Cygnus X-3

Cygnus X-3 is one of the stronger binary X-ray sources in the sky. Classified as a microquasar, it is believed to be a compact object in a binary system which is pulling in a stream of gas from an ordinary star companion.

It is observed in X rays, gamma rays,infrared, and radio, with an orbital periodicity of approximately 4.8 hours, among the shortest-known at the time of its discovery.

Although it is only the third-brightest X-ray source in the constellation Cygnus, after the more famous Cygnus X-1, it is located about 23,000 light-years (7.1 kiloparsecs) away. It is heavily obscured by intervening interstellar gas and dust near the galactic plane, and fainter than 23rd-magnitude in the optical, but is easily observable in the J, H, & K near-infrared bands.

Taking its distance and extinction into account, it appears to be one of the two or three most intrinsically luminous objects in the galaxy.

It has also received attention because it is one of the few sources of ultra-high-energy cosmic rays, with energies in the 100–1000 TeV range. Its most unusual aspect is the production of anomalous cosmic ray events in a proton decay detector deep in Minnesota's Soudan iron mine. These events have defied analysis and have led to questions about whether Cygnus X-3 is a standard neutron star or perhaps something more exotic, like a star made of quarks.