Andrew Yee
August 31st 05, 09:00 PM
Public Affairs
Harvard-Smithsonian Center for Astrophysics
Cambridge, Massachusetts
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
For Release: EMBARGOED until 1:00 p.m. EDT Wednesday, August 31, 2005
Release No.: 05-27
How to Build a Big Star
Cambridge, MA -- The most massive stars in our galaxy weigh as much as 100
small stars like the Sun. How do such monsters form? Do they grow rapidly
by swallowing smaller protostars within crowded star-forming regions? Some
astronomers thought so, but a new discovery suggests instead that massive
stars develop through the gravitational collapse of a dense core in an
interstellar gas cloud via processes similar to the formation of low mass
stars.
"In the past, theorists have had trouble modeling the formation of
high-mass stars and there has been an ongoing debate between the merger
versus the accretion scenarios." said astronomer Nimesh Patel of the
Harvard-Smithsonian Center for Astrophysics (CfA). "We've found a clear
example of an accretion disk around a high-mass protostar, which supports
the latter while providing important observational constraints to the
theoretical models."
Patel and his colleagues studied a young protostar 15 times more massive
than the Sun, located more than 2,000 light-years away in the
constellation Cepheus. They discovered a flattened disk of material
orbiting the protostar. The disk contains 1 to 8 times as much gas as the
Sun and extends outward for more than 30 billion miles -- eight times
farther than Pluto's orbit.
The existence of this disk provides clear evidence of gravitational
collapse, the same gradual process that built the Sun. A disk forms when a
spinning gas cloud contracts, growing denser and more compact. The angular
momentum of the spinning material forces it into a disk shape. The planets
in our solar system formed from such a disk 4.5 billion years ago.
Evidence in favor of high-mass accretion has been elusive since massive
stars are rare and evolve quickly, making them tough to find. Patel and
his colleagues solved this problem using the Submillimeter Array (SMA)
telescope in Hawaii, which offers much sharper and highly sensitive
imaging capabilities compared to single-dish submillimeter telescopes. SMA
is currently a unique instrument that makes such studies possible by
allowing astronomers to directly image the dust emission at submillimeter
wavelengths and also to detect emission from highly excited molecular gas.
The team detected both molecular gas and dust in a flattened structure
surrounding the massive protostar HW2 within the Cepheus A star formation
region. SMA data also showed a velocity shift due to rotation, supporting
the interpretation that the structure is a gravitationally bound disk.
Combined with radio observations showing a bipolar jet of ionized gas, a
type of outflow often observed in association with low-mass protostars,
these results support theoretical models of high-mass star formation via
disk accretion rather than by the merging of several low-mass protostars.
"Merging low-mass protostars wouldn't form a circumstellar disk and a
bipolar jet," said co-author Salvador Curiel of the National Autonomous
University of Mexico (UNAM), who is on sabbatical leave at CfA. "Even if
they had circumstellar disks and outflows before the merger, those
features would be destroyed during the merger."
The team plans more detailed observations using the SMA and the National
Radio Astronomy Observatory's Very Large Array, which initially detected
the bipolar jet.
The researchers, in addition to Patel, Ho, and Curiel, are: P. T. Ho, T.
K. Sridharan, Q. Zhang, T. R. Hunter and J. M. Moran, of CfA; Jose M.
Torrelles, Institute for Space Studies of Catalonia (IEEC)-Spanish
Research Council (CSIC), Spain; and J. F. Gomez and G. Anglada, Instituto
de Astrofisica de Andalucia (CSIC), Spain.
This research is being reported in the September 1, 2005, issue of Nature.
The SMA is a joint project between the Smithsonian Astrophysical
Observatory and the Academia Sinica Institute of Astronomy and
Astrophysics in Taiwan and is funded by the Smithsonian Institution and
the Academia Sinica.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.
Headquartered in Cambridge, Massachusetts, 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 seven research divisions study the origin,
evolution, and ultimate fate of the universe.
Note to editors: High-resolution artwork is available online at
http://www.cfa.harvard.edu/press/pr0527image.html
Harvard-Smithsonian Center for Astrophysics
Cambridge, Massachusetts
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
For Release: EMBARGOED until 1:00 p.m. EDT Wednesday, August 31, 2005
Release No.: 05-27
How to Build a Big Star
Cambridge, MA -- The most massive stars in our galaxy weigh as much as 100
small stars like the Sun. How do such monsters form? Do they grow rapidly
by swallowing smaller protostars within crowded star-forming regions? Some
astronomers thought so, but a new discovery suggests instead that massive
stars develop through the gravitational collapse of a dense core in an
interstellar gas cloud via processes similar to the formation of low mass
stars.
"In the past, theorists have had trouble modeling the formation of
high-mass stars and there has been an ongoing debate between the merger
versus the accretion scenarios." said astronomer Nimesh Patel of the
Harvard-Smithsonian Center for Astrophysics (CfA). "We've found a clear
example of an accretion disk around a high-mass protostar, which supports
the latter while providing important observational constraints to the
theoretical models."
Patel and his colleagues studied a young protostar 15 times more massive
than the Sun, located more than 2,000 light-years away in the
constellation Cepheus. They discovered a flattened disk of material
orbiting the protostar. The disk contains 1 to 8 times as much gas as the
Sun and extends outward for more than 30 billion miles -- eight times
farther than Pluto's orbit.
The existence of this disk provides clear evidence of gravitational
collapse, the same gradual process that built the Sun. A disk forms when a
spinning gas cloud contracts, growing denser and more compact. The angular
momentum of the spinning material forces it into a disk shape. The planets
in our solar system formed from such a disk 4.5 billion years ago.
Evidence in favor of high-mass accretion has been elusive since massive
stars are rare and evolve quickly, making them tough to find. Patel and
his colleagues solved this problem using the Submillimeter Array (SMA)
telescope in Hawaii, which offers much sharper and highly sensitive
imaging capabilities compared to single-dish submillimeter telescopes. SMA
is currently a unique instrument that makes such studies possible by
allowing astronomers to directly image the dust emission at submillimeter
wavelengths and also to detect emission from highly excited molecular gas.
The team detected both molecular gas and dust in a flattened structure
surrounding the massive protostar HW2 within the Cepheus A star formation
region. SMA data also showed a velocity shift due to rotation, supporting
the interpretation that the structure is a gravitationally bound disk.
Combined with radio observations showing a bipolar jet of ionized gas, a
type of outflow often observed in association with low-mass protostars,
these results support theoretical models of high-mass star formation via
disk accretion rather than by the merging of several low-mass protostars.
"Merging low-mass protostars wouldn't form a circumstellar disk and a
bipolar jet," said co-author Salvador Curiel of the National Autonomous
University of Mexico (UNAM), who is on sabbatical leave at CfA. "Even if
they had circumstellar disks and outflows before the merger, those
features would be destroyed during the merger."
The team plans more detailed observations using the SMA and the National
Radio Astronomy Observatory's Very Large Array, which initially detected
the bipolar jet.
The researchers, in addition to Patel, Ho, and Curiel, are: P. T. Ho, T.
K. Sridharan, Q. Zhang, T. R. Hunter and J. M. Moran, of CfA; Jose M.
Torrelles, Institute for Space Studies of Catalonia (IEEC)-Spanish
Research Council (CSIC), Spain; and J. F. Gomez and G. Anglada, Instituto
de Astrofisica de Andalucia (CSIC), Spain.
This research is being reported in the September 1, 2005, issue of Nature.
The SMA is a joint project between the Smithsonian Astrophysical
Observatory and the Academia Sinica Institute of Astronomy and
Astrophysics in Taiwan and is funded by the Smithsonian Institution and
the Academia Sinica.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.
Headquartered in Cambridge, Massachusetts, 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 seven research divisions study the origin,
evolution, and ultimate fate of the universe.
Note to editors: High-resolution artwork is available online at
http://www.cfa.harvard.edu/press/pr0527image.html