Andrew Yee[_1_]
August 12th 08, 02:11 AM
Media Relations
University of California-Berkeley
Media Contacts:
Robert Sanders, (510) 643-6998 / (510) 642-3734
FOR IMMEDIATE RELEASE: 7 July 2008
Open clusters like Orion have low fertility rate
By Robert Sanders, Media Relations
BERKELEY -- A detailed survey of stars in the Orion Nebula has found that
fewer than 10 percent have enough surrounding dust to make Jupiter-sized
planets, according to a report by astronomers at the University of
California, Berkeley, the California Institute of Technology (Caltech) and
the Harvard-Smithsonian Center for Astrophysics.
Because stars like the sun probably formed in hot open clusters like Orion,
the finding suggests that sun-like stars have a low probability of forming
planets, or at least, planets the size of Jupiter or larger.
"We think that most stars in the galaxy are formed in dense, Orion-like
regions, so this implies that systems like ours may be the exception rather
than the rule," said lead author Joshua Eisner, a Miller postdoctoral fellow
at UC Berkeley. This is consistent with the results of current planet
searches, which are finding that only about 6 percent of stars surveyed have
planets the size of Jupiter or larger.
The study by Eisner, Caltech astronomer John M. Carpenter and their
colleagues will appear in the August 10 print edition of The Astrophysical
Journal.
The Orion Nebula is a brilliant cluster only a million years old and glowing
with the light of newly formed stars like a jewel in the sword of the hunter
Orion. The cluster is also very dense, Eisner said, with 1,000 stars packed
into a region several light years on a side. For comparison, in the
neighborhood of the sun, there's only one star within that volume of space.
Four billion years ago, however, the sun may have been in a dense, open
cluster like Orion. Because open clusters like Orion eventually become
gravitationally unbound, they disperse over the course of billions of years,
and as a result, the sun's birth neighbors are long gone.
Studying star clusters like the Orion Nebula Cluster "helps our
understanding of the typical mode of star and planet formation," Eisner
said.
The new findings come from some of the first observations of a radio
telescope array jointly operated by UC Berkeley, Caltech, the University of
Maryland and the University of Illinois and located at Cedar Flat in eastern
California's Inyo Mountains near the city of Bishop. The Combined Array for
Research in Millimeter Astronomy (CARMA) was created in 2004 by relocating
the nine 6-meter telescopes of the Berkeley-Illinois-Maryland Association
(BIMA) array from Hat Creek, Calif., and the six 10-meter telescopes of
Caltech's Owens Valley Radio Observatory (OVRO) millimeter-wave array to
Cedar Flat. The 15-dish array conducted its first observations in 2006.
The CARMA array observes at millimeter wavelengths, which is ideal for
piercing the clouds of dust and gas surrounding young stars to see their
dense, dusty disks. Eisner and his colleagues also used the Submillimeter
Array (SMA) atop Mauna Kea in Hawaii for this study. The combination of
CARMA and the SMA enabled the sensitivity and high image quality needed to
observe the dusty disks in Orion.
The astronomers' observations of Orion's central region of more than 250
known stars showed that only about 10 percent emit 1.3-millimeter wavelength
radiation typically emitted by a warm disk of dust. Even fewer -- less than
8 percent of stars surveyed -- were judged to have dust disks with masses
greater than one-hundredth the mass of the sun, a mass thought to be the
lower limit for formation of Jupiter-sized planets. The average mass of a
protoplanetary disk in the region was only one-thousandth of a solar mass,
the researchers calculated.
Eisner noted that previous surveys he and Carpenter have conducted of other
young, open clusters that are older or younger than Orion show an
evolutionary trend in the average masses of disks in the different regions.
Older clusters tend to show less dust, perhaps because much of it has
already gathered into planets.
Previous surveys of another lower-density, star-forming region -- the Taurus
cluster -- showed that more than 20 percent of its stars have enough mass to
form planets. The difference is probably related to the tightly packed, hot
stars of the Orion cluster, said Carpenter, a senior research astronomer and
deputy director of OVRO.
"Somehow, the Orion cluster environment is not conducive to forming high
mass disks or having them survive long, presumably due to the ionization
field from the hot, massive OB stars , which you might expect would
photoevaporate dust and lead to small disk masses," he said.
Many of the stars in Orion imaged by CARMA had been photographed earlier by
the Hubble Space Telescope and were dubbed proplyds, short for
protoplanetary disks. While Hubble saw the dust disks silhouetted against
the star, CARMA directly detected emissions from the dust itself.
"CARMA is an ideal instrument for this type of study, with its 15 telescopes
providing the fine resolution needed to resolve protoplanetary disks so that
we can determine their structure and measure their masses more precisely,"
Eisner said.
Carpenter noted that future improvements to the CARMA array could allow
detection of even smaller disks capable of giving rise to sub-Jupiter
planets. To detect even smaller disks able to form large Earth-like planets,
or super-Earths, will require a more extensive array, such as the Atacama
Large Millimeter Array (ALMA) now being built in Chile.
Coauthors on the journal paper are Richard L. Plambeck of UC Berkeley,
graduate student Stuartt A. Corder of Caltech and Chunhua Qi and David
Wilner of the Harvard Smithsonian Center for Astrophysics, which operates
the Submillimeter Array.
IMAGE CAPTION:
[http://www.berkeley.edu/news/media/releases/2008/07/images/orion.png (9KB)]
While a Hubble Space Telescope image of visible light emitted by a
protoplanetary disk in the Orion Nebula called proplyd 170-337 shows hot,
ionized gas (red) surrounding and streaming off of a disk (yellow), 1.3 mm
radio observations by CARMA and SMA reveal the dust disk hiding within the
hot gas (contours). This protoplanetary disk has a mass more than one
hundredth that of the sun, the minimum needed to form a Jupiter-sized
planet. (Bally et al 2000/Hubble Space Telescope & Eisner et al 2008/CARMA,
SMA)
University of California-Berkeley
Media Contacts:
Robert Sanders, (510) 643-6998 / (510) 642-3734
FOR IMMEDIATE RELEASE: 7 July 2008
Open clusters like Orion have low fertility rate
By Robert Sanders, Media Relations
BERKELEY -- A detailed survey of stars in the Orion Nebula has found that
fewer than 10 percent have enough surrounding dust to make Jupiter-sized
planets, according to a report by astronomers at the University of
California, Berkeley, the California Institute of Technology (Caltech) and
the Harvard-Smithsonian Center for Astrophysics.
Because stars like the sun probably formed in hot open clusters like Orion,
the finding suggests that sun-like stars have a low probability of forming
planets, or at least, planets the size of Jupiter or larger.
"We think that most stars in the galaxy are formed in dense, Orion-like
regions, so this implies that systems like ours may be the exception rather
than the rule," said lead author Joshua Eisner, a Miller postdoctoral fellow
at UC Berkeley. This is consistent with the results of current planet
searches, which are finding that only about 6 percent of stars surveyed have
planets the size of Jupiter or larger.
The study by Eisner, Caltech astronomer John M. Carpenter and their
colleagues will appear in the August 10 print edition of The Astrophysical
Journal.
The Orion Nebula is a brilliant cluster only a million years old and glowing
with the light of newly formed stars like a jewel in the sword of the hunter
Orion. The cluster is also very dense, Eisner said, with 1,000 stars packed
into a region several light years on a side. For comparison, in the
neighborhood of the sun, there's only one star within that volume of space.
Four billion years ago, however, the sun may have been in a dense, open
cluster like Orion. Because open clusters like Orion eventually become
gravitationally unbound, they disperse over the course of billions of years,
and as a result, the sun's birth neighbors are long gone.
Studying star clusters like the Orion Nebula Cluster "helps our
understanding of the typical mode of star and planet formation," Eisner
said.
The new findings come from some of the first observations of a radio
telescope array jointly operated by UC Berkeley, Caltech, the University of
Maryland and the University of Illinois and located at Cedar Flat in eastern
California's Inyo Mountains near the city of Bishop. The Combined Array for
Research in Millimeter Astronomy (CARMA) was created in 2004 by relocating
the nine 6-meter telescopes of the Berkeley-Illinois-Maryland Association
(BIMA) array from Hat Creek, Calif., and the six 10-meter telescopes of
Caltech's Owens Valley Radio Observatory (OVRO) millimeter-wave array to
Cedar Flat. The 15-dish array conducted its first observations in 2006.
The CARMA array observes at millimeter wavelengths, which is ideal for
piercing the clouds of dust and gas surrounding young stars to see their
dense, dusty disks. Eisner and his colleagues also used the Submillimeter
Array (SMA) atop Mauna Kea in Hawaii for this study. The combination of
CARMA and the SMA enabled the sensitivity and high image quality needed to
observe the dusty disks in Orion.
The astronomers' observations of Orion's central region of more than 250
known stars showed that only about 10 percent emit 1.3-millimeter wavelength
radiation typically emitted by a warm disk of dust. Even fewer -- less than
8 percent of stars surveyed -- were judged to have dust disks with masses
greater than one-hundredth the mass of the sun, a mass thought to be the
lower limit for formation of Jupiter-sized planets. The average mass of a
protoplanetary disk in the region was only one-thousandth of a solar mass,
the researchers calculated.
Eisner noted that previous surveys he and Carpenter have conducted of other
young, open clusters that are older or younger than Orion show an
evolutionary trend in the average masses of disks in the different regions.
Older clusters tend to show less dust, perhaps because much of it has
already gathered into planets.
Previous surveys of another lower-density, star-forming region -- the Taurus
cluster -- showed that more than 20 percent of its stars have enough mass to
form planets. The difference is probably related to the tightly packed, hot
stars of the Orion cluster, said Carpenter, a senior research astronomer and
deputy director of OVRO.
"Somehow, the Orion cluster environment is not conducive to forming high
mass disks or having them survive long, presumably due to the ionization
field from the hot, massive OB stars , which you might expect would
photoevaporate dust and lead to small disk masses," he said.
Many of the stars in Orion imaged by CARMA had been photographed earlier by
the Hubble Space Telescope and were dubbed proplyds, short for
protoplanetary disks. While Hubble saw the dust disks silhouetted against
the star, CARMA directly detected emissions from the dust itself.
"CARMA is an ideal instrument for this type of study, with its 15 telescopes
providing the fine resolution needed to resolve protoplanetary disks so that
we can determine their structure and measure their masses more precisely,"
Eisner said.
Carpenter noted that future improvements to the CARMA array could allow
detection of even smaller disks capable of giving rise to sub-Jupiter
planets. To detect even smaller disks able to form large Earth-like planets,
or super-Earths, will require a more extensive array, such as the Atacama
Large Millimeter Array (ALMA) now being built in Chile.
Coauthors on the journal paper are Richard L. Plambeck of UC Berkeley,
graduate student Stuartt A. Corder of Caltech and Chunhua Qi and David
Wilner of the Harvard Smithsonian Center for Astrophysics, which operates
the Submillimeter Array.
IMAGE CAPTION:
[http://www.berkeley.edu/news/media/releases/2008/07/images/orion.png (9KB)]
While a Hubble Space Telescope image of visible light emitted by a
protoplanetary disk in the Orion Nebula called proplyd 170-337 shows hot,
ionized gas (red) surrounding and streaming off of a disk (yellow), 1.3 mm
radio observations by CARMA and SMA reveal the dust disk hiding within the
hot gas (contours). This protoplanetary disk has a mass more than one
hundredth that of the sun, the minimum needed to form a Jupiter-sized
planet. (Bally et al 2000/Hubble Space Telescope & Eisner et al 2008/CARMA,
SMA)