Press Release

PG1115+080 (Gravitational Lens)

January 28, 1999

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Object Name: PG1115+080 (Gravitational Lens)
Telescope: Subaru Telescope / Cassegrain Focus
Instrument: CISCO (J, K'), Suprime-Cam (R)
Filter: R (red), J (1.25 micron), K' (2.15 micron)
Color: Blue (R), Green (J), Red (K')
Date: UT 1999 Jan 13 (R), Jan 14 (J), Jan 12 (K')
Exposure: 420 sec (R), 35 sec (J), 275 sec (K')
Field of View: 4.7 arcsec by 5 arcsec
Orientation: North up, east left

Einstein's Theory of General Relativity predicts that the gravitational pull from massive objects is able to deflect rays of light in the same way as do lenses. Many examples of this "gravitational lensing" have been discovered, where light from a distant object is deflected by an intervening galaxy or group of galaxies whose gravity deforms the space around them. Subaru has observed one such object, known as PG1115+080, where a distant quasar (10 billion light years away) is located almost directly behind a much closer galaxy (3 billion light years away). When the alignment is as good as this, light can take multiple routes from the quasar to the observer, and many images are seen. The left panel, a combination of optical and near-infrared images, shows four bright images of the quasar around the central, red galaxy which is acting as the lens. The excellent image quality obtained by Subaru (0.33 arcsec FWHM for this image) clearly separates all the images. The panel on the right shows faint, extended light suggestive of a ring which is expected when the source and lensing galaxy are this closely aligned. Astronomers can use the relative brightness and position of the individual images in a gravitationally-lensed system to determine how rapidly the Universe is expanding and whether it will continue to expand forever, or if it will eventually slow down and collapse in a Big Crunch.



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