181 research outputs found
Analysing Astronomy Algorithms for GPUs and Beyond
Astronomy depends on ever increasing computing power. Processor clock-rates
have plateaued, and increased performance is now appearing in the form of
additional processor cores on a single chip. This poses significant challenges
to the astronomy software community. Graphics Processing Units (GPUs), now
capable of general-purpose computation, exemplify both the difficult
learning-curve and the significant speedups exhibited by massively-parallel
hardware architectures. We present a generalised approach to tackling this
paradigm shift, based on the analysis of algorithms. We describe a small
collection of foundation algorithms relevant to astronomy and explain how they
may be used to ease the transition to massively-parallel computing
architectures. We demonstrate the effectiveness of our approach by applying it
to four well-known astronomy problems: Hogbom CLEAN, inverse ray-shooting for
gravitational lensing, pulsar dedispersion and volume rendering. Algorithms
with well-defined memory access patterns and high arithmetic intensity stand to
receive the greatest performance boost from massively-parallel architectures,
while those that involve a significant amount of decision-making may struggle
to take advantage of the available processing power.Comment: 10 pages, 3 figures, accepted for publication in MNRA
The Galactic Exoplanet Survey Telescope (GEST)
The Galactic Exoplanet Survey Telescope (GEST) will observe a 2 square degree
field in the Galactic bulge to search for extra-solar planets using a
gravitational lensing technique. This gravitational lensing technique is the
only method employing currently available technology that can detect Earth-mass
planets at high signal-to-noise, and can measure the frequency of terrestrial
planets as a function of Galactic position. GEST's sensitivity extends down to
the mass of Mars, and it can detect hundreds of terrestrial planets with
semi-major axes ranging from 0.7 AU to infinity. GEST will be the first truly
comprehensive survey of the Galaxy for planets like those in our own Solar
System.Comment: 17 pages with 13 figures, to be published in Proc. SPIE vol 4854,
"Future EUV-UV and Visible Space Astrophysics Missions and Instrumentation
Mirage: A New Package for the Simulation of Gravitationally Microlensed Quasars
We present Mirage, a new package for simulating gravitationally lensed quasars that allows simulation of arbitrarily sized emitting regions of the quasar’s accretion disk. We develop a robust, large-scale simulator, wirtten in Python, to model gravitationally lensed quasars. Numerical simulation of gravitationally microlensed quasars provides a tool to determine the physical size and temperature profile of quasars accretion disks which is impossible through direct observation. The method consists of ray-tracing approximately 1010 paths through a simulated starfield, taking advantage of the latest technologies in cluster computing,to calculate flux received by the observer from each lensed image from different regions of the accretion disk as the quasar moves relative to the lensing galaxy. We compare our simulations to observations of QSO2237+0305 in optical and X-ray wavebands to place constraints on the relative size of the x-ray and optical emitting regions of the quasar’s accretion disk
Gravitational microlensing
The formulation of the Theory of General Relativity and the observational evidence for the expansion of the universe provided the basis for much of the work
carried out in the field of cosmology over the past hundred years. Huge volumes of
research have been conducted to find reliable values for cosmological parameters
and to describe the amount and nature of the matter in the universe. Chapter 1
of this thesis attempts to summarise current theoretical and observational thinking on these matters and, in particular, examines the wide-ranging application of
gravitational lensing to the search for so-called dark matter. The use of gravitational microlensing to investigate a cosmological population of compact objects,
their effects on the long term variability of the apparent luminosity of quasars
and on the results of the on-going observations of high redshift supernovae is
discussed. Such investigation forms the basis for this thesis.The main tool for this investigation is a computer model which simulates the
gravitational lensing effect of a population of compact object over a period of
time. Chapter 2 sets out the theoretical background for this simulation. In
particular, the methods used to set the physical parameters of the simulation,
such as its volume, the redshifts of the lenses and their masses, are outlined.Chapter 3 presents the implementation of the computer model. Modelling techniques used by other researchers are discussed, as are alternative approaches
considered for the implementation of this model. In order to simulate the evolving distribution of the lensing objects over time, the simulation was designed to
run on high performance parallel supercomputers. The method by which the
simulation was designed to take advantage of this type of computing platform is
also discussed.In order to examine the effects of a cosmological distribution of compact objects
on high redshift sources properly, it is necessary to have observational data. For
this thesis, the observational data consists of a set of lightcurves from high redshift
quasars observed over a 25 year period. This data set is outlined in Chapter 4.
The results from the computer simulation are then presented, including both example light curves and power spectra for a variety of cosmological models, source
sizes, source redshifts and lens masses. This observational data is compared with
the simulation data and is found to have comparable levels of power for a number
of simulation models.Chapter 5 examines the effect of a cosmological population of compact objects
on the ongoing high redshift supernovae searches. The effects of such objects are
modelled for a number of cosmological models for the range of redshifts proposed
for the SNAP and VISTA searches. It is found that the proposed number counts
for supernovae detection in each redshift bin are sufficient to differentiate between
the different cosmological models
Observational signatures of microlensing in gravitational waves at LIGO/Virgo frequencies
Microlenses with typical stellar masses (a few ) have
traditionally been disregarded as potential sources of gravitational lensing
effects at LIGO/Virgo frequencies, since the time delays are often much smaller
than the inverse of the frequencies probed by LIGO/Virgo, resulting in
negligible interference effects at LIGO/Virgo frequencies. While this is true
for isolated microlenses in this mass regime, we show how, under certain
circumstances and for realistic scenarios, a population of microlenses (for
instance stars and remnants from a galaxy halo or from the intracluster medium)
embedded in a macromodel potential (galaxy or cluster) can conspire together to
produce time delays of order one millisecond which would produce significant
interference distortions in the observed strains. At sufficiently large
magnification factors (of several hundred), microlensing effects should be
common in gravitationally lensed gravitational waves. We explore the regime
where the predicted signal falls in the frequency range probed by LIGO/Virgo.
We find that stellar mass microlenses, permeating the lens plane, and near
critical curves, can introduce interference distortions in strongly lensed
gravitational waves. For those lensed events with negative parity, (or saddle
points, never studied before in the context of gravitational waves), and that
take place near caustics of macromodels, they are more likely to produce
measurable interference effects at LIGO/Virgo frequencies. This is the first
study that explores the effect of a realistic population of microlenses, plus a
macromodel, on strongly lensed gravitational waves.Comment: 16 page
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