Using the National Science Foundation’s Very Long Baseline Array (VLBA)
radio telescope, astronomers have discovered a newly-exploded star, or
supernova, hidden deep in a dust-enshrouded "supernova factory" in a
galaxy some 140 million light-years from Earth.

"This supernova is likely to be part of a group of super star clusters
that produce one such stellar explosion every two years," said James
Ulvestad, of the National Radio Astronomy Observatory (NRAO) in Socorro,
NM. "We’re extremely excited by the tremendous insights into star
formation and the early Universe that we may gain by observing this
‘supernova factory,’" he added.

Ulvestad worked with Susan Neff of NASA’s Goddard Space Flight Center in
Greenbelt, MD, and Stacy Teng, a graduate student at the University of
Maryland, on the project. The scientists presented their findings to the
American Astronomical Society’s meeting in Nashville, TN.

"These super star clusters likely are forming in much the same way that
globular clusters formed in the early Universe, and thus provide us with
a unique opportunity to learn about how some of the first stars formed
billions of years ago," Neff said.

The cluster is in an object called Arp 299, a pair of colliding
galaxies, where regions of vigorous star formation have been found in
past observations. Since 1990, four other supernova explosions have been
seen optically in Arp 299.

Observations with the NSF’s Very Large Array (VLA) earlier showed a
region near the nucleus of one of the colliding galaxies which had all
the earmarks of prolific star formation. The astronomers focused on this
region, prosaically dubbed "Source A," with the VLBA and the NSF’s
Robert C. Byrd Green Bank Telescope in 2002, and found four objects in
this dusty cloud that are likely young supernova remnants. When they
observed the region again in February 2003, there was a new, fifth,
object located only 7 light-years from one of the previously detected
objects.

More observations on April 30-May 1, 2003, showed that this new object
has typical characteristics of a supernova explosion by a young, massive
star.

"This supernova is exploding in a very dense environment, quite
different from the environments of supernova explosions that can be seen
in visible light," Teng said. "This is the kind of dense environment in
which stars likely formed in the early Universe," she added.

The astronomers believe the super star cluster in Arp 299 saw its most
recent peak of star formation some 6-8 million years ago, and now its
massive stars, 10-20 times (or more) as massive as the Sun, are ending
their lives in supernova explosions. Super star clusters typically
contain up to a million stars, which is why the scientists think Source
A will see frequent supernova explosions.

"We plan to keep watching this region, and hope that we can study
numerous supernovae, and gain important new information about the
processes of star formation, both in the early Universe and at the
present time," Neff said.

"Because of the dust and the distance, only a radio telescope with the
VLBA’s ability to see fine detail can find the supernovae in this
region," Ulvestad said.

The VLBA is a continent-wide system of ten radio-telescope antennas,
ranging from Hawaii in the west to the U.S. Virgin Islands in the east,
providing the greatest resolving power, or ability to see fine detail,
in astronomy. Dedicated in 1993, the VLBA is operated from the NRAO’s
Array Operations Center in Socorro, New Mexico.

The VLBA has made landmark contributions to astronomy, including making
the most accurate distance measurement ever made of an object beyond the
Milky Way Galaxy; the first mapping of the magnetic field of a star
other than the Sun; "movies" of motions in powerful cosmic jets and of
distant supernova explosions; the first measurement of the propagation
speed of gravity; and long-term measurements that have improved the
reference frame used to map the Universe and detect tectonic motions of
Earth’s continents.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.

IMAGE CAPTIONS:

[Image 1:
http://www.nrao.edu/pr/2003/arp299/beforeafter.shtml]
VLBA IMAGES of "Source A" in Arp 299. At left, image made in 2002 shows
only two prominent objects in the field of view. A 2003 image, right,
shows bright new object later confirmed as a supernova.

CREDIT: Ulvestad, Neff & Teng, NRAO/AUI/NSF

[Image 2:
http://www.nrao.edu/pr/2003/arp299/arp299radopt.crop.jpg (188KB)]
Multiwavelength Image of the colliding-galaxy pair Arp 299 using data
from the VLA and Hubble Space Telescope. Here, radio emission is shown
as red, infrared as green, and ultraviolet as blue.

CREDIT: NRAO/AUI/NSF, STScI, NASA

[Image 3:
http://www.nrao.edu/pr/2003/arp299/gsfc1.jpg (304KB)
QuickTime movie: (5.4MB)
http://www.gsfc.nasa.gov/gsfc/spacesci/pictures/2003/0527snfactory/Supernova.mov]
Artist’s Conception of the dust-enshrouded supernova factory in Arp 299.
Bright circles are the shocks from new supernova explosions.

CREDIT: NASA/Walt Feimer