Letteratura scientifica selezionata sul tema "Laser interferometer space antenna (satellite artificiel)"

Taiji-1, which is the first experimental satellite for space gravitational wave detection in China, relies on key technologies which include the laser interferometer, the gravitational reference sensor (GRS), the micro-thruster and the satellite platform. Similarly to the Laser Interferometer Space Antenna (LISA) pathfinder, except for the science interferometer, the optical bench (OB) of Taiji-1 contains reference and test mass (TM) interferometers. Limited by the lower mechanical strength of the carrier rocket and by the orbit environment, the OB of Taiji-1 is made of invar steel and fused silica, and it is aimed to achieve a sensitivity of the order of 100[Formula: see text]pm/[Formula: see text]. The experimental results from in-orbit tests of Taiji-1 demonstrate that the interferometer can reach a sensitivity of 30[Formula: see text]pm/[Formula: see text] in the frequency range of 0.01–10[Formula: see text]Hz, which satisfies the requirements of Taiji-1 mission.

ABSTRACT White dwarf stars are a well-established tool for studying Galactic stellar populations. Two white dwarfs in a tight binary system offer us an additional messenger – gravitational waves – for exploring the Milky Way and its immediate surroundings. Gravitational waves produced by double white dwarf (DWD) binaries can be detected by the future Laser Interferometer Space Antenna (LISA). Numerous and widespread DWDs have the potential to probe shapes, masses, and formation histories of the stellar populations in the Galactic neighbourhood. In this work we outline a method for estimating the total stellar mass of Milky Way satellite galaxies based on the number of DWDs detected by LISA. To constrain the mass we perform a Bayesian inference using binary population synthesis models and considering the number of detected DWDs associated with the satellite and the measured distance to the satellite as the only inputs. Based on a fiducial binary population synthesis model we find that for large satellites the stellar masses can be recovered to within (1) a factor 2 if the star formation history (SFH) is known and (2) an order of magnitude when marginalizing over different SFH models. For smaller satellites we can place upper limits on their stellar mass. Gravitational wave observations can provide mass measurements for large satellites that are comparable, and in some cases more precise, than standard electromagnetic observations.

In 1859, Le Verrier discovered the mercury perihelion advance anomaly. This anomaly turned out to be the first relativistic-gravity effect observed. During the 141 years to 2000, the precisions of laboratory and space experiments, and astrophysical and cosmological observations on relativistic gravity have been improved by 3 orders of magnitude. In 1999, we envisaged a 3–6 order improvement in the next 30 years in all directions of tests of relativistic gravity. In 2000, the interferometric gravitational wave detectors began their runs to accumulate data. In 2003, the measurement of relativistic Shapiro time-delay of the Cassini spacecraft determined the relativistic-gravity parameter γ to be 1.000021 ± 0.000023 of general relativity — a 1.5-order improvement. In October 2004, Ciufolini and Pavlis reported a measurement of the Lense–Thirring effect on the LAGEOS and LAGEOS2 satellites to be 0.99 ± 0.10 of the value predicted by general relativity. In April 2004, Gravity Probe B (Stanford relativity gyroscope experiment to measure the Lense–Thirring effect to 1%) was launched and has been accumulating science data for more than 170 days now. μSCOPE (MICROSCOPE: MICRO-Satellite à trainée Compensée pour l'Observation du Principle d'Équivalence) is on its way for a 2008 launch to test Galileo equivalence principle to 10-15. LISA Pathfinder (SMART2), the technological demonstrator for the LISA (Laser Interferometer Space Antenna) mission is well on its way for a 2009 launch. STEP (Satellite Test of Equivalence Principle), and ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) are in good planning stage. Various astrophysical tests and cosmological tests of relativistic gravity will reach precision and ultra-precision stages. Clock tests and atomic interferometry tests of relativistic gravity will reach an ever-increasing precision. These will give revived interest and development both in experimental and theoretical aspects of gravity, and may lead to answers to some profound questions of gravity and the cosmos.

ABSTRACT White dwarf binaries with orbital periods below 1 h will be the most numerous sources for the space-based gravitational wave detector Laser Interferometer Space Antenna (LISA). Based on thousands of individually resolved systems, we will be able to constrain binary evolution and provide a new map of the Milky Way and its close surroundings. In this paper we predict the main properties of populations of different types of detached white dwarf binaries detected by LISA over time. For the first time, we combine a high-resolution cosmological simulation of a Milky Way-mass galaxy (taken from the FIRE project) with a binary population synthesis model for low- and intermediate-mass stars. Our Galaxy model therefore provides a cosmologically realistic star formation and metallicity history for the Galaxy and naturally produces its different components such as the thin and thick disc, the bulge, the stellar halo, and satellite galaxies and streams. Thanks to the simulation, we show how different Galactic components contribute differently to the gravitational wave signal, mostly due to their typical age and distance distributions. We find that the dominant LISA sources will be He–He double white dwarfs (DWDs) and He–CO DWDs with important contributions from the thick disc and bulge. The resulting sky map of the sources is different from previous models, with important consequences for the searches for electromagnetic counterparts and data analysis. We also emphasize that much of the science-enabling information regarding white dwarf binaries, such as the chirp mass and the sky localization, becomes increasingly rich with long observations, including an extended mission up to 8 yr.

Context. Milky Way dwarf satellites are unique objects that encode the early structure formation and therefore represent a window into the high redshift Universe. So far, their study has been conducted using electromagnetic waves only. The future Laser Interferometer Space Antenna (LISA) has the potential to reveal Milky Way satellites through gravitational waves emitted by double white dwarf (DWD) binaries. Aims. We investigate gravitational wave signals that will be detectable by LISA as a possible tool for the identification and characterisation of the Milky Way satellites. Methods. We used the binary population synthesis technique to model the population of DWDs in dwarf satellites and we assessed the impact on the number of LISA detections when making changes to the total stellar mass, distance, star formation history, and metallicity of satellites. We calibrated predictions for the known Milky Way satellites on their observed properties. Results. We find that DWDs emitting at frequencies ≳3 mHz can be detected in Milky Way satellites at large galactocentric distances. The number of these high frequency DWDs per satellite primarily depends on its mass, distance, age, and star formation history, and only mildly depends on the other assumptions regarding their evolution such as metallicity. We find that dwarf galaxies with M⋆ > 106 M⊙ can host detectable LISA sources; the number of detections scales linearly with the satellite’s mass. We forecast that out of the known satellites, Sagittarius, Fornax, Sculptor, and the Magellanic Clouds can be detected with LISA. Conclusions. As an all-sky survey that does not suffer from contamination and dust extinction, LISA will provide observations of the Milky Way and dwarf satellites galaxies, which will be valuable for Galactic archaeology and near-field cosmology.

Les transitions de phase du premier ordre (PT) dans l'univers primitif se produisent par la nucléation de bulles dont les parois peuvent se dilater à des vitesses ultra-relativistes. Les interactions du bain thermique à la paroi produisent des particules qui s'accumulent dans des coquilles à la paroi. Les coquilles évoluent jusqu'à ce qu'elles entrent en collision avec celles des bulles voisines. Dans cette thèse, nous étudions d'abord l'évolution de ces coquilles, en incluant pour la première fois les interactions de changement de nombre de la coquille à l'intérieur d'elle-même et avec le bain thermique. En particulier, nous calculons les taux des processus de diffusion 3 → 2 dominants, et nous trouvons qu'ils peuvent être plus importants que tous les autres processus considérés dans la littérature précédente. Nous identifions les régions de l'espace des paramètres du PT où les coquilles sont libres, c'est-à-dire qu'elles ont des interactions négligeables en elles-mêmes et avec le bain. Nous utilisons ensuite ces résultats pour prédire la vitesse et l'énergie avec lesquelles les particules de bulles opposées entrent en collision. Nous constatons que ces collisions de particules peuvent atteindre des énergies de diffusion bien supérieures à l'échelle du PT, qui peuvent à leur tour être utilisées pour produire des particules hautement énergétiques ou des particules bien plus lourdes que l'échelle du PT, réalisant ainsi un "bubbletron" cosmologique. À titre d'exemple, nous montrons que l'on peut produire de la matière noire lourde avec des masses supérieures à 10^3 TeV pour des échelles de PT d'environ 10 MeV, et avec des masses supérieures à l'échelle du GUT pour des échelles de PT supérieures à environ 10^9 GeV. Les PT avec des parois ultra-relativistes sont également pertinents pour tout autre processus reposant sur la production de particules hors équilibre. Si l'interaction entre les particules de la coquille viole également le nombre de baryons, C et CP, alors les trois conditions de Sakharov sont remplies et l'on peut utiliser ces PT pour expliquer l'asymétrie des baryons dans l'univers. Pour ce faire, nous proposons un mécanisme de baryogénèse à partir de PT confinants surfondus. Nous calculons également la signature des ondes gravitationnelles dues aux PT dans tous les scénarios susmentionnés. Nous constatons qu'elles pourraient être observées par les réseaux de synchronisation des pulsars et les interféromètres d'ondes gravitationnelles comme LISA et le télescope d'Einstein, établissant ainsi un nouveau lien entre ces télescopes et l'origine possible de la matière noire et de l'asymétrie des baryons dans l'univers
First order phase transitions (PT) in the early universe happen via the nucleation of bubbles whose walls can expand at ultra-relativistic velocities. Interactions of the thermal bath at the wall produce particles which accumulate in shells at the wall. The shells evolve until they collide with those from neighboring bubbles. In this thesis we first study the evolution of these shells, including for the first time number changing interactions of the shell within itself and with the thermal bath. In particular, we calculate the rates of the dominant 3 → 2 scattering processes, and find they can be more important than all other processes considered in previous literature. We identify the regions of parameter space of the PT where the shells free stream, i.e. they have negligible interactions within themselves and with the bath. We then use these results to predict the rate and energy with which particles of opposite bubbles collide. We find that these particle collisions can reach scattering energies much larger than the scale of the PT, which in turn can be used to produce highly energetic particles or particles much heavier than the scale of the PT, realising a cosmological 'bubbletron'. As an example, we show that one can produce heavy dark matter with masses above 10^3 TeV for scales of the PT of around 10 MeV, and with masses above the GUT scale for scales of the PT above about 10^9 GeV. PTs with ultra-relativistic walls are also relevant for any other process relying on out-of-equilibrium particle production. If the interaction between particles in the shell also violates Baryon number, C, and CP, then all three Sakharov conditions are satisifed, and one can use these PTs to explain the baryon asymmetry of the universe. We do so by proposing a mechanism of baryogenesis from supercooled confining PTs. We also compute the gravitational wave signature due to the PT in all the above scenarios. We find they could be seen by pulsar timing arrays and gravitational wave interferometers like LISA and the Einstein Telescope, realizing a new link between these telescopes and the possible origin of dark matter and of the baryon asymmetry of the universe

The LISA (Laser Interferometer Space Antenna) mission is one of the most challenging endeavours to be undertaken by ESA whose objective is to study gravitational waves. The mission consists of three identical spacecraft in a triangular formation, with an inter-satellite distance of 2.5 million km, flying in a heliocentric orbit. Each spacecraft contains two test masses (TM) that are confined within an electrode housing with electrostatic sensing and actuation capability. Two telescopes are present, pointing towards the two other spacecraft, which includes a sophisticated optical metrology system to measure the distance between TMs of opposing spacecraft with pico-metre accuracy. In order to maintain formation tracking, the angle between the telescopes is variable so that it can keep the opposing spacecraft within its field of view (FoV). The science phase of the LISA DFACS (Drag-Free Attitude Control System) consists of leaving the TMs in free fall in the direction of the line-of-sight (LoS) between spacecraft while being suspended in the other directions using the electrostatic sensors and actuators. The spacecraft will perform a drag-free control by following the TMs’ geodesic path using micro-Newton thrusters while simultaneously maintaining formation via attitude control and corresponding telescope angle commands. The stringent pointing requirements to maintain formation is achieved via laser measurements providing relative angles with respect to the LoS between spacecraft. A study was carried out for ESA by SENER Aeroespacial as part of a development risk mitigation activity in Phase A/B1 with the objective to investigate control system architectures and advanced design methodologies. The full nonlinear DKE models, which include all the degrees of freedom (DoF) of the coupled spacecraft dynamics were developed by Deimos Engenharia to perform the validation activities of the GNC (Guidance, Navigation and Control). The LISA spacecraft, once placed in a heliocentric orbit, will execute a sequence of operations that consists of: - Inertial pointing of the individual spacecraft (including slew manoeuvre to target) - Release of the two test masses (either sequentially or simultaneously) - Acquisition of the flight formation - Science observations Within the activity, a full-fledged GNC was designed and implemented that is capable of autonomously executing the above sequence, including all the necessary functions for mode management, guidance, navigation (state determination) and control and the switch between sensor/actuator HW depending on the phase within the sequence. This paper presents the design process of the GNC. Considering the large quantity of work performed, a general overview is provided of the design activities covering various aspects of relevance. In particular, the following topics will be addressed: - GNC functional architecture and control problem formulation - Guidance strategy of the formation acquisition - Spacecraft attitude estimation filter based on the TM dynamics The topics related to the control design as well as the validation and verification (V&V) campaign are addressed in an accompanying paper. The LISA DFACS needs to control a total of 16DoF, which are the spacecraft attitude, the relative attitude and position of the two TMs and the inter-telescope angle. Needless to say, it is a complex MIMO (Multiple Input Multiple Output) system that needs a proper assessment. In fact, as the three spacecraft transition through the various phases in the above sequence, the number of DoFs to control varies as well. This requires a careful design of the control architecture and control problem formulation as it drives both the GNC functional architecture and the intended control design and analysis methodologies. One of the critical areas is the formation acquisition, which involves a dedicated scan and search strategy that combines attitude manoeuvres with inter-telescope angle commands. The telescopes emit a laser beam, which is captured by the Constellation Acquisition Sensor (CAS) of the opposing spacecraft. One of the main challenges is the fact that there is no communication exchange between spacecraft hence they do not know if the other spacecraft have observed the incoming laser beams so that it can “stop” scanning. A systematic search strategy has been designed to cope with these issues, which has shown to be successful in Monte Carlo simulations. The formation acquisition requires a high attitude pointing accuracy and stability in order to obtain a lock between spacecraft due to the very narrow FoV of the laser beam. The Star Trackers (STR) are not expected to provide the necessary accuracy to guarantee a successful acquisition. Therefore, a Kalman filter was developed that uses the dynamics and electrostatic actuation of the TMs to improve the spacecraft attitude estimation during the search and scanning pattern. The presence of actuation errors and Solar Radiation Pressure (SRP) lead to drift issues, which necessitates the inclusion of the STR measurements within the filter to ensure bounding the state propagation errors, which is crucial as the duration of the acquisition can take up to 48 hours. The performed study has successfully led to a complete GNC design, capable of autonomously transitioning through all the modes while meeting all the control pointing requirements in a Monte Carlo campaign within a detailed nonlinear simulation environment.