News and Updates

With our latest preprint [arXiv:2306.03148] (led by Cornell graduate student Jooheon Yoo), we present a numerical relativity surrogate model trained on SXS waveforms with memory effects and post-Newtonian hybridization! So what’s the hype about?!

With our latest preprint [arXiv:2208.07380] (led by Caltech grad student Keefe Mitman), SXS simulations have conclusively shown the presence of nonlinearities in black hole ringdowns. What does it all mean?

On 14 September 2015 at 4:50:45 AM Eastern standard time, LIGO detected its first gravitational waves. The waves descended on Earth from the southern hemisphere, passed through the Earth, and emerged at the Earth’s surface first at the LIGO interferometer in Livingston, Louisiana, and then, 7 milliseconds later, at the LIGO interferometer in Hanford, Washington (shown below).

To detect and characterize gravitational waves from neutron star binaries, LIGO needs good models of all possible signals. Numerical relativity can’t practically be used for every case, but it is needed to test and calibrate the simpler models that LIGO can use. Inspiral waveforms from binaries with neutron stars differ from binary black hole waveforms by the presence of tidal forces. In a recent paper, Tanja Hinderer and collaborators use SXS black hole-neutron star simulations to validate a new model of these tidal forces. They find that tidal effects can be stronger than previously expected when they come close to resonance with a neutron star’s preferred ways of ringing (its normal modes of oscillation).

Matter flung out into space during black hole-neutron star mergers may well be one of the major contributors to the “r-process” heavy-elements in the universe such as gold and lead. To test this idea, we calculated the nuclear reactions taking place in the ejected matter from our black hole-neutron star mergers using the “SkyNet” nucleosynthesis code written by SXS member Jonas Lippuner. Our first studies found that it is very easy for our ejecta to produce the high-mass r-process elements (in abundance ratios not terribly different from what’s in the sun), but very little of the low-mass r-process elements are made, meaning they would have to come from a different source. We then found that this underproduction can be ameliorated (but not removed) by the effect of neutrinos given off by the merger remnant being absorbed by the outgoing matter, which changes its composition. Read the paper here [arXiv:1601.07942].