Giant Radio Jet Coming From Wrong Kind of Galaxy

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. Using the combined
power of the
Hubble Space Telescope, the

Very Large Array (VLA)
and the
8-meter Gemini-South Telescope, astronomers have
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,” said
William Keel, a
University of Alabama astronomer who led the
research team. Keel worked with Michael Ledlow of
Gemini
Observatory and Frazer Owen of the
National Radio Astronomy
Observatory. The scientists reported their findings at the

American Astronomical Society’s meeting in Seattle,
Washington.

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

In addition, Owen said, “The loose-knit nature of the cluster
of galaxies in which this galaxy resides may play a part in
allowing this particular spiral to produce jets.”

Astronomers believe such jets originate at the cores of
galaxies, where supermassive black holes provide the
tremendous gravitational energy to accelerate 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
supermassive 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 its
surroundings.

The story began more than 20 years ago, when Owen began a
survey of 500 galaxy clusters using the
National Science
Foundation’s then-new 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 Ph.D dissertation at the
University of
New Mexico. An optical image from
Kitt Peak National
Observatory gave a hint that this galaxy, clearly seen with
a jet in the VLA images, might be a spiral.

Nearly a billion light-years from Earth, 0313-192
proved an elusive target, however. 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 still 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.

Several factors may have combined, the researchers feel.

“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. He added, “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.”

Owen points out that 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,” Owen said.
Thus, 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 unique example provided by this jet-producing
spiral galaxy “raises questions about some of our basic
assumptions regarding jet production in galaxies,” Owen said.

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..

Media Contacts:

Dave Finley, NRAO
Socorro, NM
(505) 835-7302
dfinley@nrao.edu

Elizabeth M. Smith, University of Alabama
(205) 348-3782
esmith@ur.ua.edu

Ray Villard, STScI
(410) 338-4514
villard@stsci.edu

Peter Michaud, Gemini Observatory
(808) 974-2510
pmichaud@gemini.edu