XTE J1859-226

On October 9, 1999, the orbiting Rossi X-Ray Timing Explorer (RXTE) spacecraft detected a bright burst of X-rays from the constellation Vulpecula, the fox. The outburst continued to grow brighter for about two weeks, then spent about five months fading out. The object was classified as an X-ray nova.

From satellite X-ray observations, combined with optical observations by ground-based telescopes, astronomers concluded that XTE J1859-226 consisted of a black hole and a normal companion star. It produced the nova outburst when blobs of gas from the companion star fell onto the accretion disk of hot gas around the black hole. As the blobs hit, the shock wave heated them to hundreds of millions of degrees, so they produced bright outbursts of X-rays.

XTE J1859-226 has produced several smaller outbursts since then, with the system's X-ray brightness varying by several percent in a matter of minutes or seconds. The high-speed change indicates that the object is relatively small, which provides further evidence that it consists of a black hole with a surrounding accretion disk.

A 2011 study measured the mass of the black hole at 5.42 times the mass of the Sun. It determined that the black hole and its companion orbit each other once every 6.6 hours. Other studies, however, have produced different values for both the mass of the black hole and the orbital period of the two stars. Astronomers also disagree on the distance t

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This document was last modified: March 5, 2013.