NuSTAR Probes Black Hole Jet Mystery

A paper with participation by many members of the NuSTAR X-ray binaries group (and SSL) entitled, “An elevation of 0.1 light-seconds for the optical jet base in an accreting Galactic black hole system” by Gandhi et al. was published in the journal Nature Astronomy this week.  The primary result was based on X-ray and optical observations of V404 Cyg, which is an accreting black hole transient that had an extremely bright outburst in 2015.  It was found that fluctuations in the optical light from the black hole were delayed by 0.1 seconds relative to the X-ray fluctuations, providing a measurement of the location of the optical emission zone in the jet.  The delay was only seen after a plasma jet was detected at radio wavelengths, demonstrating that the optical emission arises from the jet.  A news release is available at