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Stellar Nurseries

Millimeter Radiomap: Orion KL

JPEG Image (71K); Caption, Credits and Copyright

Introduction to Starbirth

As little as 30 years ago astronomers discovered that space isn't empty; a significant amount of mostly gaseous material lies between the stars, coalesced into Giant Molecular Clouds. Deep within these massive clouds, also called GMC's, stars are born. A prominent star forming region within the Orion Nebula, called Orion KL, is pictured in the above radiomap.

Optical studies of star-forming regions have been much enhanced by the success of NASA efforts to correct the Hubble Space Telescope's optics in 1993.

Orion Nebula: Optical View via HST

In December 1993, the HST captured a series of magificient images of the Orion Nebula, presented here as a mosaic. Further images, also of protoplanetary disk surrounding a very young star, can be viewed at the Space Telescope Science Institute's server.
JPEG Image (70K); Caption, Credits and Copyright

Spanning the many light years that separate most star systems, Giant Molecular Clouds consist of dust and cool gas, mostly molecular hydrogen. When these swirling, gaseous clouds become massive enough they begin to collapse, forming a central dense, central region. Warmer than the surrounding gases, this dense region, called a protostar, becomes yet more massive and heats up. As it continues to do so, its internal pressure mounts, igniting nuclear reactions in its core. A star is born.

Starbirth Movie
Star Formation Movie button

This movie summarizes how a star might form through the collapse of a Giant Molecular Cloud. The movie also shows how planets might form around the nascent star.

Credits and Acknowledgements
QuickTime (1.8 MB); MPEG (488K); Sound File (553K); Thumbnail (21K); Text

Stellar Winds

While intervening dust and gas obscures visible light from protostars buried deep within Orion KL, radio emissions reveal their formation. Employing radiotelescopes such as the BIMA array, astronomers can trace the flow of energy from the protostar into the surrounding gases and determine how this energy drives stellar winds. Protostars typically eject gaseous streams in opposite directions. Some protostars generate highly focused or collimated outflows, while others produce more oval-shaped winds.

Jack Welch, Univ.of California at Berkeley, on-camera
Movie/Sound Byte
QuickTime Movie (1.6 MB); Sound File (987K); Text

It is not clear what produces these outflows, yet astronomers believe magnetic fields and the growing accretion disk around the newborn star play crucial roles. As a protostar attracts more and more material, it spins faster and faster. Its increasing rotational energy could focus the stellar winds along the axis of rotation. Powerful magnetic fields may further constrain this outflow, resulting in bipolar jets.

Jack Welch, on-camera continued
Movie/Sound Byte
QuickTime Movie (1.1 MB); Sound File (693K); Text

Extending several light years, bipolar outflows greatly disrupt the surrounding GMC gases. How these gases interact and possibly affect the protostars' evolution can be better understood by carefully analyzing the motions of all the gases. The BIMA array's high spatial and spectroscopic resolutions result in radiomaps with exemplary precision on the locations and motions of the various gases. The array's large field of view yields high-precision radiomaps of the winds as well as the surrounding cloud.

Through spectroscopic studies and computer simulations, astronomers are studying the strength of the magnetic fields around the protostar, the gravitational and rotational forces acting upon the gases, which give rise to protostellar outflow, and how, in turn, the outflow influences the surrounding gases in the GMC.

Protostars In Other Wavebands

Protostars release heat in the form of ultraviolet radiation. Absorbing this radiation, the surrounding molecular gases break apart into atoms. The hot atomic gases are ejected in bipolar outflows which radiate centimeter radiation. Further out from the protostar, the outflowing gases cool down and recombine into molecules that typically emit millimeter radiation. By mapping of all these emissions, astronomers can obtain a detailed picture of the protostellar region.

Orion Bar Overlay

This image overlays observations in the infrared, centimeter, and millimeter regions of the spectrum. The three emissions interconnect to yield a coherent picture of the stellar winds from Orion KL.
JPEG Image (37K); Credits and Copyrights

Just very recently, the Hubble Space Telescope yielded yet more spectacular optical images of starbirth, this time in the Eagle Nebula or MI6, a gigantic cloud of cool hydtrogen gas and dust situated about 7000 light years from Earth. The images lend further support to current models of stellar birth, including the evaporation of surrounding clouds by ultraviolet radiation emitted from the hot nascent stars. Scientists believe that this radiation constitutes one of the external forces constraining the size and mass attained by newborn stars; the radiation limits the amount of material available for their formation.

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Copyright © 1995: Board of Trustees, University of Illinois

NCSA. Last modified, 11/11/95