UA Professor Says Giant Radio Jet is Coming from ‘Wrong’ Kind of Galaxy

TUSCALOOSA, Ala. – Giant jets of subatomic particles moving at nearly the speed of light have been found coming from thousands of galaxies across the universe, but always from elliptical galaxies or galaxies in the process of merging — until now. Dr. Bill Keel, professor of astronomy at The University of Alabama, led a research team that discovered a huge jet coming from a spiral galaxy similar to our own Milky Way.

“We’ve always thought spirals were the wrong kind of galaxy to generate these huge jets, but now we’re going to have to re-think some of our ideas on what produces these jets,” Keel said.

Keel worked with Michael Ledlow of the Gemini Observatory in Chile and Frazer Owen of the National Radio Astronomy Observatory in New Mexico. The scientists reported their findings at the American Astronomical Society’s meeting in Seattle, Wash. on Jan. 8, 2003.

“Further study of this galaxy may provide unique insights into just what needs to happen in a galaxy to produce these powerful jets of particles,” Keel said.

The team used the combined power of three telescopes — the Hubble Space Telescope, the National Science Foundation’s Very Large Array (VLA) in New Mexico and the 8-meter Gemini-South Telescope in Chile.

Astronomers believe such jets originate at the cores of galaxies, where super massive black holes provide the tremendous gravitational energy that accelerates particles to nearly the speed of light. Magnetic fields twisted tightly by spinning disks of material being sucked into the black hole are presumed to narrow the speeding particles into thin jets, like a nozzle on a garden hose.

Both elliptical and spiral galaxies are believed to harbor these super massive black holes at their cores.

The discovery that the jet was coming from a spiral galaxy, dubbed 0313-192, required using a combination of radio, optical and infrared observations to examine the galaxy and it surroundings.

The story began more than 20 years ago when Owen began a survey of 500 galaxy clusters using the National Science Foundation’s VLA to make radio images of the clusters. In the 1990s, Ledlow joined the project, making optical-telescope images of the same clusters as part of his research for a doctoral dissertation at the University of New Mexico. An optical image from New Mexico’s Kitt Peak National Observatory gave a hint that this galaxy, clearly seen with a jet in the VLA images, might be a spiral.

However, 0313-192 is nearly a billion light years from Earth, and it proved an elusive target. Subsequent observations with the VLA and the 3.5-meter telescope at Apache Point Observatory supported the idea that the galaxy might be a spiral but were inconclusive. In the spring of 2002, astronauts installed the Advanced Camera for Surveys on the Hubble Space Telescope. This new facility produced a richly detailed image of 0313-192, showing that it is a dust-rich spiral seen almost exactly edge-on.

“The finely-detailed Hubble image resolved any doubt and proved that this galaxy is a spiral,” Ledlow said. Infrared images with the Gemini-South telescope complemented the Hubble images and further confirmed the galaxy’s spiral nature.

Now, the astronomers seek to understand why this one spiral galaxy, unlike all others seen so far, is producing the bright jets seen with the VLA and other radio telescopes. The researchers feel several factors may have combined.

“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.”

0313-192 resides in a cluster of galaxies called Abell 428. The scientists have discovered that Abell 428 is not a dense cluster, but rather a loose collection of small groups of galaxies.

In order to see the large jets so common to elliptical galaxies, Owen said, “you may need pressure from a cluster’s intergalactic medium to keep the particles and magnetic fields from dispersing so rapidly that the jet can’t stay together.”

However, a spiral won’t survive in a dense cluster. The looser collection of galaxy groups that makes up Abell 428 may be just the right environment to allow the spiral to survive but still to provide the pressure needed to keep the jets together.

In any case, the scientists say the unique example provided by this jet-producing spiral galaxy raises questions about some basic assumptions regarding jet production in galaxies.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities Inc. The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy Inc., for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. Gemini is an international partnership managed by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation.

The department of physics and astronomy is part of the College of Arts and Sciences, UA’s largest division and the largest public liberal arts college in the state, with approximately 5,000 undergraduate and 1,000 graduate students. The College has received national recognition for academic excellence, and A&S students have been selected for many of the nation’s top academic honors, including 15 Rhodes Scholarships, 13 Goldwater Scholarships, seven Truman Scholarships and 11 memberships on USA Today’s Academic All-American teams.

For a downloadable photograph of the galaxy with a cutline, go to: http://www.aoc.nrao.edu/epo/pr/2003/spiraljet/