CONTACT: Megan Galbraith 518-276-6050 firstname.lastname@example.org
say new star structures found in the Milky Way alter galactic model
N.Y. - Heidi Jo Newberg, associate professor of physics at Rensselaer
Polytechnic Institute, and Brian Yanny, an astrophysicist at Fermi
National Accelerator Laboratory, who are leading a team of
researchers with the Sloan Digital Sky Survey (SDSS), announced today
they have identified new star structures in the halo of the Milky Way
that could alter the standard model of the galaxy. The research also
has implications for how the Milky Way was formed.
research, presented at a meeting of the American Astronomical Society
D. C., may be a first step in the development of
complete galactic models for the halo. The star streams were
identified from positions, colors, and brightnesses of five million
stars detected in the Sloan Digital Sky Survey. The SDSS is an
international scientific collaboration which is cataloging the
heavens to an unprecedented depth, area, and accuracy.
and Yanny say the results yielded by the SDSS database provide a
deeper, more global picture of the Milky Ways stellar
unexpectedly large number of blue stars have been found within 20
degrees of the galactic plane, say Newberg and Yanny. These stars
could be part of a disrupted dwarf galaxy, or a disk-like
distribution of stars that is puffier than accepted models of stellar
disks in the galaxy, and flatter than the spherical distribution in
clumpiness of the stellar distribution in the Milky Way halo suggests
that our galactic model needs to be reconsidered, says Newberg.
Although we originally set out to measure properties of a
smooth halo, we now find it difficult to determine which, if any, of
the structures of the halo belong to that population.
in the halo appear to be grouped into distinct streams in the sky,"
says Yanny. "A careful look at the stellar properties
shows that they come from yet unidentified parent populations,
perhaps other dwarf galaxies which have long since been torn apart."
and Yanny are the principal authors, along with 17 SDSS researchers,
of a paper to be published by The Astrophysical Journal.
says the findings are significant because they have an impact on
several active fields of astronomical research, including: galactic
structure, evolution of the Milky Way, the distribution of mass in
the galaxy, and galaxy formation in the early Universe.
and Yanny presented plots of color versus brightness for stars in two
previously discovered, tidally disrupted structures. The distribution
of stars in these plots, which indicate stellar age and metallicity,
are consistent with those of the Sagittarius dwarf galaxy, but the
stars are spread across 110 square degrees of sky, 75 degrees away
from the center of the Sagittarius dwarf.
and Yanny have identified at least five additional overdensities of
stars in the galactic halo. Four of these may be pieces of the same
halo structure, which would cover a region of the sky at least 40
degrees across, at a distance of 11 kpc (36,000 light years) from the
sun which is18 kpc, or 60,000 light years from the center of the
galaxy. For reference, the Sun is 25,000 light years from the center
of the galaxy.
is striking that in this direction in the sky all the stars appear to
be at the same distance, said Connie Rockosi, a researcher at
the University of Washington, who initially found the group of blue
stars. This suggests that our galaxy might be encircled by a
narrow ring of stars, possibly the result of a dwarf satellite galaxy
paper, titled "Halo Streams and Milky Way Components from the
Sloan Digital Sky Survey," can be found at
more information contact: Dr. Heidi J. Newberg (518) 276-2652 or
Brian Yanny (630) 840-4413 or email@example.com.
An image of the disk of a spiral galaxy like the Milky Way is shown as
if one could step outside the Galaxy and view it from a great
distance. The Galactic Center (GC) is marked with a faint open blue
circle and the Sun's location is labeled by an orange dot.
The magenta ring at radius 18 kpc (60,000 light years) from the
Galaxy's center shows the proposed extrapolated location of a 'ring'
or 'metal-weak thick disk' component of Galactic structure. Areas
where the Sloan Digital Sky Survey (SDSS) has observed the structure
are indicated in red.
The sky blue ring at greater distance (115,000 light years from the
GC) shows possible locations for the tidal debris of stars from a
small dwarf galaxy in the Sagittarius constellation, as they are
stripped by the Galaxy's gravitational forces. The remaining nucleus
of Sagittarius is indicated in dark blue. The red regions of the ring
show where the stellar populations of individual tidal stars have been
detected in the SDSS. Stars in these regions have been confirmed to be
of similar age and metalicity to those in the Sagittarius dwarf
Digital Sky Survey
for the creation and distribution of the SDSS Archive has been
provided by the Alfred P. Sloan Foundation, the participating
institutions, the National Aeronautics and Space Administration, the
National Science Foundation, the U.S. Department of Energy, the
Japanese Monbukagakusho, and the Max Planck Society. The
participating institutions are The University of Chicago, Fermilab,
the Institute for Advanced Study, the Japan Participation Group, The
Johns Hopkins University, the Max-Planck-Institute for Astronomy
(MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico
State University, Princeton University, the United States Naval
Observatory, and the University of Washington. For further
information, consult the SDSS Web site at http://www.sdss.org/.
Rensselaer Polytechnic Institute
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