Andrew Yee
December 27th 05, 07:45 PM
Public Affairs Office
Harvard-Smithsonian Center for Astrophysics
For more information, contact:
David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
Dave Finley
National Radio Astronomy Observatory
505-835-7302
For Immediate Release: Tuesday, December 27, 2005
Release No.: 05-41
Galaxy's Neighboring Spiral Arm Is Closer Than Thought
Cambridge, MA -- The Perseus spiral arm, the nearest spiral arm in the
Milky Way outside the Sun's orbit, lies only half as far from Earth as
some previous studies had suggested. An international team of astronomers
measured a highly accurate distance to the Perseus arm for the first time
using a globe-spanning system of radio dishes known as the Very Long
Baseline Array (VLBA), which offers the sharpest vision of any telescope
in existence. Additional VLBA measurements will help astronomers to
determine the true structure of the Milky Way.
"We know less about the structure of our own galaxy than we do about many
nearby galaxies like Andromeda," said Smithsonian astronomer and team
leader Mark Reid (Harvard-Smithsonian Center for Astrophysics). "We
literally can't see the forest for the trees because we are embedded
inside our own galaxy, and interstellar dust blocks our view."
The team's results were published in the December 8, 2005 online issue of
Science Express and will appear in print in the January 6, 2006 issue of
Science. Reid also will speak about the findings on January 9 at the 207th
meeting of the American Astronomical Society in Washington, DC.
Previous estimates of the distance to the Perseus arm varied by a factor
of two. Studies based on the motions of stars yielded a distance of more
than 14,000 light-years, while observations comparing the apparent
brightness of massive, young stars with estimates of their intrinsic
brightness yielded a distance of only about 7,200 light-years. The new
VLBA measurements confirm with an accuracy of 2 percent that the Perseus
spiral arm is located about 6,400 light-years from the Earth.
"Our neighbors are closer than we thought," stated first author Ye Xu
(Shanghai Astronomical Observatory).
Obtaining accurate distances in astronomy is a difficult challenge. The
most reliable method for measuring astronomical distances is called
trigonometric parallax, a technique similar to the triangulation used by
land surveyors. A trigonometric parallax is determined by observing the
change in position of a star relative to a very distant, essentially fixed
object like a quasar, as the Earth moves in its orbit around the Sun. Just
as a finger held at arm's length appears to shift against the far wall
when viewed with one eye or the other, a nearby object will appear to
shift position relative to a more distant one. Mathematical calculations
then yield the distance to the closer object. The parallax method is
powerful but requires exceptional accuracy.
"I have spent more than a decade developing the calibration techniques we
needed to obtain this result," said Reid.
The team achieved an accuracy of 10 micro-arcseconds, which is a factor of
100 better than previous methods. That resolution is equivalent to looking
from the Earth to a person standing on the Moon's surface and telling
whether that person is holding a flashlight in their right or left hand.
The VLBA is the only telescope able to provide such high resolution.
Reid and his colleagues used the VLBA to examine the region near a newly
formed star in the Perseus arm called W3OH. They gathered radiation from
bright, compact radio sources known as methanol masers. (Masers amplify,
or strengthen, radio-wave emission the same way that lasers amplify light
emission. Masers can form naturally in outer space.)
With a distance in hand, the team was able to determine the motion of W3OH
in three-dimensional space. They found that W3OH is orbiting the galactic
center more slowly than the galaxy spins, and is "falling" toward the
center of the Milky Way. Such peculiar motions can be studied to determine
the distribution of mass in the Milky Way.
The team has been awarded additional VLBA observing time to measure other
regions of the galaxy. Over time, such studies will help map the spiral
structure of the Milky Way and determine the distribution of unseen dark
matter believed to surround it.
The VLBA is part of the National Radio Astronomy Observatory (NRAO), a
research facility of the National Science Foundation (NSF). Dedicated in
1993, the VLBA consists of 10, 25-meter-diameter dish antennas spread from
Hawaii to St. Croix in the Caribbean. The antennas all work together as a
single telescopic system roughly the size of the Earth. The NRAO is
operated for the NSF under a cooperative agreement by Associated
Universities, Inc.
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.
Harvard-Smithsonian Center for Astrophysics
For more information, contact:
David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
Dave Finley
National Radio Astronomy Observatory
505-835-7302
For Immediate Release: Tuesday, December 27, 2005
Release No.: 05-41
Galaxy's Neighboring Spiral Arm Is Closer Than Thought
Cambridge, MA -- The Perseus spiral arm, the nearest spiral arm in the
Milky Way outside the Sun's orbit, lies only half as far from Earth as
some previous studies had suggested. An international team of astronomers
measured a highly accurate distance to the Perseus arm for the first time
using a globe-spanning system of radio dishes known as the Very Long
Baseline Array (VLBA), which offers the sharpest vision of any telescope
in existence. Additional VLBA measurements will help astronomers to
determine the true structure of the Milky Way.
"We know less about the structure of our own galaxy than we do about many
nearby galaxies like Andromeda," said Smithsonian astronomer and team
leader Mark Reid (Harvard-Smithsonian Center for Astrophysics). "We
literally can't see the forest for the trees because we are embedded
inside our own galaxy, and interstellar dust blocks our view."
The team's results were published in the December 8, 2005 online issue of
Science Express and will appear in print in the January 6, 2006 issue of
Science. Reid also will speak about the findings on January 9 at the 207th
meeting of the American Astronomical Society in Washington, DC.
Previous estimates of the distance to the Perseus arm varied by a factor
of two. Studies based on the motions of stars yielded a distance of more
than 14,000 light-years, while observations comparing the apparent
brightness of massive, young stars with estimates of their intrinsic
brightness yielded a distance of only about 7,200 light-years. The new
VLBA measurements confirm with an accuracy of 2 percent that the Perseus
spiral arm is located about 6,400 light-years from the Earth.
"Our neighbors are closer than we thought," stated first author Ye Xu
(Shanghai Astronomical Observatory).
Obtaining accurate distances in astronomy is a difficult challenge. The
most reliable method for measuring astronomical distances is called
trigonometric parallax, a technique similar to the triangulation used by
land surveyors. A trigonometric parallax is determined by observing the
change in position of a star relative to a very distant, essentially fixed
object like a quasar, as the Earth moves in its orbit around the Sun. Just
as a finger held at arm's length appears to shift against the far wall
when viewed with one eye or the other, a nearby object will appear to
shift position relative to a more distant one. Mathematical calculations
then yield the distance to the closer object. The parallax method is
powerful but requires exceptional accuracy.
"I have spent more than a decade developing the calibration techniques we
needed to obtain this result," said Reid.
The team achieved an accuracy of 10 micro-arcseconds, which is a factor of
100 better than previous methods. That resolution is equivalent to looking
from the Earth to a person standing on the Moon's surface and telling
whether that person is holding a flashlight in their right or left hand.
The VLBA is the only telescope able to provide such high resolution.
Reid and his colleagues used the VLBA to examine the region near a newly
formed star in the Perseus arm called W3OH. They gathered radiation from
bright, compact radio sources known as methanol masers. (Masers amplify,
or strengthen, radio-wave emission the same way that lasers amplify light
emission. Masers can form naturally in outer space.)
With a distance in hand, the team was able to determine the motion of W3OH
in three-dimensional space. They found that W3OH is orbiting the galactic
center more slowly than the galaxy spins, and is "falling" toward the
center of the Milky Way. Such peculiar motions can be studied to determine
the distribution of mass in the Milky Way.
The team has been awarded additional VLBA observing time to measure other
regions of the galaxy. Over time, such studies will help map the spiral
structure of the Milky Way and determine the distribution of unseen dark
matter believed to surround it.
The VLBA is part of the National Radio Astronomy Observatory (NRAO), a
research facility of the National Science Foundation (NSF). Dedicated in
1993, the VLBA consists of 10, 25-meter-diameter dish antennas spread from
Hawaii to St. Croix in the Caribbean. The antennas all work together as a
single telescopic system roughly the size of the Earth. The NRAO is
operated for the NSF under a cooperative agreement by Associated
Universities, Inc.
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.