The project is essentially a combination of NASA's Swift and now-retired
Rossi X-ray Timing Explorer (RXTE) satellites.
Evidence for the clouds comes from records collected over 16 years by NASA's
Rossi X-ray Timing Explorer, a satellite in low-Earth orbit equipped with instruments that measured variations in X-ray sources.
The galaxies, which were selected from the All-Sky Slew Survey Catalog produced by NASA's
Rossi X-ray Timing Explorer satellite, were all located less than 1.3 billion light-years away.
NASA's
Rossi X-ray Timing Explorer discovered the neutron star in 1999 when it emitted bursts of X rays.
NASA's
Rossi X-ray Timing Explorer concentrates on the rapid brightness variations of X-ray-emitting stars.
NASA's
Rossi X-Ray Timing Explorer and Chandra X-ray Observatory, ESA's XMM-Newton and Japan's Suzaku satellite, as well as the ground-based Gran Telescopio Canarias and the Green Bank Telescope, were alerted and the star's activity was monitored until April 2012, during which time the outburst began to decay.
Armed with the new, precise distance measurement, scientists using the Chandra X-Ray Observatory, the
Rossi X-Ray Timing Explorer, the Advanced Satellite for Cosmology and Astrophysics, and visible-light observations made over more than two decades, calculated that the black hole in Cygnus X-1 is nearly 15 times more massive than our Sun and is spinning more than 800 times per second.
In 90 hours of archival data from NASA's
Rossi X-ray Timing Explorer (RXTE) satellite, the bright X-ray source Scorpius X-1 exhibited 58 random dips in brightness lasting just a few milliseconds.