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March 27, 1995 Press Contact: Steve Koppes
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Extragalactic Object Observed in Extreme Ultraviolet

Using the NASA Extreme Ultraviolet Explorer (EUVE) satellite, scientists have been able to measure the spectrum–for the first time–of the brightest extragalactic object in the extreme ultraviolet region of the electromagnetic spectrum. This region of the spectrum was thought to be opaque to astronomers trying to look outside our own galaxy because the radiation is almost completely absorbed by the interstellar gas. University of Chicago astrophysicist Arieh Königl will present the results of his observations at the International Astronomical Union colloquium on astrophysics in the extreme ultraviolet, Monday, March 27, at the University of California at Berkeley.

Königl’s research provides some surprising new data about a class of extremely bright, quasar-like astronomical objects known as “BL Lacertae" objects, or “BL Lacs.” Königl’s observations of the BL Lac PKS 2155-304 show that it is not a distant quasar made brighter through “gravitational lensing,” as some scientists thought, but a relatively nearby galaxy–with a nucleus of a very massive black hole, up to one hundred million times the mass of our sun.

“Using the extreme ultraviolet we are able to probe very close to the center of this galaxy,” Königl said. “Emerging from the vicinity of the nucleus there are extremely powerful relativistic jets, spewing out matter at nearly the speed of light.” In other wavelengths, the emission from the relativistic jets swamps that of the underlying nucleus, but Königl was able to obtain the observations of the gas cloud surrounding the active galactic nucleus through its absorption signature in the extreme ultraviolet.

Königl, Professor of Astronomy & Astrophysics at Chicago, said that these kind of observations would not have been possible without the EUVE satellite. “People didn’t think you could see outside our own galaxy,” he said, “but it turns out there are windows through the interstellar medium through which we can see extragalactic objects.”

NASA’s EUVE satellite was launched in 1992. Observations in the extreme ultraviolet cannot be made from the ground because light at these wavelengths is absorbed by the earth’s atmosphere. The field of extreme ultraviolet astronomy has flourished only in the past five years with the launch of EUVE (70-760 Å) and a companion satellite, the British ROSAT Wide-Field Camera (60-200 Å).

Königl will publish a paper on the results of his work with BL Lacs in the June 20 issue of the Astrophysical Journal.

His work was funded by NASA. Other collaborators included John Kartje, a graduate student at Chicago; and Stuart Bowyer, Steven Kahn and Chorng-Yuan Hwang from Berkeley.
Last modified at 03:50 PM CST on Wednesday, June 14, 2000.

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