beecee Posted June 2, 2018 Posted June 2, 2018 https://newatlas.com/neutron-star-collision-black-hole/54861/ NASA sheds light on strange object created in cosmic collision: In August 2017, astronomers were treated to one of the most spectacular stellar light shows ever seen – a collision between two neutron stars. The smashup was so powerful it sent gravitational ripples through the very fabric of spacetime, and produced flares in visible light, radio waves, x-rays and a gamma ray burst. Now that things have quietened down, astronomers have studied the strange object created in the cosmic collision. The LIGO facility was the first to notice something big was happening. On August 17 last year, the instrument detected gravitational waves coming from a source now officially known as GW170817, which lies about 138 million light-years away. Gravitational waves alone are old news, but there was something different about this one – it wasn't caused by invisible black holes merging, but the very-visible crash of two neutron stars. About 70 observatories around the world quickly trained their sights on the location, and weren't disappointed. Across the various instruments, signals were detected in visible light, radio waves, x-rays and a short gamma ray burst. The fireworks were expected to be short-lived, but to make things even weirder, the afterglow actually seemed to get brighter over the next few months. more at link................... ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: the paper: http://iopscience.iop.org/article/10.3847/2041-8213/aac3d6 GW170817 Most Likely Made a Black Hole: Abstract: There are two outstanding issues regarding the neutron-star merger event GW170817: the nature of the compact remnant and the interstellar shock. The mass of the remnant of GW170817, ~2.7 , implies that the remnant could be either a massive rotating neutron star, or a black hole. We report Chandra Director's Discretionary Time observations made in 2017 December and 2018 January, and we reanalyze earlier observations from 2017 August and 2017 September, in order to address these unresolved issues. We estimate the X-ray flux from a neutron star remnant and compare that to the measured X-ray flux. If we assume that the spin-down luminosity of any putative neutron star is converted to pulsar wind nebula X-ray emission in the 0.5–8 keV band with an efficiency of 10−3, for a dipole magnetic field with 3 × 1011 G < B < 1014 G, a rising X-ray signal would result and would be brighter than that observed by day 107; we therefore conclude that the remnant of GW170817 is most likely a black hole. Independent of any assumptions of X-ray efficiency, however, if the remnant is a rapidly rotating magnetized neutron star, the total energy in the external shock should rise by a factor ~102 (to ~1052 erg) after a few years; therefore, Chandra observations over the next year or two that do not show substantial brightening will rule out such a remnant. The same observations can distinguish between two different models for the relativistic outflow, either an angular or radially varying structure.
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