He reported the finding earlier this month at a workshop on black holes at the European Southern Observatory in Garching, Germany. In another study, Andrew C. Fabian of the University of Cambridge in England estimates the contribution of black holes to cosmic radiation based on the average density of supermassive black holes near our galaxy and the intensity of the sky's X-ray background. Neither stars nor the known population of quasars can account for the background, and Fabian argues that it's produced by a vast population of quasars that have not yet been detected because they lie behind a veil of dust. Astronomers had previously come up with estimates of only a few percent because they based their calculations on the relatively few quasars seen in visible light, Fabian says. Looking for hidden quasars isn't easy.
Dust absorbs both ultraviolet and visible light and reradiates it as far-infrared radiation.
Astronomers, however, have few high-resolution telescopes to detect this wavelength band. Aside from illuminating the universe, a population of previously unknown quasars could complicate galaxy formation, Fabian speculates. For example, quasar winds might blow gas out of young galaxies. Such winds might also hinder the growth of the slender arms and disks of spiral galaxies, notes Roger D. Blandford of Caltech. Reference and sources for this article From Science News , Vol.