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Black Hole Born in Dark Silence
By Robert Roy Britt
Senior Science Writer
posted: 02:00 pm ET
24 April 2003
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EMBARGOED FOR Thursday 4/24 2 pThe classic explanation for black hole birth describes an incredibly explosive and luminous event. A massive star explodes, then implodes, hovers a while, then collapses into an incredibly small region of stunning density. But new observations revealed today suggest some black holes are born in the dark without any noisy fanfare. Nobody can see black holes. By definition, their gravitational clutches are so powerful that matter and light cannot escape. Astronomers study them by examining what's emitted from their surroundings as matter spirals inward and is superheated, producing X-rays, visible light, radio waves and more. In the standard model, a stellar black hole -- containing the mass of a handful or even a few dozens suns -- forms after an exploded star first collapses into a neutron star, explained Felix Mirabel of the French Service d'Astrophysique and Instituto de Astronomía Físcia del Espacio in Buenos Aires. The neutron star is very dense, but not as dense as a black hole. It is unstable, however, and leads to the formation of a black hole. Mirabel recently found evidence for this standard model in a runaway black hole, an object shooting across the galaxy, and one he figures was launched by the supernova of its birthplace. But until now there was no evidence black holes are created without associated supernova. Mirabel and his colleague, Irapuan Rodrigues, say they found this evidence in a black hole named Cygnus X-1. "We propose that the way this black hole formed is different," Mirabel told SPACE.com. "The massive stellar progenitor imploded, that is it collapsed and formed the black hole directly, without launching matter and light far away. There was no luminous explosion for an external observer when it formed." The conclusion results from speculation of the environment of the black hole's birth based on an examination of massive stars in the region today and how Cygnus X-1 moves in relation to the other stars. The progenitor star was about 40 times the mass of the Sun, the researchers write in paper published today in the online version of the journal Science. The resultant black hole contains about 10 solar masses. The researchers say this setup could not have involved the sudden expulsion of more than about 1 solar mass of material, which is much less than supernovae are known to cough up. "The observations suggest that high-mass stellar black holes may form promptly, when massive stars disappear silently," they write.
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