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Harvard-Smithsonian Center for Astrophysics
Cambridge, Massachusetts

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David A. Aguilar
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For Immediate Release: February 28, 2003
Release No.: 03-07

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 morning.

Barnard 68 spans about 12,000 times the average distance between the 
Earth and the Sun, or about one 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 
once-massive cloud. 

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," 
Lada confirms. 

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://cfa-www.harvard.edu/press/pr0307image.html
Photo courtesy of the European Southern Observatory
(http://www.eso.org). More image information is online at
   http://www.eso.org/outreach/press-rel/pr-1999/phot-20-99.html 

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.

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