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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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9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

The Extreme Spin of the Black Hole Cygnus X-1

Remarkably, an astronomical black hole is completely described by the two numbers that specify its mass and its spin. Knowledge of spin is crucial for understanding how, for example, black holes produce relativistic jets. Recently, it has become possible to measure the spins of black holes by focusing on the very inner region of an accreting disk of hot gas orbiting the black hole. According to General Relativity (GR), this disk is truncated at an inner radius 1 that depends only on the mass and spin of the black hole. We measure the radius of the inner edge of this disk by fitting its continuum X-ray spectrum to a fully relativistic model. Using our measurement of this radius, we deduce that the spin of Cygnus X-1 exceeds 97% of the maximum value allowed by GR.

Gou, Lijun↗
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 NTRS2007

The Constellation-X Mission

This viewgraph presentation reviews the goals, the instrumentation that will be aboard the Con-X spacecrafts, and the current status of the mission. Two science goals driving the need for this mission are: (1) Black Moles: precisions tests of GR in the strong field limit and determination of Black Hole spin in a large sample (2) Neutron Stars: Precision measurements of the mass-radius relation of neutron stars to determine the Equation of State (EOS) of ultra-dense matter

Cottam, Jean↗
NASA NTRS2006

Black Hole Solar Systems Extreme Mass Ratio Inspirals

Waveforms known well enough to detect some EMRIs today. Soon, enough to realize Gair et al estimate of approx. 100's to 1000's of detections to z = 1. Not yet enough to for precision parameter estimation of Barack and Cutler (mass and spin to 10(exp -4)). Some turning to the more exotic: non-Kerr background, gas interaction, third body, ... More status and refs: Drasco, gr-qc/0604115.

general relativity↗
NASA NTRSDate not supplied

Variety in the Variability of Accreting Supermassive Binary Black Holes

Accreting supermassive binary black holes are key multi-messenger sources for LISA, yet are challenging to simulate realistically as solving the radiation magnetohydrodynamics (MHD) equations over the full dynamic spatio-temporal range of the problem is computationally infeasible at present. We report on our collaboration's progress simulating these systems using general relativistic MHD simulations and dynamic GR. In order to cover a larger temporal range in one set of simulations, we constrain our view to the circumbinary disk region and measure the effects binary mass ratio, accretion disk size, and black hole spin have on the structure and variability of the accretion flow. We particularly emphasize how these parameters influence the overdensity feature, which orbits the binary near the edge of the cavity, since it is responsible for most of the electromagnetic emission's variability and variability is a key signature of a system being a binary. Extending to smaller length scales, we will report on simulations following accretion all the down to the event horizons so that we can begin to investigate how black hole spin affects mini-disk dynamics, accretion rate, and jet power.

Scott C Noble↗
NASA NTRS2021

Variety in the Variability of Accreting Supermassive Binary Black Holes

Accreting supermassive binary black holes are key multi-messenger sources for LISA, yet are challenging to simulate realistically as solving the radiation magnetohydrodynamics (MHD) equations over the full dynamic spatio-temporal range of the problem is computationally infeasible at present. We will provide a brief summary of the the progress made in the field to understand these systems theoretically and what new directions groups are pursuing. We will also report on our collaboration's progress to simulate these systems using general relativistic MHD and dynamic GR. In order to cover a larger temporal range in one set of simulations, we constrain our view to the circumbinary disk region and measure how the binary mass ratio, accretion disk size, and black hole spin have on the structure and variability of the accretion flow. We particularly emphasize how these parameters influence the overdensity feature, which orbits the binary near the edge of the cavity, since it is responsible for most of the electromagnetic emission's variability and variability is a key signature of a system being a binary. Extending to smaller length scales, we will report on simulations following accretion all the down to the event horizons so that we can begin to investigate how black hole spin affects mini-disk dynamics, accretion rate, and jet power. The novel computational methods enabling inclusion of the black holes in the domain, including multi-patch methods, will be described.

Scott C Noble↗
NASA NTRS2012

Prospects for Probing Strong Gravity with a Pulsar-Black Hole System

The discovery of a pulsar (PSR) in orbit around a black hole (BH) is expected to provide a superb new probe of relativistic gravity and BH properties. Apart from a precise mass measurement for the BH, one could expect a clean verification of the dragging of space-time caused by the BH spin. In order to measure the quadrupole moment of the BH for testing the no-hair theorem of general relativity (GR), one has to hope for a sufficiently massive BH. In this respect, a PSR orbiting the super-massive BH in the center of our Galaxy would be the ultimate laboratory for gravity tests with PSRs. But even for gravity theories that predict the same properties for BHs as GR, a PSR-BH system would constitute an excellent test system, due to the high grade of asymmetry in the strong field properties of these two components. Here we highlight some of the potential gravity tests that one could expect from different PSR-BH systems.

gravity↗
NASA NTRS2020

Tests of General Relativity with Stellar-Mass Black Hole Binaries Observed by LISA

We consider the observation of stellar-mass black holes binaries with the Laser Interferometer Space Antenna(LISA). Preliminary results based on Fisher information matrix analyses have suggested that gravitational waves from those sources could be very sensitive to possible deviations from the theory of general relativity (GR) andfrom the strong equivalence principle during the low-frequency binary inspiral. We perform a full Markov Chain Monte Carlo Bayesian analysis to quantify the sensitivity of these signals to two phenomenological modifications of GR, namely a putative gravitational dipole emission and a non-zero mass for the graviton, properly accounting for the detector’s response. Moreover, we consider a scenario where those sources could be observed also with Earth-based detectors, which should measure the coalescence time with precision better than 1 ms. This constraint on the coalescence time further improves the bounds that we can set on those phenomenological deviations from GR. We show that tests of dipole radiation and the graviton’s mass should improve respectively by seven and half an order(s) of magnitude over current bounds. Finally, we discuss under which conditions one may claim the detection of a modification to General Relativity.

Alexandre Toubiana↗
NASA NTRS2009

Black Holes, Gravitational Waves, and LISA

Binary black hole mergers are central to many key science objectives of the Laser Interferometer Space Antenna (LISA). For many systems the strongest part of the signal is only understood by numerical simulations. Gravitational wave emissions are understood by simulations of vacuum General Relativity (GR). I discuss numerical simulation results from the perspective of LISA's needs, with indications of work that remains to be done. Some exciting scientific opportunities associated with LISA observations would be greatly enhanced if prompt electromagnetic signature could be associated. I discuss simulations to explore this possibility. Numerical simulations are important now for clarifying LISA's science potential and planning the mission. We also consider how numerical simulations might be applied at the time of LISA's operation.

Baker, John↗