Wind bubble found around young super star cluster
Posted: June 11, 2001

An international team of astronomers has detected a wind bubble associated with a super star cluster in a nearby galaxy -- a key indicator that helps explain how this extremely young cluster is evolving.

NGC 5253
Pseudo-color image of dwarf galaxy NGC 5253. Blue channel: Hubble Space Telescope image, in optical light; red: infrared image from the Keck Telescope. The gas cloud (nebula) associated with the wind bubble is the brightest infrared source, the topmost bright knot. HST image courtesy of Daniela Calzetti (STScI).
"We have detected supersonic motions in the nebula surrounding this super star cluster," says Jean L. Turner, UCLA professor and principal investigator. "We know of smaller wind bubbles around young stars in our own Milky Way, but this wind is far more powerful, with the potential to seriously disrupt its parent galaxy."

The findings of the team, which includes Lucian P. Crosthwaite and David S. Meier, UCLA graduate students, and Sara C. Beck of Tel Aviv University, were reported at the meeting of the American Astronomical Society in Pasadena, CA. The discovery, supported by funding from the National Science Foundation, the U.S.-Israel Binational Science Foundation, and the Sigma Xi Society, was made with infrared data taken at the W. M. Keck Observatory in Hawaii, operated jointly by the University of California and the California Institute of Technology, with support from NASA.

"We're measuring wind speeds of about 3000 miles per minute in the hydrogen gas," says Crosthwaite. "These are not unusual speeds for stellar winds. But stellar winds normally involve only a little mass. This wind is exceptional because it is pushing a million earth masses of gas, so it's far more powerful than what we have seen before".

Infrared image of super star clusters in NGC 5253 made with the Keck Telescope. Wind bubble cloud/nebula is the topmost bright knot.
The wind arises in a gas cloud that hides what may be the youngest known super star cluster, located in a galaxy about 12 million light years away in the direction of the constellation Centaurus. The star cluster -- estimated to contain a million young stars -- is so young, in astronomical terms, that it is still hidden from optical view by a hot and glowing cloud of gas and dust. These luminous young stars drive winds by the sheer force of their radiation pressure, and their winds combine to drive the wind bubble. Although only a few light years across, the distance from our Sun to the nearest star, the cluster and its windy cocoon emit the power of a billion suns, and are responsible for nearly one quarter of the energy output of the entire galaxy.

"We estimate from its current rate of expansion that this phase of the life of the super star cluster can last at most 15,000 years, unless gravity is slowing the expansion, which is likely," says Meier. "Even so, the wind bubble is expanding rapidly and the shock waves from the bubble may prevent future star formation near the cluster."

Super star clusters were formed in the Milky Way billions of years ago, and were more common in the early universe. The effects of these luminous young clusters on galaxies are unknown. According to Beck, "We've known for some time that galaxies undergoing bursts of star formation make super star clusters and we've suspected that the winds of these clusters could affect the evolution of the parent galaxies. But this is a short-lived phase in the life of the cluster so it's hard to catch one in the act. We are lucky that NGC 5253 is at the right place and the right time for us to detect this extraordinary wind-blown bubble."

Artist's depiction of the young super star cluster within the wind bubble cloud. Credit: Nalini Saba.

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