FOR RELEASE: 9:20 a.m., January 14, 1997
GIANT CAVITY BLOWN BY WIND FROM NEWBORN STAR
Astronomers have obtained images of a star-forming gas cloud that reveal with unprecedented clarity a giant cavity, half a light year in extent, that is being excavated by a powerful wind and jet of gas from a newborn star. The report is being presented by graduate student Neil Nagar and Drs. Stuart Vogel, James Stone and Eve Ostriker of the University of Maryland, College Park, Maryland to the American Astronomical Society meeting in Toronto, Canada. The result is important because it shows how a newborn star sweeps away its natal gas cloud, unveiling the star and limiting its growth.
Stars form in giant gas clouds that are light years in extent. At sites within such clouds, gravity pulls in gas to form a rotating disk; the disk feeds gas to a growing star at its center, and can make planets like our solar system. Recently, astronomers have learned that as newborn stars accumulate gas from their disk, they eject a significant portion of it in a wind or jet of gas moving at hundreds of miles per second away from the star. This wind then sweeps up much of the surrounding natal gas cloud. As the cloud is cleared away, the star becomes visible, and its further growth is limited. However, the mechanism for sweeping away the gas is poorly understood.
The astronomers detected carbon monoxide (CO), which they used to trace the molecular gas surrounding a forming star, IRAS 0591+0247, located in a gas cloud in the constellation of Orion at a distance of 1500 light years. The star is known to have a narrow jet of gas moving away from the star at speeds of over 200 miles per second (300 kilometers per second). The new observations reveal a conical cavity in the surrounding natal cloud, with the star at the point of the cone and the jet along the center of the cone (see accompanying photos). The gas lining the walls of the cavity has been swept up by the wind and jet and is moving away from the star at speeds of over 15 miles per second. They find that there is more than a tenth of the mass of the sun in the swept-up gas, and that the excavation of the cavity began about 10,000 years ago.
Stuart Vogel, professor of astronomy at the University of Maryland, said that ``cavities blown by newborn stars have been inferred before, but never seen so clearly.'' ``There are competing theories that try to explain how a star drives gas away from a star,'' Vogel said ``it's not easy to accelerate a big fraction of the mass of a star to these high speeds. The data strain existing ideas on how to do this, and not all of them will survive.'' The new observations ``show us how a star limits its growth, and how a star reveals itself to the universe'', he said.
The astronomers used the Berkeley-Illinois-Maryland (BIMA) radio telescope near Hat Creek, California, which consists of 9 radio dishes, each 6 meters (20 feet) in diameter and separated by up to 1 kilometer (0.6 miles), operating at the highest radio frequencies (70 to 270 gigahertz); the dishes are connected electronically to synthesize a giant radio telescope that has subarcsecond resolution. More information about the BIMA telescope can be found on the Internet at http://bima.astro.umd.edu.
For further information: Dr. Stuart Vogel (301)-405-2134
FOR RELEASE: 9:20 a.m., January 14, 1997
PHOTO CREDIT: Neil Nagar, University of Maryland
Figure 1 shows the cavity excavated by the jet and wind from the newborn star. It was obtained with the BIMA radio telescope by the University of Maryland astronomers using radiation from the carbon monoxide molecule (CO) to trace the molecular gas (similar in some ways to biologists using cell-staining to highlight parts of a cell or the military using infrared detectors to find tanks). This image shows a slice through the middle of the cone-shaped cavity; the walls of the cavity give off radiation from the CO molecule. The jet of gas, unseen here, lies along the middle of the cone. The cavity is the region interior to the cone.
Figure 2 shows a schematic to help interpret the photo in Figure 1. The walls of the conical cavity (shown by the blue line) are traced by CO emission detected by the BIMA telescope. The newborn star is indicated in red as a , and the location of the jet is indicated by the red line.
Figure 3 shows another photo of the expanding conical molecular shell obtained with the BIMA telescope. It shows a cut through the conical shell at right angles to the slice shown in Figure 1 (like slicing a ring from an ice cream cone).
This material was presented to the American Astronomical Society meeting in Toronto, Canada on January 14, 1997.
Editors: The images included here, along with additional images (including black and white versions) are available over the Internet via http://www.astro.umd.edu/neil/toronto.html