SS433

Because SS433 is relatively close, at just 16,000 light-years, and it is a bright source of several types of energy, including radio waves and X-rays, it is one of the most intensively studied black hole systems in the galaxy. By piecing together decades of observations made at different wavelengths, astronomers have devised a detailed model of how the system works.

SS433 (the 433rd object in a catalog compiled by astronomers Bruce Stephenson and Nick Sanduleak) consists of two stars -- a black hole and a white supergiant. They orbit each other once every 13 days, at a distance of about 15 million miles (25 million km), which is about one-third the distance between the Sun and Mercury, the innermost planet.

At that close range, the black hole’s gravity pulls gas off the surface of the companion star. The gas forms an accretion disk around the black hole. Powerful magnetic fields shoot some of the gas in this disk back into space at 26 percent of the speed of light (175 million mph/78,000 km per second), forming long jets. Near the black hole, the gas in these jets is heated to 100 million degrees centigrade.

For reasons that astronomers do not yet understand, the jets “wobble” like a spinning top, so they shoot out in a corkscrew pattern, like water from a spinning lawn sprinkler. Both X-ray and radio observations show that the jets extend trillions of miles into space, growing wider and fainter as they spiral outward.

Because of the accretion disk and high-speed jets, astronomers classify SS433 as a “microquasar.” It’s a small-scale version of quasars, which are powered by accretion disks as big as our solar system orbiting supermassive black holes. True quasars are all billions of light-years away, so the microquasars in our own galaxy allow astronomers to study the physics of quasars in greater detail.

Astronomer Larry Krumenaker discovered the odd nature of this system in 1975. He named it K16, although the Stephenson and Sanduleak catalog superceded the name.

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This document was last modified: March 14, 2012.