Andrew Yee
October 24th 04, 05:49 PM
Sloan Digital Sky Survey
CONTACTS:
Beth Willman
New York University
(212) 992-8792,
Julianne Dalcanton
University of Washington
(206) 685-2155,
Michael Strauss
Scientific Spokesperson, The Sloan Digital Sky Survey (SDSS)
(609) 258-3808,
Gary S. Ruderman
Public Information Officer, The Sloan Digital Sky Survey
(312) 320-4794,
James Devitt
Office of Public Affairs, New York University
(212) 998-6808,
October 20, 2004
SLOAN DIGITAL SKY SURVEY FINDS MYSTERIOUS NEW MILKY WAY COMPANION
A building block of the Milky Way
Most of the stars in our Milky Way galaxy lie in a very flat, pinwheel-shaped
disk. Although this disk is prominent in images of galaxies similar to the Milky
Way, there is also a very diffuse spherical "halo" of stars surrounding and
enclosing the disks of such galaxies.
Recent discoveries have shown that this outer halo of the Milky Way is probably
composed of small companion galaxies ripped to shreds as they orbited the Milky Way.
A discovery announced today by the Sloan Digital Sky Survey (SDSS) reveals a
clump of stars unlike any seen before. The findings may shed light on how the
Milky Way's stellar halo formed.
This clump of newly discovered stars, called SDSSJ1049+5103 or Willman 1, is so
faint that it could only be found as a slight increase in the number of faint
stars in a small region of the sky.
"We discovered this object in a search for extremely dim companion galaxies to
the Milky Way," explains Beth Willman of New York University's Center for
Cosmology and Particle Physics. "However, it is 200 times less luminous than any
galaxy previously seen."
Another possibility, adds Michael Blanton, an SDSS colleague of Willman's at New
York University, is that Willman 1 is an unusual type of globular cluster, a
spherical agglomeration of thousands to millions of old stars."
"Its properties are rather unusual for a globular cluster. It is dimmer than all
but three known globular clusters. Moreover, these dim globular clusters are all
much more compact than Willman 1," explains Blanton. "If it's a globular
cluster, it is probably being torn to shreds by the gravitational tides of the
Milky Way."
The real distinction between the globular cluster and dwarf galaxy
interpretations is that galaxies are usually accompanied by substantial
quantities of dark matter, says Julianne Dalcanton, an SDSS researcher at the
University of Washington. "Clearly the next step is to carry out additional
measurements to determine whether there is any dark matter associated with
Willman 1."
SDSS consortium member Daniel Zucker of the Max Planck Institute for Astronomy
in Heidelberg, Germany, says the Sloan Digital Sky Survey has proven to be "a
veritable gold mine for studies of the outer parts of our galaxy and its
neighbors, as shown by Dr. Willman's discovery, and by our group's earlier
discovery of a giant stellar structure and a new satellite galaxy around the
Andromeda Galaxy."
If Willman 1 does turn out to be a dwarf galaxy, this discovery could shed light
on a long-standing mystery.
The prevailing 'Cold Dark Matter' model predicts that our own Milky Way galaxy
is surrounded by hundreds of dark matter clumps, each a few hundred light years
in size and possibly populated by a dwarf galaxy.
However, only 11 dwarf galaxies have been discovered orbiting the Milky Way.
Perhaps some of these clumps have very few embedded stars, making the galaxies
particularly difficult to find.
"If this new object is in fact a dwarf galaxy, it may be the tip of the iceberg
of a yet unseen population of ultra-faint dwarf galaxies," suggests Willman.
The Milky Way has been an area of intense research by SDSS consortium members.
"The colors of the stars in Willman 1 are similar to those in the Sagittarius
tidal stream, a former dwarf companion galaxy to the Milky Way now in the
process of merging into the main body of our Galaxy," explains Brian Yanny, an
SDSS astrophysicist at The Department of Energy's Fermi National Accelerator
Laboratory, a leader in research on the Milky Way's accretion of material.
Continues Yanny: "If Willman 1 is a globular cluster, then it may have
piggybacked a ride into our Galaxy's neighborhood on one of these dwarf
companions, like a tiny mite riding in on a flea as it, in turn, latches onto a
massive dog."
"Whether it is a globular cluster or a dwarf galaxy, this very faint object
appears to represent one of the building blocks of the Milky Way," Willman said.
Authors of the findings are:
Beth Willman
New York University, Center for Cosmology and Particle Physics
4 Washington Place, New York, NY 10003
Michael Blanton
New York University
Andrew A. West
Department of Astronomy, University of Washington
Box 351580, Seattle, WA, 98185
Julianne J. Dalcanton
University of Washington
David W. Hogg
New York University
Donald P. Schneider
Department of Astronomy and Astrophysics, Pennsylvania State University
University Park, PA 16802
Brian Yanny
Fermi National Accelerator Laboratory
PO Box 500, Batavia, IL 60510
Jon Brinkmann
Apache Point Observatory
PO Box 59, Sunspot, NM 88349
IMAGE CAPTION:
[http://www.sdss.org/news/releases/scaledhalf_smooth_SDSS_color_new.jpg (6KB)]
This clump of newly discovered stars in Ursa Major is in a region the size of
the full moon centered on Willman 1. To be able to see this ultra-faint object
in the SDSS data, the distribution of stars was filtered to enhance its signal
relative to the much more numerous closer stars of the Milky Way Galaxy.
(SOURCE: Beth Willman, New York University, The Sloan Digital Sky Survey).
CONTACTS:
Beth Willman
New York University
(212) 992-8792,
Julianne Dalcanton
University of Washington
(206) 685-2155,
Michael Strauss
Scientific Spokesperson, The Sloan Digital Sky Survey (SDSS)
(609) 258-3808,
Gary S. Ruderman
Public Information Officer, The Sloan Digital Sky Survey
(312) 320-4794,
James Devitt
Office of Public Affairs, New York University
(212) 998-6808,
October 20, 2004
SLOAN DIGITAL SKY SURVEY FINDS MYSTERIOUS NEW MILKY WAY COMPANION
A building block of the Milky Way
Most of the stars in our Milky Way galaxy lie in a very flat, pinwheel-shaped
disk. Although this disk is prominent in images of galaxies similar to the Milky
Way, there is also a very diffuse spherical "halo" of stars surrounding and
enclosing the disks of such galaxies.
Recent discoveries have shown that this outer halo of the Milky Way is probably
composed of small companion galaxies ripped to shreds as they orbited the Milky Way.
A discovery announced today by the Sloan Digital Sky Survey (SDSS) reveals a
clump of stars unlike any seen before. The findings may shed light on how the
Milky Way's stellar halo formed.
This clump of newly discovered stars, called SDSSJ1049+5103 or Willman 1, is so
faint that it could only be found as a slight increase in the number of faint
stars in a small region of the sky.
"We discovered this object in a search for extremely dim companion galaxies to
the Milky Way," explains Beth Willman of New York University's Center for
Cosmology and Particle Physics. "However, it is 200 times less luminous than any
galaxy previously seen."
Another possibility, adds Michael Blanton, an SDSS colleague of Willman's at New
York University, is that Willman 1 is an unusual type of globular cluster, a
spherical agglomeration of thousands to millions of old stars."
"Its properties are rather unusual for a globular cluster. It is dimmer than all
but three known globular clusters. Moreover, these dim globular clusters are all
much more compact than Willman 1," explains Blanton. "If it's a globular
cluster, it is probably being torn to shreds by the gravitational tides of the
Milky Way."
The real distinction between the globular cluster and dwarf galaxy
interpretations is that galaxies are usually accompanied by substantial
quantities of dark matter, says Julianne Dalcanton, an SDSS researcher at the
University of Washington. "Clearly the next step is to carry out additional
measurements to determine whether there is any dark matter associated with
Willman 1."
SDSS consortium member Daniel Zucker of the Max Planck Institute for Astronomy
in Heidelberg, Germany, says the Sloan Digital Sky Survey has proven to be "a
veritable gold mine for studies of the outer parts of our galaxy and its
neighbors, as shown by Dr. Willman's discovery, and by our group's earlier
discovery of a giant stellar structure and a new satellite galaxy around the
Andromeda Galaxy."
If Willman 1 does turn out to be a dwarf galaxy, this discovery could shed light
on a long-standing mystery.
The prevailing 'Cold Dark Matter' model predicts that our own Milky Way galaxy
is surrounded by hundreds of dark matter clumps, each a few hundred light years
in size and possibly populated by a dwarf galaxy.
However, only 11 dwarf galaxies have been discovered orbiting the Milky Way.
Perhaps some of these clumps have very few embedded stars, making the galaxies
particularly difficult to find.
"If this new object is in fact a dwarf galaxy, it may be the tip of the iceberg
of a yet unseen population of ultra-faint dwarf galaxies," suggests Willman.
The Milky Way has been an area of intense research by SDSS consortium members.
"The colors of the stars in Willman 1 are similar to those in the Sagittarius
tidal stream, a former dwarf companion galaxy to the Milky Way now in the
process of merging into the main body of our Galaxy," explains Brian Yanny, an
SDSS astrophysicist at The Department of Energy's Fermi National Accelerator
Laboratory, a leader in research on the Milky Way's accretion of material.
Continues Yanny: "If Willman 1 is a globular cluster, then it may have
piggybacked a ride into our Galaxy's neighborhood on one of these dwarf
companions, like a tiny mite riding in on a flea as it, in turn, latches onto a
massive dog."
"Whether it is a globular cluster or a dwarf galaxy, this very faint object
appears to represent one of the building blocks of the Milky Way," Willman said.
Authors of the findings are:
Beth Willman
New York University, Center for Cosmology and Particle Physics
4 Washington Place, New York, NY 10003
Michael Blanton
New York University
Andrew A. West
Department of Astronomy, University of Washington
Box 351580, Seattle, WA, 98185
Julianne J. Dalcanton
University of Washington
David W. Hogg
New York University
Donald P. Schneider
Department of Astronomy and Astrophysics, Pennsylvania State University
University Park, PA 16802
Brian Yanny
Fermi National Accelerator Laboratory
PO Box 500, Batavia, IL 60510
Jon Brinkmann
Apache Point Observatory
PO Box 59, Sunspot, NM 88349
IMAGE CAPTION:
[http://www.sdss.org/news/releases/scaledhalf_smooth_SDSS_color_new.jpg (6KB)]
This clump of newly discovered stars in Ursa Major is in a region the size of
the full moon centered on Willman 1. To be able to see this ultra-faint object
in the SDSS data, the distribution of stars was filtered to enhance its signal
relative to the much more numerous closer stars of the Milky Way Galaxy.
(SOURCE: Beth Willman, New York University, The Sloan Digital Sky Survey).