CfA Press Release
Release No.: 03-07 |
For Immediate Release: February 28, 2003
Molecular Cloud Has A Heartbeat
February is a month known for its holiday celebrating matters of the
heart. Therefore, it is fitting that this month would see the
announcement of an appropriately themed astronomical discovery - a
celestial object that beats like a heart. Astronomer Charles Lada of
the Harvard-Smithsonian Center for Astrophysics (CfA) and colleagues
have discovered that the dark molecular cloud known as Barnard 68
seems to pulsate like a heavenly tribute to Saint Valentine.
"We studied Barnard 68 to find out if it was rotating, expanding, or
contracting," says Lada. "Instead, we found that this molecular cloud
appears to have a heartbeat."
Barnard 68 is the only molecular cloud known to pulsate in this manner.
The Dark Heart Of Barnard 68
Barnard 68, located 300 light-years away in the constellation
Ophiuchus, is a typical example of small, dark molecular clouds known
as Bok Globules. Such dense, cold clouds of dust and gas appear black
in photos because the dust blocks visible light from background stars.
Molecular clouds are stellar nurseries. Young stars form from
collapsing molecular clouds. Barnard 68, however, is a stable cloud
containing no newborn stars.
Barnard 68 holds as much material as one and a half Suns, chilled to
a temperature of only 10 degrees above absolute zero (-440 degrees
F). It is one of the coldest objects in the Universe. Appropriately
for such a frigid temperature, it pulsates very slowly, considerably
more slowly than the heart of an earthbound lizard on a cold fall
Barnard 68 spans about 24,000 times the average distance between the
Earth and the Sun, or about two trillion miles. If our Sun were
placed at the center of Barnard 68, the cloud would extend out to 300
times the orbit of Pluto. Our solar system would be a lonely place,
because the cloud's thick dust would obscure light from the
surrounding stars and galaxies that fill the cosmos. Our night sky
would be as black as coal, showing only the occasional pinpoint of
light from the other nearby planets.
Whacked By A Supernova
While its composition is typical of molecular clouds, its motions
make Barnard 68 unique. By studying it with the IRAM 30-meter radio
telescope in Spain, Lada's team found the signatures of both
infalling and outflowing material at different locations across the
face of the cloud. The complex pattern of motions cannot be explained
by simple rotation, collapse, or expansion. Instead, the outer layers
of Barnard 68 must be pulsating like a wiggling bowl of Jello.
What force could have struck Barnard 68 to make it ring like a bell?
Lada speculates that the shockwave from an exploding star may have
smacked into the molecular cloud in the relatively recent past. The
blast from a supernova easily could provide the impulse that started
these pulsations. This theory is supported by other observations
showing that Barnard 68 is located inside a hot "bubble" within the
interstellar medium - a rarefied zone cleared out by a supernova.
The supernova shockwave may even have been powerful enough to rip off
the outer layers of Barnard 68, leaving behind the ringing core of a
A Molecular Cloud That Behaves Like A Star
Stars like our Sun commonly pulsate. Indeed, there is an entire
branch of astronomy called "helioseismology" devoted to studying the
Sun's pulsations in order to learn about the solar interior.
Molecular clouds are another matter.
"Stars are known to pulsate, but clouds are not known to pulsate,"
In this respect, Barnard 68 behaves like a star. It shows clear
differences from the Sun, but also surprising similarities given the
very different environments involved.
Pulsations are described by "modes." Each pulsation mode is
essentially a sound wave with a characteristic amplitude and
timescale. The Sun shows thousands of pulsation modes, while Barnard
68 seems to have only a few. Also, the Sun pulsates on a short
timescale of minutes, while Barnard 68 pulsates on a much longer
timescale of about 250,000 years.
"Still, it's remarkable that the same equations which describe
stellar structure and pulsations also apply to Barnard 68, even
though they're very different systems with different physics
involved," says Lada.
Lada now plans to examine the handful of other molecular clouds that
are close enough for high-resolution observations in order to see if
any others show signs of pulsation.
The research on Barnard 68 will be published in the March 20, 2003,
issue of The Astrophysical Journal in a paper co-authored by Lada,
Edwin Bergin (CfA), Joćo Alves (European Southern Observatory) and
Tracy Huard (CfA).
NOTE TO EDITORS: A high-resolution image of Barnard 68 is available
online at http://www.cfa.harvard.edu/news/archive/pr0307image.html. Photo
courtesy of the European Southern Observatory (http://www.eso.org).
More image information is online at
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.
For more information, contact:
David A. Aguilar
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Harvard-Smithsonian Center for Astrophysics
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Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016