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All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Using the HHT to Search for Gravitational Waves

Gravitational waves are a consequence of Einstein's theory of general relativity applied to the motion of very dense and massive objects such as black holes and neutron stars. Their detection will reveal a wealth of information about these mysterious objects that cannot be obtained with electromagnetic probes. Two projects are underway to attempt the detection of gravitational waves: NASA's Laser Interferometer Space Antenna (LISA), a space based mission being designed to search for waves from supermassive black holes at the centers of galaxies, and the NSF's Laser Interferometer Gravitational Wave Observatory (LIGO), a ground based facility that is now searching for waves from supernovae. pulsars, and the coalescence of black hole and neutron star systems. Because general relativity is an inherently non-linear theory, many of the predicted source waveforms show strong frequency modulation. In addition, the LIGO and LISA detectors are highly sensitive devices that produce a variety of non-linear transient noise features. Thus the unique capabilities of the HHT. the extraction of intrawave modulation and the characterization of non-linear and non-stationary signals, have a natural application to both signal detection and experimental characterization of the detectors. In this talk I will give an overview of the status of the field. including some of the expected sources of gravitational waves, and I will also describe the LISA and LIGO detectors. Then I will describe some applications of the HHT to waveform detection and detector noise characterization.

Camp, Jordan↗
NASA NTRS1968

Gravitational waves.

Gravitational wave detection covering principles and technique for measuring Riemann curvature tensor, noting gravimeter system diagram

Weber, J.↗
NASA NTRS2011

Testing Gravitational Physics with Space-based Gravitational-wave Observations

Gravitational wave observations provide exceptional and unique opportunities for precision tests of gravitational physics, as predicted by general relativity (GR). Space-based gravitational wave measurements, with high signal-to-noise ratios and large numbers of observed events may provide the best-suited gravitational-wave observations for testing GR with unprecedented precision. These observations will be especially useful in testing the properties of gravitational waves and strong-field aspects of the theory which are less relevant in other observations. We review the proposed GR test based on observations of massive black hole mergers, extreme mass ratio inspirals, and galactic binary systems.

Baker, John G.↗
NASA NTRS1990

The electric field induced by a gravitational wave in a superconductor - A principle for a new gravitational wave antenna

This paper investigates the effect of gravitational waves on a superconductor. It is found that the key properties of a superconductor, namely zero resistance and perfect diamagnetism, give rise to an important new effect, the presence of an induced electric field E in the interior of the superconductor. The E field reacts with the ions and superelectrons. It is argued that the induced E field might provide a significantly more sensitive means of detecting gravitational waves. It appears likely that existing resonant-mass superconducting antennas with L about 3m, Q about 10 to the 8th could be readily modified to detect E fields induced by GWs of dimensionless amplitude h about 10 to the -24th.

Peng, Huei↗
NASA NTRS1982

The implications of precise timekeeping of Doppler gravitational wave observations

Gravitational radiation from galactic and extragalactic astrophysical sources will induce spatial strains in the solar system, strains which can be measured directly by the Doppler radio link to distant spacecraft. Current noise sources in Pioneer and Voyager Doppler data are delineated and a comparison is made with expected signal levels from gravitational wave sources. The main conclusion is that it is possible to detect gravitational radiation with current DSN hydrogen maser systems stable in fractional frequency + or - 2 x 10 to the minus 14th power over 1000 sec. In the future, however, a serious Doppler observational program in gravitational wave astronomy will require frequency systems stable to at least 10 to the minus 16th power, but at the same time the current single frequency S-band uplink transmission will have to be replaced by a dual frequency capability.

Anderson, J. D.↗
NASA NTRS2019

Gravitational-Wave Astronomy in the 2020s and Beyond: A View Across the Gravitational Wave Spectrum

One of the most notable developments since the 2010 Decadal Survey is the addition of gravitationalwaves (GW) to the astronomers' suite of tools for understanding the Universe. LIGO's2015 detection of gravitational waves (Abbott et al. 2016) from the merger of a pair of black holesroughly 30 times the mass of our Sun garnered tremendous excitement from both the public andthe scientific community and raised interesting questions as to the origin of such systems. To datea total of 11 confirmed detections have been announced, including the first GW signals from themerger of neutron stars in 2017 seen by LIGO and Virgo (Abbott et al. 2017). That event wasassociated with a gamma ray burst; the subsequent kilonovae and afterglow was perhaps the mostthoroughly-observed astronomical event of all time (Abbott et al. 2017b). In the coming decades,with continued investment, the ground-based network will continue to improve in both the numberand sensitivity of detectors at high frequencies, pulsar timing arrays such as NANOGrav willuncover stochastic sources of gravitational waves and then single sources at low frequencies, andLISA will begin to probe the mid-frequency band from space. In this white paper, we presenta broad outline of the scientific impact of these facilities in the coming decade and the 2030s,emphasizing the ways in which

Shoemaker, David↗
NASA NTRS2023

Imaging the Milky Way with Millihertz Gravitational Waves

Modern astronomers enjoy access to all-sky images across a wide range of the electromagnetic spectrum from long-wavelength radio to high-energy gamma rays. The most prominent feature in many of these images is our own Galaxy, with different features revealed in each wave band. Gravitational waves (GWs) have recently been added to the astronomers’ toolkit as a nonelectromagnetic messenger. To date, all identified GW sources have been extra-Galactic and transient. However, the Milky Way hosts a population of ultracompact binaries (UCBs), which radiate persistent GWs in the milliHertz band that is not observable with today’s terrestrial gravitational-wave detectors. Space-based detectors such as the Laser Interferometer Space Antenna will measure this population and provide a census of their location, masses, and orbital properties. In this work, we will show how this data can be used to form a false-color image of the Galaxy that represents the intensity and frequency of the gravitational waves produced by the UCB population. Such images can be used to study the morphology of the Galaxy, identify interesting multimessenger sources through cross-matching, and for educational and outreach purposes.

Gravitational Waves↗
NASA NTRS2021

First Demonstration of Early Warning Gravitational-wave Alerts

Gravitational-wave observations became commonplace in Advanced LIGO-Virgo's recently concluded third observing run. 56 nonretracted candidates were identified and publicly announced in near real time. Gravitational waves from binary neutron star mergers, however, remain of special interest since they can be precursors to high-energy astrophysical phenomena like γ-ray bursts and kilonovae. While late-time electromagnetic emissions provide important information about the astrophysical processes within, the prompt emission along with gravitational waves uniquely reveals the extreme matter and gravity during—and in the seconds following—merger. Rapid communication of source location and properties from the gravitational-wave data is crucial to facilitate multimessenger follow-up of such sources. This is especially enabled if the partner facilities are forewarned via an early warning (pre-merger) alert. Here we describe the commissioning and performance of such a low-latency infrastructure within LIGO-Virgo. We present results from an end-to-end mock data challenge that detects binary neutron star mergers and alerts partner facilities before merger. We set expectations for these alerts in future observing runs.

Ryan Magee↗
NASA NTRS1974

How to test gravitation theories by means of gravitational-wave measurements

Gravitational-wave experiments are a potentially powerful tool for testing gravitation theories. Most theories in the literature predict rather different polarization properties for gravitational waves than are predicted by general relativity; and many theories predict anomalies in the propagation speeds of gravitational waves.

Thorne, K. S.↗
NASA NTRS2014

Optimizing Vetoes for Gravitational-wave Transient Searches

Interferometric gravitational-wave detectors like LIGO, GEO600 and Virgo record a surplus of information above and beyond possible gravitational-wave events. These auxiliary channels capture information about the state of the detector and its surroundings which can be used to infer potential terrestrial noise sources of some gravitational-wave-like events. We present an algorithm addressing the ordering (or equivalently optimizing) of such information from auxiliary systems in gravitational-wave detectors to establish veto conditions in searches for gravitational-wave transients. The procedure was used to identify vetoes for searches for unmodelled transients by the LIGO and Virgo collaborations during their science runs from 2005 through 2007. In this work we present the details of the algorithm; we also use a limited amount of data from LIGO's past runs in order to examine the method, compare it with other methods, and identify its potential to characterize the instruments themselves. We examine the dependence of Receiver Operating Characteristic curves on the various parameters of the veto method and the implementation on real data. We find that the method robustly determines important auxiliary channels, ordering them by the apparent strength of their correlations to the gravitational-wave channel. This list can substantially reduce the background of noise events in the gravitational-wave data. In this way it can identify the source of glitches in the detector as well as assist in establishing confidence in the detection of gravitational-wave transients.

Transient↗
NASA NTRS2021

Tests of General Relativity with Binary Black Holes from the second LIGO–Virgo Gravitational-Wave Transient Catalog

Gravitational waves enable tests of general relativity in the highly dynamical and strong-field regime. Using events detected by LIGO-Virgo up to 1 October 2019, we evaluate the consistency of the data with predictions from the theory. We first establish that residuals from the best-fit waveform are consistent with detector noise, and that the low- and high-frequency parts of the signals are in agreement. We then consider parametrized modifications to the waveform by varying post-Newtonian and phenomenological coefficients, improving past constraints by factors of ∼2; we also find consistency with Kerr black holes when we specifically target signatures of the spin-induced quadrupole moment. Looking for gravitational-wave dispersion, we tighten constraints on Lorentz-violating coefficients by a factor of ∼2.6 and bound the mass of the graviton to m(g)≤1.76 x 10^(-23) eV/sq. c with 90% credibility. We also analyze the properties of the merger remnants by measuring ringdown frequencies and damping times, constraining fractional deviations away from the Kerr frequency to δ{\hat {f}}(220)=0.03(+0.38,-0.35) for the fundamental quadrupolar mode, and δ{\hat {f}}(221)=0.04(+0.27,-0.32) for the first overtone; additionally, we find no evidence for postmerger echoes. Finally, we determine that our data are consistent with tensorial polarizations through a template-independent method. When possible, we assess the validity of general relativity based on collections of events analyzed jointly. We find no evidence for new physics beyond general relativity, for black hole mimickers, or for any unaccounted systematics.

R. Abbott↗
NASA NTRS2011

Gravitational Wave Astrophysics: Opening the New Frontier

The gravitational wave window onto the universe is expected to open in ~ 5 years, when ground-based detectors make the first detections in the high-frequency regime. Gravitational waves are ripples in spacetime produced by the motions of massive objects such as black holes and neutron stars. Since the universe is nearly transparent to gravitational waves, these signals carry direct information about their sources such as masses, spins, luminosity distances, and orbital parameters through dense, obscured regions across cosmic time. This article explores gravitational waves as cosmic messengers, highlighting key sources, detection methods, and the astrophysical payoffs across the gravitational wave spectrum. Keywords: Gravitational wave astrophysics; gravitational radiation; gravitational wave detectors; black holes.

Centrella, Joan↗
NASA NTRS1989

Earth-orbiting resonant-mass gravitational wave detectors

Earth-based gravitational wave detectors suffer from the need to support the large antenna masses against the earth's gravity without transmitting a significant amount of seismic noise. Passive vibration isolation is difficult to achieve below 1 Hz on the earth. Vibration-free space environment thus gives an opportunity to extend the frequency window of gravitational wave detection to ultralow frequencies. The weightless condition of a space laboratory also enables construction of a highly symmetric multimode antenna which is capable of resolving the direction of the source and the polarization of the incoming wave without resorting to multiantenna coincidence. Two types of earth-orbiting resonant-mass gravitational wave detectors are considered. One is a skyhook gravitational wave detector, proposed by Braginsky and Thorne (1985). The other is a spherical detector, proposed by Forward (1971) and analyzed by Wagoner and Paik (1976).

Paik, Ho Jung↗
NASA NTRS1981

Doppler-cancelled response to VLF gravitational waves

The interaction of long periodic gravitational waves with a three link microwave system known as the Doppler Cancelling System is discussed. This system, which was developed for a gravitational redshift experiment, uses one-way and two-way Doppler informatin to construct the beat signal of two reference oscillators moving with respect to each other. The geometric optics approximation is used to derive the frequency shift produced on a light signal propagating in a gravitational wave space-time. The signature left on the Doppler-cancelled beat by burst and continuous gravitational waves is analyzed. A comparison is made between the response to gravitational waves of the Doppler Cancelling System and that of a Doppler tracking system which employs two-way, round-trip radio waves. A three-fold repetition of the gravitational wave form is found to be a common feature of the response functions of both systems. These two functions otherwise exhibit interesting differences.

Caporali, A.↗
NASA NTRS1988

Cosmological gravitational waves

A cosmological background of gravitational waves would alter the propagation of radiation, inducing redshift fluctuations, apparent source position deflections, and luminosity variations. By comparing these astrophysical effects with observations, it is possible to deduce upper limits on the energy density present in gravitational waves. Emphasis is placed on microwave background anisotropy from the redshift deviations and galaxy clustering correlation functions from the angular deviations. Many of the gravitational wave effects are shown to be generalizations of the gravitational lensing formalism.

Linder, Eric V.↗
NASA NTRS1988

Microwave background anisotropy induced by gravitational waves

A cosmological background of gravitational waves induces redshift perturbations in light transversing it. Calculations of this Sachs-Wolfe effect on the microwave background are presented in an Omega = 1 Friedmann universe as a function of angular scale and gravitational wave spectrum. Blurriness of the last-scattering surface can cause nonnegligible dilution of the anisotropy for wavelengths less than about 100 Mpc. The limit implied for the energy density of the gravitational waves is given. A difficulty in associating a linear scale with an angular anisotropy, due to the clumpiness of the universe, is also pointed out.

Linder, Eric V.↗
NASA NTRS2012

Gravitational Waves and Time Domain Astronomy

The gravitational wave window onto the universe will open in roughly five years, when Advanced LIGO and Virgo achieve the first detections of high frequency gravitational waves, most likely coming from compact binary mergers. Electromagnetic follow-up of these triggers, using radio, optical, and high energy telescopes, promises exciting opportunities in multi-messenger time domain astronomy. In the decade, space-based observations of low frequency gravitational waves from massive black hole mergers, and their electromagnetic counterparts, will open up further vistas for discovery. This two-part workshop featured brief presentations and stimulating discussions on the challenges and opportunities presented by gravitational wave astronomy. Highlights from the workshop, with the emphasis on strategies for electromagnetic follow-up, are presented in this report.

Centrella, Joan↗