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Science 23 April 1999:
Vol. 284. no. 5414, p. 566
DOI: 10.1126/science.284.5414.566
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News of the Week

ASTRONOMY:
Black Holes Enter the Middleweights

Mark Sincell

Black holes have seemed to come in only two varieties: "supermassive" ones, which power brilliant galaxies called quasars and weigh millions to billions of times more than the sun, and "stellar mass" black holes, which have about the mass of one large star. But at the meeting of the High Energy Astrophysics Division of the American Astronomical Society in Charleston, South Carolina, last week, two groups reported the discovery of a new class of black holes right in the middle, leaving astronomers to debate their origins.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)