Where a Black Hole Roams

Black hole candidate XTE J1118+480 is known to roam the halo of our Milky Way Galaxy. This exotic system - thought to be a stellar mass black hole consuming matter from a companion star - was discovered only last year as a flaring celestial x-ray source. Suggestively termed a microquasar , recent radio and archival optical observations of its motion through the sky have now allowed its orbit to be calculated . Illustrated above, the black hole's present galactic location is indicated by the purple dot, with the Sun's position in yellow. A mere 6,000 light-years from the Sun now, XTE J1118+480's orbit is traced by the orange line, backtracked for some 230 million years into the past based on models of the Galaxy . Astronomers note this black hole's orbit about the galactic center, looping high above and below the Galaxy's plane of gas, dust,and stars, is similar to orbits of globular star clusters , ancient denizens of our Galaxy. It seems likely that XTE J1118+480 too has its origins in the early history and halo of the Milky Way.