Chandra Lensed Quasar
Credit: NASA/George Chartas (PSU), Marshall Bautz (MIT)

Through an X-ray Lens Brightly

Active galaxies called quasars (quasi-stellar radio objects) are very distant objects - so distant that the entire galaxy appears as a single point of light. Quasars are extremely luminous, and their radiative power is thought to be produced by accretion of portions of the galaxy's onto a central supermassive black hole. If a nearby galaxy falls in front of a more distant quasar, the matter in the nearby galaxy can act as a "gravitational lens", bending the light from the quasar, causing the image of the quasar to be split into many mirror images. Now astronomers using the Chandra X-ray observatory have observed that a distant quasar called RXJ 0911.4+0551, split into 4 separate images by the gravity of a foreground galaxy. The 4 images of the quasar are shown in the image above. Since quasars can vary in X-ray brightness, astronomers can use differences in the variation as reflected in each separate image to tell important information about the workings of gravity and the expansion of the universe. For example, the lower charts show how the X-ray brightness of 2 quasar images (image A1 and A2) varies with time. Even though the images above originate from the same quasar, an abrupt increase in the brightness of the quasar is clearly seen in the chart on the lower left. In the same time interval, the chart on the lower right shows that no such flare was seen in image A1.

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Page Author: Dr. Michael F. Corcoran
Last modified December 18, 2000