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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
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NASA NTRS2019

Multimessenger Science Opportunities with mHz Gravitational Waves

LISA will open the mHz band of gravitational waves (GWs) to the astronomy community. Thestrong gravity which powers the variety of GW sources in this band is also crucial in a numberof important astrophysical processes at the current frontiers of astronomy. These range fromthe beginning of structure formation in the early universe, through the origin and cosmic evolutionof massive black holes in concert with their galactic environments, to the evolution ofstellar remnant binaries in the Milky Way and in nearby galaxies. These processes and theirassociated populations also drive current and future observations across the electromagnetic(EM) spectrum. We review opportunities for science breakthroughs, involving either direct coincidentEM+GW observations, or indirect multimessenger studies. We argue that for the UScommunity to fully capitalize on the opportunities from the LISA mission, the US efforts shouldbe accompanied by a coordinated and sustained program of multi-disciplinary science investment,following the GW data through to its impact on broad areas of astrophysics. Supportfor LISA-related multimessenger observers and theorists should be sized appropriately for aflagship observatory and may be coordinated through a dedicated mHz GW research center.

Baker, John↗
DOE OSTI2021

Relic cosmological vector fields and inflationary gravitational waves

Here we show that relic vector fields can significantly impact a spectrum of primordial gravitational waves in the postinflationary era. We consider a triplet of U(1) fields in a homogeneous, isotropic configuration. The interaction between the gravitational waves and the vector fields, from the end of reheating to the present day, yields novel spectral features. The amplitude, tilt, shape, and net chirality of the gravitational wave spectrum are shown to depend on the abundance of the electric- and magneticlike vector fields. Our results show that even a modest abundance can have strong implications for efforts to detect the imprint of gravitational waves on the cosmic microwave background polarization. We find that a vector field comprising less than 2% of the energy density during the radiation-dominated era can have a greater than order unity effect on the predicted inflationary gravitational wave spectrum.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Gravitational Waves from Rapid Structure Formation on Microscopic Scales before Matter-Radiation Equality

We propose a new scenario for the formation of asteroid-mass primordial black holes (PBHs). Our mechanism is based on the annihilation of the string-wall network associated with thebreaking of a U(1) global symmetry into a discrete ZN symmetry. If the potential hasmultiple local minima (N > 1) the network is stable, and the annihilation is guaranteed by a biasamong the different vacua. The collapse of the string-wall network is accompanied bycatastrogenesis, a large production of pseudo-Goldstone bosons (pGBs) — e.g. axions,ALPs, or majorons — gravitational waves, and PBHs. If pGBs rapidly decay into products thatthermalize, as predicted e.g. in the high-quality QCD axion and heavy majoron models, they do notcontribute to the dark matter population, but we show that PBHs can constitute 100% of the darkmatter. The gravitational wave background produced by catastrogenesis with heavy unstable axions,ALPs, or majorons could be visible in future interferometers.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRSDate not supplied

AMEGO-X: MeV Gamma-Ray Astronomy in the Multimessenger Era

Recent detections of gravitational wave signals and neutrinos from gamma-ray sources have ushered in the era of multi-messenger astronomy, while highlighting the importance of gamma-ray observations for this emerging field. AMEGO-X, the All-sky Medium Energy Gamma-Ray Observatory eXplorer, is an MeV gamma-ray instrument that will survey the sky in the energy range from hundreds of keV to one GeV with unprecedented sensitivity. AMEGO-X will detect gamma-ray photons both via Compton interactions and pair production processes, bridging the “sensitivity gap” between hard X-rays and high-energy gamma rays. AMEGO-X will provide important contributions to multi-messenger science and time-domain gamma-ray astronomy, studying e.g. high-redshift blazars, which are probable sources of astrophysical neutrinos, and gamma-ray bursts. I will present an overview of the instrument and science program.

Henrike Fleischhack↗
DOE OSTI2022

Gravitational wave timing array

We describe the design of a gravitational wave timing array, a novel scheme that can be used to search for low-frequency gravitational waves by monitoring continuous gravitational waves at higher frequencies. We show that observations of gravitational waves produced by Galactic binaries using a space-based detector like LISA provide sensitivity in the nanohertz to microhertz band. While the expected sensitivity is several magnitudes worse than what can be achieved by pulsar timing arrays, it supplements other recent proposals for gravitational wave searches in the microhertz regime. This regime is below the frequencies to which LISA is directly sensitive, and above the frequency range generally targeted by pulsar timing array searches. Here, the low-frequency extension of sensitivity does not require any experimental design change to space-based gravitational wave detectors, and can be achieved with the data products that would already be collected by them.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Designing an Optimal Kilonova Search Using DECam for Gravitational-wave Events

We address the problem of optimally identifying all kilonovae detected via gravitational-wave emission in the upcoming LIGO/Virgo/KAGRA observing run, O4, which is expected to be sensitive to a factor of ~7 more binary neutron star (BNS) alerts than previously. Electromagnetic follow-up of all but the brightest of these new events will require >1 m telescopes, for which limited time is available. We present an optimized observing strategy for the DECam during O4. We base our study on simulations of gravitational-wave events expected for O4 and wide-prior kilonova simulations. We derive the detectabilities of events for realistic observing conditions. We optimize our strategy for confirming a kilonova while minimizing telescope time. For a wide range of kilonova parameters, corresponding to a fainter kilonova compared to GW170817/AT 2017gfo, we find that, with this optimal strategy, the discovery probability for electromagnetic counterparts with the DECam is ~80% at the nominal BNS gravitational-wave detection limit for O4 (190 Mpc), which corresponds to an ~30% improvement compared to the strategy adopted during the previous observing run. For more distant events (~330 Mpc), we reach an ~60% probability of detection, a factor of ~2 increase. For a brighter kilonova model dominated by the blue component that reproduces the observations of GW170817/AT 2017gfo, we find that we can reach ~90% probability of detection out to 330 Mpc, representing an increase of ~20%, while also reducing the total telescope time required to follow up events by ~20%.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Gravitational wave background from mergers of large primordial black holes

The Peters formula, which tells how the coalescence time of a binary system emitting gravitational radiation is determined by the initial size and shape of the elliptic orbit, is often used in estimating the merger rate of primordial black holes and the gravitational wave background from the mergers. Valid as it is in some interesting scenarios, such as the analysis of the LIGO-Virgo events, the Peters formula fails to describe the coalescence time if the orbital period of the binary exceeds the value given by the formula. This could underestimate the event rate of mergers that occur before the cosmic time t ~ 10 13 s. As a result, the energy density spectrum of the gravitational wave background could develop a peak, which is from mergers occurring at either t ~ 10 13 s (for black holes with mass M ≳ 10 8 M ⊙ ) or t ~ 10 26 (M/M ⊙ ) -5/3 s (for 10 5 M ⊙ ≲ M ≲ 10 8 M ⊙ ). This can be used to constrain the fraction of dark matter in primordial black holes (denoted by f) if potential probes (such as SKA and U-DECIGO) do not discover such a background, with the result f ≲ 10 -6 –10 -4 for the mass range 10– 10 9 M ⊙ . Finally, we then consider the effect of mass accretion onto primordial black holes at redshift z ~ 10, and find that the merger rate could drop significantly at low redshifts. The spectrum of the gravitational wave background thus gets suppressed at the high-frequency end. This feature might be captured by future detectors such as ET and CE for initial mass M = Script $\mathcal{O}$(10–100) M ⊙ with f ≳ 10 -4 .

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Phase transition phenomenology with nonparametric representations of the neutron star equation of state

Astrophysical observations of neutron stars probe the structure of dense nuclear matter and have the potential to reveal phase transitions at high densities. Most recent analyses are based on parametrized models of the equation of state with a finite number of parameters and occasionally include extra parameters intended to capture phase-transition phenomenology. However, such models restrict the types of behavior allowed and may not match the true equation of state. We introduce a complementary approach that extracts phase transitions directly from the equation of state without relying on, and thus being restricted by, an underlying parametrization. We then constrain the presence of phase transitions in neutron stars with astrophysical data. Current pulsar mass, tidal deformability, and mass-radius measurements disfavor only the strongest of possible phase transitions (latent energy per particle ≳ 100 MeV). Weaker phase transitions are consistent with observations. Here we further investigate the prospects for measuring phase transitions with future gravitational-wave observations and find that catalogs of O (100) events will (at best) yield Bayes factors of ~ 10 : 1 in favor of phase transitions even when the true equation of state contains very strong phase transitions. Our results reinforce the idea that neutron star observations will primarily constrain trends in macroscopic properties rather than detailed microscopic behavior. Fine-tuned equation of state models will likely remain unconstrained in the near future.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Core collapse supernova gravitational wave emission for progenitors of 9.6, 15, and 25 M ⊙

Here, we present gravitational wave emission predictions based on three core collapse supernova simulations corresponding to three different progenitor masses. The masses span a large range, between 9.6 and 25M ⊙ , are all initially nonrotating, and are of two metallicities: zero and solar. We compute both the temporal evolution of the gravitational wave strains for both the plus and the cross polarizations, as well as their spectral decomposition and characteristic strains. The temporal evolution of our zero metallicity 9.6M ⊙ progenitor model is distinct from the temporal evolution of our solar metallicity 15M ⊙ progenitor model and our zero metallicity 25M ⊙ progenitor model. In the former case, the high-frequency gravitational wave emission is largely confined to a brief time period ~75 ms after bounce, whereas in the latter two cases high-frequency emission does not commence until ~125 ms after bounce or later. The excitation mechanisms of the high-frequency emission in all three cases correspond to proto-neutron star convection and accretion onto the proto-neutron star from the convective gain layer above it, with the former playing the dominant role for most of the evolution. The low-frequency emission in all three models exhibits very similar behavior. At frequencies below ~250 Hz, gravitational waves are emitted by neutrino-driven convection and the standing accretion shock instability (SASI). This emission extends throughout the simulations when a gain region is present. In all three models, explosion is observed at ~125, ~500, and ~250 ms after bounce in the 9.6, 15, and 25M ⊙ progenitor models, respectively. At these times, the low-frequency gravitational wave emission is joined by very low-frequency emission, below ~10 Hz. These very low-frequency episodes are the result of explosion and begin at the above designated explosion times in each of our models. Our characteristic strains tell us that, in principle, all three gravitational wave signals would be detectable by current-generation detectors for a supernova at a distance of 10 kpc. However, our 9.6M ⊙ progenitor model is a significantly weaker source of gravitational waves, with strain amplitudes approximately 5–10 times less than in our other two models. The characteristic strain for this model tells us that such a supernova would be detectable only within a much more narrow frequency range around the maximum sensitivity of today’s detectors. Finally, in our 9.6M ⊙ progenitor model, we see very high-frequency gravitational radiation, extending up to ~2000 Hz. This feature results from the interaction of shock- and deleptonization-induced convection with perturbations introduced in the progenitor by nuclear burning during core collapse. While unique to the 9.6M ⊙ progenitor model analyzed here, this very high-frequency emission may, in fact, be a generic feature of the predictions for the gravitational wave emission from all core collapse supernova models when simulations are performed with three-dimensional progenitors.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

What if GW190425 did not produce a black hole promptly?

ABSTRACT It is widely believed that the binary neutron star merger GW190425 produced a black hole promptly upon merger. Motivated by the potential association with the fast radio burst FRB 20190425A, which took place 2.5 h after the merger, we revisit the question of the outcome of GW190425 by means of numerical relativity simulations. We show that current laboratory and astrophysical constraints on the equation of state of dense matter do not rule out the formation of a long-lived remnant. However, the formation of a stable remnant would have produced a bright kilonova, in tension with upper limits by ZTF at the location and time of FRB 20190425A. Moreover, the ejecta would have been optically thick to radio emission for days to months, preventing a putative FRB from propagating out. The predicted dispersion measure is also several orders of magnitude larger than that observed for FRB 20190425A. Our results indicate that FRB 20190425A and GW190425 are not associated. However, we cannot completely rule out the formation of a long-lived remnant, due to the incomplete coverage of the relevant sky regions. More observations of GW190425-like events, including potential upper limit, have the potential to constrain nuclear physics. To this aim, it is important that follow-up observational campaigns of gravitational wave events are informed by the properties of the source, such as their chirp mass, and we urge the LIGO-Virgo-KAGRA collaboration to promptly release them publicly.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Tidal Love numbers of novel and admixed celestial objects

A sub-fraction of dark matter or new particles trapped inside celestial objects can significantly alter their macroscopic properties. Here, we investigate the new physics imprint on celestial objects by using a generic framework to solve the Tolman-Oppenheimer-Volkoff (TOV) equations for up to two fluids. We test the impact of populations of new particles on celestial objects, including the sensitivity to self-interaction sizes, new particle mass, and net population mass. Applying our setup to neutron stars and boson stars, we find rich phenomenology for a range of these parameters, including the creation of extended atmospheres. These atmospheres are detectable by their impact on the tidal love number, which can be measured at upcoming gravitational wave experiments such as Advanced LIGO, the Einstein Telescope, and LISA. We release our calculation framework as a publicly available code at this URL, allowing the TOV equations to be generically solved for arbitrary new physics models in novel and admixed celestial objects.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Bayesian inference of multi-messenger astrophysical data: Joint and coherent inference of gravitational waves and kilonovae

Multi-messenger observations of binary neutron star mergers can provide information on the neutron star’s equation of state (EOS) above the nuclear saturation density by directly constraining the mass-radius diagram. We present a Bayesian framework for joint and coherent analyses of multi-messenger binary neutron star signals. As a first application, we analyze the gravitational-wave GW170817 and the kilonova (kN) AT2017gfo data. These results are then combined with the most recent X-ray pulsar analyses of PSR J0030+0451 and PSR J0740+6620 to obtain new EOS constraints.We extend the bajes infrastructure with a joint likelihood for multiple datasets, support for various semi-analytical kN models, and numerical-relativity (NR)-informed relations for the mass ejecta, as well as a technique to include and marginalize over modeling uncertainties. The analysis of GW170817 used the TEOBResumS effective-one-body waveform template to model the gravitational-wave signal. The analysis of AT2017gfo used a baseline multicomponent spherically symmetric model for the kN light curves. Various constraints on the mass-radius diagram and neutron star properties were then obtained by resampling over a set of ten million parameterized EOSs, which was built under minimal assumptions (general relativity and causality).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Phase effects from strong gravitational lensing of gravitational waves

Assessing the probability that two or more gravitational wave (GW) events are lensed images of the same source requires an understanding of the properties of the lensed images. For short enough wavelengths where wave effects can be neglected, lensed images will generically have a fixed relative phase shift that needs to be taken into account in the lensing hypothesis. For non-precessing, circular binaries dominated by quadrupole radiation these lensing phase shifts are degenerate with either a shift in the coalescence phase or a detector and inclination dependent shift in the orientation angle. This degeneracy is broken by the presence of higher harmonic modes with |m| ≠ 2 in the former and |m| ≠ l in the latter. The presence of precession or eccentricity will also break this degeneracy. This implies that a lensed GW image will not necessarily be consistent with (unlensed) predictions from general relativity (GR). Therefore, unlike the conventional scenario of electromagnetic waves, strong lensing of GWs can lead to images with a modified phase evolution that can be observed. However, we find that templates with a shifted orientation angle remain a good approximation, with signal-to-noise ratio differences of less than 1% for mass ratios up to 1/18, and less than 5% for precession parameters up to 0.5 and eccentricities up to 0.4. We conclude that an optimal strong lensing search strategy would incorporate phase information in all stages of the identification of strong-lensing, with an exact treatment in the final assessment of the probability of multiple lensed events. Here, this work clarifies the role that strong lensing plays in the phase evolution of GWs: how it can lead to apparent deviations from GR, how it can affect the detectability of GW events, and how it can be exploited to help identify cases of strong gravitational lensing of gravitational wave sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Gravitational waves from fully general relativistic oscillon preheating

As long-lived quasisolitons from the fragmentation of a scalar condensate, oscillons may dominate the preheating era after inflation. During this period, stochastic gravitational waves can also be generated. Here we quantify the gravitational-wave production in this period with simulations accounting for full general relativity to capture all possible nonperturbative effects. We compute the gravitational-wave spectra across a range of choices of the oscillon preheating models and compare our results to a conventional perturbative approach on a Friedmann-Lemaître-Robertson-Walker (FLRW) background. We clarify the gauge ambiguities in computing induced gravitational waves from scenarios where dense nonperturbative objects such as oscillons are being formed. In particular, we find that the synchronous gauge tends to contain large artificial enhancements in the gravitational-wave spectrum due to gauge modes if gravity plays an important role in the formation of the oscillons, while other gauge choices, such as the radiation gauge or a suitably chosen “1+log” gauge, can efficiently reduce the contributions of gauge modes. The full general-relativistic simulations indicate that gravitational-wave spectra obtained from the perturbative approach on the FLRW background are fairly accurate, except when oscillon formation induces strong gravitational effects, for which case there can be an order unity enhancement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗