Andrew Yee[_1_]
January 6th 07, 03:41 AM
National Radio Astronomy Observatory
P.O. Box O
Socorro, NM 87801
http://www.nrao.edu
Contact:
Dave Finley, Public Information Officer
(505) 835-7302
December 15, 2006
How Do Multiple-Star Systems Form? VLA Study Reveals "Smoking Gun"
Astronomers have used the National Science Foundation's Very Large Array
(VLA) radio telescope to image a young, multiple-star system with
unprecedented detail, yielding important clues about how such systems are
formed. Most Sun-sized or larger stars in the Universe are not single, like
our Sun, but are members of multiple-star systems. Astronomers have been
divided on how such systems can form, producing competing theoretical models
for this process.
The new VLA study produced a "smoking gun" supporting one of the competing
models, said Jeremy Lim, of the Institute of Astronomy & Astrophysics,
Academia Sinica, in Taipei, Taiwan, whose study, done with Shigehisa
Takakuwa of the National Astronomical Observatory of Japan, is published in
the December 10 issue of the Astrophysical Journal.
Ironically, their discovery of a third, previously-unknown, young star in
the system may support a second theoretical model. "There may be more than
one way to make a multiple-star system," Lim explained.
The astronomers observed an object called L1551 IRS5, young, still-forming
protostars enshrouded in a cloud of gas and dust, some 450 light-years from
Earth in the direction of the constellation Taurus. Invisible to optical
telescopes because of the gas and dust, this object was discovered in 1976
by astronomers using infrared telescopes. A VLA study in 1998 showed two
young stars orbiting each other, each surrounded by a disk of dust that may,
in time, congeal into a system of planets.
Lim and Takakuwa re-examined the system, using improved technical
capabilities that greatly boosted the quality of their images. "In the
earlier VLA study, only half of the VLA's 27 antennas had receivers that
could collect the radio waves, at a frequency of 43 GigaHertz (GHz), coming
from the dusty disks. When we re-observed this system, all the antennas
could provide data for us. In addition, we improved the level of detail by
using the Pie Town, NM, antenna of the Very Long Baseline Array, as part of
an expanded system," Lim said. The implementation and improvement of the 43
GHz receiving system was a collaborative program among the German Max Planck
Institute, the Mexican National Autonomous University, and the U.S. National
Radio Astronomy Observatory.
Two popular theoretical models for the formation of multiple-star systems
are, first, that the two protostars and their surrounding dusty disks
fragment from a larger parent disk, and, second, that the protostars form
independently and then one captures the other into a mutual orbit.
"Our new study shows that the disks of the two main protostars are aligned
with each other, and also are aligned with the larger, surrounding disk. In
addition, their orbital motion resembles the rotation of the larger disk.
This is a 'smoking gun' supporting the fragmentation model," Lim said.
However, the new study also revealed a third young star with a dust disk.
"The disk of this one is misaligned with those of the other two, so it may
be the result of either fragmentation or capture," Takakuwa said.
The misalignment of the third disk could have come through gravitational
interactions with the other two, larger, protostars, the scientists said.
They plan further observations to try to resolve the question.
"We have a very firm indication that two of these protostars and their dust
disks formed from the same, larger disk-like cloud, then broke out from it
in a fragmentation process. That strongly supports one theoretical model for
how multiple-star systems are formed. The misalignment of the third
protostar and its disk leaves open the possibility that it could have formed
elsewhere and been captured, and we'll continue to work on reconstructing
the history of this fascinating system," Lim summarized.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.
[NOTE: Images supporting this release are available at
http://www.nrao.edu/pr/2006/multidisk/graphicspage.shtml ]
P.O. Box O
Socorro, NM 87801
http://www.nrao.edu
Contact:
Dave Finley, Public Information Officer
(505) 835-7302
December 15, 2006
How Do Multiple-Star Systems Form? VLA Study Reveals "Smoking Gun"
Astronomers have used the National Science Foundation's Very Large Array
(VLA) radio telescope to image a young, multiple-star system with
unprecedented detail, yielding important clues about how such systems are
formed. Most Sun-sized or larger stars in the Universe are not single, like
our Sun, but are members of multiple-star systems. Astronomers have been
divided on how such systems can form, producing competing theoretical models
for this process.
The new VLA study produced a "smoking gun" supporting one of the competing
models, said Jeremy Lim, of the Institute of Astronomy & Astrophysics,
Academia Sinica, in Taipei, Taiwan, whose study, done with Shigehisa
Takakuwa of the National Astronomical Observatory of Japan, is published in
the December 10 issue of the Astrophysical Journal.
Ironically, their discovery of a third, previously-unknown, young star in
the system may support a second theoretical model. "There may be more than
one way to make a multiple-star system," Lim explained.
The astronomers observed an object called L1551 IRS5, young, still-forming
protostars enshrouded in a cloud of gas and dust, some 450 light-years from
Earth in the direction of the constellation Taurus. Invisible to optical
telescopes because of the gas and dust, this object was discovered in 1976
by astronomers using infrared telescopes. A VLA study in 1998 showed two
young stars orbiting each other, each surrounded by a disk of dust that may,
in time, congeal into a system of planets.
Lim and Takakuwa re-examined the system, using improved technical
capabilities that greatly boosted the quality of their images. "In the
earlier VLA study, only half of the VLA's 27 antennas had receivers that
could collect the radio waves, at a frequency of 43 GigaHertz (GHz), coming
from the dusty disks. When we re-observed this system, all the antennas
could provide data for us. In addition, we improved the level of detail by
using the Pie Town, NM, antenna of the Very Long Baseline Array, as part of
an expanded system," Lim said. The implementation and improvement of the 43
GHz receiving system was a collaborative program among the German Max Planck
Institute, the Mexican National Autonomous University, and the U.S. National
Radio Astronomy Observatory.
Two popular theoretical models for the formation of multiple-star systems
are, first, that the two protostars and their surrounding dusty disks
fragment from a larger parent disk, and, second, that the protostars form
independently and then one captures the other into a mutual orbit.
"Our new study shows that the disks of the two main protostars are aligned
with each other, and also are aligned with the larger, surrounding disk. In
addition, their orbital motion resembles the rotation of the larger disk.
This is a 'smoking gun' supporting the fragmentation model," Lim said.
However, the new study also revealed a third young star with a dust disk.
"The disk of this one is misaligned with those of the other two, so it may
be the result of either fragmentation or capture," Takakuwa said.
The misalignment of the third disk could have come through gravitational
interactions with the other two, larger, protostars, the scientists said.
They plan further observations to try to resolve the question.
"We have a very firm indication that two of these protostars and their dust
disks formed from the same, larger disk-like cloud, then broke out from it
in a fragmentation process. That strongly supports one theoretical model for
how multiple-star systems are formed. The misalignment of the third
protostar and its disk leaves open the possibility that it could have formed
elsewhere and been captured, and we'll continue to work on reconstructing
the history of this fascinating system," Lim summarized.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.
[NOTE: Images supporting this release are available at
http://www.nrao.edu/pr/2006/multidisk/graphicspage.shtml ]