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Faraway Galaxy Mystery
31 January 2001 7:00 pm
Three familiar galaxies lurking at the edge of the visible universe are not, as previously thought, powered entirely by the fading embers of exploding supernovae, astronomers report in the current issue of Astronomy and Astrophysics. New images of the three radio sources, produced by a giant European telescope network, suggest the galaxies harbor black holes. The findings, although puzzling, seem to imply that black holes and star formation have been intimately connected since almost the beginning of time.
The three galaxies--named VLA J123644+621133, VLA J123642+621331, and VLA J123646+621404, in case you keep track of these things--were first discovered in the 1996 Hubble Space Telescope Deep Field (HDF). By staring intently at an apparently empty patch of sky smaller than a grain of sand held at arm's length, the HDF team discovered an amazing diversity of hidden galaxies dating more than half way back to the beginning of the universe. Astronomers immediately tried to probe the galaxies with radio, submillimeter, infrared, and x-ray telescopes. They discovered radio waves coming from several of the galaxies, probably from remnants of the earliest generations of stars.
Now, sharper radio images have blurred this picture. In November 1999, a team of astronomers trained seven radio telescopes across Europe on the HDF for 32 hours. When the data were synthesized into the highest ever resolution image of such faint objects--using a technique called Very Long Baseline Interferometry (VLBI)--the team found three pinpoints of light that coincided with known galaxies. The spots are probably generated by material falling into black holes; the light is too concentrated to be caused entirely by supernova remnants spread over an entire galaxy, says team member Tom Muxlow of the Jodrell Bank Observatory in the U.K. But at least some of the emission could still be from those remnants: "It is possible that both things are there," says lead author Mike Garrett, an astronomer at the Joint Institute for VLBI in Europe (JIVE) in Dwingeloo, the Netherlands.
"Nobody is quite sure what to make of it," agrees Space Telescope Science Institute astronomer Mark Dickinson. Garrett, for one, is eager to get back to the telescope and find the answer. "This was just a pilot observation," he says, "We hope to go four times deeper with three times better resolution within the next year."