Scorpious X-1 is the most brilliant pulsating X-ray source in the sky. It is the brightest of all non-transient cosmic X-ray sources and is potentially a dead neutron star that has been reactivated by a companion. Scorpious X-1 is important to X-ray astronomy because it is the first extrasolar X-ray source to be discovered from rocket data by Riccardo Giacconi, Herbert Gursky, Frank Paolini and Bruno Rossini in June 1962. Their mission was ironically to search for X-rays from the Moon. Incidentally, the same rocket flight conducted from White Sands, New Mexico, also provided the first evidence for extragalactic X-ray background. Since the discovery of Scorpious X-1, it has been the subject of close scrutiny by astronomers. Initially, astronomers were unable to confirm the discrete source for Scorpious X-1. The visible counterpart for Scorpious X-1 was only optically discovered in 1967 to be a 13^th magnitude star called V818 Sco which has an unusual emission spectrum.. Scorpious X-1 is also now confirmed to be a low mass X-ray binary (LMXB) system with an orbital period of 0.78 days. Astronomers also found that Scorpious X-1 has an apparent double radio source. Radio transmission from Scorpious X-1 is strongest when the compact object and a small accretion disk dominate the X-ray emission and weakest when the accretion environment becomes more stable as it increases in size. The distance to Scorpious X-1 is currently accepted as between 300 to 600 parsecs. Even though Scorpious X-1 appears extremely bright in the sky, by comparison with the first discovered quasar 3C273 for example, Scorpious X-1 produces X-ray energies 100,000,000 times less. The faintness of 3C273 results from the fact that it is extremely distant at about 2 billion light years.
About 10 years ago, astronomers detected strange signals from Scorpious X-1 as well as other X-ray sources. They seem to be emitting elusive pulses of X-rays that come and go at very short time intervals of a few hundred seconds - these are now called  “quasi-periodic oscillations” or QPOs for short. Astronomers theorise that QPOs are the result of short noise - a kind of flickering of certain X-rays that can be modelled by assuming random emission of bunches of X-ray photons.