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    Cloverleaf Quasar (H1413+117)

    Cloverleaf Quasar
    Chandra X-ray view of the Cloverleaf quasar.
    Credit: NASA/CXC/Penn State/G.Chartas et al
    A quasar, discovered in 1988 and located about 11 billion light-years away in Leo, that appears as four different images because of a gravitational lens effect caused by a foreground elliptical galaxy. Molecular gas (notably CO) detected in the host galaxy associated with the quasar is the oldest molecular material known and provides evidence of large-scale star formation in the early universe.

    Data on the Cloverleaf collected by the Chandra X-ray Observatory in 2004 was compared with that gathered by optical telescopes. One of the X-ray components (A) in the Cloverleaf is brighter than the others in both optical and X-ray light but was to be relatively brighter in X-ray than in optical light. The X-rays from iron atoms were also enhanced relative to X-rays at lower energies. Since the amount of brightening due to gravitational lensing doesn't vary with the wavelength, this means that an additional object has magnified the X-rays. The increased magnification of the X-ray light can be explained by gravitational microlensing, an effect which has been used to search for compact stars and planets in our galaxy. Microlensing occurs when a star or a multiple star system passes in front of light from a background object. If a single star or a multiple star system in one of the foreground galaxies passed in front of the light path for the brightest image, then that image would be selectively magnified. The X-rays would be magnified much more than the visible light, if they came from a smaller region around the central supermassive black hole of the lensing galaxy than did the visible light. The enhancement of the X-rays from iron ions would be due to this same effect. The analysis indicates that the X-rays are coming from a very small region, about the size of the solar system, around the central black hole. The visible light is coming from a region ten or more times larger. The angular size of these regions at a distance of 11 billion light years is tens of thousands times smaller than the smallest region that can be resolved by the Hubble Space Telescope. This provides a way to test models for the flow of gas around a supermassive black hole.


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