The formation of black hole from the collapsingcore of a massive star is thought to be heralded by a spectacularsupernova explosion.Such an extremely energetic collapse is also leading explanationfor the mysterious cosmic gamma-ray bursts.But researchers now suggest that the Milky Way's mostfamous black hole Cygnus X-1, was born when a massivestar collapsed - withoutany supernova explosion at all.Their dynamical evidence is summarized in thiscolor image of a gorgeou region in Cygnus,showing Cyg X-1 and a cluster of massive stars(yellow circles) known as Cygnus OB3.Arrows compare the measured direction and speed of Cyg X-1and the average direction and speed of the massive starsof Cyg OB3.The similar motions indicate thatCyg X-1's progenitor star was itself a cluster memberand that its path was not altered at all when itbecame a black hole.In contrast, if Cyg X-1 were born in a violent supernovait would have likely received fiercekick, changing its course.If not a supernova, coul the formationof the Cyg X-1 blackhole have produced a darkgamma-ray burst i theMilky Way?
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