Andrew Yee[_1_]
September 8th 08, 04:44 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
617-495-7463
For Release: Wednesday, September 03, 2008 01:00:00 PM EDT
Release No.: 2008-16
Closest Look Ever at the Edge of a Black Hole
Cambridge, MA -- Astronomers have taken the closest look ever at the giant
black hole in the center of the Milky Way. By combining telescopes in
Hawaii, Arizona, and California, they detected structure at a tiny angular
scale of 37 micro-arcseconds -- the equivalent of a baseball seen on the
surface of the moon, 240,000 miles distant.
"This technique gives us an unmatched view of the region near the Milky
Way's central black hole," said Sheperd Doeleman of MIT, first author of the
study that will be published in the Sept. 4 issue of the journal Nature.
"No one has seen such a fine-grained view of the galactic center before,"
agreed co-author Jonathan Weintroub of the Harvard-Smithsonian Center for
Astrophysics (CfA). "We've observed nearly to the scale of the black hole
event horizon -- the region inside of which nothing, including light, can
ever escape."
Using a technique called Very Long Baseline Interferometry (VLBI), a team of
astronomers led by Doeleman employed an array of telescopes to study radio
waves coming from the object known as Sagittarius A* (A-star). In VLBI,
signals from multiple telescopes are combined to create the equivalent of a
single giant telescope, as large as the separation between the facilities.
As a result, VLBI yields exquisitely sharp resolution.
The Sgr A* radio emission, at a wavelength of 1.3 mm, escapes the galactic
center more easily than emissions at longer wavelengths, which tend to
suffer from interstellar scattering. Such scattering acts like fog around a
streetlamp, both dimming the light and blurring details. VLBI is ordinarily
limited to wavelengths of 3.5 mm and longer; however, using innovative
instrumentation and analysis techniques, the team was able to tease out this
remarkable result from 1.3-mm VLBI data.
The team clearly discerned structure with a 37 micro-arcsecond angular
scale, which corresponds to a size of about 30 million miles (or about
one-third the earth-sun distance) at the galactic center. With three
telescopes, the astronomers could only vaguely determine the shape of the
emitting region. Future investigations will help answer the question of
what, precisely, they are seeing: a glowing corona around the black hole, an
orbiting "hot spot," or a jet of material. Nevertheless, their result
represents the first time that observations have gotten down to the scale of
the black hole itself, which has a "Schwarzschild radius" of 10 million
miles.
"This pioneering paper demonstrates that such observations are feasible,"
commented theorist Avi Loeb of Harvard University, who is not a member of
the discovery team. "It also opens up a new window for probing the structure
of space and time near a black hole and testing Einstein's theory of
gravity."
In 2006, Loeb and his colleague, Avery Broderick, examined how
ultra-high-resolution imaging of the galactic center could be used to look
for the shadow or silhouette of the supermassive black hole lurking there,
as well as any "hot spots" within material flowing into the black hole.
Astronomers now are poised to test those theoretical predictions.
"This result, which is remarkable in and of itself, also confirms that the
1.3-mm VLBI technique has enormous potential, both for probing the galactic
center and for studying other phenomena at similar small scales," said
Weintroub.
The team plans to expand their work by developing novel instrumentation to
make more sensitive 1.3-mm observations possible. They also hope to develop
additional observing stations, which would provide additional baselines
(pairings of two telescope facilities at different locations) to enhance the
detail in the picture. Future plans also include observations at shorter,
0.85-mm wavelengths; however, such work will be even more challenging for
many reasons, including stretching the capabilities of the instrumentation,
and the requirement for a coincidence of excellent weather conditions at all
sites.
"The technical capabilities that have been developed for the Smithsonian's
Submillimeter Array on Mauna Kea are a crucial contribution to this
program," said Jim Moran, one of the CfA participants in this work.
Other CfA or former CfA researchers who participated on the project include
Ken Young and Dan Marrone.
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.
[NOTE: Illustrations supporting this release are available at
http://cfa-www.harvard.edu/press/2008/pr200816_images.html ]
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
617-495-7463
For Release: Wednesday, September 03, 2008 01:00:00 PM EDT
Release No.: 2008-16
Closest Look Ever at the Edge of a Black Hole
Cambridge, MA -- Astronomers have taken the closest look ever at the giant
black hole in the center of the Milky Way. By combining telescopes in
Hawaii, Arizona, and California, they detected structure at a tiny angular
scale of 37 micro-arcseconds -- the equivalent of a baseball seen on the
surface of the moon, 240,000 miles distant.
"This technique gives us an unmatched view of the region near the Milky
Way's central black hole," said Sheperd Doeleman of MIT, first author of the
study that will be published in the Sept. 4 issue of the journal Nature.
"No one has seen such a fine-grained view of the galactic center before,"
agreed co-author Jonathan Weintroub of the Harvard-Smithsonian Center for
Astrophysics (CfA). "We've observed nearly to the scale of the black hole
event horizon -- the region inside of which nothing, including light, can
ever escape."
Using a technique called Very Long Baseline Interferometry (VLBI), a team of
astronomers led by Doeleman employed an array of telescopes to study radio
waves coming from the object known as Sagittarius A* (A-star). In VLBI,
signals from multiple telescopes are combined to create the equivalent of a
single giant telescope, as large as the separation between the facilities.
As a result, VLBI yields exquisitely sharp resolution.
The Sgr A* radio emission, at a wavelength of 1.3 mm, escapes the galactic
center more easily than emissions at longer wavelengths, which tend to
suffer from interstellar scattering. Such scattering acts like fog around a
streetlamp, both dimming the light and blurring details. VLBI is ordinarily
limited to wavelengths of 3.5 mm and longer; however, using innovative
instrumentation and analysis techniques, the team was able to tease out this
remarkable result from 1.3-mm VLBI data.
The team clearly discerned structure with a 37 micro-arcsecond angular
scale, which corresponds to a size of about 30 million miles (or about
one-third the earth-sun distance) at the galactic center. With three
telescopes, the astronomers could only vaguely determine the shape of the
emitting region. Future investigations will help answer the question of
what, precisely, they are seeing: a glowing corona around the black hole, an
orbiting "hot spot," or a jet of material. Nevertheless, their result
represents the first time that observations have gotten down to the scale of
the black hole itself, which has a "Schwarzschild radius" of 10 million
miles.
"This pioneering paper demonstrates that such observations are feasible,"
commented theorist Avi Loeb of Harvard University, who is not a member of
the discovery team. "It also opens up a new window for probing the structure
of space and time near a black hole and testing Einstein's theory of
gravity."
In 2006, Loeb and his colleague, Avery Broderick, examined how
ultra-high-resolution imaging of the galactic center could be used to look
for the shadow or silhouette of the supermassive black hole lurking there,
as well as any "hot spots" within material flowing into the black hole.
Astronomers now are poised to test those theoretical predictions.
"This result, which is remarkable in and of itself, also confirms that the
1.3-mm VLBI technique has enormous potential, both for probing the galactic
center and for studying other phenomena at similar small scales," said
Weintroub.
The team plans to expand their work by developing novel instrumentation to
make more sensitive 1.3-mm observations possible. They also hope to develop
additional observing stations, which would provide additional baselines
(pairings of two telescope facilities at different locations) to enhance the
detail in the picture. Future plans also include observations at shorter,
0.85-mm wavelengths; however, such work will be even more challenging for
many reasons, including stretching the capabilities of the instrumentation,
and the requirement for a coincidence of excellent weather conditions at all
sites.
"The technical capabilities that have been developed for the Smithsonian's
Submillimeter Array on Mauna Kea are a crucial contribution to this
program," said Jim Moran, one of the CfA participants in this work.
Other CfA or former CfA researchers who participated on the project include
Ken Young and Dan Marrone.
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.
[NOTE: Illustrations supporting this release are available at
http://cfa-www.harvard.edu/press/2008/pr200816_images.html ]