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No. 48: Nov-Dec 1986

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An 11-minute binary

4U1820-30 is an X-ray binary star located in the heart of the globular cluster NGC 6624. Its claim to fame is a very short period of rotation -- only 685 seconds. In just a shade over 11 minutes, a neutron star orbits a white dwarf, according to present thinking. The orbit diameter is only 1/7 the radius of our sun, which implies the stars themselves are also small. 4U1820-30 is the shortest-period binary ever found -- so short that astronomers are looking for other explanations.

Another curious fact mentioned in this item is that X-ray binaries are much more common in globular clusters than elsewhere in the universe. What is so different about globular clusters?

(King, A.R., and Watson, M.G.; "The Shortest Period Binary Star," Nature, 323:105, 1986.)

From Science Frontiers #48, NOV-DEC 1986. © 1986-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:

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  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada>, Vol. 81, no. 1 (1987), p. 24., 02/1987