes of vibration
associated with the photon sphere; (iii) we study for the first time
equal-mass, head-on collisions of two ultracompact boson stars and compare
their gravitational-wave signal to that produced by a pair of black-holes. If
the initial objects are compact enough as to mimic a binary black-hole
collision up to the merger, the final object exceeds the maximum mass for boson
stars and collapses to a black-hole. This suggests that - in some
configurations - the coalescence of compact boson stars might be almost
indistinguishable from that of black-holes. On the other hand, generic
configurations display peculiar signatures that can be searched for in
gravitational-wave data as smoking guns of exotic compact objects.Comment: 13 pages, RevTex4. v2: typo in equation 7 corrected, references
added, to appear in PR
- …