David Aguilar
(617) 495-7462

Christine Pulliam
(617) 495-7463


CfA Press Release


FOR RELEASE: 10:00 a.m. CDT June 1, 1999

Scientists at the Harvard-Smithsonian Center for Astrophysics haveobtained the longest and most complete optical light curve to date ofan X-ray nova -- a violent and extremely energetic celestial eventthat usually signals the presence of a black hole.

An X-ray nova is a system containing a star, usually comparable to ourown Sun, that orbits a much more massive, central object -- most oftena black hole. X-ray novae, also known as soft X-ray transients, arecharacterized by a dramatic, million-fold increase in X-ray intensityas material from the secondary star falls onto the black hole andcauses a giant outburst of radiation. As illustrated here, theoutburst is followed by a decay period that lasts several months,which is then followed by years or decades of quiescence. Two optical"mini-outbursts" in 1993 and an X-ray ``micro-outburst'' inquiescence shown here are unusual behavior for an X-ray nova. Byobserving and analyzing the outbursts -- and then the subsequent decayof radiation - scientists may discern some of the physical propertiesof the black hole. Studies have shown that J0422+32 contains a blackhole with a mass at least five times that of our Sun.

GRO J0422+32 was discovered in outburst on August 5, 1992 by theCompton Gamma-ray Observatory. Astronomers have been tracking its radiationfor the 6.7 years since then, making it one of the best-studiedobjects of its kind. Nearly all of the optical data were taken usingthe 1.2-meter telescope at the Fred L. Whipple Observatory onMt. Hopkins, AZ. The X-ray data were taken by the RXTE All-skyMonitor and were obtained from the RXTE public archive web site athttp://space.mit.edu/XTE/ASM_lc.html.

PHOTO CREDIT: Ping Zhao and Jeffrey E. McClintock, Harvard-Smithsonian Center for Astrophysics. Email: zhao@cfa.harvard.edu

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