Hasil untuk "Astronomy"

J. Baars

Preface to the Second Edition. Preface to the First Edition. Introduction and Historical Review. Introductory Theory of Interferometry and Synthesis Imaging. Analysis of the Interferometer Response. Geometric Relationships and Polarimetry. Antennas and Arrays. Response of the Receiving System. Design of the Analog Receiving System. Digital Signal Processing. Very-Long-Baseline Interferometry. Calibration and Fourier Transformation of Visibility Data. Deconvolution, Adaptive Calibration, and Applications. Interferometer Techniques for Astrometry and Geodesy. Propagation Effects. Van Cittert-Zernike Theorem, Spatial Coherence, and Scattering. Radio Interference. Related Techniques. Principal Symbols. Author Index. Subject Index.

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D. Reitze, R. Adhikari, S. Ballmer et al.

This white paper describes the research and development needed over the next decade to realize "Cosmic Explorer," the U.S. node of a future third-generation detector network that will be capable of observing and characterizing compact gravitational-wave sources to cosmological redshifts.

G. Ashton, M. Huebner, P. Lasky et al.

Bayesian parameter estimation is fast becoming the language of gravitational-wave astronomy. It is the method by which gravitational-wave data is used to infer the sources’ astrophysical properties. We introduce a user-friendly Bayesian inference library for gravitational-wave astronomy, Bilby. This Python code provides expert-level parameter estimation infrastructure with straightforward syntax and tools that facilitate use by beginners. It allows users to perform accurate and reliable gravitational-wave parameter estimation on both real, freely available data from LIGO/Virgo and simulated data. We provide a suite of examples for the analysis of compact binary mergers and other types of signal models, including supernovae and the remnants of binary neutron star mergers. These examples illustrate how to change the signal model, implement new likelihood functions, and add new detectors. Bilby has additional functionality to do population studies using hierarchical Bayesian modeling. We provide an example in which we infer the shape of the black hole mass distribution from an ensemble of observations of binary black hole mergers.

T. P. Robitaille, E. Tollerud, P. Greenfield et al.

We present the first public version (v0.2) of the open-source and community-developed Python package, Astropy. This package provides core astronomy-related functionality to the community, including support for domain-specific file formats such as flexible image transport system (FITS) files, Virtual Observatory (VO) tables, and common ASCII table formats, unit and physical quantity conversions, physical constants specific to astronomy, celestial coordinate and time transformations, world coordinate system (WCS) support, generalized containers for representing gridded as well as tabular data, and a framework for cosmological transformations and conversions. Significant functionality is under active development, such as a model fitting framework, VO client and server tools, and aperture and point spread function (PSF) photometry tools. The core development team is actively making additions and enhancements to the current code base, and we encourage anyone interested to participate in the development of future Astropy versions.

M. Sasaki, T. Suyama, Takahiro Tanaka et al.

This article reviews current understanding of primordial black holes (PBHs), with particular focus on those massive examples (≳1015 g) which remain at the present epoch, not having evaporated through Hawking radiation. With the detection of gravitational waves by LIGO, we have gained a completely novel observational tool to search for PBHs, complementary to those using electromagnetic waves. Taking the perspective that gravitational-wave astronomy will make significant progress in the coming decades, the purpose of this article is to give a comprehensive review covering a wide range of topics on PBHs. After discussing PBH formation, as well as several inflation models leading to PBH production, we summarize various existing and future observational constraints. We then present topics on formation of PBH binaries, gravitational waves from PBH binaries, and various observational tests of PBHs using gravitational waves.

The Casa Team, Benjamin Bean, S. Bhatnagar et al.

CASA, the Common Astronomy Software Applications, is the primary data processing software for the Atacama Large Millimeter/submillimeter Array (ALMA) and the Karl G. Jansky Very Large Array (VLA), and is frequently used also for other radio telescopes. The CASA software can handle data from single-dish, aperture-synthesis, and Very Long Baseline Interferometery (VLBI) telescopes. One of its core functionalities is to support the calibration and imaging pipelines for ALMA, VLA, VLA Sky Survey, and the Nobeyama 45 m telescope. This paper presents a high-level overview of the basic structure of the CASA software, as well as procedures for calibrating and imaging astronomical radio data in CASA. CASA is being developed by an international consortium of scientists and software engineers based at the National Radio Astronomy Observatory (NRAO), the European Southern Observatory, the National Astronomical Observatory of Japan, and the Joint Institute for VLBI European Research Infrastructure Consortium (JIV-ERIC), under the guidance of NRAO.

G. Pilbratt, J. Riedinger, T. Passvogel et al.

Herschel was launched on 14 May 2009, and is now an operational ESA space observatory o ering unprecedented observational capabilities in the far-infrared and submillimetre spectral range 55 671 m. Herschel carries a 3.5 metre diameter passively cooled Cassegrain telescope, which is the largest of its kind and utilises a novel silicon carbide technology. The science payload comprises three instruments: two direct detection cameras/medium resolution spectrometers, PACS and SPIRE, and a very high-resolution heterodyne spectrometer, HIFI, whose focal plane units are housed inside a superfluid helium cryostat. Herschel is an observatory facility operated in partnership among ESA, the instrument consortia, and NASA. The mission lifetime is determined by the cryostat hold time. Nominally approximately 20,000 hours will be available for astronomy, 32% is guaranteed time and the remainder is open to the worldwide general astronomical community through a standard competitive proposal procedure.

F. Harrison, R. Kennicutt, Julianne Dalcanton et al.

S. Chandrasekhar

W. Cash

Sabine Fenstermacher

M. Tse, Haocun Yu, N. Kijbunchoo et al.

The Laser Interferometer Gravitational Wave Observatory (LIGO) has been directly detecting gravitational waves from compact binary mergers since 2015. We report on the first use of squeezed vacuum states in the direct measurement of gravitational waves with the Advanced LIGO H1 and L1 detectors. This achievement is the culmination of decades of research to implement squeezed states in gravitational-wave detectors. During the ongoing O3 observation run, squeezed states are improving the sensitivity of the LIGO interferometers to signals above 50 Hz by up to 3 dB, thereby increasing the expected detection rate by 40% (H1) and 50% (L1).

Ž. Ivezić, A. Connolly, J. Vanderplas et al.

Statistics, Data Mining, and Machine Learning in Astronomy is the essential introduction to the statistical methods needed to analyze complex data sets from astronomical surveys such as the Panoramic Survey Telescope and Rapid Response System, the Dark Energy Survey, and the Large Synoptic Survey Telescope. Now fully updated, it presents a wealth of practical analysis problems, evaluates the techniques for solving them, and explains how to use various approaches for different types and sizes of data sets. Python code and sample data sets are provided for all applications described in the book. The supporting data sets have been carefully selected from contemporary astronomical surveys and are easy to download and use. The accompanying Python code is publicly available, well documented, and follows uniform coding standards. Together, the data sets and code enable readers to reproduce all the figures and examples, engage with the different methods, and adapt them to their own fields of interest. An accessible textbook for students and an indispensable reference for researchers, this updated edition features new sections on deep learning methods, hierarchical Bayes modeling, and approximate Bayesian computation. The chapters have been revised throughout and the astroML code has been brought completely up to date. Fully revised and expanded Describes the most useful statistical and data-mining methods for extracting knowledge from huge and complex astronomical data sets Features real-world data sets from astronomical surveys Uses a freely available Python codebase throughout Ideal for graduate students, advanced undergraduates, and working astronomers

M. Bailes, B. Berger, P. Brady et al.

The 100 years since the publication of Albert Einstein’s theory of general relativity saw significant development of the understanding of the theory, the identification of potential astrophysical sources of sufficiently strong gravitational waves and development of key technologies for gravitational-wave detectors. In 2015, the first gravitational-wave signals were detected by the two US Advanced LIGO instruments. In 2017, Advanced LIGO and the European Advanced Virgo detectors pinpointed a binary neutron star coalescence that was also seen across the electromagnetic spectrum. The field of gravitational-wave astronomy is just starting, and this Roadmap of future developments surveys the potential for growth in bandwidth and sensitivity of future gravitational-wave detectors, and discusses the science results anticipated to come from upcoming instruments. In the past few years, gravitational-wave observations provided stunning insights into some of the most cataclysmic events in the Universe, heralding a bright future for gravitational-wave physics and astronomy. This is a Roadmap for the field in the coming two decades. Gravitational-wave observations of binary black hole and neutron star mergers by LIGO and Virgo in the past five years have opened a completely new window on the Universe. The gravitational-wave spectrum, extending from attohertz to kilohertz frequencies, provides a fertile ground for exploring many fundamental questions in physics and astronomy. Pulsar timing arrays currently probe the nanohertz to microhertz frequency band to detect gravitational-wave remnants from past mergers of super-massive black holes. The space-based Laser Interferometer Space Antenna (LISA) will target gravitational-wave sources from microhertz up to hundreds of millihertz and trace the evolution of black holes from the early Universe through the peak of the star formation era. Einstein Telescope and Cosmic Explorer, two future ground-based observatories now under development for the 2030s, are pursuing new technologies to achieve a tenfold increase increase in sensitivity to study compact object evolution to the beginning of the star formation era. Gravitational-wave observations of binary black hole and neutron star mergers by LIGO and Virgo in the past five years have opened a completely new window on the Universe. The gravitational-wave spectrum, extending from attohertz to kilohertz frequencies, provides a fertile ground for exploring many fundamental questions in physics and astronomy. Pulsar timing arrays currently probe the nanohertz to microhertz frequency band to detect gravitational-wave remnants from past mergers of super-massive black holes. The space-based Laser Interferometer Space Antenna (LISA) will target gravitational-wave sources from microhertz up to hundreds of millihertz and trace the evolution of black holes from the early Universe through the peak of the star formation era. Einstein Telescope and Cosmic Explorer, two future ground-based observatories now under development for the 2030s, are pursuing new technologies to achieve a tenfold increase increase in sensitivity to study compact object evolution to the beginning of the star formation era.

Muhammad Fitrah Alfian Rangga Sakti

We construct the exact stellar configurations that contain an ordinary perfect-fluid matter that interacts minimally with a condensate of gravitons with distinct pressure conditions on the surface. We propose vanishing transverse pressure on the surface for, namely graviton condensate type 1 and vanishing radial pressure on the surface for type 2. The condition for the radial pressure of type 1 requires the existence of a thin shell that will balance the pressure discontinuity while for type 2, the discontinuity on transverse pressure does not require the additional thin shell. It is found that the Buchdahl inequality of the resulting stellar configurations depends on the parameter related to the graviton condensate, such that we can find the ultra-compact regime of the stellar models. Moreover, the echo time and echo frequency within the ultra-compact regime are computed. At the same compactness, it is found that the presence of the graviton condensate will delay the gravitational echoes for type 2 and will expedite the gravitational echoes for type 1 compared to constant density star, τecho2 > τCDS > τecho1. Furthermore, the gravitational perturbation of a massless scalar wave is also investigated to support these results. These results could open more opportunities for the observational study of graviton in the near future, mostly from the compact astrophysical objects.

Akash Kundu, Leopoldo Sarra

Abstract Quantum computing offers exciting opportunities for simulating complex quantum systems and optimizing large-scale combinatorial problems, but its practical use is limited by device noise and constrained connectivity. Designing quantum circuits, which are fundamental to quantum algorithms, is therefore a central challenge in current quantum hardware. Existing reinforcement learning-based methods for circuit design lose accuracy when restricted to hardware-native gates and device-level compilation. Here, we introduce gadget reinforcement learning (GRL) that combines learning with program synthesis to automatically construct composite gates that expand the action space while respecting hardware constraints. We show that this approach improves accuracy, hardware compatibility, and scalability for transverse-field Ising and quantum chemistry problems, reaching systems of up to ten qubits within realistic computational budgets. This framework demonstrates how learned, reusable circuit building blocks can guide the co-design of algorithms and hardware for quantum processors.

Joseph O’Leary, Andrew Melatos, Tom Kimpson et al.

X-ray timing studies of the persistent, Galactic, accretion-powered pulsar 4U 1626−67 reveal torque reversals, during which the pulse frequency ν ( t ) alternates between multiyear episodes of secular acceleration and deceleration, separated by transitions lasting ≲150 days. Here an unscented Kalman filter is applied to track the ν ( t ) fluctuations observed in 22.7 yr (3340 samples) of publicly available Compton Gamma-Ray Observatory and Fermi Gamma-Ray Space Telescope data to test the canonical picture of magnetocentrifugal accretion for consistency with prograde–prograde and retrograde–prograde accretion disk configurations on either side of the 2008 torque reversal. It is found that the retrograde–prograde model is preferred, with a log Bayes factor equal to 0.44 and a maximum a posteriori log likelihood ratio equal to 2.5. The mass accretion rate Q ( t ) and magnetocentrifugal fastness ω ( t ) transition smoothly between episodes of deceleration and acceleration: Q ( t ) shifts by ≤0.34 dex across the reversal, and one measures ω ( t ) ≈ 0.25 and ω ( t ) ≈ 0.30 during deceleration and acceleration, respectively. The angular acceleration $\dot{{\rm{\Omega }}}(t)$ satisfies $-9\,\lesssim \,\dot{{\rm{\Omega }}}(t)/(1{0}^{-12}\,{\rm{rad}}\,{{\rm{s}}}^{-2})\,\lesssim \,-5$ and $2\,\lesssim \,\dot{{\rm{\Omega }}}(t)/(1{0}^{-12}\,{\rm{rad}}\,{{\rm{s}}}^{-2})\,\lesssim \,9$ before and after the 2008 reversal, respectively, compared to $\dot{{\rm{\Omega }}}\approx -3.0\,\times 1{0}^{-12}\,{\rm{rad}}\,{{\rm{s}}}^{-2}$ before reversal and $\dot{{\rm{\Omega }}}\approx 2.5\times 1{0}^{-12}\,{\rm{rad}}\,{{\rm{s}}}^{-2}$ after reversal, as inferred from previous long-term X-ray timing and spectral analysis of 4U 1626−67.

Mike Cruise, M. Guainazzi, J. Aird et al.

Large X-ray observatories such as Chandra and XMM-Newton have been delivering scientific breakthroughs in research fields as diverse as our Solar System, the astrophysics of stars, stellar explosions and compact objects, accreting supermassive black holes, and large-scale structures traced by the hot plasma permeating and surrounding galaxy groups and clusters. The recently launched X-Ray Imaging and Spectroscopy Mission observatory is opening in earnest the new observational window of non-dispersive high-resolution spectroscopy. However, several questions remain open, such as the effect of the stellar radiation field on the habitability of nearby planets, the equation of state regulating matter in neutron stars, the origin and distribution of metals in the Universe, the processes driving the cosmological evolution of the baryons locked in the gravitational potential of dark matter and the impact of supermassive black hole growth on galaxy evolution, to mention just a few. Furthermore, X-ray astronomy has a key part to play in multimessenger astrophysics. Addressing these questions experimentally requires an order-of-magnitude leap in sensitivity, spectroscopy and survey capabilities with respect to existing X-ray observatories. This article succinctly summarizes the main areas where high-energy astrophysics is expected to contribute to our understanding of the Universe in the next decade and describes a new mission concept under study by the European Space Agency, the scientific community worldwide and two international partners (JAXA and NASA), designed to enable transformational discoveries: NewAthena. This concept inherits its basic payload design from a previous study carried out until 2022, Athena. This Perspective looks forwards to the next decade of X-ray astronomy, explaining how it will contribute to better understanding of the high-energy Universe. In this context, the authors describe the NewAthena mission, a concept led by the European Space Agency.

Roger E. Cohen, Kristen B. W. McQuinn, Alessandro Savino et al.

Radial stellar population gradients within dwarf galaxies provide a promising avenue for disentangling the drivers of galaxy evolution, including environment. Within the Local Volume, radial stellar age gradient slopes correlate with interaction history, contrary to model predictions, so dwarfs that are isolated provide a critical control sample. We measure radial stellar age gradients in the relatively isolated gas-rich dwarf irregular Wolf–Lundmark–Melotte Galaxy (WLM), combining JWST NIRCam and NIRISS imaging with six archival Hubble Space Telescope fields over semimajor axis equivalent distances of 0 ≲  R _SMA  ≲ 4 kpc (≲3 R _hl ). Fitting lifetime star formation histories to resolved color–magnitude diagrams, radial age gradients are quantified using τ _90 and τ _50 , the lookback times to form 90% and 50% of the cumulative stellar mass. We find that globally, the outskirts of WLM are older on average, with ( δτ _90 , δτ _50 )/ δ R _SMA  = (0.82 ${}_{-0.10}^{+0.10}$ , 1.60 ${}_{-0.22}^{+0.23}$ ) Gyr kpc ^−1 (stat.), in good agreement with simulations. However, we also detect an azimuthal dependence of radial stellar age gradients, finding that stars on the leading edge of WLM (relative to its proper motion) are both younger and have a flatter age gradient compared to the trailing edge. This difference persists over 0.6 ≲  R _SMA  ≲ 3.2 kpc (∼0.5–2.5 R _hl ) and lookback times up to ∼8 Gyr, and is robust to the assumed stellar evolutionary model. Our results are consistent with star formation triggered by ram pressure stripping from a circumgalactic and/or intergalactic medium, suggested by recent H I observations. If confirmed, processes typifying dense environments, such as ram pressure stripping, may be more relevant to the evolution of isolated galaxies than previously thought.