Astronomers capture "stellar sonogram" of a star in the making

July 13, 1999

GAINESVILLE --- A University of Florida astronomer is part of an international team that has captured the first images of the very earliest stages of a "dark cloud" -- the coldest astronomical object in the universe -- becoming a new star and planetary system.

The images, akin to a deep-space sonogram of a baby at the zygote stage, will give astronomers a new understanding of how stars begin to form and even what was happening when our own solar system began to come to life about 4.5 billion years ago, said team member Elizabeth Lada, an associate professor of astronomy at UF.

"Here we have an outstanding example of a cloud that appears to have just initiated collapse to form a star, and we can study the structure in detail," Lada said.

Lada is collaborating on the project with her brother, Charles, an astronomer at the Harvard-Smithsonian Center for Astrophysics; and Joao Alves, an astronomer with the European Southern Observatory.

The team got the images in March at the European Southern Observatory at La Silla in the Chilean Andes, using the observatory's 3.5-meter Very Large Telescope and a near-infrared detector known as SOFI.

The dark cloud, also known as a dark globule, is called Barnard 68 and is in front of a dense star field in the Milky Way. Barnard 68, also known as B68, is about 500 light years from Earth.

Dark clouds are made up of interstellar molecular gas and dust and are the coldest objects in the universe, with temperatures around -263 degrees Celsius, or 10 degrees above absolute zero. Astronomers have known for some time that such clouds contract and eventually turn into hydrogen-burning stars, but the details of exactly how that happened remain unclear.

Dark clouds appear dark because the dust within them is opaque to visible radiation, so they blot out the light of stars beyond them. Otherwise, they are invisible because they are made up almost entirely of molecular hydrogen, which is too cold to glow in visible light. But with the new work by Lada and her colleagues, the veil is beginning to lift.

Previously, radio telescope were used to study dark clouds, but the interpretation of radio emission is not straightforward. With the near-infrared method they developed, Lada and her colleagues were able to for the first time "see" through the cloud and detect the stars behind it. By measuring the change in the color of the background stars caused by the presence of intervening dust in the cloud, they were able to directly map out the distribution of matter within the cloud itself.

"There are theories about how the formation of a star begins," Lada said, "but our observations of B68 gives us some of the best evidence to test those theories."

The team caught the cloud just as it was beginning its collapse, a process that takes about 100,000 to 200,000 years. To get an idea of how early on in development B68 is, Lada said, it will be another 10 million years or so after the collapse before the star will burn hydrogen and shine like the sun.

"We're looking at things that are very comparable to what our Sun would have looked like" when it was forming, Lada said.
-end-
Writer: Steve Orlando, sfo@ufl.edu
Source: Elizabeth Lada, 352-72-0361, lada@astro.ufl.edu

University of Florida

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