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Hubble images reveal unusual galactic jet.

Viewed from Earth in visible light, the elliptical galaxy NGC 3862 doesn't look like much. Indeed, its flat emission pattern apparently devoid of sharp peaks and dips in intensity, once prompted researchers to describe this galaxy as "optically dull."

But orbiting 380 miles above Earth, the Hubble Space Telescope now reveals that the nucleus of NGC 3862 spews out a short jet of radiation, too short to have been detected with ground-based telescopes, in both visible light and the near ultraviolet. Moreover, this jet shines more brightly in the ultraviolet -- at the shorter end of the electromagnetic spectrum -- than at longer wavelengths, a feature diametrically opposite to the energy output of any other galactic jet yet observed.

"It appears that we are seeing a new type of phenomenon," says Philippe Crane of the European Southern Observatory (ESO) in Garching, Germany.

Researchers believe that a typical jet, possibly powered by a massive black hole or other potent energy source at the center of a galaxy, radiates because of the acceleration of electrons that circle strong galactic magnetic fields. This radiation, know as synchrotron radiation, has a higher intensity at redder, or longer, wavelengths. The well-studied jet in the galaxy M87, for example, fits this model perfectly, says Crane (SN: 1/25/92, p.52).

Crane speculates that the unique radiation pattern from NGC 3862, a resident of the Abell cluster of galaxies, could represent a combination of two types of emissions: standard synchrotron radiation as well as radiation, primarily in the ultraviolet, from atoms that surround the jet and are heated by it. If this interpretation proves correct, it would mark the first time that astronomers have observed both types of radiation from a jet.

Crane notes, however, that recent observations with the ESO's New Technology Telescope in La Serena, Chile, found no evidence of atomic emissions. Alternatively, he adds, the jet's output may stem from galactic mechanisms not yet understood.
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Title Annotation:NGC 3862
Author:Cowen, Ron
Publication:Science News
Date:May 30, 1992
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