SEATTLE - Nature loves to play tricks on astronomers. In uncovering the latest deception, researchers are left to wonder how and why a huge jet of subatomic particles zooming at nearly light speed is emanating from a spiral galaxy.
The jet of material, stretching across many thousands of light-years, has been known to radio astronomers for many years. Only now, however, have they learned that the galaxy, called 0313-192, has a spiral shape like our own Milky Way.
The galaxy is nearly a billion light-years away, and it is seen edge-on, so that it looks like the elliptical-shaped galaxies commonly associated with the high-energy jets. Three powerful telescopes were required to reveal the galaxy for what it is.
Jets are seen coming from some other spiral galaxies, but they are typically in the middle of a merger process that fuels hyperactivity. Otherwise, spirals are typically quieter.
"We've always thought spirals were the wrong kind of galaxy to generate these huge jets," said William Keel of the University of Alabama. "But now we're going to have to rethink some of our ideas."
The finding was presented here today at a meeting of the American Astronomical Society.
The jets are thought to be produced by supermassive black holes. These gravity wells sit at the cores of many galaxies, both elliptical and spiral. As matter is drawn near a black hole, it is accelerated to nearly the speed of light. Some of the matter is consumed, but some is spat out, ejected into space in two opposing jets along the galaxy's axis of rotation.
Frazer Owen, of the National Radio Astronomy Observatory and another member of the discovery team, said one factor that might go into jet production is out of a galaxy's hands. Pressure generated by nearby galaxies may be needed to keep a jet focused in the fashion that is commonly observed.
This pressure, Owen explained, might be generated by intergalactic medium -- gas and dust in space -- that infuses galaxy clusters. Many jets have been observed coming from galaxies that are members of dense clusters.
But a spiral galaxy won't survive in a dense cluster, Owen said. As it turns out, 0313-192 is part of a rather loose collection of galaxies, a cluster but not a dense one. It might be "just the right environment to allow the spiral to survive but still to provide the pressure needed to keep the jets together," he said.
Other factors may be at work.
"This galaxy's disk is twisted, and that may indicate that it has been disturbed by a close passage of another galaxy or may have swallowed up a companion dwarf galaxy," Keel said. "This galaxy shows signs of having a very massive black hole at its core, and the jets are taking the shortest path out of the galaxy's own gas."
More study is needed to understand the true nature of the jets in this galaxy and elsewhere, and how they are produced, the researchers said.
Michael Ledlow of the Gemini Observatory also participated in the study. The discovery was made using the Very Large Array and the Gemini-South Telescope, with the final piece of the puzzle provided by the Hubble Space Telescope.
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