Cambridge, MA — A team of astronomers at the Harvard-Smithsonian
Center for Astrophysics (CfA) led by Chris Martin and Antony Stark has
mapped molecular clouds near the center of our galaxy in unprecedented
detail at submillimeter wavelengths. Their data are being presented
today at a meeting of the American Astronomical Society in Albuquerque,
NM. Their results suggest that we are headed for some celestial
fireworks. Sometime in the next 300 million years, the galactic center
will experience a dramatic burst of star formation and will shine with
the light of thousands of newborn suns.
The effects of these starbursts will be dramatic. “Many of the stars
that form will be very massive and short-lived,” says Stark. “They’ll
quickly use up their fuel and explode as supernovae. Right now, we see
one supernova in our galaxy about every 100 years. When the starburst
happens, we’ll see one supernova every year.”
The team mapped the molecular clouds using submillimeter emissions
from carbon monoxide molecules. Submillimeter radiation has
wavelengths of less than one millimeter and lies between the infrared
(heat) and radio portions of the electromagnetic spectrum. The map
spans an area of the sky about 3/4 of a square degree in size, or
about three times the area covered by the full moon. At the galactic
center, this corresponds to a map about 400 light-years on a side.
Using this submillimeter map, astronomers now can determine the
temperature and density of material near the center of the Milky Way
in great detail.
“Most of the matter in these molecular clouds is very cold, at
temperatures just a few tens of degrees above absolute zero. At
those low temperatures, gas emits subillimeter radiation rather than
visible light,” says Martin. “We can combine our map with the recent
X-ray map of the galactic center taken by NASA’s Chandra X-ray
Observatory as well as with observations at other wavelengths of
light. Together, the data allow us to build a complete picture of
the environment near the center of our galaxy.”
The observations were made using the Antarctic Submillimeter
Telescope and Remote Observatory (AST/RO). AST/RO is a 67-inch
(1.7-meter) diameter telescope operated by CfA in collaboration
with the University of Arizona, Caltech, and the University of
Cologne, Germany. AST/RO is located at the National Science
Foundation’s Amundsen-Scott Station at the South Pole. This telescope
offers unique capabilities unmatched by other submillimeter
observatories around the world. The air at the South Pole is very dry
and cold, so radiation that would be absorbed by water vapor at other
sites can make it to the ground and be detected.
AST/RO operates in a strange and forbidding environment where
temperatures can plummet to minus 100 degrees F. The South Pole sees
only one sunrise and one sunset each year, so visitors experience six
months of constant daylight followed by six months of darkness. Yet
the darkness offers delights of its own, such as aurorae that paint
the sky with dancing green fire and the opportunity to observe the
same area of sky 24 hours a day, 7 days a week.
“There’s a certain irony to our work,” says Martin. “We point a
giant thermometer into space and measure the temperature of the
galactic center from the coldest place on Earth.”
The observations also show that the gas clouds are near a critical
density beyond which they will collapse into the center of the
galaxy. This infall of material will lead to a great burst of star
formation, with stars being born at 10-100 times the current rate.
The process will then begin again as more gas collects around the
outskirts of the galactic center, gradually accumulating in a smooth
ring. When that ring reaches a critical density, it coagulates into
one or two giant molecular clouds, each one millions of times more
massive than the Sun. These clouds fall inward to the galactic
center where another starburst takes place. The cycle repeats
approximately every 500 million years.
Astronomers see starbursts in other galaxies such as the nearby
irregular galaxy dubbed M82. Studying a similar process in our home
galaxy offers a unique advantage. The Earth’s distance from the
galactic center of 25,000 light-years enables astronomers to observe
the process in much greater detail than can be seen in galaxies
millions of light-years away.
The infalling gas will also feed the black hole at the center of the
Milky Way. As the matter spirals around the black hole, some material
will be ejected outward in two long jets toward the north and south
galactic pole.
“We’re lucky that the energy from these jets is directed out away
from the plane of the Milky Way. If it weren’t, the Earth might be
periodically sterilized of all life,” says Stark.
Other CfA researchers who contributed to this work are Adair P. Lane
and Sungeun Kim.
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: An image to accompany this release can be found at
http://cfa-www/press/spimage.html .
For more information, contact:
David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu
Christine Lafon
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
clafon@cfa.harvard.edu
